WCDMA RADIO THEORY

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Ericsson Internal | 2011-05-05 |

COURSE OBJECTIVES› At the end of this course, you will be able to:

Master channel encoding of WCDMAMaster spread spectrum principle of WCDMA Master modulation of WCDMA


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CONTENT

›The basic principles of wireless communication› Radio Propagation CharacteristicsRadio Propagation Characteristics

› Multi AccessMulti Access

› Spread spSpread spectrum ectrum TechnologyTechnology

› Channel CodingChannel Coding

› InterleavInterleavee Technology Technology

› WCDMA wireless technologyWCDMA wireless technology


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CHARACTERISTIC OF RADIO PROPAGATION› Electromagnetic propagation: direct radiation, reflection, diffraction

and scattering› Signal attenuation:

Path loss ： Loss of electromagnetic waves in large scope of the spread reflects the trend of the received signal in the spreading 。

Slow fading ： Loss because of being blocked by the building and hill in the propagation path

Fast fading ： Electromagnetic signals rapidly decline in a few dozens wavelength ranges

› Description of Fast fading distributionRayleigh distribution ： non line-of –sight transmissionRice distribution ： line-of –sight transmission

Radio propagation characteristics


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Frequency Frequency off-setoff-set caused by the movement of caused by the movement of mobile mobile ，， that is Doppler effectthat is Doppler effect

Sending signal Accepting signal

Interference Interference

0dB

Sending signal

-25dB

Accepting signal

fadingfading

0 + Sending signal Accepting signal

delaydelay

0 2 3 + Sending signal Accepting signal

ditheringdithering

CHARACTERISTICS OF RADIO PROPAGATION



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MULTI-PATH EFFECTS

receiving signalreceiving signal

timetime

strengthstrength

00

sending signalsending signal



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CONTENT

›The basic principles of wireless

communication› Radio Propagation CharacteristicsRadio Propagation Characteristics


› SpreadSpread spectrum spectrum Technology Technology


› Interleave TechnologyInterleave Technology



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FrequencyTime

Power

FrequencyTime

Power

FrequencyTime

Power

FDMA

TDMA

CDMA

Frequency division multiple access technology Channels in different frequency are allocated to different users, e.g. TACS 、 AMPS。Time division multiple access technologychannels in different time are allocated to different users, e.g. GSM 、 DAMPS。

Code division multiple access technologyUsers distinguished by scramble code, e.g. CDMA

MULTIPLE ACCESS

Multiple access


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CONTENT









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PRINCIPLE OF SPREADING SPECTRUM› A technology of transmission technology after spreading

frequency of signal.

› Theoretical Basis: Shannon theory C=Wlog2(1+S/N)

FastSpreadingSequence

SlowInformation

Sent

TX

SlowInformationRecovered

RX

FastSpreadingSequence

WidebandSignal

Spreading technology


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f

S （ f ）

f0Before spreading

signal

S （ f ）

ff0After spreading

signal

S （ f ）

ff0After despreading

signalWhite noise

f

S （ f ）

f0Before despreading

signalWhite noise

signal interference White noise

SKETCH MAP OF SPREADING Spreading technology


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SPREADING MODE› Direct sequence spread （ DS － SS):-

Base band data is spreaded by multiplication of pseudo-noise sequence and base-band pulse, the pseudo-noise sequence generated by the pseudo-noise generator

BER subject to Multiple Access Interference and near-far effectPower control can overcome the near-far effect, but it is limited by

power detection accuracyWCDMA uses DS-SS

› Frequency hopping spread （ FH-SS):-Data is transmitted in the random channel by the carrier frequency

hoppingBefore FH again, data is transmitted using traditional narrowband

modulationNo near-far effect



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CHARACTERISTICS OF SPREADING COMMUNICATION

High anti-multi-path- interference capability

High security

Lower transmitting power

Easy to implement large-capacity Multiple Access

Communication

Occupy band wide

Complex realization



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CONTENT




› Spread spectrum TechnologySpread spectrum Technology



› WCDMA wireless technology


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PURPOSE OF CHANNEL CODING› Purpose:

By adding redundant information in the original data stream, receivers can detect and correct the error signal, and improve data transmission rates.

Error-correcting ability obtains by adding redundancy in the original

data

Channel coding

W C D M AT U R B OS P E A K

W W C C D D M M A AT T U U R R B B O OS S P P E E A A K K

W ？ C C D D M M A A

T T U ？ R R B B O O

S S P P E E A ？ K K


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PRINCIPLE OF CHANNEL CODING› Channel coding

Convolution coding and Turbo coding （ 1/2 ， 1/3 ） are

widely applied.

Increase redundancy and transmission time

Suitable to correct few non-continuous errors

No correct coding: BER<10-1 ~ 10-2Can not satisfy

the communication

Convolutional coding ： BER<10-3Can satisfy the

speech communication

Turbo coding ： BER<10-6Can satisfy the

data communication

Channel coding


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CONTENT







› WCDMA wireless technology


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PRINCIPLE OF INTERLEAVE TECHNOLOGY› Advantage:

Interleave is to change the sequence of data to discretize the burst continuous errors

Advance the correcting validity

› Disadvantage:Increase the processing delayEspecially, Several independent random errors may intertwined for

the unexpected error .

x1 x6 x11 x16 x21x2 x7 … x22x3 x8 … x23x4 x9 … x24x5 x10 … x25

Data input A = (x1 x2 x3 x4 x5 … x25)

Data output A’= (x1 x6 x11 x16… x25)

e.g.

Interleaving technology


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ENCODING AND INTERLEAVING

W C D M AT U R B OS P E A K

W W C C D D M M A AT T U U R R B B O OS S P P E E A A K K

W T S W T SC U P C U PD R E D R EM B A M B AA O K A O K

W ? ? C D D M M A AT ? ? U R R B B O O

S ? ? P E E A A K K

Encoding Interleaving

W T S ? ? ?? ? ? C U PD R E D R EM B A M B AA O K A O K

DeinterleavingDecoding

Interleaving technology


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CONTENT









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UE Data Encoding & Interleaving

Spreading & Scrambling

RF Transmission

RF ReceivingDemodulationDispreading & Descrambling

Decoding & De-interleaving

UE Data

DATA TRANSMISSION PROCEDURE

Modulation

Baseband

demodulation

WCDMA wireless technology


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CONVOLUTIONAL CODE

Mainly used in the voice channel and control signal channel

Coding rate is ½ and 1/3 。

Output 0 G0 = 557 (octal)

Input D D D D D D D D



Rate 1/3 convolutional coder



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CHARACTERISTICS OF CONVOLUTIONAL CODE

Easy decode

Short delay

Generally use the Viterbi Algorithm

Channel bit error rate is 10 － 3 magnitude

Suitable to real-time service

– e.g. speech and video service.



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TURBO CODEUsed in Data service channelCode Rate is 1/3Can be implemented in the transmission for large block and long delay

servicesTurbo coding structure is based on two or more weak error control code Turbo coding structure is based on two or more weak error control code

combinations. The information bits are interleaved in the two Encoder, and combinations. The information bits are interleaved in the two Encoder, and generate two information flow. At last, this information can be multiplexed generate two information flow. At last, this information can be multiplexed and puncturedand punctured

Decoding needs cycle iterative calculationDecoding needs cycle iterative calculation

InterleaverEncoder 1

Encoder 2M

ultip

lex

inputoutput



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CHARACTERISTICS OF TURBO CODES› Complex decoding› Use the LOG-MAP arithmetic› Channel bit error rate is 10 － 6 magnitude› Very suitable to non-real-time package service which is BER

sensitive & delay insensitive.– e.g. WWW, FTP, E_mail , multimedia transmission .



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INTERLEAVING TECHNOLOGY OF WCDMA

› Intra-frame interleave

Bits transform in the internal frame

› Inter-frame interleave

Data transform among the frames

› Intra-Turbo codes interleave

Complex nesting of intra-frame and inter-frame interleave



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Spreading & Scrambling Modulation

RF Transmission



UE Data




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Symbol rate × SF = 3.84McpsSymbol rate × SF = 3.84McpsWCDMAWCDMA ，， SF of uplink channelized codeSF of uplink channelized code ：： 4~2564~256

SF of downlink channelized code:4~512SF of downlink channelized code:4~512OVSF: Orthogonal Variable Spreading Factor OVSF: Orthogonal Variable Spreading Factor

OVSF Code Scramble Code

Data bitChip after Spreadin

g

SPREADING OF WCDMA



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DESPREADING OF WCDMA› Method of dispreading

Input signal

Local PN code

When T=Ts, judge

Output after dispreading

integral

0

Ts(*)dt



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Symbol

Spreading

Despreading

1-1

1-1

1

-1

1-1

1-1

Data = 010010

Spreading code

Spread signal= Data × code

Spreading code =1 -1 -1 1 -1 1 1 -1 ( SF = 8 )

Data = Spread signal × Spread code

Chip

SPREADING AND DESPREADING



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CONCEPT OF ORTHOGONAL CODE

Orthogonal—the result of multiplying and sum is 0

Code1 +1-1+1+1-1+1-1-1

Code2 -1+1+1-1-1+1+1-1

Mul -1-1+1-1+1+1-1+1

Sum 0

Orthogonal

Code1 +1-1+1-1-1+1-1-1

Code2 +1+1-1+1-1-1+1-1

Mul +1-1-1-1+1-1-1+1

Sum -2

Non-orthogonal



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CODE RESOURCE ALLOCATION

› Channelization code:Channelization codes are based on the orthogonal variable Channelization codes are based on the orthogonal variable

spreading factor (OVSF) technology. Transmission from a spreading factor (OVSF) technology. Transmission from a single source are separated by channelization codes.single source are separated by channelization codes.

› Scrambling code:Scrambling codes are used after spreading, which will not Scrambling codes are used after spreading, which will not

change the signal bandwidth. They are only used to change the signal bandwidth. They are only used to differentiate different UEs or Node Bs.differentiate different UEs or Node Bs.

In WCDMA, code resources are mainly divided into channelization codes and scrambling codes.



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CHANNELIZATION CODE

› Adopt OVSF code– C ch,SF,k ： describe channelization

code,› SF ： spread factor ，› k ： code number, 0 < k<SF-1



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SF=8

SF=32

SF=16

CHARACTERISTIC OF CHANNELIZATION CODE

› Premise of code allocation:Ensure not occupied for the code in the root direction and

downwards sub tree› Result of code allocation:

Block all low rate SC in sub tree and high rate in upwards root direction



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EXAMPLE

SF=64

SF=32

SF=16

SF= 8

0 1 2 3 4 5 6 7` ` ` `

` `0 1 2 3

` 0 1

0

SF=64

SF=32

SF=16

SF= 8

0 1 2 3 4 5 6 7` ` ` `

` `0 1 2 3

` 0 1

0

0 1 2 3 4 5 6 7` ` ` `

` `0 1 2 3

` 0 1

0

0 1 2 3 4 5 6 7` ` ` `

` `0 1 2 3

` 0 1

0

(a) (b)

(c) (d)

`

Idle

Allocated

Blocked



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OVSF Code Scramble Code

Data bitChip after Spreadin

g

SCRAMBLING CODE

› In addition to spreading, part of the process in the transmitter is the scrambling operation. This is needed to separate terminals or base stations from each other. Scrambling is used on top of spreading, so it does not change the signal bandwidth but only makes the signals from different sources separable from each other.



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SCRAMBLING CODE OF WCDMA

› WCDMA scrambling code is generated from Gold sequenceGold has excellent self_correlation. Mutual_correlation is very small between subsection

serial. It is used to identify cell and user for multiple address.

›WCDMA Scrambling code is pseudo random binary sequence (PN code)

It has similar noise array character , is that one kind is seemingly random

but cyclicity binary system array. Can make the user data a further

randomization , strengthened by scrambling a code to keep secret the

function, at the same time easy to carry out multiple access

communication.



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CHARACTERISTIC OF SCRAMBLING CODE› There are 224 Uplink Scrambling Codes, they are used to distinguish

different users in one cell. › Uplink Scrambling codes include long scrambling codes and short

scrambling codes. The Short Scrambling codes are used for multi-user detecting

› There are 218-1 Downlink Scrambling Codes, used to distinguish different cells–Scrambling codes in common use are 0 ， 1 ，……， 8191 ， they are divided into 512 aggregations ， each aggregation has 1primary scrambling code and 15 secondary scrambling codes.– 512 primary scrambling codes can be divided into 64 scrambling

code groups ,there is 8 primary scrambling in each group.



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Spreading & Scrambling

Modulation

RF Transmission



UE Data




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WCDMA MODULATION

UL: BPSKDL:QPSK （ HSDPA introduce 16QAM ）



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WCDMA RADIO THEORY

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