Wcdma air interface

WCDMA Air Interface

LZT 123 7279 R5B © Ericsson 2005 - 1 -

WCDMA Air Interface

STUDENT BOOK LZT 123 7279 R5B

WCDMA Air Interface

- 2 - © Ericsson 2005 LZT 123 7279 R5B

DISCLAIMER This book is a training document and contains simplifications. Therefore, it must not be considered as a specification of the system. The contents of this document are subject to revision without notice due to ongoing progress in methodology, design and manufacturing. Ericsson assumes no legal responsibility for any error or damage resulting from the usage of this document. This document is not intended to replace the technical documentation that was shipped with your system. Always refer to that technical documentation during operation and maintenance.

© Ericsson 2005 This document was produced by Ericsson. • It is used for training purposes only and may not be copied or

reproduced in any manner without the express written consent of Ericsson.

This Student Book, LZT 123 7279, R5B supports course number LZU 108 5306 .

Table of Contents

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Table of Contents

WCDMA AIR INTERFACE.....................................................................1

1 WCDMA WIRELESS TECHNOLOGY...........................................9

IT’S ALL ABOUT SERVICES ..............................................................13

WCDMA BACKGROUND ....................................................................13

WCDMA AIR INTERFACE ...................................................................14

WCDMA MILESTONES .......................................................................14

EVOLUTION FROM 2G TO 3G............................................................15

PRESENT FUNCTIONALITY...............................................................15 WCDMA RADIO ACCESS BEARERS (RABS)...............................................16 MULTIPLE ACCESS TECHNOLOGIES .........................................................17

TDMA TRANSMITTER.........................................................................18

WCDMA TRANSMITTER.....................................................................19 VOICE CODING..............................................................................................21 ADAPTIVE MULTI-RATE................................................................................24 ERROR DETECTION AND CORRECTION - CRC AND FEC CODING.........26 CHANNELIZATION CODES ...........................................................................40 SCRAMBLING CODES...................................................................................47 MODULATION ................................................................................................56 FILTERING .....................................................................................................58

2 WCDMA POWER CONTROL, RAKE RECEIVER AND HANDOVER ................................................................................65

WCDMA RECEPTION ISSUES ...........................................................69

WCDMA POWER CONTROL ..............................................................70

MULTIPATH FADING ...........................................................................72

THE RAKE RECEIVER........................................................................74

WCDMA HANDOVER..........................................................................78

CELL PLANNING ................................................................................82 FDMA/TDMA...................................................................................................82

WCDMA Air Interface

WCDMA ..........................................................................................................83

CAPACITY MANAGEMENT ................................................................86 ADMISSION CONTROL .................................................................................87 CONGESTION CONTROL .............................................................................87

3 WCDMA PHYSICAL LAYER.......................................................89

3GPP....................................................................................................93 WCDMA OSI MODEL .....................................................................................99

WCDMA DOWNLINK.........................................................................102 LOGICAL CHANNELS ..................................................................................105 TRANSPORT CHANNELS ...........................................................................105 PHYSICAL CHANNELS................................................................................106 CHANNELIZATION CODE INDEX ...............................................................108 COMMON PILOT CHANNEL........................................................................109 PRIMARY COMMON CONTROL PHYSICAL CHANNEL AND SYNCHRONIZATION CHANNEL .................................................................110 SECONDARY COMMON CONTROL PHYSICAL CHANNEL ......................111 PAGING INDICATOR CHANNEL .................................................................111 DEDICATED PHYSICAL CONTROL AND DATA CHANNEL.......................112 MULTIPLEXING............................................................................................117

WCDMA UPLINK ...............................................................................121 DEDICATED PHYSICAL CONTROL AND DATA CHANNEL.......................123 MULTIPLEXING............................................................................................125 RANDOM ACCESS CHANNEL ....................................................................126 HPSK MODULATION ...................................................................................127

4 SYNCRONIZATION AND RANDOM ACCESS .........................131

BASE STATION DOWNLINK TIMING ...............................................135

SYNCHRONIZATION PROCEDURE .................................................136 DOWNLINK SCRAMBLING CODES ............................................................136 SYNCHRONIZATION CODES......................................................................136

RANDOM ACCESS PROCEDURE....................................................140

DEDICATED CHANNEL PROCEDURE.............................................145

WCDMA SOFT HANDOVER .............................................................146

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Table of Contents

5 HSDPA GENERAL PRINCIPLES..............................................149

INTRODUCTION................................................................................151

INTRODUCTION................................................................................151

GENERAL PRINCIPLES ...................................................................152 SHORT TTI (2 MS) .......................................................................................153 SHARED CHANNEL TRANSMISSION.........................................................153 HIGHER-ORDER MODULATION .................................................................154 FAST LINK ADAPTATION ............................................................................157 FAST CHANNEL DEPENDENT SCHEDULING ...........................................159 FAST HYBRID ARQ WITH SOFT COMBINING ...........................................160 DYNAMIC POWER ALLOCATION ...............................................................163

HSDPA CHANNEL STRUCTURE......................................................164 HS-DSCH - HIGH-SPEED DOWNLINK SHARED CHANNEL......................165 HS-PDSCH - HIGH-SPEED PHYSICAL DOWNLINK SHARED CHANNEL.166 HS-SCCH - HIGH SPEED - SHARED CONTROL CHANNEL......................167 HS-DPCCH - HIGH-SPEED DEDICATED PHYSICAL CONTROL CHANNEL .....................................................................................................169 OVERALL TIMING RELATION .....................................................................173

APPENDIX A: ABBREVIATIONS......................................................175

INDEX ................................................................................................181

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WCDMA Air Interface

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Table of Contents

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1 WCDMA Wireless Technology

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Objectives

Upon completion of this chapter the student will be able to:

• Explain the fundamental principles of cellular WCDMA technology.

• Explain and compare TDMA and WCDMA multiple access methods.

• Explain on an overview level, the WCDMA transmitter architecture.

• Explain the data protection coding methods: CRC Coding, FEC Coding, Viterbi decoding, block interleaving, turbo codes.

• Explain the use of channelization and scrambling codes.

• Explain the modulation and filtering in a WCDMA system. Figure 1-1: Objectives

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Contents

IT’S ALL ABOUT SERVICES ..............................................................13

WCDMA BACKGROUND ....................................................................13

WCDMA AIR INTERFACE ...................................................................14

WCDMA MILESTONES .......................................................................14

EVOLUTION FROM 2G TO 3G............................................................15

PRESENT FUNCTIONALITY...............................................................15 WCDMA RADIO ACCESS BEARERS (RABS)...............................................16 MULTIPLE ACCESS TECHNOLOGIES .........................................................17

TDMA TRANSMITTER.........................................................................18

WCDMA TRANSMITTER.....................................................................19 VOICE CODING..............................................................................................21 ADAPTIVE MULTI-RATE................................................................................24 ERROR DETECTION AND CORRECTION - CRC AND FEC CODING.........26 CHANNELIZATION CODES ...........................................................................40 SCRAMBLING CODES...................................................................................47 MODULATION ................................................................................................56 FILTERING .....................................................................................................58

WCDMA Air Interface

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IT’S ALL ABOUT SERVICES Third Generation (3G) networks can be implemented using a number of different technologies. As long as they can provide the wanted services that is all that is required. However, some technologies have more advantages than others in terms of efficiency of spectrum usage and flexibility.

WCDMA BACKGROUND In 1992, the World Administrative Conference (WARC) of the ITU (International Telecommunications Union) chose frequencies around 2 GHz as available for use by third generation mobile systems.

Within the ITU these third generation systems are called International Mobile Telephony 2000 (IMT-2000).

Within IMT-2000, several different air interfaces are defined for third generation systems based on either Wideband Code Division Multiple Access (WCDMA) or TDMA technology.

The same air interface, WCDMA, is to be used in Europe and Asia, including Japan and Korea using the frequency bands around 2 GHz.

World Administrative Radio Conference (WARC) of the ITU (International Telecommunications Union) in 1992 chose frequencies around 2 GHz as available for use by third generation mobile systems.Within the ITU these third generation systems are called International Mobile Telephony 2000 (IMT-2000).Within IMT-2000, several different air interfaces are defined for third generation systems based on either CDMA or TDMA technology.The same air interface,WCDMA, is to be used in Europe and Asia, including Japan and Korea using the frequency bands around 2 GHz.In North America that spectrum has already been allocated for operators using second generation systems and no new spectrum is available for IMT-2000. Thus third generation services must be implemented within the existing bands.

Figure 1-2: WCDMA Air Interface

WCDMA Air Interface

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WCDMA AIR INTERFACE As well as WCDMA, the other air interfaces that can be used are EDGE and cdma2000.

EDGE (Enhanced Data Rates for GSM Evolution) can provide bit rates up to 500kbps within a GSM carrier spacing of 200kHz.

Cdma2000 can be used as an upgrade for the existing IS-95 operators.

Spectrum allocation in Europe, Japan and Korea is 1920 – 1980 MHz uplink and 2110 – 2170 MHz downlink.

As well as WCDMA the other air interfaces that can be used are EDGE and cdma2000.

EDGE (Enhanced Data Rates for GSM Evolution) can provide bit rates up to 500 kbps within a GSM carrier spacing of 200kHz.

Cdma2000 can be used as an upgrade for the existing IS - 95 operators

Spectrum allocation in Europe, Japan and Korea is 1920 - 1980 MHz uplink and 2110 - 2170 MHz downlink for Frequency Division Duplexing . 1900 - 1920 MHz uplink and 2020 - 2025 MHz downlink for Time Division Duplexing .

Frequency Division Duplex use different frequency bands for uplink and downlink while Time Division Duplex use the same frequency for both uplink and downlink.

Figure 1-3: WCDMA Air Interface

WCDMA MILESTONES In January 1998, the European standardization body ETSI decided upon WCDMA as the third generation air interface. Pre-commercial testing phase took place in Europe at the beginning of 2002.

The first commercial network was opened in Japan during 2001 for commercial use in key areas


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EVOLUTION FROM 2G TO 3G As can be seen in Figure 1-4 below, the second generation (2G) networks are designed and optimized for circuit switched services such as voice and low bit-rate circuit switched data. They are not optimized for packet data and can offer at best a maximum data throughput of 14.4 kbps (per timeslot). It should be noted that there are various enhancements becoming available such as GPRS and EDGE to improve the 2G network’s data handling capabilities, to increase its data transfer rate and allow packet data services.

Third Generation (3G) networks, on the other hand, have been designed for data transmissions, and support not only circuit switched voice and circuit switched data but also high-speed packet switched data as well as multi services.

Circuit-Switched Voice

Circuit-Switched Data

Circuit-Switched AMR coded voice

Circuit-Switched data

Packet Data

Streaming

Short Message Service (SMS)

2G

3G

Multiservice: AMR coded voice + Packet data

Figure 1-4: From 2G to 3G.

The demands on the 3G networks are going to be very different to the basic voice communication requirement of the 2G networks. This will require a very flexible air interface that can meet the demands of both circuit switched voice or data and packet services, and handle these in the most efficient way.

PRESENT FUNCTIONALITY The following Radio Functionality is included in the WCDMA Radio Access Network, WCDMA RAN Phase 4.

WCDMA Air Interface

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WCDMA RADIO ACCESS BEARERS (RABS)

The purpose of a Radio Access Bearer (RAB) is to provide a connection segment using the WCDMA RAN for support of a UMTS bearer service. The WCDMA RAN can provide Radio Access Bearer connections with different characteristics in order to match requirements for different UMTS bearers. In Figure 1-5 the different RABs supported in the P4 WCDMA RAN are illustrated.

Variable rate Packet Switched RACH/FACH, 64/64, 64/128, 64/384, 64/HS, 384/HS

Combination of Conversational Speech and Interactive 64/64

Conversational/speech RABConversational/speech RAB

Conversational 64 kbps CS RABConversational 64 kbps CS RAB

Interactive or background PS RABInteractive or background PS RAB

Streaming 57.6 kbps RAB

PS Streaming RABPS Streaming RAB

12.2 kbps Circuit switched

64 kbps Circuit switched

57.6 kbps Circuit switched

Maximum Bitrate 16/64 Guaranteed Bitrate 8/54

Multi-RAB

Figure 1-5: WCDMA Radio Access Bearers (RABs)

The conversational speech RAB is tailored to 12.2 kbps Adaptive Multi Rate (AMR) speech and will also be used to carry emergency calls.

Video telephony service may be offered across the Conversational 64 kbps Circuit Switched (CS) RAB.

Streaming 57.6 kbps is used to support v.90 modem connections.

The maximum data rate supported by the Interactive or Background Packet Switched (PS) RAB is 384 kbps in the downlink and 64 kbps in the uplink, making it ideal for email or web browsing. High Speed Downlink Packet Access (HSDPA) enables up to 4.32 Mbps (in P5 up to 14 Mbps) in the downlink and 384 kbps in the uplink.

The Multi-RAB is used for both 12.2 kbps AMR and PS 64/64 kbps.


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MULTIPLE ACCESS TECHNOLOGIES

There are three basic air interface multiple access techniques, frequency, time and code division multiple access Figure 1-6.

Frequency Division Multiple Access

Each User has a unique frequency

(1 voice channel per user)

All users transmit at the same time

AMPS, NMT, TACS

Use

r 1

Use

r 2

Use

r 3

Frequency

Frequency Division Multiple Access

Each User has a unique frequency

(1 voice channel per user)

All users transmit at the same time

AMPS, NMT, TACS

Use

r 1

Use

r 2

Use

r 3

Frequency

Each Transmitter has a unique Scrambling Code

Each Data Channel has a uniqueChannelization code

Many users share the same frequency and time

IS-95, cdma2000, WCDMA

Frequency

CodeDivision Multiple Access

SpreadSpectrumMultipleAccess

Multiple Transmitters

and

Multiple Data Channels

Each Transmitter has a unique Scrambling Code

Each Data Channel has a uniqueChannelization code



Frequency





Multiple Transmitters

and

Multiple Data Channels

Each User has a unique time slot

Each Data Channel has a uniqueposition within the time slot

Several users share the same frequency

IS-136, GSM, PDC

Time Division Multiple Access

Use

r 1

Use

r 2

Use

r 3

Use

r N

Time

Each User has a unique time slot

Each Data Channel has a uniqueposition within the time slot

Several users share the same frequency

IS-136, GSM, PDC

Time Division Multiple Access

Use

r 1

Use

r 2

Use

r 3

Use

r N

Time

Figure 1-6: Multiple Access Approaches.

Frequency Division Multiple Access (FDMA) is very common in the first generation of mobile communication systems. Examples of systems using this technique are NMT, TACS and AMPS. The available spectrum is divided into physical channels of equal bandwidth. One physical channel is allocated per subscriber. The physical channel allocated to the subscriber is used during the entire duration of the call and is unavailable for use by another subscriber during this time.

In Time Division Multiple Access (TDMA) the available spectrum for one carrier, is divided in time. The subscriber is allocated a set amount of time referred to as a time slot. Subscribers can only use the air interface for this amount of time. An example of a system that uses this principle is D-AMPS, which explains why D-AMPS is sometimes called TDMA. Since other mobile telephony systems that use TDMA, for example GSM, also split the available frequency band into several distinct carriers, in a sense they are hybrids using both TDMA and FDMA.

WCDMA Air Interface

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Wideband Code Division Multiple Access (WCDMA) allows many subscribers to use the same frequency at the same time. In order to distinguish between the users, the information undergoes a process known as spreading that is, the information is multiplied by a channelization and scrambling code, hence WCDMA is referred to as a spread spectrum technology. This technology was first developed by the military to avoid the possibility of their signals being jammed or listened to by the enemy.

TDMA TRANSMITTER The TDMA transmitter is illustrated in Figure 1-7.

Data Multiplexer

Data Multiplexer Transmit

GatingTransmit Gating

Control/Signaling

Data

Filtering+

RF Modulation

Filtering+

RF Modulation

RF Out

Sync. Bits

User Data Channel N

Error Protection

Error Protection

TimeslotSelector

Error Protection

Error Protection

User Data Channel 1

Error Protection

Error Protection

VocoderVocoder Error Protection

Error Protection

The Multiplexer allows various data channels to share the same timeslot.

The timeslot selector allows multiple transmitters to share the same carrier frequency, by assigning a unique timeslot to each transmitter.

Figure 1-7: TDMA Transmitter

The voice channel is passed through a vocoder, which produces a digital representation of the input analogue signal. After error protection this is fed into a data multiplexer where it is multiplexed with synchronization bits and control/signaling data and user data channels. This combined signal is passed to the transmit gating device. This allows transmission during the specified timeslot for a particular user, in the way a ‘push-to-talk’ button is used in a two-way radio. This allows multiple transmitters to share the same frequency by assigning a unique time slot to each. Finally, filtering and RF modulation is performed and the signal is passed to an antenna system.


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WCDMA TRANSMITTER The WCDMA transmitter looks similar to the TDMA transmitter, with the synchronization, control/signaling and multiple user data channels. However, in this case, neither time nor frequency is used to separate different users, but codes in an operation known as spreading.

Filtering+

RF Modulation

Filtering+

RF Modulation

RF OutLinear

Summation

Linear

Summation

Control/Signaling

Data

Sync. Bits

User Data Channel N

Error Protection

Error Protection

Error Protection

Error Protection

User Data Channel 1

Error Protection

Error Protection

VocoderVocoder Error Protection

Error Protection

Frequency

User 1User 2User 3

...

Channelization code 4

Channelization code N



Channelizationcode 1

Channelization Codes provide unique identification of each data channel

Scrambling Codes (SC) provide unique identification of each transmitter

Scrambling Code

Scrambling Code

Scrambling Code

Scrambling Code

Scrambling Code

Scrambling Code

Scrambling Code

Scrambling Code

Scrambling Code

Scrambling Code

Figure 1-8: The WCDMA transmitter

In the case of the TDMA transmitter these data channels were time multiplexed. However, the WCDMA transmitter simply multiplies each channel by a different binary code known as a channelization code. This process provides the necessary separation between the data channels, which can then simply be added together in a summation device. The output of this block is a digital data stream that contains different logical levels depending on the number of channels that were added together. If for example two data streams, that contain levels between +1 and -1 when added together will contain a stream that contains levels between +2 and –2. Three data streams added produce levels between +3 and -3 and so on. In reality this varying level, depending on the number of channels, cannot be sent to the modulator so each channel is weighted to ensure that the combined result is a fixed level. This explains why power is the shared resource.

WCDMA Air Interface

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The WCDMA transmitter now needs some method of providing separation between this signal and other transmitters, but cannot use time slots like the TDMA case. This separation is achieved by multiplying this composite signal by another binary code called a scrambling code.

Filtering and RF modulation are then performed to produce an RF output that contains all the information from all the users at the same time and on the same frequency.

It is important to note that this transmitter diagram is not accurate and is included merely to show some of the main points of the technology. The next transmitter diagram figure 1-9 is more realistic.

The receiver needs to know the scrambling code to perform the reverse process and then use the same channelization codes to retrieve each data channel.

Figure 1-9 shows schematically the various blocks contained in a WCDMA transmitter (detailed). Note that the 1:2 de-multiplexing part is only valid in the downlink.

CRC CodingCRC Coding FEC Coding

FEC Coding

Maps binary bits to real

value symbols

0 → +1

1 → -1

Pre-coded data (bits)

Pulse Shaping

Filter

Pulse Shaping

FilterRF Out

Data Channel

1

Data Channel

N

ΣΣ

Channelization Code 1

Pulse Shaping

Filter

Pulse Shaping

Filter

I/Q ModulatorI/Q Modulator

Inter-leaving

Inter-leaving


FEC Coding Inter-

leaving

Inter-leaving

D/AD/A

I

Q

Allows for error detection in the

receiver

Allows for error

correction in the receiver

Improves error correction

in the receiver

Gives a unique identity to each

data stream

Contains transmitted frequency spectrum

Allows both signals from I and Q branch to

share the same RF bandwidth

Data Symbols Chips

I

Q

Modulation Symbols

1:2Demux

1:2Demux

Provides 2x higher data

rate

(WCDMA,cdma2000 downlink)

1:2Demux

1:2Demux

I

Q

scrambling Code 1

Channelization Code n

D/AD/AI

Q

I

Q

scrambling Code 1

Gives a unique identity to this

transmitter

I

Q

Modulation Mapping


FEC Coding

Maps binary bits to real

value symbols

0 → +1

1 → -1

Pre-coded data (bits)

Pulse Shaping

Filter

Pulse Shaping

FilterRF Out

Data Channel

1

Data Channel

N

ΣΣ

Channelization Code 1

Pulse Shaping

Filter

Pulse Shaping

Filter


Inter-leaving

Inter-leaving


FEC Coding Inter-

leaving

Inter-leaving

D/AD/A

I

Q

Allows for error detection in the

receiver

Allows for error

correction in the receiver

Improves error correction

in the receiver

Gives a unique identity to each

data stream

Contains transmitted frequency spectrum

Allows both signals from I and Q branch to

share the same RF bandwidth

Data Symbols Chips

I

Q

Modulation Symbols

1:2Demux

1:2Demux

Provides 2x higher data

rate

(WCDMA,cdma2000 downlink)

1:2Demux

1:2Demux

I

Q

scrambling Code 1

Channelization Code n

D/AD/AI

Q

I

Q

scrambling Code 1

Gives a unique identity to this

transmitter

I

Q

Modulation Mapping

Figure 1-9: WCDMA Transmitter (detailed)


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Error detection and error protection of the data channels are performed using Cyclic Redundancy Check (CRC) coding, Forward Error Correction (FEC) and interleaving. It should be remembered that this user data could be voice from a vocoder, user data or control data.

The next stage is to perform a 1:2 de-multiplexing of the stream (downlink only). This effectively doubles the data rate by taking all the even bits from the input stream and placing them on the I-branch and all the odd bits onto the Q-branch. This step is used to take advantage of an RF modulation scheme known as I/Q-modulation.

The data is then converted from a binary signal ranging from 0 to 1 to an real value signal that ranges from –1 to +1.

The error-protected signal is then multiplied by a particular channelization code to provide the necessary channel separation. This is necessary since all the channels will be added together, which will produce a composite data stream.

Scrambling of the signal is then performed using a complex multiplier, effectively using a separate scrambling code for the I- and Q- branches. This complex scrambling code is generated using a linear shift register.

The channels are then summed together.

After pulse shape filtering, the I- and Q-branch are passed to the I/Q-modulator, which will produce an RF output that can be fed to the antenna system.

Each of these stages is explained in more detail in the rest of this chapter.

VOICE CODING

A simple analogy to explain the concept of voice coding is to use that of a saxophone concert Figure 1-10.

WCDMA Air Interface

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Record the sax player onto a CD... ... and play back the CD

20 MB per song

Write down the notes he plays... ... and have a friend play the same notes

20 kB per song

Figure 1-10: Voice Coding; Example: Two ways to hear the sax player.

Suppose you have tickets for a concert but find that at the last minute you cannot attend. You then find someone else who can attend in your place. However, this person offers you two choices: He/she can take a recorder and create a compact disk of the concert using perhaps 20MB of storage area per song or go to the concert and write down the notes as they are played, creating perhaps only 20 KB per song.

Obviously the first option produces the best reproduction of the concert since the second option involves someone playing the music from the recorded notes. However, if this person is going to charge you for the amount of data required for each option, the choice is not so simple.

In the case of mobile communications where system bandwidth is at a premium, the second option would be best suited since all users must share the same bandwidth. Less bandwidth per connection will allow more users in the system.

In cordless phone systems Adaptive Differential Pulse Code Modulation (ADPCM) coding is used offering a 32kbps channel for each connection, whereas the coding in GSM, for example, uses a vocoder that only requires a data channel at a rate of 13 kbps (full- rate).


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Human speech is made up of two types of sounds: those produced by the vocal cords, ‘ah’, ‘v’ and ‘mm’ which make up approximately 80% of the time and those produced by air passing through the teeth, ‘ss’, ‘ff’, and ‘sh’. All that is required is to pass these sounds through the throat, which will act as a filter and make the voice sound distinctive. The vocoder (Figure 1-11) needs only to send noise and pitch parameters along with details of the resonance of the vocal tract filter (Hs). This will reduce the bandwidth required to transmit the voice.

At the receiver the voice can be re-synthesized by combining the output of a white noise generator and a pulse generator to mimic the vocal cords. After passing the output through the filter to recreate the vocal tract a good representation of the original voice should be produced.

Human Voice:

‘ss’, ‘ff’, ‘sh’ … ~20% of time‘ah’, ‘v’, ‘mm’ , … ~80% of time

Transmitted Parameters8~12 kb/s typical,

vs.64 kbps for log-PCM32 kbps for ADPCM

Vocoder

White Noise Generator

Pulse GeneratorΣ

Voice Re-Synthesis at the Receiver

Noiseparameters

Pitch parameters

H(s)

Filter poles correspond to

resonances of the vocal tract

SpeechOutput

H(s)

Figure 1-11: Voice Coding

WCDMA Air Interface

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ADAPTIVE MULTI-RATE

The type of voice coding used for WCDMA (Figure 1-12) is a combination of coding called Algebraic Code Excited Linear Predictive (ACELP), which uses codebook references to represent speech sounds and Adaptive Multi Rate (AMR) coding, which allows different speech rates to be used, depending on the environment or application. Another feature of this coder is that a sample of the background noise is periodically sent to the receiver. Since most voice conversations are made up of approximately 50% silence this sample can be used to recreate the background noise, thus reducing the amount of data to be sent and hence increasing system capacity, since no interference will be caused during the idle periods. The process uses a closed loop system that compares the sound sample of the voice with what is stored under a predicted code reference. The output from this process will represent the error between the two and is passed through a perceptual weighting device that will mimic the sensitivity of the human ear to gauge how much distortion this error will produce. After error analysis a new codebook reference may be chosen that should be a better match to the incoming speech. This closed loop should produce a very close codebook reference that can be used in the receiver to recreate the speech.

The receiver will simply contain the same codebook, a speech generator and a filter.

The Voice, tone activity detectors will handle the multiplexing of the background noise to be used in the receiver for idle periods. Discontinuous transmission bits indicate when to use this background noise.

The two main advantages of using discontinuous transmission are:

• Less power will be transmitted by the mobile and hence less interference which will result in an increase in capacity.

• Longer mobile battery life.


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A/D

Linear Predictive

Coding(LPC)

Filter

CodebookIndex

Codebook

PerceptualWeighting

ErrorAnalysis

SpeechGenerator

VocoderOutput BitsMUX

Voice, Tone Activity

Detectors

• Mode Indication bits

• Comfort Noise

• Tone Emulation

• DTX IndicationΣ

(+)

(-)

PredictionError

Benefits of Activity Detection:

1)

2) Figure 1-12: ACELP/AMR Voice Coding

The multi-rate speech coder is a single integrated speech codec with eight source rates: 12.2 (GSM), 10.2, 7.95, 7.40, 6.70 (PDC), 5.90, 5.15 and 4.75 kbps. The AMR rates can be controlled by the radio access network. To facilitate interoperability with existing cellular networks some of the modes are the same as in existing cellular networks. The AMR is capable of switching its bit rate every 20 ms speech frame upon command.

The speech service in UMTS will employ the Adaptive Multi - rate technique.

This is a single integrated codec with eight source rates: 12.2, 10.2, 7.95, 7.40, 6.70, 5.90, 5.15 and 4.75 kbps. To facilitate interoperability with existing cellular networks some of the modes are the same as in existing networks.

Figure 1-13: AMR (Adaptive Multi-rate)

The bit rate of the AMR speech connection is controlled by the radio access network depending on the air interface loading and the quality of the speech connections. During high loading, such as during busy hours it is possible to use lower AMR bit rates to offer higher capacity while providing slightly lower speech quality. Also if the mobile is running out of the cell coverage area and using its maximum transmission power a lower AMR bit rate can be used to extend the cell coverage area.

WCDMA Air Interface

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Adaptive multi-rate also contains error concealment. The purpose of frame substitution is to conceal the effect of lost speech frames. If several frames are lost muting is used to prevent possibly annoying sounds as a result of the frame substitution.

ERROR DETECTION AND CORRECTION - CRC AND FEC CODING

In all radio systems the air interface will add noise to the signal (Figure 1-14). This will produce a distortion in the received signal. In the case of an analogue cellular system the human ear perform error correction of this received signal and noise. However in digital systems we do not have this luxury.

This noise will result in bit errors, that is what left the transmitter as a logic 1 could be interpreted as a logic 0 if the level of noise lowers the amplitude below the threshold for a logic 0. The same could be the case for a transmitted logic 0 being interpreted as a logic 1.

All digital systems must have some method of overcoming these errors.

Digital Cellular

Analog Cellular

Transmitted Signal Received Signal + Noise

Transmitted Signal Received Signal + Noise

Figure 1-14: Digital Cellular Error Correction

This concept can be related to addressing envelopes. The address on the left (Figure 1-15) contains just enough information to get to the destination. The envelope on the right contains some unnecessary or redundant data.

If both envelopes were subjected to the same amount of errors the one on the left would be undeliverable. However the redundant data in the right hand one would allow it to be delivered.


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A process that produces this error protection without increasing the bandwidth too much is required for cellular transmissions.

Example: Mailing a letter – Extra (redundant) symbols in address help correct lost symbols– ZIP codes used to detect errors in the address

With minimal data...Errors are uncorrectable

With redundant data...Errors are correctable

EM5 Main StreetLittletown

Eddie McConnell5 Main StreetLittletown LT1701

Figure 1-15: Digital Cellular Error Correction; Example: Mailing a letter in the US. Extra redundant symbols in address help correct symbols. ZIP codes are used to detect errors in the address.

CRC

Cyclic Redundancy Check (CRC) is used to detect if there are any uncorrected errors left after error correction.

Blocks of data are passed through a CRC generator (Figure 1-16), which will perform a mathematical division on the data producing a remainder or checksum. This is added to the block of data and transmitted.

The same division is performed on the data block in the receiver. If a different checksum is produced the receiver will know that there is an error in the block of data (alternatively there is an error in the received checksum). This knowledge is used to calculate Block Error Ratio (BLER) used in the outer loop power control.

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The longer the checksum, the greater is the accuracy of the process. In the example the checksum is twelve bits long. Twelve bits of binary information represents 4096 (212) different combinations. It could be imagined that various combinations of errors on the data and the checksum would produce the same checksum. The longer the checksum the less likely it is for this to happen.

Checksum 12 bits110010110011

Original Data

244 bits

CRC Generator

Original Data 1001011010..

CRC Generator

Re-Generated Checksum1100101100

Transmitter

Receiver

RF Transmission Path

01

Received Data 100101

Received Checksum

110010110011

If Checksums do not match, there is an error0010..

Figure 1-16: CRC Coding

WCDMA specifications (Figure 1-17) specify a range of checksum lengths ranging from 0 to 24 bits. PKzip, used to compress files in the computer industry uses a 32-bit checksum for greater accuracy.

CRC Algorithms– 0, 8, 12, 16, or 24 parity bits (determined by upper layers)

g(CRC24) = D24 + D23 + D6 + D5 + D + 1

g(CRC16) = D16 + D12 + D5 + 1

g(CRC12) = D12 + D11 + D3 + D2 + D + 1

g(CRC8) = D8 + D7 + D4 + D3 + D + 1

3GPP TS 25.212¶ 4.2.1.13GPP TS 25.212¶ 4.2.1.1

Figure 1-17 CRC Algorithms, parity bits

FEC

The next part in the transmitter is Forward Error Correction (FEC). The function of this block is to help the receiver correct bit errors caused by the air interface.


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One method for correcting these errors would be to send the information a number of times (Figure 1-18). Provided this is more than twice, the receiver could select which message is most correct by a “best out of three” decision. The more times the data is transmitted the better is the error protection. However the bandwidth is also increased proportionally

What is required is a system that provides forward error correction with minimal increase in the bandwidth.

Sendmessage

many times?

010010110,010010110,010010110,010010110,010010110,

•••

ForwardError

Correction!

Up to 6x data expansion...

But the most powerful results

Figure 1-18: FEC Coding. How do you correct errors at the receiver?

There are two basic types of FEC available, block or continuous codes.

– Block Codes (Hamming Codes, BCH Codes, Reed-Solomon Codes)Data is processed into unique CodewordsEach Codeword can be positively identified even if one or more bits are corruptedExample: “Little Town” is a code word for “LT”.

– Continuous Codes (Convolutional Codes, Turbo Codes)Data is processed continuously through FEC generatorResulting data stream has built-in redundancy that can be extracted to correct bit errors.

– IS-95, cdma2000, and WCDMA utilize Convolutional Codes for the services speech and signaling

Powerful error correctionSimple implementation allows low-latency, real-time processing

– cdma2000 and WCDMA utilize Turbo Codes for all other servicesMost powerful error correctionMore processing power (MIPS) required for decoding

Figure 1-19: FEC Coding Approaches

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Block codes work by processing the data into unique code words. This would be similar to transmitting “New York City” to represent ‘NYC’. These redundant bits provide the error correction. As this type of system works on blocks of data it is not suitable for conversational transmissions.

Continuous codes, such as convolutional codes and turbo codes, on the other hand, are continuously produced as the data is fed to the FEC. The result will contain redundant bits that help to correct errors.

WCDMA will utilize convolutional coding, for low data rates where a low latency and real time processing are required as speech and signaling. All other services where latency and processing power is not a problem turbo coding may be used. This type of coding gives a much better error correction performance than traditional methods.

Convolutional coding

Figure 1-20 gives a high level overview of the operation of the Convolutional coder.

Original Data 00011011...

FEC Generator

FEC Encoded data 1010011100110110...

Original Data 00011011

Viterbi/ Turbo

Decoder

Transmitter

Receiver



FEC Generator


FEC Generator

FEC Encoded data 1010011100110110...FEC Encoded data 1010011100110110...


Viterbi/ Turbo

Decoder


Viterbi/ Turbo

Decoder

Transmitter

Receiver



Figure 1-20: FEC Coding: The Convolutional Coder.


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The original data is fed to the FEC generator, which in this case produces twice as much data. A coder that produces this increase, that is, two bits out for one bit in is known as a 1/2 rate coder. One that produces three bits of information for one input is known as a 1/3 rate coder. This output is not simply the input data repeated; it will be subjected to noise superimposed by the RF transmission path.

In the receiver, a device known as a ‘Viterbi Decoder’ is used to correct these errors and recover the original data. This device works by taking the actual level of the data and estimating whether this was a 1 or a 0 when it left the transmitter, rather than use thresholds for 1 and 0.

D DInput Data 1010...

MUX

X2k+1

X2k

Coder Output

clock

R = 1/2 , k=2 Convolutional Coder

• For every input bit, there are two output bits

• The maximum time delay is 2 clock cycles Figure 1-21: Convolutional Coding Example.

Figure 1-21 shows how a simple Convolutional coder could be created using two shift registers, two XOR gates and a multiplexer. For every input data bit there will be two output bits produced X2k

and X2k+1.

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State DiagramFEC Coding: Example

State [00]

State [01]

State [10]

State [11]

State [00]

State [01]

State [10]

State [11]

11

00

10

01

11

x2k x2k+1 = Coder Output

ClockC cle

CurrentInput

DelayedInputs

Outputs

00

01

10

y

Dk Dk-1 Dk-2 X2k X2k+1

1 0 0 0 0 0

2 1 0 0 1 1

3 0 1 0 0 1

4 1 0 1 0 0

5 1 1 0 1 0

6 1 1 1 0 1

7 0 1 1 1 0

8 0 0 1 1 1

X2k = (Dk) XOR (Dk-2)

X2k+1 = (Dk) XOR (Dk-1) XOR (Dk-2)

STATE

Figure 1-22: FEC Coding Example Continued.

X2k will be made up from the present input bit Dk exclusive OR’d with the twice previous input bit (Dk-2). X2k+1 will be Dk exclusive OR’d with the last input bit (Dk-1) and the twice previous bit Dk-2.

Figure 1-22 shows what these outputs will be for an input data stream of 0,1,0,1,1,1,0,0. Also shown is a state diagram for this operation. By taking the present and past bit as the input state the options for sending two bits of data is reduced from (22) four to only two. This is the power behind the decoder since two bits of data are used to signal the state change of the input, which can only be one of two options.

Convolutional coding is applied for standard services requiring BERs up to 10-3, which is the case for voice applications. The constraint length for the proposed convolutional coding schemes is 9. Both 1/2 rate and 1/3 rate convolutional coding has been specified. Turbo Coding is required for high-quality services that require BERs from 10-3 to 10-4 Convolutional codes are usually described using two parameters, the code rate and the constraint length (Figure 1-23). The code rate, k/n, is expressed as the ratio of the number of bits input to the convolutional encoder (k) to the number of channel symbols output from the convolutional encoder (n) in a given encoder cycle.

The constraint length parameter, K, denotes the length of the convolutional encoder, that is, how many k-bits stages are available to feed the combinatorial logic that produces the output symbols. Closely related to K is the parameter m, which indicates how many encoder cycles an input bit is retained, and used for encoding after it first appears as input to the convolutional encoder. The m parameter can be thought of as the memory length of the encoder.


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3GPP TS 25.212¶ 4.2.3.13GPP TS 25.212¶ 4.2.3.1

DD D D D D D DDataIn

2:1MUX

DataOut

DD D D D D D DDataIn

3:1MUX

DataOut

Rate 1/2, k=9 coder: G0 = 5618 , G1 = 7538

Rate 1/3 , k=9 coder: G0 = 5578 , G1 = 6638 , G2 = 7118

Figure 1-23: WCDMA Convolutional Code Generators

Viterbi decoding

Viterbi decoding process (Figure 1-24) can be described in the following steps:

1. Calculate Branch Metric for each possible state transition

BM = (|R1 - T1| + |R2 - T2|)2

R1, R2 = Received data values

T1, T2 = Transmitted data values

2. Calculate Cumulative Path Metric.

Path Metric is the sum of “N” previous Branch Metrics (N is memory depth of Viterbi Decoder).

3. Calculate surviving path.

The surviving path is the path with the lowest Path Metric.

4. Extract the error-corrected data.

The error-corrected data sequence is equal to the first bit of each state code along the surviving path.

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Viterbi Decoding Process:

1) Calculate Branch Metric for each possiblestate transition

BM = (|R1 - T1| + |R2 - T2|)2

R1 , R2 = Received data values

T1 , T2 = Transmitted data values

2) Calculate Cumulative Path Metric

Path Metric is sum of “N” previousBranch Metrics (N is memory depthof Viterbi Decoder).

3) Calculate surviving Path

The surviving path is the pathwith the lowest Path Metric.

4) Extract the error-corrected Data

The error-corrected data sequenceis equal to the first bit of each statecode along the surviving path

Example:Received Signal R1,R2 = [0 1]

T1,T2 = [0 0]

T1,T2 = [0 1]

T1,T2 = [1 1]

T1,T2 = [1 1]

T1,T2 = [0 0]

T1,T2 = [0 1]

T1,T2 = [1 0]

T1,T2 = [1 0]

State [00]

State [01]

State [10]

State [11]

State [00]

State [01]

State [10]

State [11]

1

0

1

1

1

4

4

0

= Branch Metric

Figure 1-24: Viterbi Decoder.

The Viterbi decoder is built on top of a trellis tree consisting of stages and transitions. The basic operation consists of branch metric calculations based on path selection and back-tracing. The branch metric processing involves calculation of 2k values (k=constraint length) for each received bit. In the example given above k=2 which leaves us with four different states. For each state there exists only two possibilities, either 0 or 1. If the received signal is [01] then our initial state is either [10] and the next state is [01] or the initial state is [11] and the next state is [11]. This is true since the branch metric calculation is minimal for these transitions (BM=0).The four possible states of the encoder are depicted as four rows of horizontal dots. There is one column of four dots for the initial state of the encoder and one for each time instant during the message. For a 4-bit message with two encoder memory flushing bits, there should be six time instants in addition to t=0, which represents the initial condition of the encoder. It should be clear that since the initial condition of the encoder is state [00], and the two memory flushing bits are zeroes, the state starts out at state [00] and ends up at the same state.


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Each time we receive a pair of channel symbols, we are going to compute a metric to measure the “distance” between what we received and all the possible channel symbols pairs we could have received. The first pair channel symbol can be either 00 or 11. That is because we know the convolutional encoder was initialized to the all zero state and given one input bit 1 or 0. In the second pair channel symbols, branch metric is computed for four different possibilities. For each transition the branch metric result is added to the next transition result. The operation of adding the previous accumulated error metric to the new branch metric, comparing the results, and selecting the smallest value to be retained for the next instant is called the add-compare-select operation. Figure 1-25 shows a noise-free example where the received signal is a pure combination of 1s and 0s.

1 1

1 1

0 1

0 1

0 0

0 0

1 0

1 0

4 1 0 1

1 4

0

1 41

01 4

41 0

0 1

Transmitted Data:

Received Data:

[0 0]

[0 1]

[1 0]

[1 1]

[0 0]

[0 1]

[1 0]

[1 1]

0

0

0

0

Path with lowest path metric has the least likelihood of error

Output --->> 0 1 0 1 1 Figure 1-25: Viterbi Decoding, No Noise.

1 1

1.1 0.8

0 1

-.3 1.2

0 0

0.6 0.5

1 0

0.8 0.3

3.61 2.25 1.21 1.21

0.09

2.25

0.810.81

.25 2.25

6.25

0.25

1.211.21

Transmitted Data:

Received Data:

[0 0]

[0 1]

[1 0]

[1 1]

[0 0]

[0 1]

[1 0]

[1 1]

.09

.34

1.55

1.80

0.81 0.81

Output --->> 0 1 0 1 1

1.15 2.36

3.80

1.96

Figure 1-26: Viterbi Decoding, With Noise.

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Figure 1-26 shows how the Viterbi decoder recovers a noisy received data signal easily. Notice that the path through the trellis of the actual transmitted message, shown in bold, is associated with the accumulated error metric. The decoding process begins with building the accumulated error metric for a number of received channel symbol pairs. At each step, it accumulates the smallest accumulated error metric from the preceding state. Looking at step 3 in the example above, the path from state [01] to [00] is smaller than the path [01] to [10], but the latter path has been chosen. This is because the actual path that determines the transmitted data signal should be pointed out after computing the branch metric up to the end of the message signal for all possible paths. Then the path with the smallest accumulated error metric .

Interleaving

Many radio propagation effects such as reflection can attenuate the transmitted radio signal Figure 1-27.

Figure 1-27: Multipath Fading. The received signal contains many time-delayed replicas.

This occurs when the propagation wave reflects on an object, which is large compared to the wavelength, for example, the surface of the earth, buildings, walls, etc. This phenomenon is called multipath propagation and it has several effects, these are:

• Rapid changes in signal strength over a small area or time interval

• Random frequency modulation due to varying Doppler shifts on different multipath signals.


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• Time dispersion caused by multipath propagation delays

Multipath propagation yields signal paths of different lengths with different times of arrival at the receiver. Typical values of time delays (µs) are 0.2 in Open environment, 0.5 Suburban and 3 in Urban.

Direct S ignal

Reflected Signal

Com bined Signal

Figure 1-28: Multipath Fading.

The combination of direct and out-of-phase reflected waves at the receiver yields attenuated signals (Figure 1-28). This attenuation can result in bit errors that occur in consecutive blocks of data. As a result the Viterbi decoder fails to recover such errors. The solution to overcome this problem is to use a block interleaving technique as shown in Figure 1-29.

Time

Am

plitu

de

To Viterbi decoder

Original Data Samples1 2 3 4 5 6 7 8 9

Interleaving Matrix

1 2 34 5 67 8 9

Transmitter

Interleaved Data Samples1 4 7 2 5 8 3 6 9


Interleaved Data Samples1 4 7

ReceiverDe-

Interleaving Matrix

1 2 34 5 67 8 9

De-Interleaved Data Samples1 2 5 8 3 6 9

Errors Clustered

2 3 4 5 6 7 8 9

Errors Distributed

Figure 1-29: Block Interleaving.

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A radio channel produces bursty errors. Because convolutional codes are most effective against random errors, interleaving is used to randomize the bursty errors. The interleaving scheme can be either block interleaving or convolutional interleaving. Typically, block interleaving is used in cellular applications. The first step of interleaving is determined by the delay requirements of the service. Speech service, for example uses 20 ms of interleaving and PS 384 kbps uses 10 ms of interleaving (Figure 1-30). Different services and signaling are multiplexed together on one physical channel after frame segmentation and then a second stage of interleaving is used which is always 10 ms long.

Interleaving

– 1st-Stage InterleaverPerformed prior to service multiplexing

Interleaving depth of 1, 2, 4, or 8 columns. (10,20,40 or 80 ms)

– 2nd-Stage Interleaver

Performed after service multiplexing

Interleaving depth of 30 columns (always 10 ms)

3GPP TS 25.212 ¶ 4.2.5 , 4.2.113GPP TS 25.212 ¶ 4.2.5 , 4.2.11

Figure 1-30: 1st and 2nd Interleavers

Turbo Codes

Turbo Codes are newly introduced parallel, recursive, and systematic convolutional codes. These codes are used for channel coding and decoding in order to detect and correct errors occurring in the transmission of digital data through different channels

The iterative method of the decoding scheme helps to achieve the theoretical limit (near Shannon-limit) in error correction performance. Each decoder uses the received data and extrinsic information, which has been delivered by the preceding decoder to give decoded data and new extrinsic information. Interleaving helps the decoders to improve their correction capability by keeping the extrinsic information with the received data un-correlated.

The Turbo code structure is based on a combination of two or more weak error control codes Figure 1-31.


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Encoder #1

Encoder #2

MUX

DataDecodedData

DE-MUX

Decoder #2

D

P1

P2

D

P1

P2

D

Turbo Encoder Turbo Decoder

Interleaver

Interleaver

Inte

rlea

ver

De-

Inte

rlea

ver

Decoder #1

Figure 1-31: Turbo Coding.

The data bits are interleaved between two encoders, generating two parity streams. The whole process results in a code that has powerful error correction properties. A more detailed figure of the turbo coder is shown in Figure 1-32.

Data InRate = X

MUX

Data Out

3x input bits + 12 Termination bits

Xk

Xk

Zk

TurboInterleaver

X’k

Z’k

At end of data block, both switches go “down” to provide 12-bit Trellis Termination: [ xK+1, zK+1, xK+2, zK+2, xK+3, zK+3, x'K+1, z'K+1, x'K+2, z'K+2, x'K+3, z'K+3 ]

3GPP TS 25.212¶ 4.2.3.23GPP TS 25.212¶ 4.2.3.2

D D D

D D D

Figure 1-32: WCDMA Turbo Code Generator

Rate matching

Rate matching is performed on the data to change the data rate to one that can be accommodated by the system. It should be noted that this function could not only be used to reduce the data rate (by puncturing bits) but also to increase the data rate (by padding it with extra bits).

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– When coded data rates of services are incompatible, “Rate Matching” is used to equalize the data rates.

– Rate Matching may be performed by:

Padding with extra bits

Puncturing of bits using a pseudo-random algorithm

– For complete rate matching rules, see 3GPP TS25.212 ¶ 4.2.7

3GPP TS 25.212 ¶ 4.2.73GPP TS 25.212 ¶ 4.2.7

Figure 1-33:Rate Matching

CHANNELIZATION CODES

The main purpose of the channelization codes is to separate the data channels in the uplink and the downlink coming from the same transmitter.

Scrambling Codes (also sometimes called PN codes, Spread SpectrumMultiple Access Codes, Long codes or Spreading codes):

Allows multiple WCDMA transmitters to share the same Radio Frequency

Channelization codes (also sometimes called orthogonal codes, short codes, Walsh codes or Spreading codes)

Allows multiple data channels to be sent from each transmitter (cell or UE)

Figure 1-34: WCDMA Codes

Note that channelization codes have many names like orthogonal, short, spreading and Hadamard codes.

Channelization codes requires synchronization, since the waveforms are orthogonal only if they are aligned in time. Figure 1-35 shows three different correlation cases using channelization codes:

a) Same channelization code. This means that the receiver and transmitter use identical codes with the same time offset.


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b) Different channelization codes.

c) Same channelization code but with non-zero offset.

Input Data +1 -1 +1

-1 +1 –1 +1 +1 –1 +1 -1 -1 +1 –1 +1 +1 –1 +1 -1 -1 +1 –1 +1 +1 –1 +1 -1

-1 +1 –1 +1 +1 –1 +1 -1 +1 –1 +1 –1 –1 +1 –1 +1 -1 +1 –1 +1 +1 –1 +1 -1

-1 +1 –1 +1 +1 –1 +1 -1 +1 +1 +1 +1 +1 +1 +1 +1 -1 -1 +1 –1 +1 +1 –1 +1

+1 +1 +1 +1 +1 +1 +1 +1 +1 –1 +1 –1 –1 +1 –1 +1 +1 –1 –1 –1 +1 –1 –1 -1

Channelization codein Transmitter

TransmittedSequence

Channelization Codeused in Receiver

8 0 -4

IntegrateResult

+1 0 -0.5Divide by

Code Length

Case III: Correlation using channelization codes

(a) Same channelization code; (b) Different channelization codes; (c) Same code with non-zero time offset

x x x

Integrate Integrate Integrate

= = =

x x x

= = =

Transmitter

Receiver

Input Data +1 -1 +1

-1 +1 –1 +1 +1 –1 +1 -1 -1 +1 –1 +1 +1 –1 +1 -1 -1 +1 –1 +1 +1 –1 +1 -1

-1 +1 –1 +1 +1 –1 +1 -1 +1 –1 +1 –1 –1 +1 –1 +1 -1 +1 –1 +1 +1 –1 +1 -1

-1 +1 –1 +1 +1 –1 +1 -1 +1 +1 +1 +1 +1 +1 +1 +1 -1 -1 +1 –1 +1 +1 –1 +1

+1 +1 +1 +1 +1 +1 +1 +1 +1 –1 +1 –1 –1 +1 –1 +1 +1 –1 –1 –1 +1 –1 –1 -1

Channelization codein Transmitter

TransmittedSequence

Channelization Codeused in Receiver

8 0 -4

IntegrateResult

+1 0 -0.5Divide by

Code Length

Case III: Correlation using channelization codes

(a) Same channelization code; (b) Different channelization codes; (c) Same code with non-zero time offset

x x x

Integrate Integrate Integrate

= = =

x x x

= = =

Transmitter

Receiver

Figure 1-35: Code Correlation: Correlation Using Channelization Codes.

The correlation in case a) is 100% and the channel is perfectly reconstructed. In case b) the codes (channels) are perfectly separated and the correlation is 0%. In case c) the result is unpredictable which shows that the timing is very important to preserve the orthogonal properties of the code.

Figure 1-37 shows an example of channelization coding of four data channels (Channelization Code, CC 1-4 used) at the transmitter side. This case could represent, for example, the downlink, where each specific channel is multiplied by a channelization code. The received signal is correlated with Channelization Code (CC) 3, which reconstructs data channel 3 perfectly.

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TX, RX use same codes, at the same time offset

Channelization Codes: 100% correlation

TX, RX use different codes

Channelization Codes: 0 % correlation (perfect separation)

TX, RX use same codes, but at different time offsets

Channelization Codes: Unpredictable results (orthogonalityis lost)

Figure 1-36: Code Correlation: Key Points

In this example, the receiver correlates the composite received signal using Channelization Code 3.

The result is a perfect reconstruction of Data Channel #3, with no interference from the other data channels.

To realize this perfect cross-correlation property, it is essential that the channelization codes be received in perfect timing relation to each other.

CC 4

CC 3

CC 2

CC 1

RFModulation

RFDemod

CC 3

Data Channel 1

Data Channel 2

Data Channel 3

Data Channel 4

Receiver

Linear Addition

Transmitter

Figure 1-37: Channelization coding.

Each data symbol of the data is XOR operated with the corresponding channelization code (Figure 1-38). The length of the channelization code depends on the user data rate. After the operation, the output will always end up with a rate of 3.84 Mchips/s.


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User 1 Data:

1 10

Multiply with channelization Code

1 –1 1-1

User 1 channelization coded data:

-1 1-1 1 1-1 1-1 -1 1-1 1

You send one channelization code for every data bit!

If you want to send a digital “0”, you transmit the assigned channelizationcode

If you want to send a digital “1”, you transmit the inverted channelizationcode

Transmitted “chips”Data

Channelization code

D/A conv.

+1-1 -1

Figure 1-38: Channelization Codes.

The output from the XOR is the sum of each channel data stream and its corresponding CC.

Figure 1-39 shows an example of four different channels being coded and sent from the same transmitter. After the channelization codes are multiplied by each channel, they are added together to form a composite transmitted data stream.

Data Channel 1

0 1 0

Data Channel 2

0 0 1

Multiply with CC1

(1 1 1 1)

Multiply with CC2

(1 1-1-1)

After channelization coding

(+1+1+1+1)(-1-1-1-1)(+1+1+1+1)

∑

Composite Transmitted Data:

(+2 +2 -2 +2) (+2 -2 -2 -2) (0 0 0 +4)

Data Channel 3

1 0 1

Multiply with CC3

(1–1 1-1)

4-chipChannelization Code Set

1) 1 1 1 12) 1 1 -1 -13) 1 –1 1 -14) 1 -1 -1 1

After D/A Mapping

+1 –1 +1


(+1+1-1-1)(+1+1-1-1)(-1-1+1+1)

After D/A Mapping

+1 +1 –1


(-1+1-1+1)(+1-1+1-1)(-1+1-1+1)

After D/A Mapping

-1 +1 -1

Data Channel 4

0 0 0

Multiply with CC4

(1-1-1 1)


(+1-1-1+1)(+1-1-1+1)(+1-1-1+1)

After D/A Mapping

+1 +1 +1

Data Channel 1

0 1 0

Data Channel 2

0 0 1

Multiply with CC1

(1 1 1 1)

Multiply with CC2

(1 1-1-1)


(+1+1+1+1)(-1-1-1-1)(+1+1+1+1)

∑

Composite Transmitted Data:

(+2 +2 -2 +2) (+2 -2 -2 -2) (0 0 0 +4)

Data Channel 3

1 0 1

Multiply with CC3

(1–1 1-1)

4-chipChannelization Code Set

1) 1 1 1 12) 1 1 -1 -13) 1 –1 1 -14) 1 -1 -1 1

After D/A Mapping

+1 –1 +1


(+1+1-1-1)(+1+1-1-1)(-1-1+1+1)

After D/A Mapping

+1 +1 –1


(-1+1-1+1)(+1-1+1-1)(-1+1-1+1)

After D/A Mapping

-1 +1 -1

Data Channel 4

0 0 0

Multiply with CC4

(1-1-1 1)


(+1-1-1+1)(+1-1-1+1)(+1-1-1+1)

After D/A Mapping

+1 +1 +1

Figure 1-39: Channelization Coding example - Transmitter.

Figure 1-40 shows how the composite received data is decoded at the receiver. Notice that the properties of the channelization code are also valid for when a sum of channelization streams is decoded, regardless of how much power there is in the other codes.

WCDMA Air Interface

- 44 - © Ericsson 2005 LZT 123 7279 R5B

Integrate &

Normalize

Integrate &

Normalize

Integrate &

Normalize

Integrate &

Normalize

Result:

1 -1 1

Result:

1 1 -1

Result:

-1 1 -1

Result:

1 1 1

Integrate: Sum four consecutive values after multiplication with CC.

Normalize: Multiply by [ 1 / code length]

“Correlation”

Composite Received Data:

(+2 +2 -2 +2)(+2 -2 -2 -2)(0 0 0 +4)

Multiply with CC1

(+1 +1 +1 +1)

Multiply with CC2

(+1 +1 -1 -1)

Multiply with CC3

(+1 -1 +1 -1)

Multiply with CC4

(+1 -1 -1 +1)

Map A→D

0 1 0

Map A→D

0 0 1

Map A→D

1 0 1

Map A→D

0 0 0

4-chip Channelization Code Set

1) 1 1 1 12) 1 1 -1 -13) 1 –1 1 -14) 1 -1 -1 1

Figure 1-40: Channelization Coding example - Receiver.

Figure 1-41 shows the usage of the channelization codes in the uplink and the downlink.

CC1, CC2CC3, CC4

CC5, CC6, CC7

CC1 , CC2, CC3CC1, CC2

CC1, CC2, CC3, CC4

Uplink: Channelization Codes used to distinguish data channelscoming from each User Equipment, UE

Downlink: Channelization Codes used to distinguish data channelscoming from each cell

Figure 1-41: Uplink and Downlink Channelization Code Usage.

In the downlink, the channelization codes are used to separate the different data channels coming from each cell. For the dedicated channels, this represents the different users since only one scrambling code is used for all downlink transmission from the cell.


LZT 123 7279 R5B © 2005 Ericsson - 45 -

In the uplink, the channelization codes are used to separate the different data channels sent from the UE to the each cell. The separation of the different UEs will here be done with different scrambling codes.

Figure 1-42 shows the channelization code tree. Two codes are said to be orthogonal when their inner product is zero. The inner product is the sum of all the terms we get by multiplying two codes element by element.

For example, (1, 1, 1, 1) and (1, 1, -1, -1) are orthogonal since (1 * 1) + (1 * 1) + (1 * -1) + (1 * -1) = 0

1

11 1-1

1111 11-1-1 1-11-1 1-1-11

1111-1-1-1-111111111 11-1-1-1-11111-1-111-1-1 1-11-1-11-111-11-11-11-1 1-1-111-1-11 1-1-11-111-1

Digital/Analog Mapping

logic 0 ↔ analog +1logic 1 ↔ analog - 1

11-1-111-1-111-1-1 11-1-1

Figure 1-42: Channelization Code Generation.

The code tree corresponds to different discrete Spreading Factor (SF) levels, SF=1, 2, 4, 8…(n2). Different spreading factor levels mean different code lengths, and they are therefore normally referred to as Orthogonal Variable Spreading Factors (OSVF). The idea is to be able to combine different messages with different spreading factors and keep the orthogonality between them. We therefore need codes of different length that are still orthogonal. Of course, the chip rate remains the same for all codes, so short ones will be transmitted at a higher information rate than longer ones. The longer the code is the lower will the data rate be and the other way around. The spreading factor corresponds to the length of the code and the number of channels sending at a certain bit rate.

• SF: 4-512 is allowed in the WCDMA DL.

• SF: 4-256 is allowed in the WCDMA UL.

How much the channelization code spreads the signal depends on its variation. The scrambling codes, on the other hand, always have a high transition rate and will therefore always spread and affect the signal bandwidth needed.

WCDMA Air Interface

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1

11 1-1

1111 11-1-1 1-11-1 1-1-11

1111-1-1-1-111111111 11-1-1-1-11111-1-111-1-1 1-11-1-11-111-11-11-11-1 1-1-111-1-11 1-1-11-111-1

480 ksymbol/s 480 ksymbol/s 480 ksymbol/s 480 ksymbol/s 480 ksymbol/s 480 ksymbol/s 480 ksymbol/s 480 ksymbol/s

Chip Rate = 3.840 Mcps1

11 1-1

1111 11-1-1 1-11-1 1-1-11

1111-1-1-1-111111111 11-1-1-1-11111-1-111-1-1 1-11-1-11-111-11-11-11-1 1-1-111-1-11 1-1-11-111-1

480 ksymbol/s 480 ksymbol/s 480 ksymbol/s 480 ksymbol/s 480 ksymbol/s 480 ksymbol/s 480 ksymbol/s 480 ksymbol/s

Chip Rate = 3.840 Mcps

Figure 1-43: Usage of the channelization code tree

Figure 1-43 shows an example of the allocation of the code tree for eight users sending at the same rate of 480 ksps.

Figure 1-44 below shows an example of four users sending at SF = 8 and one user sending at SF = 2.


480 ksymbol/s 480 ksymbol/s 480 ksymbol/s 480 ksymbol/s

1

11 1-1

1111 11-1-1 1-11-1 1-1-11

1111-1-1-1-111111111 11-1-1-1-11111-1-111-1-1 1-11-1-11-111-11-11-11-1 1-1-111-1-11 1-1-11-111-1

User with 4x Bit Rate

= Unusable Code Space

1.92 Msymb/s


480 ksymbol/s 480 ksymbol/s 480 ksymbol/s 480 ksymbol/s

1

11 1-1

1111 11-1-1 1-11-1 1-1-11

1111-1-1-1-111111111 11-1-1-1-11111-1-111-1-1 1-11-1-11-111-11-11-11-1 1-1-111-1-11 1-1-11-111-1

User with 4x Bit Rate

= Unusable Code Space

1.92 Msymb/s

Figure 1-44: Usage of the channelization code tree

It should be noted that any two codes of different layers are also orthogonal except when one of the two codes is a mother code of the other. Therefore, if a UE is transmitting data with 960 kbps, SF=4, the other branches of this mother code cannot be used any more. Figure 1-45 gives a summary of the channelization codes.


LZT 123 7279 R5B © 2005 Ericsson - 47 -

Each Data Stream has a unique

Channelization Code



Frequency

CodeD ivision Multiple Access WCDMA allows multiple data streams to be

sent on the same RF carrier– Perfect isolation between data streams– Timing between data streams must be exact– Maximum number of data channels =

Channelization code lengthThe longer the code, the slower the data rate

WCDMA advantages are limited in practice– Multipath, small timing errors, and motion-

related effects diminish the usable code space

Data 1

Data 2

Data 3

...

Figure 1-45 Summary of Channelization Codes

SCRAMBLING CODES

In WCDMA each user is assigned a unique code, which it uses to encode its information-bearing signal. The receiver, knowing the code sequences of the user, decodes a received signal after reception and recovers the original data. Spreading codes are divided into scrambling codes and channelization codes (CC). Each transmitter (cell in downlink) is assigned a different scrambling code and each data channel is assigned different CC code.

Since the bandwidth of the scrambling code is chosen to be much larger than the bandwidth of the information-bearing signal, the encoding process enlarges the spectrum of the signal. The resulting signal is also called a spread spectrum signal, and WCDMA is often denoted as spread spectrum multiple access.

A simple analogy to explain the concept of scrambling codes is to use that of a cocktail party (Figure 1-46).

WCDMA Air Interface

- 48 - © Ericsson 2005 LZT 123 7279 R5B

What do YOU hear...

•If you only speak Japanese?

•If you only speak English?

•If you only speak Italian?

•If you only speak Japanese, but the Japanese-speaking person is all the way across the room?

•If you only speak Japanese, but the Spanish-speaking person is talking very loudly?

Figure 1-46: The WCDMA Cocktail Party.

Imagine that you are invited to a cocktail party where the invited people speak different languages such as Japanese, Russian, Spanish and Italian. What would you then hear:

1. If you only speak Japanese?

2. If you only speak English?

3. If you only speak Italian?

4. If you only speak Japanese, but the Japanese-speaking person is all the way across the room?

5. If you only speak Japanese, but the Spanish-speaking person is talking very loudly?

In the first case the Japanese speaking person would understand the Japanese speaking persons and be able to follow their conversation. The other persons speaking other languages will on the other hand not be possible to understand and will only be interpreted as noise.

In the second case there is no English speaking person at the cocktail party and everything will just be noise.


LZT 123 7279 R5B © 2005 Ericsson - 49 -

The third case is similar to the first with the difference that the Italian speaking person not only will understand the other Italian speaking persons, but also some Spanish, since there are common words in both the languages. The Spanish speaking persons can in this case be seen as interference. In case four, the Japanese speaking person will have to speak higher. This corresponds to a power increase due to, for example, path loss when the user is further away from the base station.

The final case shows a user that is using a power level that is too high. Since all the users in the system are transmitting at the same frequency at the same time, they will of course be dependent on the other users output power and will be strongly interfered by the by the user sending at an output power level that is too high. This shows that power is the common shared resource and that efficient and fast power control is essential in a WCDMA system to achieve and maintain a high capacity. In TDMA, during a timeslot for a particular user the base station can broadcast to the user and the user to the base station at whatever power they wish. This would be like one person shouting and everybody else staying quiet. However, WCDMA is like a cocktail party with social etiquette so everybody speaks at the same time but in a low voice so people can hear the conversation they are interested in.

Figure 1-47 shows an example of four transmitters. Each transmitter will use its unique scrambling code. All signals are sent over the air interface and received together at the receiver. To decode signal number 3 in the receiver, scrambling code number 3 will be used. The result will be that signal number 3 is recovered and all the other signals will only become low level noise as can be seen in the right part of the figure.

WCDMA Air Interface

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SC 1

RFModulation

Transmitter 1

SC2

RFModulation

Transmitter 2

SC3

RFModulation

Transmitter 3

SC4

RFModulation

Transmitter 4

RFDemod

SC3Receiver

In this example, the receiver correlates the composite received signal using Scrambling Code (SC) 3.

The result is the recovered transmission from Transmitter #3, plus some spread spectrum interference from transmitters #1, #2, and #4

Figure 1-47 Spread Spectrum Multiple Access

What can be seen from this correlation is that if the transmitter and receiver use the same codes with the same time offset there will be a 100% correlation.

What can be seen from this correlation is that if the transmitter and receiver use different codes with any time offset, the correlation will only result in a low level of noise. This correlation is proportional to the inverse of the code length (the scrambling code length is 38400 chips long). This is an important property of the code since the receiver will correlate the correct signal with all other signals at the same time. It is also important that this is valid with any time offset since the users in the uplink are not synchronized to each other and also for the RAKE receiver (chapter 2) to handle multipath components.

Figure 1-48 shows how the incoming data stream is multiplied by a scrambling code, which is generated by a linear shift register with a starting sequence called a code key. If the signal were analyzed in a spectrum analyzer, a main lobe and side lobes would be seen. The side lobes are not wanted and will just occupy frequency band. The signal will therefore be sent through a filter, only to maintain the main lobe. In the last step after modulation the resulting signal can be seen. The properties of the signal will depend on the scrambling code characteristics and not on the initial incoming chips.


LZT 123 7279 R5B © 2005 Ericsson - 51 -

Pow

er S

pect

rum

Mag

nitu

de (d

B)

Scrambling Code Generator

Chip ClockFc >> Fd

RF Modulator

cos(ωrf*t)

Nulls @ N*Rc Frf

Filter

Scrambling Code Key

”Chips”

“Chips”

0 0.1 0.2 0.3 0.4 0.5 0.6-50

-40

-30

-20

-10

0

10

Frequency0 0.1 0.2 0.3 0.4 0.5 0.6

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Pow

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0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

x 107

-40

-20

0

20

40

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80

Frequency

Pow

er S

pect

rum

Mag

nitu

de (d

B)

Pow

er S

pect

rum

Mag

nitu

de (d

B)


Chip ClockFc >> Fd

RF Modulator

cos(ωrf*t)

Nulls @ N*Rc Frf

Filter

Scrambling Code Key

”Chips”

“Chips”

0 0.1 0.2 0.3 0.4 0.5 0.6-50

-40

-30

-20

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10

Frequency0 0.1 0.2 0.3 0.4 0.5 0.6

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x 107

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Frequency

Pow

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Mag

nitu

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Chip ClockFc >> Fd

RF Modulator

cos(ωrf*t)

Nulls @ N*Rc Frf

Filter

Scrambling Code Key

”Chips”

“Chips”

0 0.1 0.2 0.3 0.4 0.5 0.6-50

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-30

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10

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x 107

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60

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Frequency

Pow

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Mag

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de (d

B)

Figure 1-48: Why is it called spread spectrum?

If multiple users transmit a spread spectrum signal at the same time (Figure 1-49), the receiver will still be able to distinguish between the users provided each user has a unique code that has a sufficiently low cross correlation with the other codes. Cross correlating the code signal with a narrow band signal will spread the power of the narrow band signal thereby reducing the interfering power in the information bandwidth. The spread spectrum signal 1 is detected together with a interference signal 2. At the receiver the spread spectrum signal 1 is despread while the interference signal (signal 2) is still spread, making it appear as a background noise compared to the despread signal. The power gain when decoding signal 1 can be approximated to the ratio between the chip rate and the bit rate and is called the processing gain Gp. The processing gain is a result of both the spreading gain and the error protection gain.

WCDMA Air Interface

- 52 - © Ericsson 2005 LZT 123 7279 R5B

⎟⎠⎞

⎜⎝⎛=

rateBit rate Chip

Both signals “mixed” in the air interface

Scrambling Code 1

Frequency

Am

plit

ude

Signal 1

Scrambling Code 2

FrequencyA

mpl

itud

e

Signal 2

Spread SpectrumProcessing Gain

Scrambling Code 1

Signal 1 is reconstructedSignal 2 looks like noise

Both signals arereceived together

AT THE RECEIVER...

Case II: Two Transmitters at the same frequency

Figure 1-49: Two Transmitters at the Same Frequency.

TX, RX use same codes, at the same time offset

Scrambling Codes: 100% correlation

TX, RX use different codes

Scrambling Codes: “Low” (noise-like) correlation at any time offset

Average correlation level proportional to 1/(code length)

TX, RX use same codes, but at different time offsets

Scrambling Codes: “Low” (noise-like) correlation for any offset > +1 chip

Figure 1-50: Code Correlation: Key Points

Figure 1-51 shows a summary of the scrambling code properties.

– Scrambling Codes may be generated using Linear Feedback Shift Registers

– Scrambling Codes are repeating, defined-length blocks of 1’s and 0’s

Approximately equal number of 1’s and 0’sThe statistics appear randomly distributed within the block

– Good Autocorrelation and Cross-Correlation propertiesScrambling Code cross-correlation properties do not depend on time alignment

Figure 1-51: Summary of scrambling code properties


LZT 123 7279 R5B © 2005 Ericsson - 53 -

Shift register sequences are not orthogonal, but they do have a narrow autocorrelation peak. The name already makes clear that the codes can be created using a shift register with feedback taps (Figure 1-52). By using a single shift register, maximum length sequences (M) can be obtained. Such sequences can be created by applying a single shift register with a number of specially selected feedback taps. If the shift register size is (n) then the length of the code is equal to 2n-1. The number of possible codes is dependent on the number of possible sets of feedback taps that produce an M sequence.

The mathematics of these generators is equivalent to the operation of ordinary algebra applied to abstract polynomials over an indeterminate X, with binary valued coefficients. Each sequence is based on a generator polynomial

G(X)= bnXn + bn-1Xn-1 + bn-2Xn-2 +……+ b1X1 + 1

The uplink codes are generated using an 24-bit key and this key is given to the UE at call setup. The downlink codes are generated using an 18-bit key and these are fixed and used as needed.

• βn values are 0 or 1 (determined by the specified “generator polynomial”)

• Maximal-length (m-sequence) has a repetitive cycle of ( 2N - 1 ) bits

• A code of 16 777 215 bits can be replicated using only a 24-bit “key” in Uplink. In downlink a 18-bit “key” is used

D D

clock

D D

β1 β2 β3 βN

1010010010001110101..

Figure 1-52: Scrambling Code Generation

Figure 1-53 shows how each transmitter is assigned a different scrambling code.

WCDMA Air Interface

- 54 - © Ericsson 2005 LZT 123 7279 R5B

SC3 SC4

SC5 SC6

SC1 SC1

Cell “1” transmits using SC 1

SC2 SC2

Cell “2” transmits using SC 2

Figure 1-53: Scrambling Code Planning.

A WCDMA system transmits using one frequency and the transmitter identification is determined by the scrambling codes. The cell planning does not require frequency planning as in GSM systems, but requires scrambling code planning. Figure 1-54 shows a pattern of scrambling codes.

SC32

SC21

SC27SC26

SC36 SC37

SC39

SC25

SC14

SC20SC19

SC30 SC31

SC35 SC38

SC28

SC34SC33

SC40 SC41

SC42

SC11

SC4

SC7SC6

SC16 SC17

SC22

SC5

SC1

SC3SC2

SC9 SC10

SC15 SC18

SC8

SC13SC12

SC23 SC24

SC29

N

S

W E

Figure 1-54: Scrambling Code Planning example.


LZT 123 7279 R5B © 2005 Ericsson - 55 -

The number of codes used in the downlink is restricted to 8192 in total. This is done to speed up the process for the UE to find the correct scrambling code. 512 of these are primary codes (the rest are secondary codes, 15 codes per primary) divided into 64 code groups each group containing 8 different codes. The UE can determine which scrambling code group a cell is using by the synchronization procedure (see chapter 5). Note that there are no restrictions for the number of codes generated by the 24 bits start key in the uplink case.

Figure 1-55 summarize the scrambling code usage.

P

Fr

Scrambling Code Utilization– Used to distinguish the transmission source

(Cell or UE) in WCDMA systemsrovides good (but not 100%) separation

between multiple transmissions in the same geographic area, on the same frequency

– Works regardless of time-of-arrival delays– Code Planning instead of Frequency Planning

equency Reuse = 1

Limitations using Scrambling Codes– Imperfect signal separation– Not good for transmitting multiple data

streams from one transmitter

Each Transmitterhas a unique

Scrambling Code

Several Transmitters share the same frequency

and time

Frequency


Tx 1

Tx 2

Tx 3

...

Figure 1-55: Scrambling Code Summary

Finally to summarize both the channelization and scrambling codes see Figure 1-56.

- Scrambling Codes are used:To distinguish between User Equipments in uplinkTo distinguish between cells

– Channelization Codes are used:To distinguish between data channels coming from each User EquipmentTo distinguish between data channels from each cellScrambling Codes

and

Channelization Codes

are simultaneously utilized

Frequency

CodeD ivision Multiple Access


User 1

User 2

User 3

...

Figure 1-56: Channelization and scrambling code summary.

WCDMA Air Interface

- 56 - © Ericsson 2005 LZT 123 7279 R5B

Figure 1-57 shows how the codes are used together in a WCDMA network.

2 data channels(voice, control)

SC3 + CC1 + CC2

2 data channels(14 kbps data, control)

SC4 + CC1 + CC2

3 data channels(voice, video, control)

SC2 + CC1 + CC2 + CC3

3 data channels(voice, video, control)

SC5 + CC1 + CC2 + CC34 data channels

(384 kbps data, voice, video, control)SC6 + CC1 + CC2 + CC3 + CC4

4 data channels(384 kbps data, voice, video, control)

SC2 + CC4 + CC5 + CC6 + CC7

2 data channels(voice, control)

SC1 + CC1 + CC2

1 data channels(control)

SC1 + CC3Voice

Conversation Uplink Packet Data

Videoconference

Videoconference with Data

Pilot, BroadcastSC1 + CCP + CCB

Pilot, BroadcastSC2 + CCP + CCB

Figure 1-57: Code usage in a WCDMA network.

MODULATION

A simple form of digital modulation is binary or Bi-Phase Shift Keying (BPSK). The phase of a constant amplitude carrier signal moves between zero and 180 degrees. There are two possible locations in the state diagram, so a binary one (bipolar value –1) or zero (bipolar value +1) can be sent. The symbol rate is one bit per modulation symbol.

A more common type (Figure 1-58) of phase modulation is Quadrature Phase Shift Keying (QPSK). It is used extensively in applications including WCDMA cellular services. Quadrature means that the signal shifts between phase states, which are separated by 90 degrees.

Data Stream #1 “ Q ”

Data Stream #2 “ I ”

90o

SUM

cos (wt)

I cos(wt)

- Q sin(wt)

+1

-1

+1

-1 Figure 1-58: I/Q Modulation - two data streams are multiplied by a common carrier frequency, but at phase offsets of 0 degrees (cosine) and 90 degrees (sine).


LZT 123 7279 R5B © 2005 Ericsson - 57 -

The signal shifts in increments of 90 degrees from 45 to 135, -45, or -135 degrees. These points are chosen as they can be easily implemented using an I/Q-modulator. Both I- and Q-branch can shift between +1 and –1, which gives two bits per modulation symbol.

In the transmitter, I- and Q-signals are mixed with the same local oscillator. A 90-degree phase shifter is used and the signals are separated by 90 degrees. This results that they are orthogonal to each other or in quadrature. Signals that are in quadrature do not interfere with each other. They are two independent components of the signal.

I

( I = 1, Q = 1 )

( I = -1, Q = -1 )

( I = -1, Q = 1 )

( I = 1, Q = -1 )

Q

1 Modulation Symbol represents 2 data bits

Modulation efficiency = 2 bits/symbol

RF Carrier amplitude

RF Carrier phase angle

Figure 1-59: QPSK Modulation - graphical representation of an I/Q modulated signal.

Figure 1-59 is an example of a state diagram of a Quadrature Phase Shift Keying (QPSK) signal. There are four states possible. It is therefore a more bandwidth-efficient type of modulation than the BPSK, potentially twice as efficient.

The composite signal with magnitude and phase (I/Q) information arrives at the receiver input (Figure 1-60). The input signal is mixed with the local oscillator signal at the carrier frequency in two forms. One is at an arbitrary zero phase. The other has a 90-degree phase shift. The composite input signal is thus broken into two components, an In-phase (I) and a Quadrature (Q) branch.

WCDMA Air Interface

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90o

DEMOD

cos(wt)

Q cos(wt)

- I sin(wt)

LPF

LPF

Data Stream #1 “ I ”

Data Stream #2 “ Q ”

+1

-1

+1

-1 Figure 1-60: I/Q Demodulation - by multiplying the sine and cosine at the receiver, the original I and Q data streams are recovered.

These two components of the signal are independent and orthogonal. One can be changed without affecting the other. Normally, information cannot be plotted in a polar format and reinterpreted as rectangular values without doing a polar to rectangular conversion. This conversion is exactly what is done by the in-phase and quadrature mixing processes in a digital radio. A local oscillator, phase shifter and two mixers can perform the conversion accurately and efficiently.

FILTERING

Filtering allows the transmitted bandwidth to be significantly reduced without losing the content of the digital data (Figure 1-61). This improves the spectral efficiency of the signal.


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RF Modulator

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-60

-50

-40

-30

-20

-10

0

10

20

Frequency

Baseband filtering of data stream is required to contain RF bandwidth

Figure 1-61: Data Filtering.

There are many different varieties of filtering. The most common are:

• Raised cosine

• Square-root raised cosine

• Gaussian

Any fast transition in a signal, whether it is amplitude, phase, or frequency, will require a wide occupied bandwidth. Any technique that helps to slow down these transitions will narrow the occupied bandwidth. Filtering serves to smooth these transitions (in I/Q modulation). On the receiver end, reduced bandwidth improves sensitivity because more noise and interference are rejected.

Filtering can also create Inter-Symbol Interference (ISI). This occurs when the signal is filtered so that the symbols blur together and each symbol affects those around it. This level of ISI is determined by the time domain response or impulse response of the filter.

A Chebyshev equiripple FIR (finite impulse response) filter is used for baseband filtering in CDMA systems. With a channel spacing of 5 MHz and a symbol rate of 3.84 MHz, it is vital to reduce leakage to adjacent RF channels. A FIR filter means that the filter’s impulse response exists for only a finite number of samples. Equiripple means that there is a rippled magnitude frequency-response envelope of equal maxima and minima in pass-bands and stop-bands.

WCDMA Air Interface

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Figure 1-62 shows the impulse or time domain response of Chebyshev FIR filters. These filters have the properties that their impulse response rings at the symbol rate. The filter is chosen to ring, or have the impulse response of the filter crossing through zero, at the symbol clock frequency.

0 20 40 60 80 100 120 140 160 180 200-2

0

2

4

6x 10

-5

Channel Filter

(Digital Chebyshev, 10-tap, Fc = 0.2Fs)

0 10 20 30 40 50 60 70 80 90 100-1

-0.5

0

0.5

1

1.5

2

Ringing may interfere with subsequent bit decisions

Figure 1-62: Data Filtering, Ordinary Channel Filter: Impulse Response.

The sharpness of a raised cosine filter is described by alpha (α). Alpha gives a direct measure of the occupied bandwidth of a system and is calculated as (Figure 1-63):

occupied bandwidth=symbol rate x (1+ α)

If the filter had a perfect characteristic with sharp transitions and an alpha of zero, the occupied bandwidth would be equal to the symbol rate.

In a perfect world, the occupied bandwidth would be the same as the symbol rate, but this is not practical. An alpha of zero is impossible to implement. At the other extreme, take a broader filter with an alpha of one, which is easier to implement. The occupied bandwidth, in this case, will be twice the symbol rate. In practice, it is possible to implement an alpha below 0.2 and make good, compact, practical radio. WCDMA specifies alpha of 0.22.


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;0

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sin12

;

⎭⎬⎫

⎩⎨⎧

⎥⎦

⎤⎢⎣

⎡⎟⎠⎞

⎜⎝⎛ −−

TTT

T

πωα

T

TT

T

/)1(

/)1(/)1(

/)1(0

παω

παωπα

παω

+≥

+≤≤−

−≤≤

=)(ωH

α = 0.1

α = 0.3

α = 0.5

α = 0.7

α = 0.9WCDMA uses alpha = 0.22WCDMA uses alpha = 0.22

Figure 1-63: Raised-Cosine Data Filter, Equations.

Figure 1-64 shows the effect of alpha (α) on ringing effects (Inter Symbol Interference).

-0.4

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α = 0.01(Narrow filter)

α = 0.3(Wide filter)

t1 t2 t3 t4 t5 t6 t7 t8 t9

Notes:

1) Ringing = 0 at exact time instants where future data points are to be sampled

2) Low ‘alpha’ provides narrowest spectrum; best for reducing adjacent channel interference

3) High ‘alpha’ provides lowest ringing amplitude; best for reducing ISI

4) Theoretically, even filters with very low ‘alpha’ provide zero ringing at future sample points

5) Practically, low-alpha filters create greater ISI when there is timing jitter present

Figure 1-64: Raised-Cosine Data Filter: Impulse Response.

• Ringing = 0 at exact time instants where future data points are to be sampled.

• Low “alpha” provides highest ringing amplitude; best for reducing adjacent channel interference.

• High “alpha” provides lowest ringing amplitude; best for reducing ISI.

WCDMA Air Interface

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• Theoretically, even filters with very low “alpha” provide zero ringing at future sample points.

• Practically, low-alpha filters create greater ISI when there is timing jitter present.

The time response of the raised cosine filter goes through zero with a time period that exactly corresponds to the symbol spacing. At these time periods, the symbol does not interfere with the adjacent symbols.

One way to view a digitally modulated signal is with an eye diagram (Figure 1-65). Separated eye diagrams can be generated, one for the I-channel data and another for the Q-channel data.

0 50 100 150-0.4

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-0.2

0

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0.6

0.8

1

1.2

1.4

RaisedCosineFilter

ChebyshevFilter

Figure 1-65: Eye Diagram Comparison between Raised-Cosine Data Filter and Chebyshev Filter.

Eye diagrams display I-and Q-magnitudes versus time in an infinite persistence mode, with retrace. QPSK has four distinct I/Q-states, one in each quadrant. There are only two levels for I, and two levels for Q. The eye is open at each symbol. A good signal has wide-open eyes with compact crossover points. As the figure illustrates, a filtered signal using raised cosine filter is a better signal than one filtered with a Chebyshev filter.


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Intentionally Blank

2 WCDMA Power Control, Rake Receiver and Handover

LZT 123 7279 R5B © 2005 Ericsson - 65 -


Objectives


• Explain the WCDMA power control, RAKE receiver and handover.

• Explain the concepts of multipath reflections, fading, and turn-the-corner effects.

• Understand the WCDMA RAKE receiver.

• Understand the necessity for open loop, inner loop and outer loop power control.

• Explain the different handover scenarios: Soft handover, softer handover, inter-frequency handover and Inter-Radio Access Technology handover.

• Explain cell reuse and code planning

• Explain the issues concerning WCDMA cell planning

• Explain WCDMA cell capacity considerations

Figure 2-1: Objectives

WCDMA Air Interface

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Intentionally Blank


LZT 123 7279 R5B © 2005 Ericsson - 67 -

WCDMA RECEPTION ISSUES ...........................................................69

WCDMA POWER CONTROL ..............................................................70

MULTIPATH FADING ...........................................................................72

THE RAKE RECEIVER........................................................................74

WCDMA HANDOVER..........................................................................78

CELL PLANNING ................................................................................82 FDMA/TDMA...................................................................................................82 WCDMA ..........................................................................................................83

CAPACITY MANAGEMENT ................................................................86 ADMISSION CONTROL .................................................................................87 CONGESTION CONTROL .............................................................................87

WCDMA Air Interface

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Intentionally Blank


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WCDMA RECEPTION ISSUES As with all radio transmissions, the WCDMA signal is subjected to multiple reflections, diffractions and attenuations caused by natural objects (buildings, hills etc) resulting in what is known as multipath propagation (see Figure 2-2). This has two effects on the received signals at each end.

The bit energy for a single chip is split between the various paths and arrives at different time intervals. The delay between these various arrivals is typically 1-2 µs in urban and suburban areas and up to 20 µs in hilly areas.

Since the WCDMA chip rate is 3.84 Mcps, the time duration of each chip is 1/3.84·106 = 0.26 µs. If the time difference in these multipath components is at least 0.26 µs, the WCDMA receiver can combine these components to obtain multipath diversity. How this is achieved is explained later in the chapter.

For certain time delay positions there are usually many paths, virtually equal in length, along which the radio signal travels. For example, when two paths have a length difference of half a wavelength (7 cm at 2 GHz), they will cancel each other out. This type of fading is known as fast, or Rayleigh, fading and takes place even as the receiver moves across short distances.

Figure 2-2: Multipath fading

WCDMA Air Interface

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WCDMA POWER CONTROL Power control is necessary in any spread spectrum system to ensure that each user transmits and receives just about the right amount of power to maintain the connection quality while at the same time causing as little interference as possible to other users. For optimum performance the power control must be fast so that the variations, caused by the rapidly changing radio environment, can be followed. The dynamic range must, in the case of the UL, be very large since a UE close to a base station may well experience a pathloss that is 60-80 dB lower than a UE at the cell border. It is crucial to combat this so-called near-far effect.

In the uplink the base station measures the received Signal-to-Interference Ratio (SIR) and compares this to a target SIR. If the measured SIR is below the target then the base station requests the mobile to increase its power (and vice versa). This type of power control is known as the Inner-loop power control and is capable of adjusting the transmit power in steps of, for example 1 dB at a rate of 1500 times per second. Inner-loop power control is only applicable for connections on dedicated channels.

Two other types of power control are also used in WCDMA, they are Outer-loop and Open-loop.

Outer-loop power control is used to adjust the target SIR in reaction to changes in the block error ratio (BLER) after decoding. If the BLER increases, then the target SIR is increased in an attempt to reduce the BLER. This process continuously changes the target SIR to maintain a minimum acceptable BLER. Outer-loop power control is only applicable for connections on dedicated channels.

Open-loop power control is used to provide an initial power setting at the beginning of a connection, that is when the UE/base station transmits on common channels (RACH/FACH) and during the initial transmission on a dedicated channel until the inner-loop is established. This is necessary since a UE transmitting a strong signal close to a base station could produce enough interference to cause dropped calls. The UE estimates the minimum transmit power required by calculating the path loss from the received signal strength and the information about the base station’s output power, which is part of the system information read from the broadcast channel. If the UE receives no response from the base station at the estimated power it will retry at a slightly higher power until an acknowledgement is received.


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Open-Loop Power Control

Compute Initial

Transmit Power

Measure received power

from RBS

Read RBS transmit power from

Broadcast Channel

Transmit Access Preamble

Access Acknowledged

?

Increase Transmit Power

by X dB

No

Yes

UE BeginsUplink DCH

Transmission

Outer-Loop (slow) Power Control Inner-Loop (fast) Power Control

BLER Acceptable

?

Raise RxPower Target

Lower RxPower Target

No

Yes

Received power

> target?

Increase UE Transmit Power

by e.g. 1 dB

Decrease UE Transmit Power

by e.g. 1 dB

No

Yes

Figure 2-3: WCDMA Power Control loops.

Figure 2-3 gives an overview of the three power control algorithms from the UE transmit power perspective. During connection setup the UE makes access attempts, known as access preambles, at increasing power levels until the base station’s receive power target is achieved. The base station acknowledges the reception of these access preambles using the acquisition indication channel (AICH). The UE then sends the message on the RACH. If a dedicated channel is set up, the inner and outer loops are used to maintain the quality of the radio link. The output power of the UE is then adjusted at a rate of 1500 times per second.

Figure 2-4 shows this process in a different way. The change in the power target becomes visible some time after the dedicated channel has been established due to a change in the SIR target, which is triggered by the Outer-loop.

Inner-loop power control(Initial receive power target)

RBS Receive Power Target

Open-loop Power ControlAccess Preambles

Outer-loop power control(Updated receive power target of inner-loop)

RBS Receive Power

time

800 updates/sec (IS-95, cdma2000)1500 updates/sec (WCDMA)

The PRACH is “power controlled” by means of preamble ramping i.e. UL open loop PC

Preambles DPCHRACH

Figure 2-4: Example of the Open-loop, Inner-loop and Outer-loop.

WCDMA Air Interface

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MULTIPATH FADING

time (mSec)

CompositeReceived

Signal Strength

Time between fades is related to

• RF frequency

• Geometry of multipath vectors

• Vehicle speed: Up to 4 fades/sec per kilometer/hour

Deep fade caused by destructive summationof two or more multipath reflections

msec

Figure 2-5: Fast (Rayleigh) fading.

Fast (Rayleigh) fading is related to the carrier frequency, the geometry of multipath vectors and the vehicle speed.

As a rule of thumb there are up to four fades per second for each kilometer per hour of travel. For example a mobile traveling at 10 km/h experiences approximately 40 fades/s.

As can be seen in

Figure 2-5, the signal at the receiver is less than ideal and therefore makes error-free reception of data bits very difficult. The methods used to overcome fading in WCDMA are as follows:

• Strong coding (convolutional or Turbo) and interleaving are used to recover any bit errors at the receiver (this was explained in the previous chapter). However, this on its own is not enough.

• The Rake receiver is used to combine the energy of the most significant multipath components.

• Inner-loop power control is used to overcome the fast (Rayleigh) fading.


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In essence, the WCDMA receiver should be able to identify the time delay position at which significant energy arrives and assign a separate receiver to each multipath component. This is the job of the RAKE receiver (each separate receiver is called a Rake finger). The output from the fingers should be combined to produce a result that is unaffected by the fading experienced in the air interface. However, this is not realistically possible and so CRC, FEC and interleaving (performed at the transmitter) is also required to enable the receiver to correct any subsequent bit errors.

WCDMA Air Interface

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THE RAKE RECEIVER Figure 2-6 shows a simplified block diagram of a Rake receiver. As you can see, a number of Rake fingers containing correlators are used to track the different multipath reflections from one scrambling code. The outputs from the fingers are fed into a combiner. One of three different types of combining processes is employed to produce an output that is the sum of the individual mulitpath components.

In order to achieve this tracking, each finger simply correlates the signal with the same scrambling code but at a different phase shift. By using a different code, a finger can quite easily be used to track another base station. This is exactly what happens in the case of Soft or Softer handovers, which are explained later.

The output from one finger is not fed into the combiner. This finger correlates the received signal with the scrambling code of known neighboring base stations in order to measure their power. This information is used to determine when to perform handovers. This finger is known as the “Searcher Finger”.

Finger #1

Finger #2

Finger #N

Searcher Finger

Combiner

Sum ofindividual multipath components

Power measurement of Neighboring Base Stations

Figure 2-6: The RAKE receiver architecture.

To make it possible for the Rake receiver to track these various components it must have some way of measuring the signal levels and phases. This is achieved by the base station transmitting known pilot symbols in the transmitted data. The Rake receiver looks for these bits and uses them to determine the phase and signal strength of each component.


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Each cell transmits a separate pilot channel, see Figure 2-7, which is used by the searcher finger in the soft handover process to determine the signal strength received from different base stations. A data stream of all 0s is multiplied by channelization code 0. The resulting output is split and spread by the scrambling code before being passed to an I/Q modulator.

The whole process is equivalent to continuously transmitting the cell’s scrambling code. This 38400 chips code is repeated every 10 ms since the WCDMA chip rate is 3.84 Mchips/s. As the base station scrambles all its transmissions with the same scrambling code this channel also serves as a phase reference for all other downlink channels.

This type of spreading is known as complex spreading as the scrambling code is applied on both the I- and Q-branch.

Pilot Channel Output

FIR Filter

FIR Filter

I/Q

Modulator

‘I’ PN Code

‘Q’ PN Code

Orthogonal Code 0

Data

All 0’s

Figure 2-7: The WCDMA Common Pilot Channel (CPICH).

Figure 2-8 shows a more detailed diagram of a WCDMA receiver showing where the RAKE receiver fits in.

The input RF signal is passed through a bandpass filter and demodulated into the I and Q components. The components are then fed to the automatically tunable delays of the various Rake fingers. These delays will compensate for the delay of the various mulitpath components of the transmitted signal. To adjust the delay of these elements the signal is correlated with the internally generated scrambling code, the I and Q branches are recombined and correlated with the pilot channelization code.

Since the code is all 0s this last step can be ignored resulting in a correlation output that depends on the time difference between the internal scrambling code and that of the received signal. The delays are adjusted until a correlation peak is obtained. At this delay, this so-called “sliding correlator” is said to be locked to one of the multipath components of the received signal. With this delay all other components produce low level noise.

WCDMA Air Interface

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The channelization code of the desired data channel can then be used to recover the wanted channel. The other fingers of the Rake receiver carry out the same process but locking to other multipath components. The result is that each finger re-produces the original data with some interference. The finger outputs can then be combined and sent to the de-interleaver, decoder and for CRC verification.

BPF LPF

“I” PNCode(+1/-1)

“Q” PNCode

(+1/-1)

Σ

Orthogonal

Code(+1/-1)

Integrateover

‘SF’ chips

De-Interleave

Data

Viterbi/Turbo

Decoder

CRCVerification

DecodedOutputBits

ErrorIndication

cos(2πfRFt)

PilotOrthogonal

Code(all zeros)

TimingAdj.

bit rate = chip rate / SF

cos(2πfIFt)

CarrierFrequencyTrackingLoop

Other Rake Receiver Finger

Σ

Rake Receiver “Finger”

D

D

I/Q

Demod

Correlator

Figure 2-8: WCDMA RAKE receiver architecture.

Figure 2-9 illustrates the time alignment process. In this example, the composite received signal is made up of three multipath components at different time delays and amplitudes. This signal is fed to the various delays, which will be centered on one of the multipath components. After correlation, the original data plus interference is re-produced. The output from the fingers can then be constructively combined since the phase difference between the multipath components has been removed. The combined output is then fed to the Viterbi decoder.

The accuracy of the delay needs to be ±½ chip. The total delay range must be able to cope with the maximum delay between components, which can be 1 to 2 µs in an urban or suburban area to 20 µs in hilly or rural areas. Most Rake receivers can cope with a delay up to 30 µs.

Three different types of combining can be performed, depending on where the Rake receiver is used. If Equal-gain combining is employed then all the components are simply added together. Maximum-likelihood (maximum ratio) combining will apply a weighting to each result depending on the probability of that result being correct before they are combined. Alternatively the strongest signal can be selected (in which case all others are discarded).


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Scrambling &, Channelization Codes

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Figure 2-9: RAKE receiver. Example of the alignment process.

WCDMA Air Interface

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WCDMA HANDOVER The connection quality has to be maintained as the User Equipment (UE) moves between cells. This is the purpose of the handover function. In a WCDMA system, handover is performed through Soft/Softer Handover, Inter-Frequency Handover, Inter-Radio Access Technology (Inter-RAT) Handover and Inter-RAT Cell Change.

Soft/Softer Handover provides the UE with the ability to add, remove, and replace radio links with the same frequency. In Soft Handover the UE is connected to more than one Radio Base Station (RBS) simultaneously. At least one radio link is always active and there is no interruption in the dataflow during the actual handover. The signals are received in the UE and combined in the RAKE receiver to give protection against fading.

Inter-Radio Access Technology (IRAT) HandoverHandover from a WCDMA system to GSM/GPRSTraffic and Control Channels are Disconnected and must be Reconnected

Inter-frequency HandoverWhen the UE must change WCDMA carrier frequency during the HandoverTraffic and Control Channels are Disconnected and must be Reconnected

Soft HandoverDuring Handover, the UE has concurrent traffic connections with two , three or four RBSs.Handover should be less noticeable

Softer HandoverSimilar to Soft Handover, but between two cells of the same siteHandover is simplified since timing sectors have identical timing

Figure 2-10: Handover

In Softer Handover the UE communicates with one RBS through several radio links, the Softer Handover is a handover between two or more cells of the same RBS.

Inter-Frequency Handover takes place when the UE makes a Handover (HO) to another WCDMA frequency. This is a form of hard handover.

The Inter-RAT Handover function preserves signal quality on dedicated channels for circuit switched services when the UE is moving from a WCDMA network to a GSM network and vice versa. This is also a form of hard handover.


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The Inter-RAT Cell Change function preserves signal quality on common and dedicated channels for packet switched services when the UE is moving from a WCDMA network to a GPRS network and vice versa. Inter-RAT Cell Change is either network initiated (for dedicated channels) or UE initiated (for common channels). No resources are reserved in the target cell before the cell change is executed.

During Inter-Frequency Handover, Inter-RAT Handover and Inter-RAT Cell Change, the UE has only one radio link active at a time. During hard handover or cell change the connection is broken off for a short period (between removal of the old radio link and establishment of the new).

WCDMA systems must use soft or softer handover to reduce interference caused by near-far problems resulting from UEs at cell borders.

Figure 2-11 shows the effect of not using soft handover in a WCDMA system. As the UE moves away from RBS 1 towards RBS 2 the signal received at RBS 2 may exceed its received power target and cause excessive UL interference in that cell. Since the UE is not connected to RBS 2, the base station has no way of reducing the transmit power of the UE. This excessive UL interference at RBS 2 could ultimately lead to dropped connections in RBS 2. Once the connection undergoes a hard handover to RBS 2, power control messages from RBS 2 can be used to reduce the UE transmit power and therefore reduce the interference.

time

Trouble zone: Prior to Hard Handover, the UE causes excessive interference to RBS2

RBS2 Receive Power Target

UE responding to RBS1power control bits

UE responding to RBS2power control bits

time


Figure 2-11: WCDMA without soft handover

WCDMA Air Interface

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Soft and softer handovers allow the UE to be power controlled by both base stations, which eliminates this excessive interference (see Figure 2-12).

One finger of the RAKE receiver is constantly scanning neighboring Common Pilot Channels.When a neighboring Common Pilot Channel reaches the t_add threshold, the new RBS is added to the active setWhen the original RBS reaches the t_drop threshold, originatingRBS is dropped from the active set

Monitor Neighbor cell Pilots Add Destination RBS Drop Originating RBS

Figure 2-12: Soft handover

Figure 2-13 shows the received signal to interference ratio Ec/No

against time for three cells. The various ‘t_add’ and ‘t_drop’ thresholds can clearly be seen. The whole process of moving from being connected to cell 1 only through soft handover with cell 1 and 2 to soft handover with cell 2 and 3 to finally being connected to cell 3 only is clearly seen.

Note that hard handover usually takes place a couple of dBs inside the equal signal strength border, (due to a hysteresis value used to avoid ping-pong handover), whereas in soft handover the addition of a new radio link occurs a couple of dBs outside the equal signal strength border.

Cell 1 Connected

Add Cell 2 Replace Cell 1with Cell 3

time

Drop Cell 3

EC / N0

Cell 1

Cell 2

Cell 3

T_ADD

T_REPLACE

Δt Δt Δt

T_DROP

Figure 2-13: Example of a soft handover with max active set of 2 cells.


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In Figure 2-14 it can be seen how both base stations control the connection during soft handover, thus reducing the problem of UL interference.

time


1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 1 1 1 12 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2

UE responding to RBS1power control commands

UE responding to RBS2power control commands

time


1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 12 2 2 2 2 2

1 1 12 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2

RBS1 RBS2 Action0 0 Reduce power0 1 Reduce power1 0 Reduce power1 1 Increase power

UE responds to power control commandsfrom both RBS1 and RBS2

Figure 2-14: WCDMA with soft handover.

While connected to RBS1 only the UE acts on power control commands from that base station alone, which maintains the receive power target for that cell. As the UE moves closer to RBS2 there will come a point when the threshold ‘t_add’ is exceeded and RBS2 is added to the active list. From this point on, the call is said to be in soft handover. The UE is now responding to power control messages from both base stations. However, it initially ignores the power increase commands from RBS 1, but responds to the power decrease commands from RBS 2.

In fact, the UE will only increase its power when requested to do so by BOTH base stations and will reduce its power when requested by EITHER base station.

In the example, the “control” of the output power of the UE is effectively changing back-and-forth between the two base stations.

UEs in soft handover will cause less interference in the system and the more cells involved in the handover the lower the interference. This is why soft handover is said to improve capacity since lower UL interference results in an increased UL air interface capacity. The effect on the downlink capacity is not as clear-cut because although there is some macro diversity gain (meaning that the UE on average will ask for less power then compared to a case where it is only connected to one base station), there are still two downlinks that have to be transmitted on.

WCDMA Air Interface

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Some key points to remember about Soft Handover are as follows:

SSMA used to distinguish all transmitters in a Cellular CDMA systemFast power control is required to sustain SSMA performanceWhen fast power control is used, soft handover is essential

– Allows UE to operate in most conservative power control modeSoft handover provides performance benefits

– “Seamless” coverage at cell edges– Handover may be less noticeable to the user– Increases apparent system capacity when system is lightly loaded

Soft handover also degrades system capacity– Uses redundant physical layer resources from adjacent or

overlapping cells

Figure 2-15: WCDMA Soft Handover key points

CELL PLANNING This chapter highlights the fundamental aspects of WCDMA cell planning and the differences between FDMA, TDMA and WCDMA systems from a cell planning point of view.

FDMA/TDMA

Cellular systems built on Frequency Division Multiple Access (FDMA) or Time Division Multiple Access (TDMA) are based upon the reuse of a set of carriers, which is obtained by dividing the area requiring coverage into many smaller areas (cells, which together form clusters). This is referred to as frequency reuse planning and is important since it impacts network capacity and performance. A cluster is a group of cells, within which all available carriers have been used once. Since the same carriers are used in cells in neighboring clusters, interference may become a problem. The frequency reuse distance (that is the distance between two sites using the same carrier) must be kept as large as possible to help prevent interference. However from a capacity point of view, the distance must be kept as small as possible. Cellular systems are often interference-limited rather than signal-strength limited.


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Figure 2-16 below shows how frequency reuse patterns of 7/21, 4/12 and 3/9 are achieved. The 7/21 reuse pattern with much higher distances is used for FDMA systems like AMPS and TACS, which are more sensitive to interference. The reuse patterns recommended for TDMA systems like GSM, are the 4/12- and the 3/9-patterns. Today even tighter reuse can be used like 1/3 and 1/1. These patterns need features improving the interference level.

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D3

C2C3

B1

B2B3

C1

C2C3

B1

B2B3

C1

C2C3

B1

B2B3

D3

D2D1

A1

A2A3

A1

A2A3

D3

D2D1

A1

B2B3

C1

C2C3

B1

B2B3D3

D2D1 C1

C2C3

B1

B2B3

C1

C2C3

A1

A2A3

D3

D2D1

A1

A2A3

D3

D2D1

A1

A2A3

D3

Reuse Pattern3/9

Reuse Pattern4/12

Figure 2-16: Frequency reuse patterns of 7/21, 4/12 and 3/9.

The output power levels must also be planned in order to maintain the signal to interference ratio (C/I) necessary for maintaining connections in the network for the specific frequency reuse pattern.

The 4/12 reuse pattern (typically used for the BCCH carrier) is compatible with the planning criterion C/I >12 dB. A shorter reuse distance (typically used for TCHs), resulting in a smaller C/I ratio, is used in the 3/9 pattern. This pattern, which has higher channel utilization, is only recommended if frequency hopping is implemented. That is, it is compatible with the planning criterion C/I > 9 dB.

WCDMA

This section looks at cell planning and capacity considerations for WCDMA.

In a WCDMA system, all users operate on the same frequency at the same time. Therefore there is no need to perform frequency reuse planning; instead scrambling code planning (Figure 2-17) is required. This type of planning is called code reuse planning.

WCDMA Air Interface

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SC32

SC21

SC27SC26

SC36 SC37

SC39

SC25

SC14

SC20SC19

SC30 SC31

SC35 SC38

SC28

SC34SC33

SC40 SC41

SC42

SC11

SC4

SC7SC6

SC16 SC17

SC22

SC5

SC1

SC3SC2

SC9 SC10

SC15 SC18

SC8

SC13SC12

SC23 SC24

SC29

N

S

W EWCDMA Frequency Reuse: 1

Scrambling Code Reuse: 512

Codes available for code planning:

512 WCDMA:

Figure 2-17: WCDMA Code Planning.

In WCDMA 512 primary (with 15 extra secondary per primary) different codes are used.

Fundamental Capacity Limitation is available RF transmit power– One RF power budget must be split between all User Equipments– Fixed portion of RF power Budget allocated to so called common

channels

SSMA interference from other RBSs– Growing problem in Microcellular and Hierarchy topologies

Dedicated channel power is allocated based on UE needs– More power allocated to distant UEs; less to nearby UEs– WCDMA use fast power control on the dedicated channels

Figure 2-18: Main Factors influencing Downlink Capacity

Intracell interference– SSMA interference from other UEs in the same cell, many

to one scenario.

Intercell interference– SSMA interference from other UEs in other cells– Interference from adjacent frequencies

Intersystem interference– Interference from other systems like GSM

Figure 2-19: Main Factors influencing Uplink Capacity


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The main limiting factors for the uplink and the downlink are different.

In the downlink, all UEs in a cell share a single transmit power budget. Each UE has to receive a certain C/I level for the specific service to achieve the correct Quality of Service needed. The number of users in the downlink therefore depends on their location in the cell. A user that is far away from the base station will typically require more power than a user close to the base station.

Noise is not the fundamental problem in WCDMA; it is instead interference due to the cross correlation properties of scrambling codes, which produces noise-like interference.

In comparison to a traditional TDMA system the coverage of WCDMA depends on the traffic load in the cells. The more traffic, the more interference and the shorter the distance must be between the RBS and the UE. In a system where the traffic load changes this will cause the cells to grow and shrink with time. This effect is often referred to as cell breathing.

Interference from other base stations affects the capacity in the downlink.

Despite the fact that downlink channels within one cell are orthogonal at the TX reference point they may not be orthogonal at the receiving end, therefore causing noise-like interference.

In the uplink all UEs have their own power budget.

Interference is an important factor in the uplink as there are many UEs.

Depending on the situation, it is the uplink or the downlink that is the limiting factor for the WCDMA system (see Figure 2-20).

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Cell 1

Cell 2

UE1

UE2

UE3

Cell 1 cannot accommodate UE3 because:

Cell 2 cannot accommodate UE2 because:

Figure 2-20: Uplink and downlink capacity limitations.

In the first scenario, cell 1 cannot accommodate UE3 because the increase in interference in the uplink by adding this connection would be too great and there would be a high risk of dropping a user. In this example the uplink interference has limited the capacity of the cell.

In the second scenario we can see that Cell 2 cannot accommodate UE2 because it is using all its available power resources to maintain the connections to the other UEs. In other words, the base station has not enough power left to achieve the required signal strength (C/I) required by UE2. Another way to understand this is to imagine that the base station has a total power output of 20 W. It allocates 5 W to broadcasting common channels and leaves 15 W available for traffic. In this instance it requires 2 W for each of the 5 ongoing connections and so has no power available to accommodate UE2. In this example the capacity is limited by the downlink.

CAPACITY MANAGEMENT Capacity Management aims to control the load in the WCDMA RAN. The purpose of Capacity Management is to maximize the capacity in WCDMA RAN while maintaining the requested Quality of Services and coverage, and stabilizing the cell carrier behavior in the air interface. Capacity Management is useful in an overload situation. An overload situation occurs due to fluctuations in the uplink interference and/or the used downlink power. These fluctuations are a natural process caused by a number of factors including fading, intercell interference, and variations in the carried traffic of the individual connections.


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ADMISSION CONTROL

The purpose of Admission Control is to selectively deny access request in order to limit the load, and so avoids excessive triggering of congestion control. Normaly Admission Control is applied at cell level on dedicated radio link setup, addition or modification where additional resources are required. The resources are a selected subset of the total resources in the RAN, whose usage is constantly monitored by Admission Control (Figure 2-21). In the situations of high load the input for admission about resources causes Admission Control to block new requests.

Max planned interference

Max planned load

Noise floor

Uplink interference

Load

New users blocked above this point

User added

Cov

erag

e

Figure 2-21: Capacity Management, Admission Control.

CONGESTION CONTROL

The purpose of Congestion Control is to solve overload situations. An overload situation occurs due to, for example, fluctuations in the UL in interference and/or the used DL power. Congestion Control is applied at cell level and becomes active when the current cell load exceeds predefined limits. The activation of Congestion Control results in a set of actions on the admitted services in a cell to reduce the cell load. Congestion Control reduces the load until it is back to an acceptable level.

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3 WCDMA Physical Layer

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Objectives


• Describe the 3GPP Standardization Committee and specification structure

• Explain the concepts of logical, transport, and physical channels

• Explain details of the WCDMA physical layer.

• Explain the different aspects of the WCDMA downlink

• Explain the different aspects of the WCDMA uplink Figure 3-1: Objectives

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CONTENTS

3GPP....................................................................................................93 WCDMA OSI MODEL .....................................................................................99

WCDMA DOWNLINK.........................................................................102 LOGICAL CHANNELS ..................................................................................105 TRANSPORT CHANNELS ...........................................................................105 PHYSICAL CHANNELS................................................................................106 CHANNELIZATION CODE INDEX ...............................................................108 COMMON PILOT CHANNEL........................................................................109 PRIMARY COMMON CONTROL PHYSICAL CHANNEL AND SYNCHRONIZATION CHANNEL .................................................................110 SECONDARY COMMON CONTROL PHYSICAL CHANNEL ......................111 PAGING INDICATOR CHANNEL .................................................................111 DEDICATED PHYSICAL CONTROL AND DATA CHANNEL.......................112 MULTIPLEXING............................................................................................117

WCDMA UPLINK ...............................................................................121 DEDICATED PHYSICAL CONTROL AND DATA CHANNEL.......................123 MULTIPLEXING............................................................................................125 RANDOM ACCESS CHANNEL ....................................................................126 HPSK MODULATION ...................................................................................127

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3GPP The Third Generation Partnership Project (3GPP) was founded on the 4th of December 1998 to accelerate IMT-2000 standardization activities. This powerful group is responsible for producing standards for third generation systems. It currently consists of the following standardization bodies:

• European Telecommunications Standardization Institute (ETSI)

• Japanese Association of Radio Industries and Business (ARIB)

• American National Standards Institute (ANSI T1)

• Telecommunications Technology Association (TTA)

• Telecommunications Technology Committee (TTC)

• China Wireless Telecommunication Standards (CWTS).

The diagram below (see Figure 4-1) shows how the 3GPP is divided in to various Technical Specification Groups. The TSG-RAN group is responsible for producing specifications that relate to the air interface.

There are also groups responsible for the Core Network, Terminals, Services and System Aspects, and GSM (EDGE radio access network standards).

Working documents and specifications can be downloaded from the website: www.3gpp.org

TSG ORGANIZATION

Project Co-ordination Group(PCG)

TSG RANRadio Access Networks

RAN WG1Radio Layer 1 specification

RAN WG2Radio Layer2 spec &

Radio Layer3 RR spec

RAN WG3lub spec lur spec lu spec &UTRAN O&M requirements

RAN WG4Radio Performance &

Protocol Aspects

RAN WG5 (ex T1)Mobile Terminal

Conformance Testing

TSG SAServices &

System Aspects

SA WG1Services

SA WG2Architecture

SA WG3Security

SA WG4Codec

SA WG5Telecom Management

TSG CTCore Network& Terminals

CT WG1 (ex CNMM/CC/SM (lu)

1)

CT WG3 (ex CN3)Interworking with External Networks

CT WG4 (ex CN4)MAP/GTP/BCH/SS

CT WG5 (eOSA

Open Service Access

x CN5)

CT WG6 (ex TSmart Card

Application Aspects

3)

TSG GERANGSM EDGE

Radio Access Network

GERAN WG1Radio Aspects

GERAN WG2Protocol Aspects

GERAN WG3Terminal TestingGERAN WG3Terminal Testing

September 2005

Figure 3-2: Third Generation Partnership Project (3GPP)

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Some of the standardization documents produced by this group and relevant to this course are shown in Figure 3-3. The most important of these documents are the 25-series documents.

WCDMA UTRAN Network3GPP TS 25.401-v410: UTRAN Overall Description3GPP TS 25.832-v400: Manifestations of Handover and SRNS Relocation3GPP TS 26.071-v400: AMR Speech Codec; General Description

WCDMA Radio Transmission and Resource Management3GPP TS 25.101-v410: UE Radio Transmission and Reception (FDD)3GPP TS 25.104-v410: BS Radio Transmission and Reception (FDD)3GPP TS 25.133-v410: Requirements for Support of Radio Resource Management

WCDMA Physical Layer Specifications (FDD and TDD)3GPP TS 25.201-v400: Physical Layer General Description3GPP TS 25.301-v410: Radio Interface Protocol Architecture3GPP TS 25.302-v410: Services Provided by the Physical Layer

WCDMA FDD, TDD Mode Standards:3GPP TS 25.211-v410: Physical channels and mapping of transport channels onto physical channels (FDD)3GPP TS 25.212-v410: Multiplexing and channel coding (FDD)3GPP TS 25.213-v410: Spreading and modulation (FDD)3GPP TS 25.214-v410: Physical layer procedures (FDD)3GPP TS 25.215-v410: Physical layer - Measurements (FDD)

3GPP TS 25.221-v400: Physical channels and mapping of transport channels onto physical channels (TDD)3GPP TS 25.222-v410: Multiplexing and channel coding (TDD)3GPP TS 25.223-v410: Spreading and modulation (TDD)3GPP TS 25.224-v410: Physical layer procedures (TDD)3GPP TS 25.225-v410: Physical layer - Measurements (TDD)

This presentation iscurrent as of TS-25 Rel-4

(3GPP June 2001 Release)

Figure 3-3: Specifications Referenced in this Course.

Many of the figures in the rest of this chapter contain a reference to the specification document and chapter from which the information was taken. These documents are checked and updated regularly.

3GPP WCDMA Overview

Both FDD (2x 5 MHz) and TDD (1x 5 MHz)modes supported– Operation specified in bands between 1850 and 2170 MHz– BS time synchronization not required for FDD mode – GPS not required– Fast Synchronization Codes allow asynchronous operation and handover

Multi-Code and Variable Spreading Factor modes supportedNetwork interface compatible with GSM - MAP / GPRS

– To be made compatible with ANSI-41 per OHG requirementPhysical Parameters:

– Chip rate = 3.840 Mcps– RF Bandwidth = 5 MHz– Physical Layer data rates of 15, 30, 60, 120, 240, 480, 960, and 1920

kb/sec– Frame length = 10 mSec– Fast Power Control: Bi-directional; 1500 updates/sec

Figure 3-4: WCDMA (ETSI/ARIB/3GPP)

Both the Frequency and Time Division Duplex (FDD&TDD) modes of operation are covered by the standardization documents. The TDD mode of operation allows a complete network to be deployed with only 5 MHz of frequency spectrum, whereas FDD requires at least 10 MHz. Therefore the TDD mode is especially useful in countries where the IMT-2000 frequency spectrum has already been allocated to another system, as is the case in the USA where PCS operators currently use the IMT-2000 spectrum. One solution is to use WCDMA TDD in the unlicensed PCS band between the uplink and downlink (1910 MHz to 1930 MHz).


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Unlike IS-95 and CDMA2000, WCDMA FDD base stations do not require GPS synchronization. This is important where the network requires indoor base stations as it may be difficult to site the GPS antenna.

Another body known as the Operators Harmonization Group (OHG) works towards ensuring that WCDMA and CDMA2000 Radio Access Networks will be hardware compatible with ANSI-41 equipment. This will make it easier for operators to add WCDMA and CMDA2000 equipment to their existing GSM or GPRS networks. The physical layer for WCDMA supports data rates of 15, 30, 60, 120, 240, 480, 960 and 1920 ksymbols/s. Note that the 2048 kbps payload rate is achieved by using several physical layer channels, or codes, simultaneously. This is known as multi-code operation.

2.1

2.1 1900 & 850

2.1

2.1 1900 & 850

Figure 3-5: WCDMA Frequency Allocations.

Figure 3-5 shows the frequency allocations used in various parts of the world.

The world is divided into three regions with different bands as the main band for the region. There are several bands available and 3GPP has standardized 6 bands with different duplex-distances, see Figure 3-6.

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45 MHz875-885 MHz830-840 MHzVI

45 MHz869-894MHz824 –849MHzV

400 MHz2110-2155 MHz1710-1755 MHzIV

95 MHz1805-1880 MHz1710-1785 MHzIII

80 MHz1930 –1990 MHz1850 –1910 MHzII

190 MHz2110 –2170 MHz1920 –1980 MHzI

Duplex distanceDL frequenciesUE receive, Node B

transmit

UL FrequenciesUE transmit, Node B

receive

Operating Band

45 MHz875-885 MHz830-840 MHzVI

45 MHz869-894MHz824 –849MHzV

400 MHz2110-2155 MHz1710-1755 MHzIV

95 MHz1805-1880 MHz1710-1785 MHzIII

80 MHz1930 –1990 MHz1850 –1910 MHzII

190 MHz2110 –2170 MHz1920 –1980 MHzI

Duplex distanceDL frequenciesUE receive, Node B

transmit

UL FrequenciesUE transmit, Node B

receive

Operating Band

Figure 3-6. The standardized operating bands.

GSM/GPRS Core Network (CN)

Iu Iu

RNS

RNC

RNS

RNC

RBS RBS RBS RBS

Iur

Iub IubIubIub

User Equipment(UE)

UTRAN=

WCDMA RAN

(UMTS Terrestrial

Radio Access Network)

PSTNISDN

Internet

Uu

MSC GPRSService Node

Iu Iu

Figure 3-7: UMTS and the WCDMA RAN


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The main WCDMA RAN interfaces are Iu, Iur, and Iub (Figure 3-7). Iu is the interface between WCDMA RAN and the core network. There are two types of interfaces in the Iu interface: the Iu interface towards the Packet-Switched (PS) network (GPRS) and the Iu interface towards the Circuit-Switched (CS) network (MSC). The Iu interface supports several functions, such as, establishing, maintaining and releasing radio access bearers (RAB), performing intra-system and inter-system handover, location services by transferring requests from the Core Network (CN) to the WCDMA RAN, and location information from the WCDMA RAN to the CN. Iur interfaces radio network controllers and is required to support inter RNC soft handover. The Iub is a logical interface that connects the RBS to the RNC.

WCDMA RAN DefinitionsRNS (Radio Network Subsystem)

– A full or partial network offering access between UE and Core Network

– Contains one RNCRNC (Radio Network Controller)

– Element of the RNS that controls physical radio resourcesRBS (Node B in specification)

– Logical Node controlling transmission and reception from one or more cells

Uu Interface– Interface between UE and RBS

Iu Interface– Interface between CN and RNS

Iur Interface– Interface between one RNS and another RNS

Iub Interface– Interface between RNC and RBS

3GPP TS 25.401 ¶ 3.03GPP TS 25.401 ¶ 3.0


WCDMA RAN Operational Functions:

Functions related to overall system access control:

• Admission Control, Congestion Control

• System information broadcasting

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• Radio channel ciphering and deciphering.

Functions related to mobility:

• Handover

• SRNS Relocation.

Functions related to radio resource management and control:

• Initial (random) access detection and handling

• Radio resource configuration and operation

• Combining/splitting control

• Radio bearer connection set-up and release (Radio Bearer Control)

• Allocation and de-allocation of Radio Bearers

• Radio protocols function

• RF power control

• Radio channel coding

• Radio channel decoding.

3GPP TS 25.401 ¶ 7.13GPP TS 25.401 ¶ 7.1WCDMA RAN Operational Functions (partial)

Functions related to overall system access control– Admission Control, Congestion Control– System information broadcasting– Radio channel ciphering and deciphering

Functions related to mobility– Handover – SRNS Relocation

Functions related to radio resource management and control– Initial (random) access detection and handling– Radio resource configuration and operation– combining/splitting control– Radio bearer connection set-up and release (Radio Bearer

Control)– Allocation and de-allocation of Radio Bearers– Radio protocols function– RF power control– Radio channel coding– Radio channel decoding



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WCDMA OSI MODEL

The Radio Access Network is divided into a user plane and a control plane (Figure 3-10). The user plane is used for sending user data while the control plane is used for signaling.

L2

L1

L2

L3

WCDMA RANUE

RRC

RLC

MAC

PHY

RRC

MAC

PHY

RLC RLC RLC

Signaling Radio Bearer

Radio Bearer

Logical Channel

Transport Channel

Physical Channel

CTRL CTRLUSERDATA

USERDATA

Figure 3-10: WCDMA RAN OSI Model.

In the WCDMA Open Systems Interconnection (OSI) model, it can be seen how the three layers are connected using logical, transport and physical channels.

The Radio Resource Control (RRC) handles most of the signaling between the UE and the RNC. It is in direct control of the physical layer for call setup, release etc.

A Radio Access Bearer (RAB) is the connection segment between the UE and the Core Network to support Quality of Service (QoS) for UMTS bearer services.

Each of the RABs is mapped onto one or more Radio Bearers. Each Radio Bearer is mapped onto one Radio Link Control (RLC) entity. Each RLC entity communicates (UE-RNC) with its peer entity using one or more logical channels.

Logical channels are grouped by information content, that is, by whether they carry user data or L3 signaling. This L3 signaling is used to send information such as measurement reports and handover commands.

These logical channels are mapped onto transport channels by the Medium Access Control (MAC) layer. The transport channels are grouped by the method of transport used (dedicated or common).

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Finally, the transport channels are mapped onto physical channels. The physical channels are distinguished by RF frequency, channelization code, scrambling code and modulation. In other words, these channels perform the actual transmission of data bits.

Services provided by the Physical Layer:

• FEC (Forward Error Correction) encoding/decoding of transport channels

• Error detection on transport channels and indication to higher layers

• Rate matching of coded transport channels to physical channels.

• Power weighting and combining of physical channels.

• Inner-loop power control

• Modulation/demodulation and spreading/de-spreading of physical channels

• Multiplexing/de-multiplexing of coded composite transport channels

• Macro diversity distribution/combining.

Procedures:

• Cell search functions

• Synchronisation (chip, bit, and frame synchronisation)

• Soft handover support

• Radio characteristics measurements, including FER (Frame Erasure Ratio), SIR (Signal-to-Interference Ratio), Interference Power and indication to higher layers

Figure 3-12 shows a summary of the different physical channels used in both uplink and downlink.

Detailed explanations of these channels are provided separately for the downlink and uplink channels.

It should be noted that the Dedicated Physical Data Channel (DPDCH) contains user data and L3 signaling, for example, handover reports and commands. The Dedicated Physical Control Channel (DPCCH) contains only L1 control data, for example, power control messages.


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Services provided by Physical Layer• Data and RF Processing Functions

− FEC encoding/decoding of transport channels− Error detection on transport channels and indication to higher layers − Rate matching of coded transport channels to physical channels− Power weighting and combining of physical channels − Closed-loop power control − Modulation/demodulation and spreading/de-spreading of physical channels − Multiplexing/de-multiplexing of coded composite transport channels− Mapping of transport channels on physical channels − Macrodiversity distribution/combining

• Operational Functions− Cell search functions− Synchronization (chip, bit, slot, and frame synchronization) − Soft Handover support− Radio characteristics measurements including FER, SIR, Interference Power,

etc., and indication to higher layers − Uplink timing advance (TDD mode)

3GPP TS 25.201 ¶ 4.1.2 , 25.301¶ 5.2.2 3GPP TS 25.201 ¶ 4.1.2 , 25.301¶ 5.2.2

Figure 3-11: Physical Layer Requirements

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Radio BaseStation

(RBS)

UserEquipment

(UE)

P-CCPCH- Primary Common Control Physical ChannelSCH - Synchronization Channel

P-CPICH - Primary Common Pilot Channel

Common physical channels

DPDCH - Dedicated Physical Data Channel

DPCCH - Dedicated Physical Control Channel

Dedicated Channels

PICH - Page Indicator Channel

S-CCPCH - Secondary Common Control Physical Channel

PRACH - Physical Random Acce ss Channel

AICH - Acquisition Indicator Channel

HS-SCCH High Speed Shared Control Channel

HS-PDSCH High Speed Physical Downlink Shared Channel

HS-DPCCH High Speed Dedicated Physical Control Channel

Radio BaseStation

(RBS)

UserEquipment

(UE)









Dedicated Channels



Dedicated Channels

PICH - Page Indicator ChannelPICH - Page Indicator Channel

S-CCPCH - Secondary Common Control Physical ChannelS-CCPCH - Secondary Common Control Physical Channel














Figure 3-12: WCDMA Physical Channels in uplink and downlink

WCDMA DOWNLINK A block diagram of a typical downlink WCDMA transmitter (cell) is shown in Figure 3-16.

Common Downlink Physical ChannelsP-CCPCH Primary Common Control Physical Channel

-Broadcasts cell informationSCH Synchronization Channel

- Fast Synch. codes 1 and 2; time-multiplexed with PCCPCHS-CCPCH Secondary Common Control Physical Channel

-Transmits control information and packet data to UE’sP-CPICH Primary Common Pilot Channel

S-CPICH Secondary Common Pilot Channel (sectored cells)

HS-PDSCH High Speed Physical Downlink Shared Channel- Transmits high-speed data to multiple users

HS-SCCH High speed Shared Control Channel-Transmits control information about HS-DPDSCH

3GPP TS 25.2113GPP TS 25.211

Figure 3-13: WCDMA Downlink Physical Channels


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Dedicated Downlink Physical Channels– DPDCH Dedicated Downlink Physical Data Channel– DPCCH Dedicated Downlink Physical Control Channel

Transmits connection-mode signaling and control to UE’sDownlink Indication Channels

– AICH (Acquisition Indication Channel)Acknowledges that RBS has acquired a UE Random Access attemptEchoes the UE’s Random Access signature

– PICH (Page Indication Channel)Informs a UE if it should monitor the Paging Channel

3GPP TS 25.2113GPP TS 25.211

Figure 3-14: WCDMA Downlink Physical Channels

Uplink Physical Channels

– Common Uplink Physical ChannelsPRACH Physical Random Access Channel

- Used by UE to initiate access to RBS

– Dedicated Uplink Physical ChannelsDPDCH Dedicated Uplink Physical Data Channel DPCCH Dedicated Uplink Physical Control Channel

- Transmits connection-mode signaling and control to RBSHS-DPCCH High Speed dedicated Physical ControlChannel

Transmits response signaling of HS-PDSCH

3GPP TS 25.2113GPP TS 25.211

Figure 3-15: WCDMA Uplink Physical Channels

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BCCHBroadcast Control Ch.

PCCHPaging Control Ch.

CCCHCommon Control Ch.

DCCHDedicated Control Ch.

DTCHDedicated Traff ic Ch. N

BCHBroadcast Ch.

PCHPaging Ch.

FACHForward Access Ch.

DCHDedicated Ch.

P-CCPCH(*)Primary Common Control Phy sical Ch.

S-CCPCHSecondary Common Control

Phy sical Ch.

DPDCH (one or more per UE) Dedicated Phy sical Data Ch.

DPCCH (one per UE)Dedicated Phy sical Control Ch.Pilot, TPC, TFCI bits

SSCi

Logical Channels(Layers 2+)

Transport Channels(Layer 2)

Physical Channels(Layer 1)

DownlinkRF Out

DPCH (Dedicated Physical Channel)One per UE

HS-DSCHHigh Speed DL Shared Ch.

CTCHCommon Traff ic Ch.

CPICHCommon Pilot ChannelNull Data

Data Encoding

Data Encoding

Data Encoding

Data Encoding

Data Encoding

HS- DPDCH (one or more per UE) High Speed Physical Downlink shared Channel

S/P

S/P

S/P

S/P

I+jQ I/QModulator

Q

ICch

Cch

Cch 256,1

Cch 256,0

Σ

GS

PSC

GP Σ

Sync Codes(*)

* Note regarding P-CCPCH and SCH

Sync Codes are trans mitted only in bits 0-255 of each timeslot;P-CCPCH trans mits only during the remaining bits of each timeslot

Σ Filter

Filter

Gain

Gain

Gain

Gain

SCH (Sync Channel)

DTCHDedicated Traff ic Ch. 1

DCHDedicated Ch.

Data Encoding

MUX

MUX

CCTrCHDCHDedicated Ch.

Data Encoding

Sdl,n

Sdl,n

Sdl,n

Sdl,n

S/P

C16 GainSdl,n

AICH (Acquisition Indicator Channel)

PICH (Paging Indicator Channel )

Access Indication data

Paging Indication bits S/P

S/P

Cch

CchGain

Gain

Sdl,n

Sdl,n

HS-SCCH (<4 per UE)High speed shared Control Channel .

S/P

C128 GainSdl,n

TFRI, UE Identity, HARQ

BCCHBroadcast Control Ch.

PCCHPaging Control Ch.

CCCHCommon Control Ch.

DCCHDedicated Control Ch.

DTCHDedicated Traff ic Ch. N

BCHBroadcast Ch.

PCHPaging Ch.

FACHForward Access Ch.

DCHDedicated Ch.

P-CCPCH(*)Primary Common Control Phy sical Ch.

S-CCPCHSecondary Common Control

Phy sical Ch.

DPDCH (one or more per UE) Dedicated Phy sical Data Ch.

DPCCH (one per UE)Dedicated Phy sical Control Ch.Pilot, TPC, TFCI bits

SSCi

Logical Channels(Layers 2+)

Transport Channels(Layer 2)


DownlinkRF Out

DPCH (Dedicated Physical Channel)One per UE

HS-DSCHHigh Speed DL Shared Ch.

CTCHCommon Traff ic Ch.

CPICHCommon Pilot ChannelNull Data

Data Encoding

Data Encoding

Data Encoding

Data Encoding

Data Encoding

HS- DPDCH (one or more per UE) High Speed Physical Downlink shared Channel

S/P

S/P

S/P

S/P

I+jQ I/QModulator

Q

ICch

Cch

Cch 256,1

Cch 256,0

Σ

GS

PSC

GP Σ

Sync Codes(*)

* Note regarding P-CCPCH and SCH

Sync Codes are trans mitted only in bits 0-255 of each timeslot;P-CCPCH trans mits only during the remaining bits of each timeslot

Σ Filter

Filter

Gain

Gain

Gain

Gain

SCH (Sync Channel)

DTCHDedicated Traff ic Ch. 1

DCHDedicated Ch.

Data Encoding

MUX

MUX

CCTrCHDCHDedicated Ch.

Data Encoding

Sdl,n

Sdl,n

Sdl,n

Sdl,n

S/P

C16 GainSdl,n

S/P

C16 GainSdl,n





S/P

Cch

CchGain

Gain

Sdl,n

Sdl,n





S/P

Cch

CchGain

Gain

Sdl,n

Sdl,n

HS-SCCH (<4 per UE)High speed shared Control Channel .

S/P

C128 GainSdl,n

S/P

C128 GainSdl,n

TFRI, UE Identity, HARQ

Figure 3-16: WCDMA Downlink (FDD).

This figure shows how the logical channels are mapped onto transport channels and further onto physical channels. The transport channels are going through data encoding (CRC, FEC, Interleaving) before they are mapped onto the physical channels. The downlink indication channels do not have transport channels mapped onto them, as they only exist in the physical layer.

The physical channels are passed through a serial to parallel (S/P) converter to create two separate data streams, the I- and the Q-branch. These are then multiplied with the channelization code to achieve the 3.84 Mchips/s. The scrambling code is then applied for every channel. This is due to that an alternative code tree can be needed if compressed mode (see dedicated physical channels) is used for dedicated channels. In this case a secondary scrambling code is used. After this a power gain factor is applied on each physical channel and these are then summarized.

The synchronization codes are added after the summation is performed. The reason for this is that they indicate which scrambling code used in the cell. Finally the signal is filtered, modulated, amplified and sent out in the air. Each channel will be described further in this chapter.


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LOGICAL CHANNELS

Logical channel types are classified into two groups:

• Control channels for the transfer of control information

• Traffic channels for the transfer of user information.

The Broadcast Control Channel (BCCH) is a downlink channel for broadcasting system information. Paging Control Channel (PCCH) is a downlink channel that transfers paging information and is used when the UE is in idle mode. The Common Control Channel (CCCH) is a bi-directional channel that transfers control information between the network and UE. This channel is used by the UE needs to access the network. The Dedicated Control Channel (DCCH) is a point-to-point bi-directional channel that transmits dedicated control information between UE and the network. This channel is established through a RRC connection setup procedure. The Dedicated Traffic Channel (DTCH) is a point-to-point channel, dedicated to one UE, for transferring user information. A DTCH can exist in the uplink and downlink.

TRANSPORT CHANNELS

A transport channel is defined by how, and with what characteristics, data is transferred over the air interface. There are two types of transport channels:

• Common channels

• Dedicated channels.

There is one dedicated transport channel, the Dedicated Channel (DCH), which is used in both downlink and uplink. The DCH is characterized by the possibility of fast rate change and fast power control.

The Broadcast channel (BCH) is a downlink transport channel that is used to broadcast system and cell specific information. The BCH is always transmitted over the entire cell with a low fixed bit rate. The Forward Access Channel (FACH) is a downlink transport channel that carries control information to UEs when a random access message has been sent by the UE to the base station. The Paging Channel (PCH) is a downlink transport channel used for paging.

The transport channels used by HSDPA is described in chapter 5.

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PHYSICAL CHANNELS

A brief explanation of the function of the physical channels that are transmitted to all UEs are referred to as ‘common downlink physical channels’, follows.

Common Downlink Physical Channels:

• Primary Common Control Physical Channel (P-CCPCH):

Broadcasts system information.

• Synchronization Channel (SCH):

Carries Primary and Secondary Synchronization Codes, used for slot synchronization, frame synchronization and the detection of the scrambling code group (one out of 64). It is time multiplexed (only first 10%) with the P-CCPCH (remaining 90% of timeslot).

• Secondary Common Control Physical Channel (S-CCPCH):

Carries both the Paging Channel (PCH) and the Forward Access Channel (FACH). Transmits idle-mode signaling and control information to UE. Can also be used for sending short infrequent data.

• Primary Common Pilot Channel (P-CPICH):

Sends the scrambling code of the cell. Provides coherent phase reference for DL channels and aids channel estimation (handover and cell selection).

Downlink channels that are transmitted to particular UEs are called Dedicated Physical Channels.

Dedicated Downlink Physical Channels:

• Dedicated Downlink Physical Data Channel (DPDCH):

Used for sending dedicated data and L3 signaling.

• Dedicated Downlink Physical Control Channel (DPCCH):

Transmits layer 1 signaling to UE including Transmit Power Control (TPC) bits, pilot bits and Transport Format Combination Indicator (TFCI) bits.


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• HS-PDSCH - High-Speed Physical Downlink Shared Channel: physical downlink channel that carries the user data and layer 2 overhead bits over the air interface.

• HS-SCCH - High-Speed Shared Control Channel(s): physical downlink channel that carries control information how to decode the information on HS-PDSCH and which UE that shall decode it.

HS-DPCCH - High-Speed Dedicated Physical Control Channel: physical uplink channel to send ACK/NAK reports and channel quality reports

Common Downlink Logical ChannelsBCCH (Broadcast Control Channel)

- Broadcasts cell and system information to all UE

PCCH (Paging Control Channel)- Transmits paging information to a UE when the UE’s location

is unknown

CCCH (Common Control Channel)- Transmits control information to a UE when there is no RRC

Connection

CTCH (Common Traffic Channel)- Traffic channel for sending traffic to a group of UE’s.

Dedicated Downlink Logical ChannelsDCCH (Dedicated Control Channel)

- Transmits control information to a UE when there is a RRC Connection

DTCH (Dedicated Traffic Channel)- Traffic channel dedicated to one UE

3GPP TS 25.301¶ 5.3.1.13GPP TS 25.301¶ 5.3.1.1

Figure 3-17: Downlink Logical Channels

Common Downlink Transport Channels

BCH (Broadcast Channel)- Continuous transmission of system and cell information

PCH (Paging Channel)- Carries control information to UE when location is

unknown- Pending activity indicated by the PICH (paging indication

channel)

FACH (Forward Access Channel)- Used for transmission of idle-mode control information to

a UE- Control signaling during call set-up- Packet data transmission- No closed-loop power control

3GPP TS 25.301¶ 5.2.1.13GPP TS 25.301¶ 5.2.1.1

Figure 3-18: Downlink Transport Channels

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HS-PDSCH (High Speed Downlink Shared Channel)– User data in short TTI (2ms)– Packet data transmission– No power control, coding rate controlled by UE:s CQI – One transport block of dynamic size per 2 ms TTI.– Supports link adaptation and hybrid ARQ with soft combining.– Always associated with a DPCH.– Never in soft handover.– Mapped to one or several HS-PDSCH (SF=16).

Dedicated Downlink Transport Channels

DCH (Dedicated Channel)– Carries dedicated traffic and control data to one UE

Figure 3-19: Downlink Transport Channels

The list of channels below concentrates on the downlink physical channels that are used to indicate a particular situation to the UE. These channels can be referred to as ‘downlink indication channels’. These channels only exist in the physical layer, that is, they do not have any transport channels mapped onto them.

Downlink Indication Channels:

• Acquisition Indicator Channel (AICH):

Acknowledges that the RBS has acquired a UE Random Access attempt (Echoes the UE’s Random Access signature).

• Paging Indicator Channel (PICH):

Informs a UE to monitor the next paging frame.

CHANNELIZATION CODE INDEX

As explained earlier, channelization codes vary in length, depending on the input data rate. This gives rise to these codes being called Orthogonal Variable Spreading Factors (OSVF). The codes are created from the Channelization Code Tree. Figure 3-20 shows the beginning of this tree. Each branch is sub-divided in two to create two new codes, one is simply the code repeated and the other is the code followed by the inverse of the code. The Spreading Factor (SF) increases as the codes increase in length, that is, short codes produce a low spreading factor while longer codes produce a higher spreading factor. The various codes are denoted by “CSF,code number” .


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1

1 -1

1 1

1 1 1 1

1 1 -1 -1

1 -1 1 -1

1 -1 -1 1

C1,0

C2,0

C2,1

C4,0

C4,1

C4,2

C4,3

SF = 1 SF = 2 SF = 4

Figure 3-20: Channelization Code Index.

COMMON PILOT CHANNEL

The Common Pilot Channel (CPICH) shown in Figure 3-21, provides a coherent phase reference for the downlink channels. The CPICH continuously sends the scrambling code for the cell. It also aids channel estimation for cell selection/reselection and handover for the UE. By adjusting the CPICH power level, the cell size and load between different cells can be balanced.

Pilot Symbol Data (10 symbols per slot)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

1 Frame = 15 slots = 10 mSec

1 timeslot = 2560 Chips = 10 symbols = 20 bits = 666.667 uSec

3GPP TS 25.211¶ 5.3.33GPP TS 25.211¶ 5.3.3

Figure 3-21: The Common Pilot Channel.

WCDMA uses 18 shift registers to create the scrambling codes used in the downlink. This produces a code length of 262,143 (218-1) chips; however, only the first 38400 chips are used by the system. Since the chip rate is 3.84 Mchips/s it will take the system 10 ms (38400/3.84·106) to send 38400 chips. This time duration is referred to as one frame. The frame is sub-divided into 15 slots, each containing 2560 (38400/15) chips. The duration of one slot is (10·10-3/15) s, i.e. 666.667 μs.

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Figure 3-21 shows how the Common Pilot Channel is mapped onto one of these timeslots. The length of the channelization code used for this channel (C256,0) is 2560 chips, therefore ten modulation symbols, or (10·2) 20 bits of pilot information, can be contained in one slot.

PRIMARY COMMON CONTROL PHYSICAL CHANNEL AND SYNCHRONIZATION CHANNEL

The Primary Common Control Physical Channel (P-CCPCH) is used to carry the broadcast channel (BCH) and the synchronization channel (SCH). Figure 3-22 shows the structure of the Primary Common Control Physical Channel (P-CCPCH) which shows that the SCH and P-CCPCH are time multiplexed.

This channel has a fixed rate of 30 kbps (SF=256). Common control physical channels are not inner-loop power controlled and are continuously transmitted over the entire cell. C256,1 is always used for this channel since it needs to be decoded by all UEs.

Broadcast Data (18 bits)SSCi

BCH Spreading Factor = 2561 Slot = 0.666 mSec = 18 BCH data bits / slot


2304 Chips256 ChipsSCH BCH

3GPP TS 25.211¶ 5.3.3.23GPP TS 25.211¶ 5.3.3.2

PSC

1 2 3 4 5 6 7 8 9 10 11 12 13 140

Figure 3-22: Synchronization Channel/Primary Common Control Channel.

As with the pilot channel, each slot contains 2560 chips, however, the first 256 chips are used to transmit the synchronization channel that contains a primary and a secondary synchronization code. This leaves (2560 - 256) 2304 chips to carry the broadcast channel. Since the spreading factor is 256, each slot contains (2304/256) 9 modulation symbols or (9·2) 18 bits of broadcast information.


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SECONDARY COMMON CONTROL PHYSICAL CHANNEL

The Secondary Common Control Physical Channel (S-CCPCH), Figure 3-23, is used to transmit two different transport channels: the forward access channel (FACH) and the paging channel (PCH).

Spreading Factor = 256 to 41 Slot = 0.666 mSec = 2560 chips = 20 * 2k data bits; k = [0..6]


20 to 1256 bits0, 2, or 8 bits

3GPP TS 25.211¶ 5.3.3.23GPP TS 25.211¶ 5.3.3.2

DataTFCI or DTX Pilot

0, 8, or 16 bits

1 2 3 4 5 6 7 8 9 10 11 12 13 140

Figure 3-23: The Secondary Common Control Channel.

This channel is mainly monitored by the UE in idle mode but can also be used in connected mode (Cell_FACH). In Cell_FACH it is used to send low rate PS services as well as L3 signaling. As the type of transport channel transmitted using this physical channel varies, Transport Format Combination Indication (TFCI) or Discontinuous Transmission (DTX) bits need to be sent to inform the receiving side of the channel types and bit rates. Zero, eight or sixteen bits are used at the end of the frame as a pilot sequence for coherent detection. The data carried in this channel has a spreading factor of 256 to 4.

PAGING INDICATOR CHANNEL

Figure 3-24 below depicts the structure of the Paging Indicator Channel (PICH).

b1b0

288 bits for paging indication 12 bits (undefined)

One radio frame (10 ms)

b287 b288 b299

Figure 3-24: The Paging Indicator Channel.

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This channel is used together with the Paging Channel (PCH) to provide UEs with an efficient sleep mode operation to save battery in idle mode. The PICH is used to alert UEs of an incoming page sent on the S-CCPCH. This is a Layer 1 channel only, that is, it originates in the physical layer.

The PICH channel consists of 300 bits over one radio frame and uses a spreading factor of 256 which is given on the P-CCPCH. Only the first 288 of these bits are used to carry the Paging Indicators (PIs), which leaves the last 12 bits undefined. One PI requires 2–16 bits and so the number of PIs in one frame can vary from 18-144. The UEs are divided into paging groups and each paging group belongs to a specific PI. The UE calculates the PI using its IMSI number. The UE reads how often it should listen to the PI on the P-CCPCH. This time period is defined as the Discontinuous Reception (DRX) cycle. If the PI is set to 1, there is an incoming paging message and the UEs belonging to that PI wakes up and monitors the PCH message carried on the S-CCPCH. The IMSI is used to identify which UE that is paged. The rest of the UEs in the paging group will go back to idle mode. If the PI is set to 0 the UE remains in sleep mode.

DEDICATED PHYSICAL CONTROL AND DATA CHANNEL

Figure 3-25 below shows how the dedicated physical data channel (DPDCH) and the dedicated physical control channel (DPCCH) are time multiplexed onto one WCDMA slot in the downlink.

Data 2TFCIData 1 TPC

1 Slot = 0.666 mSec = 2560 chips = 10 x 2̂ k bits, k = [0... 7]SF = 512/2 k = [512, 256, 128, 64, 32, 16, 8, 4]


DPDCH

Pilot

DPDCH DPCCH DPCCH

The DPDCH carries user traffic, layer 2 overhead bits, and layer 3 signaling data.

The DPCCH carries layer 1 control bits: Pilot, TPC, and TFC

Downlink Closed -Loop Power Control steps of 1 dB

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

I

, 0.5 dB

The DPDCH carries user traffic, layer 2 overhead bits, and layer 3 signaling data.

The DPCCH carries layer 1 control bits: Pilot, TPC, and TFCI

Downlink Closed -Loop Power Control steps of 1 dB

Figure 3-25: The DPDCH and DPCCH.

The DPDCH carries user traffic and Layer 3 signaling. The DPCCH carries Layer 1 control bits, which are as follows:


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• Pilot bits, which are used by the receiver to make different types of measurements.

• Transmit Power Control (TPC) bits, which are used in the inner loop power control.

• Transport Format Combination Indicator (TFCI) bits, which are used to inform the receiver about the transport format used.

The SF varies from 512 to 4 to allow it to carry variable data rates.

Bits/Frame Bits/ Slot

DPCCH

Channel BitRate

(kbps)

ChannelSymbol

Rate(ksps)

SF

TOTAL DPDCH DPCCH TOTAL DPDCH

TFCI TPC PILOT

60 30 128 600 510 90 40 34 0 2 4

Bits/Frame Bits/ Slot

DPCCH

Channel BitRate

(kbps)

ChannelSymbol

Rate(ksps)

SF

TOTAL DPDCH DPCCH TOTAL DPDCH

TFCI TPC PILOT

60 30 128 600 510 90 40 34 0 2 4

120 60 64 1200 900 300 80 60 8 4 8

1920 960 4 19,200 18,720 480 1280 1248 8 8 16

120 60 64 1200 900 300 80 60 8 4 8

1920 960 4 19,200 18,720 480 1280 1248 8 8 16

Coded Data1.920 Mb/sec

(19,200 bits per 10 mSec frame)

S/P Converter

Channelization Coding =>3.84 Mcps)

960 kb/sec

Figure 3-26: Downlink Data Rates.

Figure 3-26 shows how various user data rates are carried by the DPDCH and the DPCCH. Note that the symbol rate is always half the channel bit rate because of the serial to parallel conversion.

If the required data rate is 15 kbps then after serial to parallel conversion the data is carried at a rate of (15/2) 7.5 kbps by two separate streams. These streams are multiplied by a channelization code with a spreading factor of 512. Since 512 chips are used to transfer one modulation symbol, (38400/512) 75 modulation symbols, or (75·2) 150 bits, will be carried in one frame. 60 of these are used to carry data in the DPDCH and 90 to carry L1 control information in the DPCCH.

Since there are 15 slots in a frame the number of bits per slot will be 10. The DPDCH contains 4 of those bits and the remaining 6 bits are used by the DPCCH.

Figure 3-27 provides an extract from the slot format table, which shows the specified downlink DPDCH and DPCCH slot formats.

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14 480 240 16 320 56 232 8 8* 16 1514A 480 240 16 320 56 224 8 16* 16 8-1414B 960 480 8 640 112 464 16 16* 32 8-1415 960 480 8 640 120 488 8 8* 16 15

15A 960 480 8 640 120 480 8 16* 16 8-1415B 1920 960 4 1280 240 976 16 16* 32 8-1416 1920 960 4 1280 248 1000 8 8* 16 15

16A 1920 960 4 1280 248 992 8 16* 16 8-14

DPDCHBits/Slot

DPCCHBits/Slot

SlotFormat

#i

ChannelBit Rate(kbps)

ChannelSymbol

Rate(ksps)

SF Bits/Slot

NData1 NData2 NTPC NTFCI NPilot

Transmittedslots per

radio frameNTr

0 15 7.5 512 10 0 4 2 0 4 150A 15 7.5 512 10 0 4 2 0 4 8-140B 30 15 256 20 0 8 4 0 8 8-141 15 7.5 512 10 0 2 2 2 4 15

1B 30 15 256 20 0 4 4 4 8 8-142 30 15 256 20 2 14 2 0 2 15

2A 30 15 256 20 2 14 2 0 2 8-142B 60 30 128 40 4 28 4 0 4 8-143 30 15 256 20 2 12 2 2 2 15

3A 30 15 256 20 2 10 2 4 2 8-143B 60 30 128 40 4 24 4 4 4 8-14

Figure 3-27: Downlink DPDCH/DPCCH Slot Formats.

Two points to note are:

• Slot formats with no TFCI bits are used only when there is one data service in the DCH

• Slot formats ending with A or B are used for compressed mode operation. As can be seen from the table, only 8 to 14 slots are transmitted in each frame thereby giving time for the UE to measure the signal levels from non-WCDMA networks (GSM) or to make hard handovers to WCDMA carriers on other frequencies.

Figure 3-28 shows how compressed mode can be used to create transmission gaps.


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3GPP TS 25.212 ¶ 4.4.33GPP TS 25.212 ¶ 4.4.3

1 2 3 4 5 6 7 8 9 10 11 12 13 14 151 2 3 4 511 12 13 14 15 6

1 2 3 4 5 11 12 13 14 151 2 3 4 511 12 13 14 15 6

1 2 3 4 5 6 7 8 9 10 11 12 4 511 12 13 14 15 6

10 mSec Frames (15 slots)

Normal Operation

Compressed-Mode; single-frame method

Compressed-Mode; double-frame method

Transmission Gap

Transmission Gap

The complete TFCI word must be transmitted every frame, even in Compressed Mode.Compressed Mode Slot formats (A,B) contain higher proportion of TFCI bits per slot compared with normal slots.

Figure 3-28: Compressed mode

Figure 3-29 shows how the pilot symbols are embedded in the different slots in one frame.

Npilot = 4 Npilot = 8 Npilot = 16 Symbol # 0

Pilot Bit Patterns, Downlink DPDCH (Data Channel)

1 0 1 2 3 0 1 2 3 4 5 6 7 Slot #1

2 3 4 5 6 7 8 9

10 11 12 13 14 15

11 11 11 11 11 11 11 11 11 11 11 11 11 11 11

11 00 01 00 10 11 11 10 01 11 01 10 10 00 00

11 11 11 11 11 11 11 11 11 11 11 11 11 11 11

11 00 01 00 10 11 11 10 01 11 01 10 10 00 00

11 11 11 11 11 11 11 11 11 11 11 11 11 11 11

10 10 01 00 01 10 00 00 10 11 01 11 00 11 11

11 11 11 11 11 11 11 11 11 11 11 11 11 11 11

11 00 01 00 10 11 11 10 01 11 01 10 10 00 00

11 11 11 11 11 11 11 11 11 11 11 11 11 11 11

10 10 01 00 01 10 00 00 10 11 01 11 00 11 11

11 11 11 11 11 11 11 11 11 11 11 11 11 11 11

11 11 10 01 11 01 10 10 00 00 11 00 01 00 10

11 11 11 11 11 11 11 11 11 11 11 11 11 11 11

10 00 00 10 11 01 11 00 11 11 10 10 01 00 01

Figure 3-29: Time-Embedded Pilot Symbols.

The pilot bits are used for SIR measurements used in the inner loop power control. The grey fields are called Frame Synchronization Words (FSW) and are used for synchronization measurements.

Figure 3-30 shows how the different TPC bit formats are used to request power increases or decreases.

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TPC Command NTPC = 2 NTPC = 4 NTPC = 8

Up (1) 11 1111 11111111

Down (0) 00 0000 00000000

Figure 3-30: Transmit Power Control (TPC) Bits.

Since power control is very important and no form of error protection is used on these bits, the bits are sent more than once to achieve some level of error protection. At low data rates, where the SF is high, the TPC bit is only sent twice. In the case of high data rate channels, where the SF is much smaller, up to eight TPC bits are sent.

Figure 3-31 below explains in more detail how the Transport Format Combination Indicator (TFCI) bits are generated. As this information is vital for decoding each frame, strong error protection is used, thereby increasing these 10 bits to 32 bits.

Data Channel 1

Data Channel 2

Data Channel N Channel Coding

Channel Coding

Channel Coding

Coded Composite Transport Channel

(CCTrCH)

TFI 1

TFI 2

TFI N

MUX

MUX

TFCI Word32 bits

TFI: Transport Format IndicatorTFCI: Transport Format Combination Indicator

Channel Coding10 bits

Figure 3-31: TFCI Bits.

It is vital that the whole 32-bit TFCI word is sent in each frame. This is achieved in compressed mode by sending more TFCI bits per timeslot. In slot format 3A for example, four bits are sent per slot. If only eight slots are sent per frame, this means that the complete word (8·4 = 32) will still be transmitted in each frame. In normal mode operation only 30 bits are transferred (15·2) and two bits are therefore punctured. As this word is strongly coded these two bits will be treated like errors and corrected.


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Acquisition Indicator Channel

The acquisition indicator channel (AICH) is a physical channel used to carry acquisition indicators, which corresponds to a certain signature that the UE selected randomly on the PRACH. AICH is a fixed rate (SF=256) channel. It uses 15 consecutive access slots (corresponds to 2 slots) each of length 5120 chips. Each access slot consists of two parts. The first part is the Acquisition Indicator (AI) consisting of 32 symbols. The second part consists of 1024 chips and here the transmission is off. The AI part takes the values +1, -1, and 0. The bs,j is the signature pattern.

Figure 3-32 shows the structure of the AICH as specified by the 3GPP. The AI part is derived from the UEs access preamble signature.

1024 chips

AS #0 AS #1 AS #i AS #14

a1 a2a0 a31a30

AI part

20 ms

AS #14 AS #0

(Transmission Off)∑=

=15

0,

sjssj bAIa

Figure 3-32: Acquisition Indication Channel (AICH).

MULTIPLEXING

Figure 3-33 shows the Ericsson mapping of a 12.2 kbps speech RAB, L3 signaling together with L1 signaling onto a DPCH.

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119 119 119 1192nd speech block

1 5 2 1 6 7 6 8

6 0 06 0 0

6 0 0 6 0 0

# 2 1 1 0# 1 1 1 0 1 5 2 1 6 7 6 8

476

8 tail bitsCRC 16

164148

516 Rate 1/3 CC

1st interleaving

MAC Layer4 bit MAC

136RRC UM

8 bit RLC

RRC AM or NAS DT normal priority128128144

16 bit RLC4 bit MAC

40 msec

Frame segmentation

136

2nd interleaving 510

119


119

1st interleaving

144

Figure 3-33: Downlink speech RAB mapping.

Since speech can only cope with a short interleaving delay, 20 ms blocks of speech data are used. With a data rate of 12.2 kbps this corresponds to 244 bits. This block is divided into 3 sub flows indicating the significance of the bits from the vocoder. The L3 signaling uses 40 ms blocks and passes through similar steps as the voice.

12 bits of CRC is added to voice and 16 to L3 signaling. To reset the convolutional coder, 8 tail bits must be added. The resulting bits are fed to the convolutional coder. Sub flow 1 and 2 and the L3 signaling uses 1/3 convolutional coding and sub flow 3 uses 1/2 convolutional coding. The next step is rate matching that reduces the amount of bits by puncturing to match the DPCH bit rate. The first stage of interleaving is service dependent and will in this case be 20 ms for voice and 40 ms for the L3 signaling.

To have the same time period of data two 20 ms voice blocks must be taken for each L3 signaling block. The voice and L3 signaling are multiplexed onto four 10 ms radio frames.

The second interleaving length is always 10 ms long. The frame is then divided into 15 slots and finally the L1 signaling bits are multiplexed. In this case the final symbol rate after serial to parallel conversion will be 30 ksps and a SF of 128 is used.

Figure 3-34 shows the Ericsson mapping of a 384 kbps PS RAB, L3 signaling together with L1 signaling onto a DPCH.

DPDCH 60kbps => SF=128 DPDCH 60kbps => SF=128

2 TPC 4 Pilot 2 TPC 4 Pilot

Convolutional coding8 tail bits

CRC 1293303 (1/3) 333 (1/3) 136 (1/2)

81

103 60

103 60

81

Rate matching

20 msec of each subflow

34 34 34 34 4 04 0

4 04 0

316294 172294 316 172

147 147 158 158 86 86

147 158 86 147 158 86


1 5 2 1 6 7 6 81 5 2 1 6 7 6 8

6 0 06 0 0

6 0 0 6 0 0

# 2 1 1 0# 1 1 1 0 1 5 2 1 6 7 6 81 5 2 1 6 7 6 8

476

8 tail bitsCRC 16

164148

516 Rate 1/3 CC

1st interleaving

MAC Layer4 bit MAC

136RRC UM

8 bit RLC

RRC AM or NAS DT normal priority128128144

16 bit RLC4 bit MAC

40 msec

Frame segmentation

13620 msec of each subflow


119


119

1st interleaving

144

DPDCH 60kbps => SF=128 DPDCH 60kbps => SF=128

2 TPC 4 Pilot 2 TPC 4 Pilot

Convolutional coding8 tail bits

CRC 1293303 (1/3) 333 (1/3) 136 (1/2)

81

103 60

103 60

81

Rate matching316294 172294 316 172

147 147 158 158 86 86

147 158 86 147 158 86

34 34 34 34 4 04 0 4 0

4 0


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95 95 95 95Next 3 blocks

380

8 tail bitsCRC 16

164148

516 Rate 1/3 CC

1st interleaving

MAC Layer4 bit MAC

1368 bit RLC

128128144

16 bit RLC4 bit MAC

40 msec136144

12 Trellis termination

bits

9025

95


608 608

DPDCH 480ksps => SF=8

9025

Turbo Coding 12672

16 16 16 16 16 16 16 16 16 16 16 16

320 320 320 32016 16 16 16 320 320 320 32016 16 16 16 320 320 320 32016 16 16 16

Up to 12X320 TBs in 10 msec => max data rate = 384 kbps

Rate matching

1st interleaving

8 TFCI 8 TPC 16 Pilot600600600

RRC UM RRC AM or NAS DT normal priority

Figure 3-34: Downlink 384 kbps PS RAB mapping.

Note that turbo coding is used for the PS data and that 10 ms is used for the first interleaving.

Figure 3-35 shows how several downlink DPDCHs can be used for multi coding to achieve 2Mbps. Only one DPCCH is needed. Note that Ericsson is not supporting this.

1 Slot = 0.666 mSec = 2560 chips = 10 x 2^k bits, k = [0...7]

Data 2TFCIData 1 TPC PilotPrimaryDPCCH/DPDCH

Data 4Data 3AdditionalDPCCH/DPDCH

Data NData N-1AdditionalDPCCH/DPDCH

Figure 3-35: Multi-Code Transmission.

Transmit Diversity

Different types of transmit diversity can be used at the base station to improve the capacity. Note that Ericsson is not supporting any of these today.

These are Time-Switched Transmit Diversity (TSTD) and Space-Time Transmit Diversity (STTD).

TSTD is used only on the synchronization channels. These channels are alternated between antenna 1 and 2 for each slot in the WCDMA frame as shown in Figure 3-36.

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STTD is used on all other channels. The data bits are transmitted again on the second antenna with the phase reversed for each alternative bit.

b0 b1 b2 b3

b0 b1 b2 b3

-b2 b3 b0 -b1

Antenna 1

Antenna 2

Data bits

PSC

SSCi

PSC

SSCi

PSC

SSCi

PSC

SSCi

PSC

SSCi

Antenna 1

Antenna 2

Slot #0 Slot #1 Slot #2 Slot #3 Slot #14

• STTD (Space-Time Transmit Diversity); All Other DL Channels

Note: TSTD and STTD must be supported by the UE, but are optional in BS

• TSTD (Time-Switched Transmit Diversity); SCH Only 3GPP TS 25.211 ¶ 5.33GPP TS 25.211 ¶ 5.3

Figure 3-36: RBS Transmit Diversity.

The general transmitter structure of closed-loop diversity for DPCH signals is shown in Figure 3-37. This signal is fed to both antennas and weighted with antenna specific weight factors w1 and w2. These factors are complex valued wi = ai + jbj. The UE measures the signal strength from the two antennas and computes the phase and amplitude adjustment that should be applied at the WCDMA RAN to maximize the UE received power. The UE transmits Feedback Information (FBI) bits that informs the RBS how to adjust the amplitude and phase relations between the two antennas.


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Σ

DPCCH

DPDCHMUX

DCH (or PDSCH)

W1W2

Σ

CPICH2

CPICH1

Decode FBICalculateGains, Phases

Antenna 1

Antenna 2

Weights W1, W2 are complex-valued:

Wi = ai + jbi

gaini = square root (ai2 + bi

2)phasei = tan-1(bi/ai)

• S/P Demux• Channelization• Scrambling• I/Q Modulation

Figure 3-37: Closed-Loop Transmit Diversity.

When Site Selection Transmit Diversity is used, the UE again uses the FBI bits in the DPCCH channel to report to the RBS. However, this time these are used to indicate which antenna (in a soft/softer handover scenario) that is providing the best signal. The transmission of data on the DPDCH in the downlink of the various cells is then controlled by the indication bits.

WCDMA UPLINK Figure 3-38 shows the structure of the WCDMA uplink (UE as transmitter). The main difference between uplink and downlink is that the DPCCH and DPDCH are not time multiplexed. One reason for this is to improve the peak-to-average ratio.

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Logical Channels (Layers 2+)

Transport Channels (Layer 2)


UplinkRF Out

UE Scrambling

Code

I+ jQ I/QMod.

Q

I Filter

FilterΣ

Σ I

DPDCH #1Dedicated Physical Data Ch.

DPDCH #3 (optional)Dedicated Physical Data Ch.

DPDCH #5 (optional) Dedicated Physical Data Ch.



DPDCH #6 (optional) Dedicated Physical Data Ch. Σ Q

DPCCHDedicated Physical Control Ch.Pilot, TPC, TFCI bits

Chd,3 Gd

Chd,5 Gd

Chd,2 Gd

Chd,4 Gd

Chd,6 Gd

Ch256 Gd

Σ

j

DCCH Dedicated Control Ch.

DTCH Dedicated Traffic Ch. N DCH

Dedicated Ch. Data Encoding

DTCH Dedicated Traffic Ch. 1 DCH

Dedicated Ch. Data Encoding M

U X

CCTrCH DCH Dedicated Ch. Data

Encoding

HS -DPCCHHigh Speed Dedicated Physical Control Ch.

Chd,1 Gd

Σ CCCH Common Control Ch. RACH

Random Access Ch. PRACHPhysical Random Access Ch.

Data Coding

j

RACH Control Part

Chd Gd

Chc Gc

DTCH (packet mode) Dedicated Traffic Ch.

Chd,1 Gd

Logical Channels (Layers 2+)

Transport Channels (Layer 2)


UplinkRF Out

UE Scrambling

Code

I+ jQ I/QMod.

Q

I Filter

FilterΣ

Σ I

DPDCH #1Dedicated Physical Data Ch.

DPDCH #3 (optional)Dedicated Physical Data Ch.




DPDCH #6 (optional) Dedicated Physical Data Ch. Σ Q

DPCCHDedicated Physical Control Ch.Pilot, TPC, TFCI bits

Chd,3 Gd

Chd,5 Gd

Chd,2 Gd

Chd,4 Gd

Chd,6 Gd

Ch256 Gd

Σ

j

DCCH Dedicated Control Ch.

DTCH Dedicated Traffic Ch. N DCH

Dedicated Ch. Data Encoding

DTCH Dedicated Traffic Ch. 1 DCH

Dedicated Ch. Data Encoding M

U X

CCTrCH DCH Dedicated Ch. Data

Encoding

HS -DPCCHHigh Speed Dedicated Physical Control Ch.

Chd,1 GdChd,1 Gd

Σ CCCH Common Control Ch. RACH

Random Access Ch. PRACHPhysical Random Access Ch.

Data Coding

j

RACH Control Part

Chd GdChd Gd

Chc GcChc Gc

DTCH (packet mode) Dedicated Traffic Ch.

Chd,1 GdChd,1 Gd

Figure 3-38: WCDMA Uplink.

The list below provides a brief explanation of the function of the Ericsson supported channels (from the system side) that are transmitted in the uplink.

• Physical Random Access Channel (PRACH):

This channel is used to carry access requests; control information and short data bursts. It uses only Open-loop power control and contains therefore no pilot or TPC bits.

• Dedicated Physical Data Channel (DPDCH):

The uplink DPDCH is used to carry dedicated traffic and L3 signaling.

• Dedicated Physical Control Channel (DPCCH):

The uplink DPCCH is used to carry layer 1 signaling. This information consists of pilot bits, Transmit Power Control (TPC) commands, Feedback Information (FBI) and Transport Format Combination Indicator (TFCI).


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Common Uplink Transport Channels– RACH Random Access Channel

- Carries access requests, control information, short data

- Uses only open-loop power control- Subject to random access collisions

Dedicated Uplink Transport Channels– DCH Dedicated Channel

- Carries dedicated traffic and control data from one UE

Figure 3-39: Uplink Transport Channels

DEDICATED PHYSICAL CONTROL AND DATA CHANNEL

Figure 3-40 shows the structure of the uplink DPDCH and DPCCH.

Coded Data, 10 x 2^k bits, k=0…6 (10 to 640 bits)Dedicated Physical Data Channel (DPDCH) Slot (0.666 mSec)

Pilot FBI TPCDedicated Physical Control Channel (DPCCH) Slot (0.666 mSec)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15


I

QTFCI

Figure 3-40: Uplink DPDCH/DPCCH.

The DPDCH and DPCCH are not time multiplexed. DPDCH uses the I-branch and the DPCCH uses the Q-branch. The spreading factor for the DPDCH can range from 4 to 256. The SF for the DPCCH is set to 256.

The DPCCH consists of the following:

• Pilot field, uses 3, 4, 5, 6, 7, or 8 bits.

• TFCI, that is the Transmit Format Combination Indicator relating to how the data is multiplexed etc., uses 0 (none), 2, 3, or 4 bits.

• FBI, that is the Feedback Information is used for transmit diversity. Here 0 (none) 1, or 2 bits can be used.

• TPC, that is Transmit Power Control, used in inner loop power control, uses 1 or 2 bits.

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Figure 3-41 shows different slot formats available for both the DPDCH and DPCCH. Seven different formats are available for the DPDCH ranging from slot format 0, which offers 15 kbps using a SF of 256, to slot format 6, which offers 960 kbps using a SF of 4.

Twelve different slot formats are available for the DPCCH depending on the number of pilot, TPC, TPCI and FBI bits needed. Note that the formats ending in the letters A or B are special formats required in compressed mode operation to allow time for interfrequency measurements.

S lo t Format #i C hanne l B it R ate (kbps)

C hanne l S ymbol R ate (ksps)

S F B its/ F rame

B its/ S lo t

N da ta

0 15 15 256 150 10 10 1 30 30 128 300 20 20 2 60 60 64 600 40 40 3 120 120 32 1200 80 80 4 240 240 16 2400 160 160 5 480 480 8 4800 320 320 6 960 960 4 9600 640 640

S lot Format #i

C hanne l B it R ate (kbps)

C hanne l S ymbol R ate (ksps)

S F B its/ Frame

B its/ S lo t

N pilo t N TP C N TFC I N FB I T ransmitte d slo ts pe r

rad io frame 0 15 15 256 150 10 6 2 2 0 15

0A 15 15 256 150 10 5 2 3 0 10-14 0B 15 15 256 150 10 4 2 4 0 8-9 1 15 15 256 150 10 8 2 0 0 8-15 2 15 15 256 150 10 5 2 2 1 15

2A 15 15 256 150 10 4 2 3 1 10-14 2B 15 15 256 150 10 3 2 4 1 8-9 3 15 15 256 150 10 7 2 0 1 8-15 4 15 15 256 150 10 6 2 0 2 8-15 5 15 15 256 150 10 5 1 2 2 15

5A 15 15 256 150 10 4 1 3 2 10-14 5B 15 15 256 150 10 3 1 4 2 8-9

DPDCH (Dedicated Physical Data Channel) Slot Formats

DPCCH (Dedicated Physical Control Channel) Slot Formats

Figure 3-41: Uplink DPDCH/DPCCH Slot Formats.

Figure 3-42 shows the FBI bits. The overall field is made up of 0, 1 or 2 bits, depending on the slot format used. These are sub-divided into S and D fields. During soft handover the bits in the S field are used to inform the network, which cell that is producing the strongest signal. This cell can be called the “primary cell” and the network can suspend transmission from other cells involved in the handover to reduce downlink interference. This enhancement to the soft handover process is called Site Selection Transmit Diversity (SSTD).


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3GPP TS 25.211 ¶ 5.2.13GPP TS 25.211 ¶ 5.2.1

S Field

0, 1, or 2 bits

Used for SSTD signalingduring soft handover

D Field

0 or 1 bit

Provides feedback informationfor closed-loop transmit diversity

0, 1, or 2 bits total depending on Slot Format

SSTD (Site Selection Transmit Diversity) is an enhanced soft handover process

The UE determines the cell with the strongest received signal, and indicates this “primary cell” selection using the S Field.

Cells other than the primary cell suspend transmission, so that overall downlink interference is reduced.

Figure 3-42: Feedback Information Field (FBI).

The D field bits are used in the Closed-loop transmit diversity loop, which is used to control the gain and relative phase of the RBS transmit antennas in reaction to the received levels at the UE.

MULTIPLEXING

Figure 3-43 shows the mapping of a 12.2 kbps speech RAB and L3 signaling on the DPDCH. The L1 signaling is sent on the DPCCH.

Rate match

1st Interleaving

IBranch

Q


1 5 2 1 6 7 6 8

6 0 0 bi t s ( 6 00 s ym b ol s)6 0 0 bi t s ( 6 00 s ym b ol s)

6 0 0 6 0 0

4 0 4 0

# 2 1 1 0

4 0 4 0

# 1 1 1 0 1 5 2 1 6 7 6 8

129 129 129 129

8 tail bitsCRC 16

164148

516 Rate 1/3 CC1st interleaving

MAC Layer4 bit MAC

1368 bit RLC

128128144

16 bit RLC4 bit MAC

40 msec


8 tail bits

Radio frame equalization

136144CRC 12

93

1/3 1/3 1/2

304

81

103 6020 msec of each subflow

103 60

334 136

152 167 68152 167 68

303+1 333+1 136

81

152 167 68

DPDCH 60kbps => SF=64


40 40

140Rate match 460

QPILOT TFCI TPC 6 2 2DPCCH 15kbps

152 167 68



40 40

140Rate match 460

Frame segmentationRate match

1st Interleaving

IBranch

Q


1 5 2 1 6 7 6 81 5 2 1 6 7 6 8

6 0 0 bi t s ( 6 00 s ym b ol s)6 0 0 bi t s ( 6 00 s ym b ol s)

6 0 0 6 0 0

4 0 4 0

# 2 1 1 0

4 0 4 0

# 1 1 1 0 1 5 2 1 6 7 6 81 5 2 1 6 7 6 8

129 129 129 129

8 tail bitsCRC 16

164148


MAC Layer4 bit MAC

1368 bit RLC

128128144

16 bit RLC4 bit MAC

40 msec


8 tail bits

Radio frame equalization

136144CRC 12

93

1/3 1/3 1/2

304

81

103 6020 msec of each subflow

81

103 60

334 136

152 167 68152 167 68

303+1 333+1 136

152 167 68



40 40

140Rate match 460

QPILOT TFCI TPC 6 2 2DPCCH 15kbps

152 167 68



40 40

140Rate match 460

Frame segmentation

Figure 3-43: Uplink speech RAB mapping.

The main difference between this procedure for the uplink and downlink is that for the uplink rate matching is performed after frame segmentation.

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Figure 3-44 shows the mapping of PS 64kbps RAB and L3 signaling on the DPDCH. The L1 signaling is sent on the DPCCH.

IBranch

Q

154 154 154 1542nd speech block1 5 2 1 6 7 6 8

6 0 0 bi t s ( 6 00 s ym b ol s) 6 0 0 bi t s ( 6 00 s ym b ol s)

6 0 0 6 0 0

4 0 4 0

# 2 1 1 0

4 0 4 0

# 1 1 1 0 1 5 2 1 6 7 6 8

129 129 129 129

8 tail bitsCRC 16

164148


MAC Layer4 bit MAC

1368 bit RLC

128128144

16 bit RLC4 bit MAC

40 msec

Frame segmentation

136



160 160

1542246

QPILOT TFCI TPC 6 2 2DPCCH 15kbpsDPDCH 240kbps => SF=16


160 160

1542246

Rate matching

12 Trellis termination bits

144

1st Interleaving 4236

Turbo Coding 4224

2118 2118

2246 2246

1 2 3 43 2 0 3 2 0 3 2 0 3 2 01 6 1 6 1 6 1 6

1 6 1 6 1 6 1 6336 336 336 33616 bit RLC

CRC 16

IBranch

Q

154 154 154 1542nd speech block1 5 2 1 6 7 6 8

6 0 0 bi t s ( 6 00 s ym b ol s) 6 0 0 bi t s ( 6 00 s ym b ol s)

6 0 0 6 0 0

4 0 4 0

# 2 1 1 0

4 0 4 0

# 1 1 1 0 1 5 2 1 6 7 6 81 5 2 1 6 7 6 8

129 129 129 129

8 tail bitsCRC 16

164148


MAC Layer4 bit MAC

1368 bit RLC

128128144

16 bit RLC4 bit MAC

40 msec

Frame segmentation

136



160 160

1542246

QPILOT TFCI TPC 6 2 2DPCCH 15kbpsDPDCH 240kbps => SF=16


160 160

1542246

Rate matching

12 Trellis termination bits

144


Turbo Coding 4224

2118 2118

2246 2246

1 2 3 43 2 0 3 2 0 3 2 0 3 2 01 6 1 6 1 6 1 6

1 6 1 6 1 6 1 6336 336 336 33616 bit RLC

CRC 16


Turbo Coding 4224

2118 2118

2246 2246

1 2 3 43 2 0 3 2 0 3 2 0 3 2 01 6 1 6 1 6 1 6

1 6 1 6 1 6 1 6336 336 336 33616 bit RLC

CRC 16

Figure 3-44: Uplink PS 64 kbps RAB mapping.

RANDOM ACCESS CHANNEL

The random access message, which is sent by the UE after it has received the acquisition on the AICH, is shown in Figure 3-45.

3GPP TS 25.211¶ 5.2.23GPP TS 25.211¶ 5.2.2

Random Access Message (10, 20, 40, or 80 bits per slot) RACH Data (0.667 ms)

Pilot (8 bits)

RACH Control part (0.667 ms)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1 Frame = 15 slots = 10 ms

I

Q TFCI (2 bits)

Figure 3-45: Random Access Message.


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The RACH message can be configured to be 10 or 20 ms long. Ericsson has chosen 20 ms. The RACH message is sent on the I-branch while the layer 1 signaling is sent on the Q-branch.

The control part uses SF 256 and consists of eight known pilot bits to support channel estimation for coherent detection, and two TFCI bits. The RACH message uses SF 64.

HPSK MODULATION

The top left-hand corner of below shows a vector diagram for the transmitter where the I- and Q-branches are of equal magnitude. Only the points are plotted. This represents the case in the downlink, as the DPDCH and DPCCH are time multiplexed before being divided and sent to the I- and Q-branch. After baseband filtering, shown in the top right hand diagram, (this traces the tip of the vector while the transmitter is in operation) there are a lot of zero crossings. This means that the power out put of the transmitter (represented by the length of the vector) varies a lot between zero and full power. This result in a very poor peak-to-average transmit power ratio.

QPSKmodulation pattern

I,Q Equal

Magnitude


I,QNon-EqualMagnitude

After Baseband FilteringBefore Baseband Filtering



I,Q Equal

Magnitude


I,QNon-EqualMagnitude



Figure 3-46: QPSK Modulation Pattern.

The situation is even worse in the second case where I and Q are of non-equal magnitude as in the bottom left hand diagram in

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Figure 3-46. This will be the case in the uplink, since the DPDCH is fed to the I-branch and the DPCCH is fed to the Q-branch. Due to discontinuous transmission of the DPDCH it results in more zero crossings.

Figure 3-47, of reducing this is to use a type of modulation known as Complex Spreading. This works by using a complex scrambling code that rotates the whole pattern ±45o or ±135 o to align with the I- and Q-branch. This is the type of modulation used in the downlink and the uplink when the data is multiplied by the complex scrambling code.

Complex Spreading

modulation pattern

I,Q Equal

Magnitude

Complex Spreading modulation

pattern

I,Q Non-EqualMagnitude



Complex Spreading

modulation pattern

I,Q Equal

Magnitude

Complex Spreading modulation

pattern

I,Q Non-EqualMagnitude



Figure 3-47: Complex Spreading Pattern.

As can be seen from Figure 3-47, Complex Spreading rotates the transmitter vectors resulting in a more circular pattern even when I and Q are unequal in magnitude. This produces a lower peak to average ratio in the transmitter output and hence better transmitter efficiency and increased battery life.

Hybrid Phase Shift Keying (HPSK) modulation is used in the uplink.


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As can be seen from Figure 3-48, restrictions are placed on the channelization codes that can be used in the uplink to avoid using those codes that have frequent positive and negative transitions. This reduces the number of zero crossings in the output and hence improves the peak-to-average power ratio of the RF transmitter. For the best possible transmitter efficiency, and hence longest battery life, this ratio must be kept to a minimum.

1

1 -1

1 1

1 1 1 1

1 1 -1 -1

1 -1 1 -1

1 -1 -1 1

C1,0

C2,0

C2,1

C4,0

C4,1

C4,2

C4,3

DPCCH

DPDCH 1, 2

DPDCH 3, 4

DPDCH 5, 6

Figure 3-48: Uplink Channelization Codes for HPSK.

Code C256,0 is used to spread the information from the DPCCH, as this has the least zero transitions.

After this, C4,1 is the first choice for a DPDCH of SF = 4, as this produces only one zero transition. If more DPDCHs are required (multi coding) with the same SF then DPDCH_2 can use C4,1 again (I and Q branches are orthogonal to each other), but this will be placed onto the Q branch of the modulator. The next DPDCH must use C4,3 on the I-branch and so on.

Code selection in this manner, along with the proper choice of scrambling code, increases the spectral efficiency by limiting the diagonal transmissions in the signal constellation. This also results in efficient use of the power amplifier.

Also HPSK spreading uses Walsh rotator codes. When two consecutive pairs of I and Q chips have the same values i.e. (1,1) followed by (1,1) the transmitter output vector actually has to go from (1,1) down to zero and then back up to (1,1) again. This means that the output power has to vary a lot in a short time, which is inefficient. The Walsh rotator codes multiply consecutive pairs of chips by (1,1) and (1, -1) so a (1,1) (1,1) sequence becomes (1,1) (1, -1) which is an easy 90 degree swing of the transmitter vector at constant amplitude (constant power) and is much more efficient.

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Complex Spreading

modulation pattern

versus

HPSK modulation

pattern

I,Q Equal

Magnitude

ComplexSpreading

Complex Spreading

HPSK

HPSKComplex

Spreading modulation

pattern

versus

HPSK modulation

pattern

I,Q Non-Equal Magnitude

Complex Spreading

modulation pattern

versus

HPSK modulation

pattern

I,Q Equal

Magnitude

ComplexSpreading

Complex Spreading

HPSK

HPSKComplex

Spreading modulation

pattern

versus

HPSK modulation

pattern

I,Q Non-Equal Magnitude

Figure 3-49: Complex PN Spreading vs. HPSK Spreading.

The vector diagrams in Figure 3-49 compare the constellations produced when using complex scrambling and HPSK when I and Q are equal (in the downlink) and when I and Q are unequal (in the uplink). Note that HPSK spreading is not actually used in the downlink it is merely shown here in the top right hand diagram for comparison.

It can be seen that the HPSK constellation has a reduced incidence of zero crossings and hence an improved peak-to- average power ratio.

4 Syncronization and Random Access

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Objectives


• Explain base station downlink timing

• Explain the synchronization procedure

• Explain the random access procedure

• Explain the establishment of dedicated channels

• Explain soft handover timing Figure 4-1: Objectives


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Contents

INTENTIONALLY BLANK BASE STATION DOWNLINK TIMING ....134

BASE STATION DOWNLINK TIMING ...............................................135

SYNCHRONIZATION PROCEDURE .................................................136 DOWNLINK SCRAMBLING CODES ............................................................136 SYNCHRONIZATION CODES......................................................................136

RANDOM ACCESS PROCEDURE....................................................140

DEDICATED CHANNEL PROCEDURE.............................................145

WCDMA SOFT HANDOVER .............................................................146


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BASE STATION DOWNLINK TIMING Figure 4-2 shows the transmission timing of the various downlink channels. The 256 chip gap in the beginning of each of the P-CCPCH slots is to accommodate the transmission of the SCH. The SCH is always transmitted from the base station and is transmitted at the same timing reference as the CPICH. The S-CCPCH is only transmitted when there is data available. Therefore, it has its own transmission timing. This timing offset is a multiple of 256 chips. The variable time offset for downlink dedicated channels is to enable soft handover in an unsynchronized radio access network. The PICH has a fixed time offset with respect to the S-CCPCH to be able to alert the terminal that there is a page coming on the PCH mapped onto the S-CCPCH.

Secondary SCH

Primary SCH

t S-CCPCH,k

10 ms Frame

P-CCPCH, (SFN modulo 2 = 0) P-CCPCH, (SFN modulo 2 = 1)

CPICH (Common Pilot Channel)

AICH access slots #0 #1 #2 #3 #14#13#12#11#10#9#8#7#6#5#4AICH access slots #0 #1 #2 #3 #14#13#12#11#10#9#8#7#6#5#4

t PICH

t DPCH,n

Common PilotChannel

Primary CCPCH(Broadcast Data)

Secondary CCPCH(Paging, Signaling)

Paging Indicator Channel

SCH (PSC+SSC)P-CCPCHS-CCPCHPICHAICHDPCH HSDPA

t S-CCPCH,k = N x 256 chips

t DPCH,n = N x 256 chips

t PICH = 7680 chips (3 slots)

t HS_SCCH,n= N

t HS-PDSCH,n= 2 slots

3GPP TS 25.211 ¶ 7.03GPP TS 25.211 ¶ 7.0

k:th S-CCPCH

PICH for n:th S-CCPCH

n:th DPCCH/DCDPHDedicated Physical

Control/Data Channel

High Speed Shared Control Channel

tHS-PDSCH,n

t HS-SCCH,n

Figure 4-2: Downlink Transmission Timing.

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SYNCHRONIZATION PROCEDURE

DOWNLINK SCRAMBLING CODES

There are 8192 downlink scrambling codes available in total (including secondary scrambling codes). The primary scrambling codes are 512 and these are divided into 64 different scrambling code groups. Each scrambling code group is further divided into eight codes. The grouping is done to facilitate fast cell search by the UE. This structure is shown in Figure 4-3.

Primary SC0

Secondary Scrambling

Codes

(15)


Codes

(15)


Codes

(15)


Codes

(15)

Code Group #1 Code Group #64

8192 Downlink Scrambling CodesEach code is 38,400 chips of a 218 - 1 (262,143 chip) Gold Sequence

Primary SC7 Primary SC504 Primary SC511

Figure 4-3: DL scrambling codes.

Each cell is assigned one primary scrambling code that is transmitted on the CPICH.

SYNCHRONIZATION CODES

The first 256 chips of each slot, Figure 4-4, are reserved for transmission of the primary synchronization code (PSC) and secondary synchronization codes (SSC). These codes are not scrambled with the primary scrambling code of the cell. The reason for this is that all UEs use these codes firstly to locate a WCDMA system and secondly to locate the scrambling code used in that cell.

These 256 chip codes are broadcast every slot, multiplexed with the P-CCPCH (2304 chips), which allows the UEs to quickly synchronize to the network.

PSC is used to notify the UEs that this is a WCDMA system. The PSC also provides them with a reference to synchronize themselves to the WCDMA slots. In other words after decoding the PSC the UE knows:


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• That it has found a WCDMA system.

• When the slots start. So the UE knows when to look for the secondary synchronization codes.

There are sixteen SSCs, which are arranged into 64 unique combinations to identify the scrambling code group that the cell belongs to. In other words after decoding the SSC the UE knows two more things:

• Which scrambling code group the primary scrambling code belongs to.

• When the next WCDMA frame is going to start.

Broadcast by RBS

3GPP TS 25.213 ¶ 5.2.33GPP TS 25.213 ¶ 5.2.3

256 Chips P-CCPCH

(PSC + SSC + BCH )

2304 Chips

First 256 chips of every P-CCPCH slotAllows UE to achieve fast synchronization in an asynchronous systemPrimary Synchronization Code (PSC)

Fixed 256-chip sequence with base period of 16 chipsProvides fast positive indication of a WCDMA systemAllows fast asynchronous slot synchronization

Secondary Synchronization Codes (SSC)A set of 16 codes, each 256 chips longCodes are arranged into one of 64 unique permutationsSpecific arrangement of SSC codes provide UE with frame timing, Scrambling Code Group


PSC

Figure 4-4: Synchronization Codes, i.e. PSC and SSC.

Figure 4-5 shows how the PSC is transmitted to convey the slot timing to the UEs. As can be seen, the code and the inverse of the code are sent in accordance with a particular pattern. The PSC is chosen to have a good periodic auto correlation property.

The primary SCH is used to acquire the timing for the secondary SCH and it consists of an un-modulated code of length 256 chips, which is transmitted once every slot. The primary synchronization code is the same for all cells in the system and is transmitted in line with the slot boundary.

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let a = <1, 1, 1, 1, 1, 1, -1, -1, 1, -1, 1, -1, 1, -1, -1, 1>

PSC (1...256) = < a, a, a, -a, -a, a, -a, -a, a, a, a, -a, a, -a, a, a >

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14


Note: PSC is transmitted “Clear” (Without scrambling)

3GPP TS 25.213 ¶ 5.2.33GPP TS 25.213 ¶ 5.2.3


2304 Chips256 ChipsSCH P-CCPCH

PSC

Figure 4-5: Primary Synchronization Code.

Figure 4-6 shows how the PSC is used to provide the UE with the required slot synchronization. In practice this is used to tune a matched filter to the timing of each slot. The slot timing of the cell can be obtained by detecting peaks in the matched filter output.

BCH Data

PSC[1]

BCH Data

PSC[2]

BCH Data

PSC[3]

BCH Data

PSC[4]

BCH Data

PSC[15]

Matched Filter(Matched to PSC)

10 mSec Frame (15 slots x 666.666 uSec)

MatchedFilterOutput

time

P-CCPCH

(PSC)

3GPP TS 25.214 Annex C3GPP TS 25.214 Annex C

Figure 4-6: Slot Synchronization Using Primary Synchronization Code.

The SSC is chosen from a set of sixteen different codes depending on which of the 64 different scrambling code groups the cell belongs to.

Figure 4-7 shows how the sixteen SSCs are arranged into one of 64 unique patterns. The UEs can tell from the order in which the codes are transmitted which scrambling code group the cell belongs to. Another benefit of decoding these is that once the sixteen SSCs have been received the UE knows the cell frame timing.


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slot number Scrambling Code Group

#1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14 #15

Group 1 1 1 2 8 9 10 15 8 10 16 2 7 15 7 16

Group 2 1 1 5 16 7 3 14 16 3 10 5 12 14 12 10

Group 3 1 2 1 15 5 5 12 16 6 11 2 16 11 15 12

• • •

• • •

• • •

Group 62 9 10 13 10 11 15 15 9 16 12 14 13 16 14 11

Group 63 9 11 12 15 12 9 13 13 11 14 10 16 15 14 16

Group 64 9 12 10 15 13 14 9 14 15 11 11 13 12 16 10

Note:

The SSC patterns positively identify one and only one of the 64 Scrambling Code Groups.

This is possible because no cyclic shift of any SSC is equivalent to any cyclic shift of any other SSC.

3GPP TS 25.213 ¶ 5.2.33GPP TS 25.213 ¶ 5.2.3

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14


SSC1 SSC2 SSC3 SSC4 SSC5 SSC6 SSC7 SSC8 SSC9 SSC10 SSC11 SSC12 SSC13 SSC14 SSC15 SSC16

SSCi

SSC1 SSC15

Figure 4-7: Secondary Synchronization Code Group. Sixteen fixed 256-bit codes. Codes arranged into one of 64 patterns

Figure 4-8 shows how the UE achieves frame synchronization after receiving sixteen secondary synchronization codes. This is done by correlating the received signal with all possible secondary SCH code sequences and identifying the maximum correlation value. Because the cyclic shifts of the sequence are unique, the code group and the frame synchronization are determined.

BCHData

SSC[1]

SSC[2]

BCHData

SSC[3]

BCHData

SSC[4]

BCHData

BCHData

SSC[15]

Matched Filter

Matched to SSCcode group pattern 1

10 mSec Frame (15 slots x 666.666 uSec)

MatchedFilterOutput

time

SSC1

SSC2

SSC8

SSC1

SSC10

SSC15

SSC8

SSC9

SSC16

SSC 2

SSC 7

SSC10

SSC 7

SSC16

SSC15

SSC Code Group Pattern provides

• Frame Synchronization

• Positive ID of Scrambling Code Group

Remember, no cyclic shift of any SSC is equal to any other SSC

Figure 4-8: Frame Synchronization using SSC.

Figure 4-9 summarizes how all these steps are performed by the UE to achieve synchronization.

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Initiate Cell Synchronization

P-CCPCH

(PSC + SSC + BCH)

UE Monitors Primary SCH code, detects peak in matched filter output

Slot Synchronization Determined ------>

UE Monitors Secondary SCH code, detects SCG and frame start time offset

Frame Synchronization and Code Group Determined ------>

UE Determines Scrambling Code by correlating all possible codes in group

Scrambling Code Determined ------>

UE Monitors and decodes BCH data

BCH data, Super-frame synchronization determined ------>

Cell Synchronization Complete

UE adjusts transmit timing to match timing of BS + 1.5 Chips

Figure 4-9: UE Acquisition and Synchronization.

When the UE has synchronized and found the scrambling code of the cell, it can decode the system information (BCH) sent on the P-CCPCH.

RANDOM ACCESS PROCEDURE Random access is a process where a UE requests access to the system, and the network answers the request and allocates a dedicated channel to the UE. Random access happens whenever the UE needs to contact the network for example call setup, location updating and PDP Context Activation. This process is also carried when the UE is sending PS data in Cell_FACH state. It is important to minimize the transmitted power during the random access because excessive power will degrade the WCDMA system capacity. This is essential since the random access transmission power cannot be controlled by the inner loop power control. Initial transmission with low power means a long time to access. On the other hand, high power during the initial access causes high interference to other users.

Figure 4-10 shows how the UE sends access preambles to the cell until it receives an acknowledgement in the AICH before sending the RACH message.


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Pre-amble

Pre-amble

Pre-amble

AICH

RACH

NoInd.

NoInd.

Acq.Ind.

RACH

message part(UE Identification)UE

BS

3GPP TS 25.211 ¶ 7.33GPP TS 25.211 ¶ 7.3

4096 chips(1.066 msec)

Figure 4-10: Random Access procedure.

Prior to initiating a random access procedure, the UE reads system information to receive.

Prior to initiating a Random Access attempt, the UE receives:

The preamble scrambling code for this cell

The available random access signatures and set of available RACH sub-channels

The available spreading factors for the message part

The message length (10 ms or 20 ms)

Initial preamble power parameter

The power-ramping factor Power Ramp Step [integer > 0]

The parameter Preamble Retrans Max [integer > 0]

The AICH transmission timing parameter [0 or 1]

The power offset DPp-m between preamble and the message part.

Transport Format parameters

3GPP TS 25.214 ¶ 6.13GPP TS 25.214 ¶ 6.1

Figure 4-11: Random Access procedure

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Random Access Preamble Signature

Figure 4-12 shows the sixteen available random access signatures.

The UE will use one of these when sending the preamble. When the cell replies on the AICH it will use the same signature to distinguish which UE it is responding to. It must be remembered that several UEs could be sending preambles at the same time. These preamble signatures are orthogonal codes. Therefore, the cell can identify each user making random access.

Random Access Preamble Signature Symbols Signature P0 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15

0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1 2 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 3 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 4 1 1 1 1 -1 -1 -1 -1 1 1 1 1 -1 -1 -1 -1 5 1 -1 1 -1 -1 1 -1 1 1 -1 1 -1 -1 1 -1 1 6 1 1 -1 -1 -1 -1 1 1 1 1 -1 -1 -1 -1 1 1 7 1 -1 -1 1 -1 1 1 -1 1 -1 -1 1 -1 1 1 -1 8 1 1 1 1 1 1 1 1 -1 -1 -1 -1 -1 -1 -1 -1 9 1 -1 1 -1 1 -1 1 -1 -1 1 -1 1 -1 1 -1 1 10 1 1 -1 -1 1 1 -1 -1 -1 -1 1 1 -1 -1 1 1 11 1 -1 -1 1 1 -1 -1 1 -1 1 1 -1 -1 1 1 -1 12 1 1 1 1 -1 -1 -1 -1 -1 -1 -1 -1 1 1 1 1 13 1 -1 1 -1 -1 1 -1 1 -1 1 -1 1 1 -1 1 -1 14 1 1 -1 -1 -1 -1 1 1 -1 -1 1 1 1 1 -1 -1 15 1 -1 -1 1 -1 1 1 -1 -1 1 1 -1 1 -1 -1 1

Figure 4-12: Random Access Preamble Signature

Keywords about the preamble:

• Preamble codes are 16-long Orthogonal Codes.

• Preamble = [P0, P1, … P15] repeated 256 times (4096 chips total).

• Preamble codes help the cell distinguish between UEs making simultaneous Random Access attempts.

Random Access Scrambling Codes

Also included in the system information is the scrambling code that should be used by UEs accessing the cell.


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Figure 4-13 shows that cell 1 is transmitting a message like “All UEs accessing this cell shall use random access preamble scrambling code n1”. Cell 2 would be transmitting a message like “All UEs accessing this cell shall use random access preamble scrambling code n2”.

“All UE accessing this cell shall use Random

Access Preamble Spreading Code n2 ”

“All UE accessing this cell shall use Random

Access Preamble Spreading Code n1 ”

3GPP TS 25.213 ¶ 4.3.33GPP TS 25.213 ¶ 4.3.3

Figure 4-13: Random Access Scrambling Codes.

Random Access, Packet Access

• Cell-specific Scrambling Code(s)

• Code(s) are assigned by UTRAN

• Code(s) are conveyed to UE via the BCH or FACH

• 8,192 PRACH codes

• 32,768 PCPCH codes

• Code allocation corresponds tothe cell’s DL scrambling code group

Dedicated Traffic Connection

• UE-specific Scrambling Code(s)

• Code(s) are assigned by UTRAN

• Code(s) are conveyed to UE via the FACH

• 224 possible codes

Uplink Scrambling Code Type depends on the Application

Note:

Short (256) Scrambling Codes may be used in place of thelong scrambling codes. This is to support operation of advanced BS receivers (e.g., multi-user detection receivers).See TS25.213 Section 4.3.2

Note:

Short (256) Scrambling Codes may be used in place of thelong scrambling codes. This is to support operation of advanced BS receivers (e.g., multi-user detection receivers).See TS25.213 Section 4.3.2

Figure 4-14: Uplink Scrambling Code

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Random Access Offset Timing

Figure 4-15 shows the access slots of AICH and PRACH and their relative spacing. There are fifteen access slots per two frames and they are spaced 5120 chips apart. These are used to coordinate the timing of the RACHs. The figure also shows the twelve sub-channels of RACH.

#0 #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14

Access slot set 1 Access slot set 2

AICH access slotRX at UE

PRACH access slotTX at UE

RACH sub-channelnumber

P P

P P

P P

P

P

P

# 0

# 1

# 11

# 2

# 3••

# 10

radio frame: 10 ms radio frame: 10 msSFN mod 2 = 0 SFN mod 2 = 1

#0 #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14

+ every 12th access slot





+ every 12th access slot{

Figure 4-15: Random Access Procedure. Set of available RACH sub-channels determined by upper layers, sent in system information. UE derives available access slots in the next full access slot set and selects slot based on pseudo-random algorithm.


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DEDICATED CHANNEL PROCEDURE In Figure 4-16 the establishment of a dedicated channel in the case of a mobile terminated call is shown.

UE in Idle Mode

1. PI on the PICH

2. PCH message on the S-CCPCH

3. UE ramps up the power by sending preambles

4. RBS responds on the AICH

5. UE sends the RACH message

6. FACH message on S-CCPCH

7. DL-DPCH ramp up

8. UE sends UL-DPCH

DPCH established

Figure 4-16: Dedicated channel establishment-mobile terminated call

1. The UE is in idle mode and periodically listens to its PI on the PICH, which is set to 1 when the UE is paged.

2. The actual paging message is initiated from the CN and is sent to the UE on the PCH that is mapped onto the S-CCPCH.

3. The UE reads system information to calculate the initial preamble power. The power is ramped up.

4. When the UE has achieved the correct power level on the preamble, the RBS responds on the AICH.

5. The UE sends the RACH message: “RRC Connection Request” to the RNC to request for a dedicated channel.

6. The RNC checks available resources with admission control and sends a “RRC Connection Setup” message on FACH. This message gives information about the dedicated channel to be setup.

7. The transmission of the DL-DPCH is started and the power is ramped up.

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8. The UE responds by sending the “RRC Connection Setup Complete” message on the UL-DPCH. Finally the DPCH is established and data can start to be transmitted and the inner loop power control loop is starting.

WCDMA SOFT HANDOVER In the WCDMA RAN the RBSs are asynchronous and the timing is arbitrary. The UE has to inform the network about the timing difference in the case of soft handover, see Figure 4-17.

Data 2TFCIData 1 TPC

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Pilot

CPICH 2CPICH 2CPICH 2


DPCCH/DPDCHDPCCH/DPDCHDPCCH/DPDCH

CPICH 2

CPICH 1

DPCCH/DPDCH

Toffset

10 msecframe

BS 1

BS 2

DPCCH/DPDCHDPCCH/DPDCHDPCCH/DPDCH DPCCH/DPDCH

10 msec DPCCH/DPDCH frame

0.666 msec DPCCH/DPDCH slot

Figure 4-17: WCDMA base stations have asynchronous timing reference. IS95/cdma2000 RBSs are synchronized to GPS.

Figure 4-18 shows the first four steps of WCDMA soft handover.

(2)

UE measures CPICH power and time

delay from adjacent cells

(3)

UE Reports measurements to RNC

(1)

RNC informs UE of neighboring cell

information

(4)

RNC decides the handover strategy




CPICH 2

CPICH 1

DPCCH/DPDCH

Toffset

10 msecframe

RBS 1

RBS 2

RNC

UE Reports Toffsetto RNC

Figure 4-18: Soft handover 1


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1. The RNC informs the UE of the neighboring cells to be measured on for soft handover

2. The UE measures CPICH quality and time offset (Toffset) of the cells in the neighboring list.

3. When the soft handover criterias are fulfilled, UE sends a measurement report to the RNC including the time offset.

4. The RNC will then decide if a handover should be performed based on these measurements.

Step five to eight of the soft handover procedure are shown in Figure 4-19.

(6)

UE Rake Receiver Synchronizes to RBS2

DPCCH/DPDCH

(7)

UE in soft handover with RBS1 and RBS2

DPCCH/DPDCH’s

(5)

RNC Commands RBS2 to adjust DPCCH/DPDCH’s

timing by Toffset

(8)

When RBS2 sufficiently strong compared to RBS1,

delete RBS1.



CPICH 2CPICH 2CPICH 2CPICH 2

CPICH 1

DPCCH/DPDCH

Toffset

10 msecframe

RBS 1

RBS 2

RNC

UE Reports Toffsetto RNC

RNC Commands RBS2to adjust DPCH timing

by Toffset

DPCCH/DPDCHDPCCH/DPDCHDPCCH/DPDCH DPCCH/DPDCH

Toffset

Figure 4-19: Soft Handover 2

5. The RNC commands RBS 2 to adjust the DPCH timing by Toffset.

6. The rake receiver in the UE will then synchronize to the dedicated physical data and control channels (DPDCH & DPCCH) of RBS 2.

7. The UE is now in soft handover and listens to both RBS 1 and RBS 2.

8. Finally the signal from RBS 2 is sufficiently strong to allow the connection from RBS 1 to be dropped.

9. THE END!

5 HSDPA General Principles

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Objectives


• Explain the shared transmission in HSDPA

• Explain why higher order modulation is used in HSDPA

• Detail the fast link adaptation

• List the fast channel scheduling algorithms

• Explain Fast HARQ

• Detail why HSDPA will give a more dynamic power allocation

Figure 5-1: Objectives

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INTRODUCTION................................................................................151

GENERAL PRINCIPLES ...................................................................152 SHORT TTI (2 MS) .......................................................................................153 SHARED CHANNEL TRANSMISSION.........................................................153 HIGHER-ORDER MODULATION .................................................................154 FAST LINK ADAPTATION ............................................................................157 FAST CHANNEL DEPENDENT SCHEDULING ...........................................159 FAST HYBRID ARQ WITH SOFT COMBINING ...........................................160 DYNAMIC POWER ALLOCATION ...............................................................163

HSDPA CHANNEL STRUCTURE......................................................164 HS-DSCH - HIGH-SPEED DOWNLINK SHARED CHANNEL......................165 HS-PDSCH - HIGH-SPEED PHYSICAL DOWNLINK SHARED CHANNEL.166 HS-SCCH - HIGH SPEED - SHARED CONTROL CHANNEL......................167 HS-DPCCH - HIGH-SPEED DEDICATED PHYSICAL CONTROL CHANNEL .....................................................................................................169 OVERALL TIMING RELATION .....................................................................173


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INTRODUCTION This appendix gives a description of the HSPDA radio functionality that will be supported by the P4 release of WCDMA RAN.

As the use of packet data services increases and new services are introduced, greater capacity will be needed in the WCDMA systems.

WCDMA Release 5 extends the specification with, among other things, a new downlink transport channel that enhances support for interactive, background, and to some extent, streaming services, yielding a considerable increase in capacity compared to Release 99. It also significantly reduces delay and provides peak data rates of up to 14 Mbit/s. This enhancement, commonly goes under the abbreviation HSDPA (High Speed Downlink Packet Access)

The new transport channel is called HS-DSCH (High Speed Downlink Shared Channel)

HS-DSCH transmission is based on Shared-Channel transmission, similar to release 99/4 Downlink Shared Channel (DSCH). However, HS-DSCH transmission supports several new features, not supported for DSCH.

• HS-DSCH supports the use of higher order modulation. This allows for higher peak data rates and higher capacity.

• HS-DSCH supports fast link adaptation and fast channel dependent scheduling. This means that the instantaneous radio-channel conditions can be taken into account in the selection of transmission parameters as well as in the scheduling decision and allows for higher capacity.

• HS-DSCH supports fast hybrid ARQ (Automatic Repeat reQuest) with soft combining. This reduces the number of retransmissions as well as the time between retransmissions and allows for higher capacity and a substantial reduction in delay. The use of hybrid ARQ with soft combining also adds robustness to the link adaptation.

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To support these features with minimum impact on the existing radio-interface protocol architecture, a new MAC sublayer, MAC-hs, is introduced for HS-DSCH transmission. To reduce the retransmission delay for hybrid ARQ and allow for as up-to-date channel-quality estimates as possible for the link adaptation and channel-dependent scheduling, MAC-hs is located in the Node B. For the same reasons, HS-DSCH uses a shorter TTI (Transmission Time Interval) (2 ms) compared to release 99/4 transport channels.

This document gives a description of the HS-DSCH transport channel and associated functions and procedures. Although HS-DSCH is specified for both UTRA/FDD (WCDMA) and UTRA/TDD, only the FDD mode is treated in this document. The document describes the basic ideas behind HS-DSCH and the solutions chosen for the 3GPP specifications.

GENERAL PRINCIPLES HS-DSCH transmission is based on five main technologies: shared-channel transmission, higher-order modulation, link adaptation, radio-channel-dependent scheduling, and hybrid ARQ with soft combining. HSPDA also benefit from shorter TTI and dynamic power allocation (Figure 5-2).

Shared Channel TransmissionDynamically shared in time & code

domain

Higher-order Modulation16QAM in complement to QPSK for

higher peak bit rates

2 ms

Short TTI (2 ms)Reduced round trip delay

Fast Hybrid ARQ with Soft Combining

Reduced round trip delay

Fast Radio Channel Dependent Scheduling

Scheduling of users on 2 ms time basis

Fast Link AdaptationData rate adapted to radio

conditions on 2 ms time basis

t

P

Dynamic Power AllocationEffecient power &

spectrum utilisation


domain



2 ms









domain


domain





2 ms


2 ms2 ms














t

P



t

P

t

P



Figure 5-2: HSDPA general principles.


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SHORT TTI (2 MS)

One reason for a shorter TTI is to reduce the air-interface delay by reducing the RTT (Round Trip Times). This will improve the end-user performance since shorter TTI improves the interaction with TCP/IP.

Short TTI is also necessary to benefit from other functionalities such as fast link adaptation, fast scheduling and fast hybrid ARQ.

10 ms20 ms40 ms80 ms

Earlier releases

2 msRel 5 (HS-DSCH)

10 ms20 ms40 ms80 ms

Earlier releases10 ms20 ms40 ms80 ms

Earlier releases

2 msRel 5 (HS-DSCH)2 msRel 5 (HS-DSCH)

Figure 5-3: Example of different Transmission Time Intervals (TTI).

SHARED CHANNEL TRANSMISSION

Shared-channel transmission implies that a certain amount of radio resources of a cell (code space and power) is seen as a common resource that is dynamically shared between users, primarily in the time domain.

In HSDPA, a new DL transport channel is introduced called high speed DL shared channel. The idea is that a part of the total downlink code resource is dynamically shared between a set of packet-data users, primarily in the time domain. The codes are allocated to a user only when they are actually to be used for transmission, which leads to efficient code and power utilization.

In HSDPA, maximum 15 channelization codes with Spreading Factor (SF)= 16 can be used for this new DL channel. In P4, 5 channelization codes are used enabling user data rates up to 4.32 Mbps (the system is capable of enabling 4.32 Mbps).

The main benefit with DL shared channel transmission is to reduce the risk for code-limited capacity. Sharing codes in the code domain, in other words, code multiplexing, is also possible by employing different subsets of the complete channelization code set for different users. Figure 5-4 shows an example of 4 users sharing the time and code domain (8 codes).

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Sharing in the code domain is useful for providing efficient support of small payloads when the transmitted data does not require the full set of HS-DSCH codes configured in the cell. Useful when supporting terminals cannot despread the full set of codes.

Number of codes, which will be used in each cell, is configured or slowly adapted by RNC according to number of resources needed for packet data services on HS channel and other services such as voice. The RBS dynamically allocates the codes to the users every 2 ms.

With the introduction of HS-DSCH, several other benefits of shared-channel transmission can be exploited, as described below.

Figure 5-4: Example of Shared Channel Transmissionwith 8 codes. (Code multplexing: Codes shared in both time and code domain).

HIGHER-ORDER MODULATION

WCDMA release 99/4 uses QPSK data modulation for downlink transmission. To support higher data rates, higher-order data modulation, such as 16QAM, can be used (

Figure 5-5).

Compared to QPSK modulation, higher-order modulation is more bandwidth efficient, i.e. can carry more bits per Hertz.

Channelization codes allocatedfor HS-DSCH transmission

8 codes (example)SF=16

SF=8

SF=4

SF=2

SF=1

User #1 User #2 User #3 User #4

TTI=2ms

Shared channelization

codes

time



SF=8

SF=4

SF=2

SF=1



SF=8

SF=4

SF=2

SF=1

TTI=2ms

User #1 User #2 User #3 User #4

Shared channelization

codes

time


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However, higher-order modulation is also less robust and typically requires higher energy per bit for a given error rate. In case of interference-limited capacity, which is the normal case for WCDMA, the use of higher-order modulation is thus not efficient from a system capacity point-of-view.

However, in case of shared-channel transmission, a significant part of the total cell power may instantaneously be used for transmission to a single user. In this case, the signal-to-interference ratio (SIR) may in some cases be relatively high, even in case of one-cell frequency reuse. Having to rely on QPSK modulation in such cases may lead to excess SIR, i.e. the channel conditions may support higher data rates than what can be achieved with QPSK (bandwidth limited capacity).

Thus, higher-order modulation can be used together with shared-channel transmission to support higher data rates and achieve higher capacity, assuming it is used only when the radio-channel conditions so allow.

16QAM

2 bits/symbol 4 bits/symbol

QPSK 16QAM16QAM

2 bits/symbol 4 bits/symbol

QPSKQPSK Figure 5-5: QPSK and 16QAM.

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Single Transport Block of dynamic size from MAC-hs (Pre-coded

data (bits))

Pulse Shaping

Filter

Pulse Shaping

FilterΣΣPulse

Shaping Filter

Pulse Shaping

Filter


I

Q

Symbol rate 240ksymb/s Chip rate

3.84M chip/sModulation Symbols

I

Q

Data rate

480kbit/s

CRC Coding, Turbo Coding 1/3, Interleaving, Rate Matching


Data Channel

1

Channelization Code 1- SF16

I

Q

Modulation Mapping 1:2


I

Q

scrambling Code 1

Q

I



Data Channel

1

Channelization Code n - SF16

I

Q



I

Q

scrambling Code 1

Q

I

P4 Max 5 Channelization CodesMax UserRate per data channel 416kbit/s 416kbit/s X 5 = 2.08Mbit/s

P5 Max 15 Channelization Codes

Even symbols to I-branchOdd symbols to Q-branch


data (bits))

Pulse Shaping

Filter

Pulse Shaping

FilterΣΣPulse

Shaping Filter

Pulse Shaping

Filter


I

Q


3.84M chip/sModulation Symbols

I

Q

Data rate

480kbit/s



Data Channel

1


I

Q



I

Q

scrambling Code 1

Q

ICRC Coding, Turbo Coding 1/3,

Interleaving, Rate Matching


Data Channel

1


I

Q



I

Q

scrambling Code 1

Q

I



Data Channel

1


I

Q



I

Q

scrambling Code 1

Q

I



Even symbols to I-branchOdd symbols to Q-branch

Figure 5-6. WCDMA Transmitter (downlink) QPSK


data (bits))

ΣΣ


3.84M chip/s

Pulse Shaping

Filter

Pulse Shaping

Filter

Pulse Shaping

Filter

Pulse Shaping

Filter


I

Q

I

Q

Data rate

960kbit/s



Data Channel

1


I

Q



I

Q

scrambling Code 1

Q

ICRC Coding, Turbo Coding 1/3,

Interleaving, Rate Matching


Data Channel

1


I

Q



I

Q

scrambling Code 1

Q

I



Data Channel

1


I

Q



I

Q

scrambling Code 1

Q

I



i1q1i2q2 I branch Q branch0000 0.4472 0.44720001 0.4472 1.34160010 1.3416 0.44720011 1.3416 1.34160100 0.4472 -0.44720101 0.4472 -1.34160110 1.3416 -0.44720111 1.3416 -1.34161000 -0.4472 0.44721001 -0.4472 1.34161010 -1.3416 0.44721011 -1.3416 1.34161100 -0.4472 -0.44721101 -0.4472 -1.34161110 -1.3416 -0.44721111 -1.3416 -1.3416

i1q1i2q2 I branch Q branch0000 0.4472 0.44720001 0.4472 1.34160010 1.3416 0.44720011 1.3416 1.34160100 0.4472 -0.44720101 0.4472 -1.34160110 1.3416 -0.44720111 1.3416 -1.34161000 -0.4472 0.44721001 -0.4472 1.34161010 -1.3416 0.44721011 -1.3416 1.34161100 -0.4472 -0.44721101 -0.4472 -1.34161110 -1.3416 -0.44721111 -1.3416 -1.3416

i1q1i2q2i1q1i2q2 I branchI branch Q branchQ branch00000000 0.44720.4472 0.44720.447200010001 0.44720.4472 1.34161.341600100010 1.34161.3416 0.44720.447200110011 1.34161.3416 1.34161.341601000100 0.44720.4472 -0.4472-0.447201010101 0.44720.4472 -1.3416-1.341601100110 1.34161.3416 -0.4472-0.447201110111 1.34161.3416 -1.3416-1.341610001000 -0.4472-0.4472 0.44720.447210011001 -0.4472-0.4472 1.34161.341610101010 -1.3416-1.3416 0.44720.447210111011 -1.3416-1.3416 1.34161.341611001100 -0.4472-0.4472 -0.4472-0.447211011101 -0.4472-0.4472 -1.3416-1.341611101110 -1.3416-1.3416 -0.4472-0.447211111111 -1.3416-1.3416 -1.3416-1.3416

Figure 5-7. WCDMA Transmitter (downlink) 16QAM


LZT 123 7279 R5B © 2005 Ericsson - 157 -

FAST LINK ADAPTATION

In a cellular system, the radio-channel conditions experienced by different downlink communication links will typically vary significantly, both in time and between different positions within the cell. In general, there are several reasons for these variations and differences in instantaneous radio-channel conditions:

• The channel conditions will differ significantly between different positions within the cell, due to distance dependent path loss and location-dependent shadowing.

• The channel conditions will vary due to variations in the interference level. The interference level will depend on the position within the cell, with typically higher interference level close to the cell border. However, the interference level will also depend on the instantaneous transmission activity of neighbor cells. The transmission activity of a cell could vary significantly, especially when bursty high-rate data traffic contributes a major part of the overall traffic. Note that there may not only be interference from other cells. In case of a time-disperse channel, downlink orthogonality will be lost, causing own-cell interference.

• The instantaneous channel conditions will vary rapidly due to multi-path fading. The rate of these variations depends on the speed of the mobile terminal. Typically there will be significant variations during a fraction of a second.

In WCDMA, power control is used to compensate for differences and variations in the instantaneous downlink radio channel conditions. In principle, power control allocates a proportionally larger part of the total available cell power to communication links with bad channel conditions. This ensures similar service quality to all communication links, despite differences in the radio-channel conditions. At the same time, radio resources are more efficiently utilized when they are allocated to communication links with good channel conditions. Thus, from an overall system-throughput point-of-view, power control is not the most efficient means to allocate available resources.

In general, the goal is to ensure sufficient received energy per information bit for all communication links, despite variations and differences in the channel conditions. Power control achieves this by adjusting the transmission power while keeping the data rate constant.

WCDMA Air Interface

- 158 - © Ericsson 2005 LZT 123 7279 R5B

For services that do not require a specific data rate, such as many best-effort services, adjusting the data rate, while keeping the transmission power constant, can also control the energy per information bit. This can be referred to as rate control and rate adjustment. It is also often referred to as (fast) link adaptation, although, in principle, power control can also be seen as a kind of link adaptation.

There are different means by which the data rate can be adjusted to compensate for variations and differences in the instantaneous channel conditions.

• By adjusting the channel-coding rate. The use of channel coding with higher coding rate allows for higher data rates at the expense of less robustness to channel impairments.

• By adjusting the modulation scheme. The use of higher-order modulation, such as 16QAM, allows for more bits per modulation symbol and thus for higher data rates. However, this is achieved at the expense of less robustness to channel impairments.

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rate adaptation

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rate adaptation

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Figure 5-8: Power control versus rate adaptation.


LZT 123 7279 R5B © 2005 Ericsson - 159 -

FAST CHANNEL DEPENDENT SCHEDULING

Fast Scheduling is about to decide to which terminal the shared channel transmission should be directed at any given moment.

It’s called channel-dependent scheduling because it’s dependent on the instantaneous channel condition.

The basic idea is to transmit at the fading peaks of the channel in order to increase the capacity and to use the resources more efficiently.

But this might lead to large variations in data rate of the users.

The trade-off is between the cell throughput and fairness against users. In some cases, there might be a particular user who is perhaps on the cell border which might not be allocated the radio resources because he does not have good enough C/I. Remember that we don’t have SHO for dedicated shared channel.

There are a number of scheduling algorithms that take into consideration the trade-off between throughput and fairness.

• Round Robin (RR): radio resources are allocated to communication links on a sequential basis, not taking into account the instantaneous radio-channel conditions experienced by each link.

• Proportional Fair (PF): allocates the channel to the user with relatively best channel quality. It gives rather high throughput and is rather fair.

• Max C/I Ratio: for maximum cell throughput, the radio resources should as much as possible be allocated to communication links with the best instantaneous channel conditions.

high data rate

low data rateTime

Figure 5-9: Example of Fast Channel Dependent Scheduling.

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WCDMA Air Interface

- 160 - © Ericsson 2005 LZT 123 7279 R5B

FAST HYBRID ARQ WITH SOFT COMBINING

In a conventional ARQ scheme, received data blocks that cannot be correctly decoded are discarded and retransmitted data blocks are separately decoded, In case of hybrid ARQ with soft combining, received data blocks that cannot be correctly decoded are not discarded. Instead the corresponding received signal is buffered and soft combined with later received retransmissions of the same set of information bits. Decoding is then applied to the combined signal.

The use of hybrid ARQ with soft combining increases the effective received Eb/I0 for each retransmission and thus increases the probability for correct decoding of retransmissions, compared to conventional ARQ.

There are many different schemes for hybrid ARQ with soft combining. However, there are two main approaches, frequently referred to as Chase Combining and Incremental Redundancy (IR) respectively.

These schemes differ in the structure of the retransmissions and in the way by which the soft combining is carried out at the receiver side.

• In case of Chase combining each retransmission is an identical copy of the original transmission.

• In case of Incremental Redundancy each retransmission may add new redundancy.

Typically, Incremental Redundancy is based on a low-rate code. In the first transmission only a limited number of the coded bits are transmitted, effectively leading to a high-rate code. In the retransmissions, additional coded bits are transmitted.

Figure 5-10 shows an example of the generation of different redundancy versions for Chase and IR.


LZT 123 7279 R5B © 2005 Ericsson - 161 -

First rate matching

Second rate matchingFirst transmission

CRC insertion, rate 1/3 Turbo coding, tail inclusion

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Figure 5-10: Example of the generation of different redundancy versions for Chase and IR.

WCDMA Air Interface

- 162 - © Ericsson 2005 LZT 123 7279 R5B

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Figure 5-11. Two-stage Rate Matching – Hybrid ARQ

Figure 5-12 shows that Fast hybrid ARQ allows UEs to rapidly request retransmissions of erroneously received transport blocks.

• The UE attempts to decode each transport block it receives, reporting to RBS its success or failure 5 ms after the reception of the transport block. The hybrid ARQ mechanism in RBS can rapidly respond to retransmissions requests. This leads to shorter Round Trip Times.

• The UE employs soft combining, which is it combines soft information from previous transmission attempts with the current transmission to increase the probability of decoding the transport block. This reduces error rates for retransmissions.

This functionality is mainly sort of fine tuning the effective code rate and compensating for errors made by link adaptation mechanism.

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Figure 5-12: Retransmission request and Soft Combining.


LZT 123 7279 R5B © 2005 Ericsson - 163 -

DYNAMIC POWER ALLOCATION

As mentioned above, higher-order modulation and link adaptation can be combined to maximize the instantaneous use of the fading radio channel. The HS-DSCH does not employ fast power control to compensate for channel variations. Instead, to maximize user throughput in the downlink, it adjusts the data rate to match the instantaneous radio conditions and the available transmission power in the RBS. After serving common and dedicated channels, it is thus possible to assign the remaining cell power to the HS-DSCH, resulting in more efficient use of cell power. In contrast to the HS-DSCH, the dedicated channels are designed to maintain a constant data rate by means of fast power control. With only power-controlled channels it is difficult to exploit the total cell power.

However, by using fast link adaptation for services that can tolerate some jitter in the data rate, it is possible to operate close to the maximum cell power while still providing a constant data rate for some services through dedicated channels. Figure 5-13 illustrates power allocation with and without HSDPA. Since the TTI for the HS-DSCH is relatively short (2 ms), and scheduling and link adaptation decisions are taken for each TTI, the link-adaptation function can track rapid variations in the channel. The system adjusts the data rate by

• varying the effective code rate

• changing the modulation scheme.

Besides QPSK, the HS-DSCH can use 16QAM to provide greater data rates. Higher-order modulation, such as 16QAM, makes more efficient use of bandwidth than QPSK but requires greater received energy per bit. Consequently, 16QAM is mainly useful in bandwidth-limited scenarios and not in power-limited scenarios. Bandwidth limited scenarios are primarily encountered in low disperse environments close to the base station.

WCDMA Air Interface

- 164 - © Ericsson 2005 LZT 123 7279 R5B

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Figure 5-13: Power allocation with and without HSDPA.

HSDPA CHANNEL STRUCTURE HSPDA will implement one new transport channel and three new physical channels (see Figure 5-14):

• HS-DSCH - High-Speed Downlink Shared Channel: transport channel that carries the user data.

• HS-PDSCH - High-Speed Physical Downlink Shared Channel: physical downlink channel that carries the user data and layer 2 overhead bits over the air interface.

• HS-SCCH - High-Speed Shared Control Channel(s): physical downlink channel that carries control information how to decode the information on HS-PDSCH and which UE that shall decode it.

• HS-DPCCH - High-Speed Dedicated Physical Control Channel: physical uplink channel to send ACK/NAK reports and channel quality reports.

Each connection also has an associated dedicated transport channel (A-DCH) allocated in the cell. The A-DCH will be mapped on physical channels DPDCH+DPCCH.


LZT 123 7279 R5B © 2005 Ericsson - 165 -

• Downlink A-DCH is used for layer 3 control signaling.

• Uplink A-DCH is used for layer 3 control signaling and user data.

HS-DSCHHS-SCCH

Figure 5-14: HSDPA channel structure.

HS-DSCH - HIGH-SPEED DOWNLINK SHARED CHANNEL

HS-DSCH is the transport channel that is used for data transmission. HS-DSCH is never in soft handover. HS-DSCH is mapped to one or several HS-PDSCH (SF=16), which are simultaneously received by the UE

HS-DSCH transmission uses a common channelization-code resource dynamically shared among several users.

Dynamic allocation of channelization codes from the shared code resource is done on a 2 ms HS-DSCH TTI basis. For HS-DSCH, there is only a single fixed TTI of 2 ms, i.e., shorter than the TTIs available for R99/4 transport channels. There is at most one HS-DSCH per UE. In each 2 ms TTI, there is at most one HS-DSCH transport block of dynamic size.

The use of a shorter TTI reduces the hybrid ARQ roundtrip delay and improves the tracking of fast channel variations for the link adaptation and the channel-dependent scheduling.

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WCDMA Air Interface

- 166 - © Ericsson 2005 LZT 123 7279 R5B

HS-DSCH is always associated with an uplink and a downlink DPCH (DPDCH+DPCCH).

The downlink control information necessary to operate HS-DSCH is not carried on the downlink DPCH, but on a new shared control channel, HS-SCCH. Hence, the structure of the downlink DPCH is not dependent on whether an HS-DSCH is present or not. There is also a need for HS-DSCH related uplink signaling, carried on HS-DPCCH. The overall channel structure with a UL/DL DPCH pair, including HS-DPCCH, for each UE, one or several shared control channels, and the HS-DSCH is illustrated in Figure 5-14: HSDPA channel structure.

HS-PDSCH - HIGH-SPEED PHYSICAL DOWNLINK SHARED CHANNEL

HS-PDSCH is a downlink physical channel that carries user data and layer 2 overhead bits mapped from the transport channel: HS-DSCH. The user data and layer 2 overhead bits from HS-DSCH is mapped over one or several HS-PDSCH and transferred in 2 ms subframes using one or several channelization codes with SF =16.

HS-PDSCH has no Power Control.

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1 subframe = 3 timeslots = 2 mSec 1 TTI

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1 subframe = 3 timeslots = 2 mSec 1 TTI

Figure 5-15: HS-PDSCH - High-Speed Physical Downlink Shared Channel.


LZT 123 7279 R5B © 2005 Ericsson - 167 -

HS-SCCH - HIGH SPEED - SHARED CONTROL CHANNEL

In each 2 ms interval corresponding to one HS-DSCH TTI, one HS-SCCH carries physical-layer signaling to a single UE. As there should be a possibility for HS-DSCH transmission to multiple users in parallel (code multiplex), multiple HS-SCCH may be needed in a cell. The specification allows for up to four HS-SCCHs as seen from a UE point-of view, i.e., a UE must be able to decode four HS-SCCHs in parallel. However, more than four HS-SCCHs can be configured within a cell, although this is probably not needed in most cases.

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Figure 5-16: HS-SCCH - High Speed - Shared Control Channel

HS-SCCH uses a spreading factor SFHS-SCCH = 128 and has a time structure based on a sub-frame of length 2 ms, i.e. the same length as the HS-DSCH TTI. The timing of the HS-SCCH is illustrated in Figure 5-18. The HS-SCCH sub-frame starts two slots prior to the start of the HS-PDSCH sub-frame.

WCDMA Air Interface

- 168 - © Ericsson 2005 LZT 123 7279 R5B

Up to 4 HS-SCCH as seen from UE, can be >4 per cell (In P4 only 1)Only fixed HS-SCCH power control in P4, set relative to CPICH power

TFRI – Transport Format Related Information– Modulation scheme [1 bit]– Channelization Code Set [7 bits]– Transport Block Size [6 bits]

HARQ(Hybrid Automatic Repeat reQuest)related parameters– HARQ process number [3 bits]– Redundancy version [3 bits]– New Data Indicator [1 bit]

UE identity [16 implicit bits]

needed prior to HS-PDSCH demod.(part 1)

needed prior to decoding(part 2)

need to identify which HS-SCCH prior to HS-DSCH data

Figure 5-17. HS-SCCH, High Speed – Shared Control Channel

HS-SCCH(SF=128)

HS-PDSCH(SF=16)

1 subframe = 3 slots (=1 TTI)2 slots

Part 1 (channelization code set, modulation scheme)R=1/3 convolutionally coded, scrambled with UE ID

HS-SCCH(SF=128)

HS-PDSCH(SF=16)

1 subframe = 3 slots (=1 TTI)2 slots

Part 1 (channelization code set, modulation scheme)R=1/3 convolutionally coded, scrambled with UE ID

Figure 5-18: Relation between HS-SCCH and HS-PDSCH.

The following information is carried on the HS-SCCH:

• Transport-Format and Resource-related Information (TFRI), consisting of:

o The HS-DSCH channelization-code set [7 bits].

o The HS-DSCH modulation scheme [1 bit] (QPSK/16QAM)


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o The HS-DSCH transport-block size information [6 bits]. Note that each HS-DSCH TTI consists of a single transport block with dynamic transport-block size.

• Hybrid-ARQ-related information, consisting of

o Hybrid-ARQ process number [3 bits]

o Redundancy version [3 bits]

o New-data indicator [1 bit]

• A UE ID that identifies the UE for which the HS-SCCH information is intended [16 bits]. The UE ID is not explicitly transmitted but implicitly included in the CRC calculation and HS-SCCH channel coding.

HS-DPCCH - HIGH-SPEED DEDICATED PHYSICAL CONTROL CHANNEL

The uplink HS-DSCH-related physical-layer signaling consists of:

• Acknowledgements for hybrid ARQ

• Channel Quality Indicator (CQI), i.e., information reflecting the instantaneous downlink radio-channel conditions to assist the Node B in the transport-format selection (fast link adaptation) and the scheduling.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15



Physical Channel, Uplink, SF=256, Power Control

Carries information to acknowledge Downlink transport blocks and feedback information to the system for scheduling and Link Adaptation of transport blocks.

ACK/NAK and CQI

Physical Channel, Uplink, SF=256, Power Control

Carries information to acknowledge Downlink transport blocks and feedback information to the system for scheduling and Link Adaptation of transport blocks.

ACK/NAK and CQI

3GPP TS 25.211 ¶ 5.2.13GPP TS 25.211 ¶ 5.2.1

Figure 5-19: HS-DPCCH, High Speed – Dedicated Physical Control Channel

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HS-DPCCH carries ACK/NAK and CQI from UE to Node B– one HS-DPCCH for each user in the cell

ACK/NAK– single bit, repetition coded to 10 bits (1 slot)

CQI (Channel Quality Indicator)– 5 bits coded to 20 bits (2 slots)– channel quality measurements based on CPICH– reporting rate is configurable through RRC/NBAP signaling

ACK/NAK and CQI can be repeated in multiple subframes– controlled by RRC/NBAP signaling– useful in soft handover scenarios

Figure 5-20: Associated Uplink Signaling on HS-DPCCH

Channel quality knowledge at UE needed in the RBS– Link adaptation– Scheduling– Power control of HS-SCCH

CQI– UE measures and reports a recommended transport format to

the RBS– Accounts for channel conditions and UE receiver performance

Implementation-specific algorithms!

Figure 5-21: CQI - Channel Quality Indicator

One requirement in the specification of HS-DSCH is that it shall be possible to set up an HS-DSCH for a UE in soft handover between a release 5 HS-DSCH-capable Node B and a release 99/4 Node B. Thus, HS-DSCH-related uplink signaling could not be carried within the uplink DPCCH, as the release 99/4 Node B would then not recognize the DPCCH. Instead, the HS-DSCH-related uplink physical signaling is carried on an additional new uplink physical channel, the HS-DPCCH. The HS-DPCCH is code multiplexed with the current DPDCH/DPCCH, as illustrated in Figure 5-23. The HS-DPCCH uses spreading factor 256.


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Important to secure good success rate of ACK/NAK and CQI transmission while keeping UL interference under controlACK, NAK, CQI power offsets with relation to DPCCH set by RRC signalling

Two independent mechanisms:1.Two sets of power offesets (ACK, NAK and CQI) are configured per cell in RNC. RNC reconfigures UE depending on number of RBS involved

Configuration changed at cell change and possibly after active set update2.RBS initiates update of ACK/NAK and CQI feedback cycles based on CQI detection performance

Figure 5-22. ACK/NACK

Available processing time: ~5ms (19200 ± k chips to ensure symbol alignment)

ACK/NAK CQI1 subframe (3 slots)

HS-DSCH TTI

HS-DPCCH

DPCCH

DPDCH

Not slot aligned!

Available processing time: ~5ms (19200 ± k chips to ensure symbol alignment)

ACK/NAK CQI1 subframe (3 slots)

HS-DSCH TTI

HS-DPCCH

DPCCH

DPDCH

Not slot aligned!

Figure 5-23: HS-DPCCH - High-Speed Dedicated Physical Control Channel.

As the HS-DPCCH uses SF=256, there are a total of 30 channel bits per 2 ms sub-frame (3 slots). The HS-DPCCH information is divided in such a way that the hybrid-ARQ acknowledgement is transmitted in the first slot of the subframe while the channel-quality indication is transmitted in the second and third slot, see Figure 5-23.

Hybrid-ARQ acknowledgement

The hybrid-ARQ acknowledgement consists of a single information bit, with the following interpretation:

• 1: Positive acknowledgement, i.e., data in HS-DSCH TTI correctly decoded (CRC OK)

• 0: Negative acknowledgement, i.e., data in HS-DSCH TTI not correctly decoded (CRC not OK)

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• DTX: No HS-DSCH data received, i.e., HS-SCCH not correctly decoded

The reason for using DTX for the hybrid ARQ acknowledgement is to avoid that all UEs continuously transmit (negative or positive) acknowledgements, although no HS-DSCH data is transmitted to most of the UEs in a given TTI.

The single-bit ACK is R=1/10 repetition coded to fit into the first slot of the HS-DPCCH.

The UE can, by means of RRC signaling, be configured to transmit multiple hybrid ARQ acknowledgements for a single HS-DSCH TTI. In that case, the UE transmits identical acknowledgements in N consecutive sub frames, where N=1,2,3, or 4. This increases the reliability of the hybrid ARQ acknowledgement and is especially useful in soft handover. When the UE is configured to transmit repeated acknowledgements, it cannot receive HS-DSCH data in consecutive TTIs, as the UE would then not be able to acknowledge all HS-DSCH data. Instead there must be at least N-1 idle 2 ms sub frames between each HS-DSCH TTI in which data is to be received.

Downlink Channel-Quality indication

The channel quality indicator, CQI, consists of 5 information bits, block-coded into 20 channel bits. The coding is similar to the TFCI coding.

The channel quality indicator is a recommended transport block size or, equivalently, a recommended data rate. Note that the CQI is merely a recommendation and the Node B is not forced to follow the recommendations given by the UE. The basis for the CQI reports are measurements on the CPICH, either P-CPICH or S-CPICH depending on which phase references the UE is allowed to use. The CQI shall represent the instantaneous channel conditions in a predefined 3-slot interval ending one slot prior to the CQI transmission. Specifying which interval the CQI relates to allow the

Node B to track changes in the channel quality between the CQI reports by using, e.g., the power control commands for the associated downlink DPCH.

The rate of the channel-quality reporting is configurable. In HS-DPCCH sub-frames in which no CQI is to be transmitted, the corresponding two slots are DTX.


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OVERALL TIMING RELATION

Figure 5-24 shows the overall timing relation. The RBS transmits control information on HS-SCCH, how to decode and which UE that shall decode next transport block on HS-PDSCH.

When the transport block is received on HS-PDSCH the UE will process the data and measure the quality on CPICH over 5 ms (7.5 slots).

When data is processed the UE sends ACK/NAK and CQI on HS-DPCCH:

• ACK/NAK report (based on CRC of the transport block)

• CQI report (based on measurements on CPICH

When the ACK/NAK and CQI report is received at the RBS the RBS needs 5 ms (2.5 slots) to process the data and make a scheduling decision based on the received report on HS-SCCH.

~7.5 slot

CQI

~7.5 slot

~2.5 slot

meas.

Scheduling decision

HS-SCCH

HS-PDSCH

HS-DPCCH

reference period

CPICH 1 slot

A/N

~7.5 slot

CQI

~7.5 slot

~2.5 slot

meas.

Scheduling decision

HS-SCCH

HS-PDSCH

HS-DPCCH

reference period

CPICH 1 slot

A/N

Figure 5-24: Overall timing relation.

0 Appendix A: Abbreviations

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Appendix A: Abbreviations 16QAM 16 Quadrature Amplitude Modulation AAL2 ATM Adaptation Layer type 2 ACK Acknowledgement AICH Acquisition Indicator Channel ALCAP Access Link Control Application Part AM Acknowledged Mode AMR Adaptive MultiRate speech codec AP Access Preamble ARQ Automatic Repeat reQuest ARQ Automatic Repeat Request AS Access Stratum ASC Access Service Class ATM Asynchronous Transfer Mode AUTN Authentication Token BCCH Broadcast Control Channel BCFE Broadcast Control Functional Entity BCH Broadcast Control Channel BER Bit Error Rate BLER Block Error Rate BMC Broadcast/Multicast Control BSS Base Station Sub-system BSSMAP Base Station System Management Application Part C/I Carrier-to-Interference ratio CC Call Control CCCH Common Control Channel CCPCH Common Control Physical Channel CCTrCH Coded Composite Transport Channel CFN Connection Frame Number CK Cipher Key CM Connection Management CN Core Network CPCH Common Packet Channel CPICH Common Pilot Channel CQI Channel Quality Indicator CRC Cyclic Redundancy Check CRNC Controlling RNC C-RNTI Cell RNTI

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CS Circuit Switched CTCH Common Traffic Channel DCA Dynamic Channel Allocation DCCH Dedicated Control Channel DCFE Dedicated Control Functional Entity DCH Dedicated Channel DC-SAP Dedicated Control SAP DL Downlink DPCCH Dedicated Physical Control Channel DPCH Dedicated Physical Channel DPDCH Dedicated Physical Data Channel DRAC Dynamic Resource Allocation Control DRNC Drift RNC DRNS Drift RNS DRX Discontinuous Reception DSCH Downlink Shared Channel DTCH Dedicated Traffic Channel DTX Discontinuous Transmission EP Elementary Procedure FACH Forward Access Channel FAUSCH Fast Uplink Signalling Channel FDD Frequency Division Duplex FEC Forward Error Correction FFS For Further Study FLA Fast Link Adaptation FN Frame Number FP Frame Protocol GSM Global System for Mobile Communication HARQ Hybrid Automatic Repeat reQuest HS-DPCCH HS-DSCH (related uplink) Dedicated Physical Control Channel HS-DSCH High-Speed Downlink Shared Channel HS-PDSCH High-Speed Physical Downlink Shared Channel HS-SCCH HS-DSCH Shared Control Channel ID Identifier IE Information element IMEI International Mobile Equipment Identity IMSI International Mobile Subscriber Identity IP Internet Protocol ISCP Interference on Signal Code Power kbps kilo-bits per second KSI Key Set Identifier ksps kilo-symbols per second L1 Layer 1 L2 Layer 2


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L3 Layer 3 LAI Location Area Identity MAC Medium Access Control MAC The Message Authentication Code included in AUTN,

computed using f1 Mbps Mega-bits per second MCC Mobile Country Code Mcps Mega-chips per second MM Mobility Management MNC Mobile Network Code MO Mobile Originating Call MS Mobile Station MSC Mobile services Switching Centre MT Mobile Terminal MTC Mobile Terminated Call NACK Negative Acknowledgement NAS Non Access Stratum NBAP Node B Application Protocol Nt-SAP Notification SAP NW Network O Optional ODMA Opportunity Driven Multiple Access OVSF Orthogonal Variable Spreading Factor PC Power Control PCCH Paging Control Channel P-CCPCH Primary Common Control Physical Channel PCH Paging Channel PDCP Packet Data Convergence Protocol PDSCH Physical Downlink Shared Channel PDU Protocol Data Unit PHY Physical Layer PICH Paging Indicator Channel PLMN Public Land Mobile Network PNFE Paging and Notification Control Functional Entity PRACH Physical Random Access CHannel PS Packet Switched PSCH Physical Synchronisation Channel PSTN Public Switched Telephone Network P-TMSI Packet Temporary Mobile Subscriber Identity PUSCH Physical Uplink Shared Channel Q Quintet, UMTS authentication vector QAM Quadrature Amplitude Modulation QoS Quality of Service QPSK Quadrature Phase Shift Keying

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RA Routing Area RAB Radio Access Bearer RACH Random Access Channel RAI Routing Area Identity RAN Radio Access Network RANAP Radio Access Network Application Part RB Radio Bearer RB Radio Bearer RFE Routing Functional Entity RL Radio Link RLC Radio Link Control RM Rate Matching RNC Radio Network Controller RNS Radio Network Subsystem RNSAP Radio Network Subsystem Application Part RNTI Radio Network Temporary Identifier RR Round Robin RRC Radio Resource Control RSCP Received Signal Code Power RSSI Received Signal Strength Indicator RT Real Time RX Receive SAI Service Area Identifier SAP Service Access Point SCCP Signalling Connection Control Part S-CCPCH Secondary Common Control Physical Channel SCFE Shared Control Function Entity SCH Synchronization Channel S-CPICH Secondary Common Pilot Channel SDU Service Data Unit SF Spreading Factor SFN System Frame Number SGSN Serving GPRS Support Node SHCCH Shared Control Channel SID Size Index SIR Signal to Interference Ratio SMS Short Message Service SRB Signaling Radio Bearer SRNC Serving RNC SRNS Serving RNS S-RNTI SRNC – RNTI SSDT Site Selection Diversity Transmission SSMA Spread Spectrum Multiple Access TB Transport Block


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TBS Transport Block Set TDD Time Division Duplex TE Terminal Equipment TEID Tunnel Endpoint Identifier TF Transport Format TFC Transport Format Combination TFCI Transport Format Combination Indicator TFCS Transport Format Combination Set TFI Transport Format Indicator TFRC Transport Format Resource Combination TFRI Transport Format Related Information TFS Transport Format Set TM Transparent Mode TMD Transparent Mode Data TME Transfer Mode Entity TMSI Temporary Mobile Subscriber Identity TPC Transmit Power Control Tr Transparent TrCH Transport Channel TTI Transmission Time Interval Tx Transmission UARFCN UMTS Absolute Radio Frequency Channel Number UE User Equipment UEA UMTS Encryption Algorithm UE-ID User Equipment Identifier UIA UMTS Integrity Algorithm UL Uplink UM Unacknowledged Mode UMD Unacknowledged Mode Data UMTS Universal Mobile Telecommunication System UNACK Unacknowledgement URA UTRAN Registration Area U-RNTI UTRAN-RNTI USCH Uplink Shared Channel UTRA UMTS Terrestrial Radio Access UTRAN UMTS Terrestrial Radio Access Network WCDMA Wideband Code Division Multiple Access VLR Visitor Location Register XRES Expected Response


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INDEX

A Acknowledgement, 105 Acquisition Indicator Channel, 69, 106, 115,

124 Adaptive MultiRate speech codec, 14, 22, 23 B Block Error Rate, 25, 68 Broadcast Control Channel, 81, 103, 108 C Call Control, 39, 41, 45 Carrier-to-Interference ratio, 81, 83, 84 Channel Quality Indicator, 168 Circuit Switched, 14, 95 Common Control Channel, 103 Common Control Physical Channel, 108, 110 Common Pilot Channel, 73, 104, 107 Core Network, 95 Cyclic Redundancy Check, 7, 19, 24, 25, 26,

71, 74, 102, 116 D Dedicated Channel, 103, 112 Dedicated Control Channel, 103 Dedicated Physical Channel, 115, 116, 118 Dedicated Physical Control Channel, 98, 104,

110, 111, 112, 117, 119, 120, 121, 122, 123, 124, 125, 126, 127

Dedicated Physical Data Channel, 98, 104, 110, 111, 112, 119, 120, 121, 122, 123, 124, 125, 126

Dedicated Traffic Channel, 103 Discontinuous Reception, 110 Discontinuous Transmission, 109 Downlink, 43, 85, 104 F Forward Access Channel, 68, 103, 104, 109 Forward Error Correction, 7, 19, 24, 26, 27,

28, 29, 30, 71, 98, 102 Frequency Division Duplex, 92, 93, 102 G Global System for Mobile Communication,

12, 15, 20, 23, 52, 76, 81, 91, 93, 112 H High-Speed Physical Downlink Shared

Channel, 105

HS-DSCH (related uplink) Dedicated Physical Control Channel, 105, 167, 168

HS-DSCH Shared Control Channel, 105 Hybrid Automatic Repeat reQuest, 147 I International Mobile Subscriber Identity, 110 K kilo-bits per second, 13, 14, 20, 23, 36, 44,

93, 108, 111, 115, 116, 117, 122, 123, 124 kilo-symbols per second, 44, 116 L Layer 1, 98, 111, 115, 116, 123, 124 Layer 3, 97, 98, 104, 109, 115, 116, 120,

123, 124 M Medium Access Control, 97 Mega-chips per second, 67 Mobile services Switching Centre, 95 P Packet Switched, 14, 36, 95, 109, 116, 117,

124 Paging Indicator Channel, 106, 109, 110 Paging Channel, 103, 104, 109, 110 Paging Control Channel, 103 Physical Random Access CHannel, 115, 120 Primary Common Control Physical Channel,

104, 108, 110 Q Quadrature Phase Shift Keying, 54, 55, 60,

125 Quality of Service, 97 Quintet, UMTS authentication vector, 19, 54,

55, 56, 57, 60, 73, 102, 121, 125, 126, 127, 128

R Radio Access Bearer, 14, 95, 97, 115, 116,

117, 123, 124 Radio Access Network, 13, 14, 84, 85, 91,

95, 96, 97, 118 Radio Link Control, 97 Radio Network Controller, 95, 97 Radio Resource Control, 97, 103 Random Access Channel, 68, 69, 125

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S Secondary Common Control Physical

Channel, 104, 109, 110 Serving RNS, 96 Signal to Interference Ratio, 68, 69, 98, 113 Spreading Factor, 43, 44, 106, 108, 111, 114,

115, 116, 121, 122, 125 Synchronization Channel, 104, 108 T The Message Authentication Code included

in AUTN, computed using f1, 97 Time Division Duplex, 92 Transmit Power Control, 104, 111, 113, 114,

120, 121, 122 Transport Format Combination Indicator, 104,

109, 111, 112, 114, 120, 121, 125

U Universal Mobile Telecommunication System,

14, 94, 95, 96, 97 Uplink, 43, 68, 77, 79, 85 User Equipment, 43, 44, 51, 53, 68, 69, 76,

77, 78, 79, 83, 97, 103, 104, 105, 106, 107, 109, 110, 112, 115, 118, 119, 123, 124

W Wideband Code Division Multiple Access, 7,

11, 12, 13, 14, 16, 17, 18, 22, 26, 28, 31, 37, 38, 43, 45, 46, 47, 52, 54, 58, 63, 67, 68, 69, 70, 71, 73, 74, 76, 77, 79, 80, 81, 82, 83, 84, 87, 92, 93, 94, 95, 96, 97, 100, 101, 102, 107, 110, 112, 117, 118, 119, 120

Wcdma air interface

Engineering

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