Download - CDMA presen
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Prepared byPrepared byMital Marvaniya &Mital Marvaniya &
Sonal MalavaniyaSonal Malavaniya
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INTRODUCTION TO CDMAINTRODUCTION TO CDMA
CDMA stands for Code Division MultipleCDMA stands for Code Division Multiple
Access.Access.
A digital communication technologyA digital communication technology
provides crystal clear voice quality .provides crystal clear voice quality .
Using a digital encoding spread spectrumUsing a digital encoding spread spectrumradio frequency (RF) techniques.radio frequency (RF) techniques.
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MULTIPLE ACCESSMULTIPLE ACCESS
Multiple access means that multiple, simultaneousMultiple access means that multiple, simultaneoususers can be supported.users can be supported.
There are three primary multiple access systems:There are three primary multiple access systems:
1) FDMA (analog)1) FDMA (analog)
2) TDMA (digital)2) TDMA (digital)
3) CDMA(digital)3) CDMA(digital)
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CDMACDMA
CDMA assigns eachCDMA assigns eachsubscriber a uniquesubscriber a uniquecode to put multiplecode to put multipleuser on the same wideuser on the same wide
band channel at theband channel at thesame time.same time.
And these codes areAnd these codes areused by the mobileused by the mobilestation and basedstation and basedstation to distinguishstation to distinguishbetween conversations.between conversations.
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WIRELESS LOCAL LOOP(WLL)WIRELESS LOCAL LOOP(WLL)
TheWLL is a telecommunication service that usesTheWLL is a telecommunication service that uses
wireless networks to carry communication from thewireless networks to carry communication from the
wired subscriber network.wired subscriber network.
Installation ofWLL costs no more than half that for aInstallation ofWLL costs no more than half that for a
wired system.wired system.
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WHY CDMA BETTERWHY CDMA BETTER
1) Better reception1) Better reception
2) Security of CDMA2) Security of CDMA
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GENERATION OF CDMAGENERATION OF CDMA
First generation :First generation :
AMPSAMPS
FDMAFDMA
22ndnd
Generation:Generation:TDMATDMA
GSMGSM
2.5 Generation:2.5 Generation:
GPRS & CdmaOneGPRS & CdmaOne33rdrd Gneration:Gneration:
CDMACDMA
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HOW CDMAWORKSHOW CDMAWORKS
CDMA signal genarationCDMA signal genaration
The types of code used inThe types of code used inCDMACDMA
Forward and reverse linkForward and reverse link
code channelscode channels
CDMA call processingCDMA call processing
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CDMA SIGNAL GENERATIONCDMA SIGNAL GENERATION
Analog to digitalAnalog to digitalconversion.conversion.
CDMA uses pulse codeCDMA uses pulse codemodulation techniquemodulation technique(PCM)(PCM)
to accomplish the A/Dto accomplish the A/Dconversion.conversion.
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VOICE COMPRESSIONVOICE COMPRESSION
CDMA uses a diviceCDMA uses a divicecalled vocoder tocalled vocoder toaccomplish voceaccomplish voce
compression.compression.
The term vocoder isThe term vocoder isconstaction of voice andconstaction of voice andcode.code.
VRIABLE RATEVRIABLE RATEVOCODERVOCODER
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HOW ENCODING WORKHOW ENCODING WORK
The type of encodingThe type of encodingdone at this stage isdone at this stage iscalled "convolutionalcalled "convolutionalencoding."encoding."
A burst error is a typeA burst error is a typeof error in receivedof error in receiveddigital telephonedigital telephonesignals. Burst errorssignals. Burst errors
occur in clumps ofoccur in clumps ofadjacent symbols.adjacent symbols.These errors areThese errors arecaused by fading andcaused by fading andinterference.interference.
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HOW INTERLEAVING WORKSHOW INTERLEAVING WORKS
InterleavingInterleaving
DeDe--interleavinginterleaving
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CHANNELIZING THE SIGNALCHANNELIZING THE SIGNAL
The encoded voice data isThe encoded voice data isfurther encoded to separatefurther encoded to separateit from other encoded voiceit from other encoded voicedata. The encoded symbolsdata. The encoded symbols
are then spread over theare then spread over theentire bandwidth of theentire bandwidth of theCDMA channel. This processCDMA channel. This processis called channelization.is called channelization.
Two kinds of codesTwo kinds of codes
1)Walsh code1)Walsh code
2) Pseudorandom Noise2) Pseudorandom Noise(PN) codes(PN) codes
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CODES CHANNEL USED IN CDMACODES CHANNEL USED IN CDMA
A code channel is aA code channel is a
stream of datastream of data
designated for a specificdesignated for a specific
use or person. Thisuse or person. This
channel may be voicechannel may be voice
data or overhead controldata or overhead control
data.data.
1) The forward links
2) The reverse links
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FORWORD LINK CHANNELSFORWORD LINK CHANNELS
The forward link usesThe forward link uses
four types of channelsfour types of channels
to transmit voice andto transmit voice and
control data to thecontrol data to the
mobile.mobile.
1) Pilot, 2) Sync, 3)1) Pilot, 2) Sync, 3)
Paging, 4) TrafficPaging, 4) Traffic
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REVERSE LINK CHANNELSREVERSE LINK CHANNELS
The reverse linkThe reverse link
uses two types ofuses two types of
channels to transmitchannels to transmit
voice and controlvoice and controldata to the BTS.data to the BTS.
1) Access,1) Access,
2)Traffic2)Traffic
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RECEIVER SIDE WORKSRECEIVER SIDE WORKS
Conversion of RFConversion of RF
signal to digital signalsignal to digital signal
Despreading theDespreading thesignalsignal
Deinterleaving andDeinterleaving and
decodingdecoding
Voice decompressionVoice decompression
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BENEFITS OF CDMABENEFITS OF CDMA
Capacity increases .Capacity increases .
Improved call quality.Improved call quality.
Simplified system planning through the use of theSimplified system planning through the use of the
same frequency in every sector of every cell .same frequency in every sector of every cell .Enhanced privacyEnhanced privacy
Improved coverage characteristics.Improved coverage characteristics.
Increased talk time for portablesIncreased talk time for portables
Bandwidth on demandBandwidth on demand