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Transcript of Module2 - Cellular Overview - CDMA
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Module 2
CDMA Introduction
Integrated Wireless Solutions Pvt. Ltd.
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CDMA Basics
Introduction Multiple Access
Codes
Synchronization
Power Control
Handoff
CDMA Channels
CDMA Benefits
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Introduction
Global Mobile Users - 1.52 billion
Global GSM users - 1.25 billion
Global CDMA Users - 202m
Global TDMA users - 120m
Total 3G users - 130m
#1 Mobile Country - China (300m)
#1 GSM Country - China (282m)
#1 Network In Africa - Vodacom(11m) #1 Network In Asia - Unicom (153m)
#1 Network In Japan - DoCoMo
#1 Network In Europe - T-Mobil (28m)
Number of mobile users in India 44.5m(Nov04)
#1 In Infrastructure - Ericsson
#1 in Handsets 2Q04 - Nokia(35.5%)
Global monthly SMS - 36/user
SMS Sent Global 1Q04 - 135 billion
Increased capacity within their existing spectrumallocation and easy deployment of technology
Higher capacities and lower system design costs (pluslower infrastructure costs) which will lead to a lowercost per subscriber.
A lower cost per subscriber, combined with newsubscriber features, which will help the operators toincrease their market penetration.
An increased market penetration, which will lead to anincrease in number of subscribers and a system whichoffers support for that increased capacity.
High quality calls must be maintained during the changeto or migration to any new digital technology.
One of the most exciting of thenew digital technologies, CDMAwill offer all of this to the
operators, and more.
Some Facts.
Operator Drivers.
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Bandwidth B
Frequency
Multiple users attempt to Access B
Multiple Access ProblemsMultiple Access Problems
Consider a given
Bandwidth (B) from aFrequency Spectrum(f).
The Multiple Access(MA) problem is theprocess whichattempts to allow
several users (N) toshare a commonbandwidth Bsimultaneously.
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Multiple Access Technologies
Several solutions to the Multiple
Access Problem exist. Here, we willdefine and review three strategies
Frequency Division
Multiple Access (FDMA)
Time Division Multiple
Access (TDMA)
Code Division Multiple
Access (CDMA)
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Multiple Access Comparison - FDMA
Used for Analog cellular Each user assigned a discreet slice ofRF spectrum
Number of users is limited to numberof channels
In Frequency Division Multiple Accessor FDMA strategies, the focus is onthe Frequency dimension.
Here, we divide the bandwidth (B)into N Narrow band frequency slices. So, several users are allowed to
communicate simultaneously byassigning Narrowband frequencyslices to the users: On a Dedicated or Pre-assigned basis
where a fixed frequency slice is
assigned to a designated user at alltimes. Examples of Dedicated FDMAapplications include AM Radio, FMRadio and Television Broadcasts.
On a Demand-Assigned MultipleAccess (DAMA) basis where anavailable frequency slice, or Channel,is assigned to a designated user forone call or one transaction only. An
example of DAMA FDMA applications isthe Analog cellular system.
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Multiple Access Comparison - TDMA
Each user assigned a discreet slice ofRF spectrum
Multiple users share the carrier on atime slot basis Number of Users per channel is
dependent upon number of timeslots Used for GSM and IS-54
In Time Division Multiple Access or TDMAstrategies, we create, in addition to theFrequency Dimension (f), a newDimension: Time (t).
Given a slice of the total bandwidth B,the focus is now placed on the TimeDimension: Here, several users areallowed to take turns in the Timedomain in order to share a givenNarrowband frequency slice (Fi).
Here, the time Dimension is organized orsubdivided into multiple time slices. So,several users are allowed tocommunicate simultaneously byassigning time slices to the users.
The period of time during which a usergets the chance to transmit (or receive)on the channel is referred to as TimeSlot (TS). The information contained in aTime Slot is called a Burst.
The interval of time during which all theassigned users get the chance to usetheir respective Time Slots is referred toas the TDMA Frame.
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Multiple Access Comparison - CDMA
Codes Codes In Code Division Multiple Access
or CDMA strategies, we create yetanother Dimension (in addition to
the Frequency and Timedimensions). This new, orthogonaldimension is referred to as theCode Dimension .
Given a wideband slice of the totalbandwidth B, our focus will nowbe placed on the newly createdCode Dimension: Here several
users are allowed, at all times,to access the broadbandFrequency slice. However, eachuser must employ a unique Code.
Since co-users are isolated bycodes rather than Frequencies,the ability to reuse frequencies isvery high. This further enhancesthe overall spectral efficiency.
If these codes are orthogonal,they will isolate the users in theCode Dimension. (Just likedifferent frequencies and differentTime-Slots do in the Frequencyand Time Dimensionsrespectively.)
Time
Frequency
Code
Spectral Efficiency is further Enhanced !
FrequencyTime
Codes Codes
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Multiple Access Comparison - CDMA
No time division multiplexing
Each user is assigned a code during call setup
This code is spread using a Wideband PseudorandomNoise (PN) Sequence
Wideband signal reduces interference and allow one-cellfrequency re-use
Used for IS95 based standards
Time
Fi
Code
Ci(t)
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CodesCodesCodes
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Why Use Codes?
Gives each user a unique identity User data is mixed with user
identity and is transmitted to BaseStation
Base Station uses the uniqueidentity to extract data
Used for SPREADING the user dataover a large bandwidth Base data at 9.6Kb/s needs to be
spread over 1.23 MHz bandwidth Spreading provides multiple
benefits Reduces power transmitted Reduces Interference Increases Capacity More immune to fading and
interference More resistant to jamming
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How Codes are Used - Transmitter
Let us consider the followingsteps or activities at a giventransmitter location:
an arbitrary data sequence di(t)generated by a digital source.
Now generate an arbitrary Code
sequence ci(t). Add these two sequences Modulo-2
(Exclusive-OR gate)
-1 +1 -1 +1 +1 -1 -1
+1 +1 -1 -1 -1 +1 -1
+1
-1
-1 -1 +1 +1 -1 -1 -1 +1
Di(t)Ci(t)Di(t)
Ci(t)
di(t)
ci(t)
di(t)
ci(t)
TransmitterTransmitterTransmitterTransmitter
Lets transmitthe output of theExclusive-OR
gate to a distantreceiver
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How Codes are Used - Receiver
Lets transmit the output of themultiplier to a distant receiver.
At the distant location, the resulting sequence ispicked up by the receiver
If the code ci(t) used at the transmitting location is
available at the receiver, then the original datasequence di(t) can be recovered exactly.
This is done by Multiplying the received sequencewith the locally available code ci(t).
Receive the original sequence of data
a a
a
a
a-1 +1 -1 +1 +1 -1 -1+1 -1 -1 +1 +1 -1 -1 -1 +1Di(t)
Ci(t)
Di(t)Ci(t)
+1 +1 -1 -1 -1 +1 -1-1
di(ti)
ci(t)
di(ti)
ci(ti) ci(ti)
di(ti)
ci(ti)
ReceiverReceiverReceiverReceiver
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How Codes are Used - Summary
di(t) is the data sequence
ci(t) is the code sequence
di(t) ci(t) is resulting
sequence. This is thesequence which is actuallysent to the receiver.
In order for the output of the receiverto be identical to the original data, thefollowing relationship must be true: d(t).c(t).c(t) = d(t)
In other words, c(t).c(t) must be equalto unity. Note that c(t) is a binarysequence made up of +1s and -1s.
Therefore: If c(t) is +1, c(t).c(t) is equal to +1
If c(t) is -1, c(t).c(t) is also equal to +1.
This is the Exclusive OR function
Since c(t).c(t) is equal to +1, thecondition d(t).c(t).c(t) =d(t) is met.Therefore the output of our simplereceiver is the recovered original datad(t).
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Spreading Codes
In order to spread the datasequence (Direct Sequence SpreadSpectrum), the code sequencemust be :
Much faster than the data sequence.
Exhibit some Randomness properties
Note that the data sequence has aslower speed (less transitions)than the Code sequence. By Multiplying the data sequence
with the faster code sequence, theresulting product yields a sequencewith more transitions than theoriginal data. (Faster speed).
Furthermore, in order to providegood isolation between users(Code Division Multiple Access),a set of orthogonal codes mustbe used.
The codes used in practice arenot perfectly orthogonal.However, they exhibit very goodisolation characteristics.
Linear Shift Registers are used togenerate the kind of spreadingcodes utilized in CDMA-based IS-95 systems. They are referred to as Pseudo-
random Noise (PN) codes orsequences.
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Codes used in CDMA
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SynchronizationSynchronizationSynchronization
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Synchronization Concept
So far, we are assuming that
there is no propagation delayand/or other processingdelays incurred between thetransmitter and the receiverinput
Therefore, the code copyused at the receiver isperfectly lined-up with theinitial code used at thetransmitter. These two codes
are said to be in phase or insync. (synchronization).
In practice however, a propagationdelay and other processing delays (i)are incurred between the transmitterand the receiver input
Therefore, the code copy used at thereceiver may be time-shifted relativeto the initial code used at thetransmitter. The two codes are nolonger in sync or in phase. As theresult, the output of the receiver willno longer be identical to the originaldata d(t).
In order to recover the original data,we must tune the receiver codesequence to that of the incoming codefrom the transmitter. In other words,we must deliberately and artificiallytime-shift the receiver code in order to
line it up with the incoming code. (Atthe receiver, we are artificiallycompensating or making-up for thedelays incurred during transmission.)
This process is referred toas synchronization.
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Synchronization ConceptCont
In the final stages of the encoding of the radio link from the base
station to the mobile, CDMA adds a special "pseudo-random code" tothe signal that repeats itself after a finite amount of time. Base stations in the system distinguish themselves from each other
by transmitting different portions of the code at a given time. In other words, the base stations transmit time offset versions of the same
pseudo-random code.
In order to assure that the time offsets used remain unique from eachother, CDMA stations must remain synchronized to a common timereference.
The primary source of the very precise synchronization signalsrequired by CDMA systems is the Global Positioning System (GPS). GPS is a radio navigation system based on a constellation of orbiting
satellites. Since the GPS system covers the entire surface of the earth, itprovides a readily available method for determining position and time to asmany receivers as are required.
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Power ControlPower ControlPower Control
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CDMA Power Control
The fundamental purpose of power control is to maintain a satisfactory voice quality maximizing system capacity and minimizing power consumption.
Power Control is applied to: Mobile Power on initial access Mobile Power while on the traffic channel Base Station Power
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CDMA HandoffCDMA HandoffCDMA Handoff
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CDMA Soft Handoff (SHO)
SHO reduces the average transmit power of mobiles in thehandoff area A mobile in soft handoff powers up only if all BSs involved in soft
handoff ask for more power and it powers down as soon as one of BSs ask him to power down.
Therefore statistically mobiles transmitted power is reduced andso it contributes less to interference level in the system.
A high call quality by providing a make before break connection
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Handoff
The different kinds ofhandoffs possible in acellular system are:
Hard handoff
Soft handoff Softer handoff
Idle Handoff
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Hard Handoff
Hard handoff is a break-before-make method,where a new link is set up after the link to theoriginal base station has been disconnected.
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Soft Handoff
A soft handoffestablishes a connection with the new
base station before breaking the connection with the oldone.
The CDMA handset assists the network in the handoffusing a rake receiver.
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Softer Handoff
A softer handoffoccurs when a user travels from onesector to another sector of the same base station.
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Idle Handoff
Idle handoff in CDMA happens when the handsetmoves from one cell to another while not in a call.
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CDMA ChannelsCDMA ChannelsCDMA Channels
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Forward Link/Downlink
The wireless connection over which information issent from a cellular base station to a handset isknown as the forward link or downlink.
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The types of forward linkchannels are: Pilot channel
Used by mobile to obtain initialsystem synchronization andprovide time, frequency andphase tracking of signals fromcells
Synchronization channel Provide cell ID, pilot transmit
power and cell PN phase offsetinformation. Mobile uses this toestablish system time andinitial transmit level
Paging Channel Mobile gets paged on thischannel
Traffic Channel Carries the actual traffic data
Forward Link/Downlink
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Reverse Link/Uplink
The wireless connection over which information is sent
from a handset to a cellular base station is known asthe reverse link or uplink.
Traffic
Channel
Access
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The types of Reverse link
channels are: Access Channel
Used by mobile tocommunicate to the base
station. Registration requests,
responses to pages, andcall origination
Reverse traffic channel
Carries the actual traffic datain the reverse link
Reverse Link/Uplink
Traffic
Channel
Access
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CDMA BenefitsCDMA BenefitsCDMA Benefits
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CDMA Benefits
Capacity Can balance capacity against coverage and quality
Cell planning No frequency planning required Complex optimization
Sensitivity Better sensitivity because of more sophisticated error
correction schemes
Vocoder Increases capacity through variable rate vocoding
Power control Reduction in interference by use of fast power control
Keeps the transmit power to minimum
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CDMA Benefits (Cont)
Frequency diversity Wideband signals are less
prone to fades than narrowband signals
Path diversity Three receivers receive 3
strongest signals, time shiftsthem and then adds them toenhance the signal
Soft Handoff Signal from the mobile is
received by multiple basestations
Choose the best signalfrom different paths
Reduces the probability ofdrop
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CDMA 1X OverviewCDMA 1X OverviewCDMA 1X Overview
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CDMA Application Requirements CDMA2000 1X
Peak 153 kbpscircuit/packet data
Simultaneous Voice & Data
1xEV-DO
Peak 2.4 Mbps packet data Data only services
Non real-time data services
1xEV-DV Peak 3.1 Mbps circuit/packet
data
Multimedia 3G services
Simultaneous Voice & Data
Real-time services
DOWNLOADRINGERS
VOICE
TRANSACTIONS-BASED APPS
EMAIL
SMS
LocationSpecificServices
S/WDOWNLOAD
InternetAccess
MUSICDOWNLOAD
Non-Real
TimeReal
Time
VIDEOCONFERENCE
Live VideoBroadcast
INTERACTIVEGAMING
MULTIMEDIAMESSAGING
Low Data Rate
High Data Rate
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CDMA2000 1X Solution Objectives
Support of CDMA2000 1X Air Interface Enable new revenue generating features Enable high voice capacities
Orderly Migration Maximize re-use of existing equipment
Minimize risk to existing voice services Simplify BTS upgrades
Introduce Packet Components Packet CBSC
Packet Data Service Node Authentication, Accounting, and Authorization Server
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CDMA 1X Technical Characteristics
Peak Data Rate = 153kbps; Throughput/Capacity = 150kbps
Rel A: Peak Data Rate = 614kbps; Throughput/Capacity = 415kbps Peak rate achieved through 2 channel concatenation Concatenation technology has been proven in commercial IS-95B deployments
Flexibility to Deploy Data Only Carriers to Maximize End-User Data Rates
Backward Compatible with IS-95A/B Supports handoffs between A/B/1X, carrier overlay, and overflow of both voice
and data through load management
Supports Voice, Mixed Voice/Data, and Real-Time 2-Way Services on a
Single Carrier
Dynamically Optimizes Data Capacity Based on Underlying Voice Utilization Extension of IS-95B commercial deployments
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CDMA2000 1X Highlights
Technical Improvements Support of MAC, QoS, and Turbo codes for data Fast forward and reverse link power control Backward compatible with IS-95A/B Extended Battery life through QPCH Forward link transmit diversity (G16.1)
Benefits Support of 153.6k bps data rate for new revenue
generating data applications(Note: 153.6K = 144K + Overhead)
Up to 4-6X capacity increase for data applications Up to 1.4-1.6X capacity increase for voice reduces
operating costs Delivers a cost-effective migration strategy by leveraging
IS-95A/B investments
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CDMA 2000 Evolution
Technology Maximum data rates Spectrum Services
IS-95 A/B 115.2Kbps 1.25MHz Voice and circuit
switched data
services
CDMA2000 1X Upto 614 Kbps 1.25MHz Voice, circuitswitched data and
packet data
CDMA2000 1X- EV-DO Upto 2.4 Mbps 1.25MHz Packet data service
CDMA2000 1X- EV-DV Upto 3 Mbps 1.25MHz Voice, circuit data,packet data and
multimedia service
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Hope that you enjoyed this course
Thank you
for your participation