Cdma Anjan V1

Elementary Concepts, Elementary Concepts, Standards And CDMAStandards And CDMA

Anjan.KIII Sem M.Tech

Dept Of CSEM.S.R.I.T

04/11/23 1MC: Elementary Concepts and CDMA

AgendaAgendaMobile StandardsDifferent GenerationsCDMA

◦ Need for CDMA Technology◦ cdmaOne IS-95 Architecture

Features◦ IS 95 Vs 2G systems◦ 3G Vision◦ Migrating to 3G◦ CDMA 2000

Architecture◦ WCDMA◦ TD-SCDMA

04/11/23MC: Elementary Concepts and CDMA 2

International International StandardizationStandardization

ITU (International Telecommunication Union)◦ Radio standards and spectrum

IMT-2000◦ ITU’s umbrella name for 3G which stands for

International Mobile Telecommunications 2000 National and regional standards bodies are

collaborating in 3G partnership projects◦ ARIB, TIA, TTA, TTC, CWTS. T1, ETSI - refer to

reference slides at the end for names and links 3G Partnership Projects (3GPP & 3GPP2)

◦ Focused on evolution of access and core networks


IMT-2000 Radio IMT-2000 Radio StandardsStandardsIMT-SC* Single Carrier (UWC-136): EDGE

◦ GSM evolution (TDMA); 200 KHz channels; sometimes called “2.75G”

IMT-MC* Multi Carrier CDMA: CDMA2000◦ Evolution of IS-95 CDMA, i.e. cdmaOne

IMT-DS* Direct Spread CDMA: W-CDMA◦ New from 3GPP; UTRAN FDD

IMT-TC** Time Code CDMA◦ New from 3GPP; UTRAN TDD◦ New from China; TD-SCDMA

IMT-FT** FDMA/TDMA (DECT legacy)


* Paired spectrum; ** Unpaired spectrum

Mobile Standards Mobile Standards OrganizationsOrganizations European Technical Standard Institute (Europe):

◦ http://www.etsi.org Telecommunication Industry Association (USA):

◦ http://www.tiaonline.org Standard Committee T1 (USA):

◦ http://www.t1.org China Wireless Telecommunication Standard (China):

◦ http://www.cwts.org The Association of Radio Industries and Businesses

(Japan):◦ http://www.arib.or.jp/arib/english/

The Telecommunication Technology Committee (Japan):◦ http://www.ttc.or.jp/e/index.html

The Telecommunication Technology Association (Korea):◦ http://www.tta.or.kr/english/e_index.htm


First GenerationFirst GenerationAdvanced Mobile Phone Service (AMPS)

◦ US trials 1978; deployed in Japan (’79) & US (’83)

◦ 800 MHz band — two 20 MHz bands◦ TIA-553◦ Still widely used in US and many parts of the

world Nordic Mobile Telephony (NMT)

◦ Sweden, Norway, Demark & Finland◦ Launched 1981; now largely retired◦ 450 MHz; later at 900 MHz (NMT900)

Total Access Communications System (TACS)◦ British design; similar to AMPS; deployed 1985◦ Some TACS-900 systems still in use in Europe


Second Generation — Second Generation — 2G2GDigital systems Leverage technology to increase capacity

◦ Speech compression; digital signal processing Utilize/extend “Intelligent Network”

concepts Improve fraud prevention Add new services There are a wide diversity of 2G systems

◦ IS-54/ IS-136 North American TDMA; PDC (Japan)

◦ iDEN◦ DECT and PHS◦ IS-95 CDMA (cdmaOne)◦ GSM


Need for CDMA Need for CDMA TechnologyTechnologyHigher capacityImproved performance in multipath by

diversityLower mobile transmit power = longer battery

life◦ Power control◦ Variable transmission rate with voice activity

detectionAllows soft handoffSectorization gainHigh peak data rates can be accommodatedCombats other-user interference = lower reuse

factors04/11/23

MC: Elementary Concepts and CDMA 9

CDMA????CDMA????Both an access method and air-

interfaceRest of the network is very similar

◦Radio resource management, mobility management, security are similar

◦Power control and handoffs are differentUses DSSS and ECCFrequency reuse factor is 1Three CDMA systems

◦ IS-95 2G◦CDMA2000 ◦W-CDMA


CDMA AnalogyCDMA Analogy10 people in a room.

◦5 speak English, 2 speak Spanish, 2 speak Chinese, and 1 speaks Russian.

Everyone is talking at relatively the same time over the same medium – the air.

Who can listen to whom and why?Who can’t you understand?Who can’t speak to anyone else?

CDMA Standards - IS-CDMA Standards - IS-9595TIA standard Interim Standard (IS) -95 (ANSI-

95) in 1993 IS-95 deployed in the 800 MHz cellular band

◦ J-STD-08 variant deployed in 1900 MHz US “PCS” band

Evolution fixes bugs and adds data◦ IS-95A provides data rates up to 14.4 kbps◦ IS-95B provides rates up to 64 kbps (2.5G)◦ Both A and B are compatible with J-STD-08

All variants designed for TIA IS-41 core networks (ANSI 41)

CDMA was first commercialized by its founder A.J Verterbi at Qualcomm in 1995.


CDMA Standards - IS-95ACDMA Standards - IS-95AIS-95A is the CDMA-based second

generation (2G) standard for mobile communication. The following are the key aspects of this standard:

• Support for data rates of upto 14.4 kbps

• IS-95A has been used exclusively for circuit-switched voice

• Convolutional Channel coding used

• Modulation technique used is BPSK

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CDMA Standards - IS-95BCDMA Standards - IS-95B IS-95B is the evolved version of IS-95A and is designated as

2.5G. IS-95B maintains the Physical Layer of IS-95A, but due to an

enhanced MAC layer, is capable of providing for higher speed data services. The following are the key aspects of the standard:• Theoretical data rates of upto 115 kbps, with generally

experienced rates of 64 kbps

• Additional Walsh codes and PN sequence masks, which enable a mobile user to be assigned up to eight forward or reverse code channels simultaneously, thus enabling a higher data rate

• Code channels, which are transmitted at full data rates during a data burst

• Convolutional Channel coding

• Binary Phase Shift Keying (BPSK) as the Modulation technique used

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IS-95 CDMA Features-IS-95 CDMA Features-(1)(1) Bandwidth Recycling

Enhancing the system capacity due to the increase of reuse efficiency.

Achieving higher bandwidth efficiency (interference limited) and simplifying the system planning.

Achieving flexibility due to the bandwidth on demand. Power Control

Reducing the interference and increasing the talk time of mobile

station by using the efficient power control scheme. Soft handoffs

Contributing to the achievement of the diversity and reduce the

chance of loss of link midway through the conversation.


IS-95 CDMA Features-IS-95 CDMA Features-(2)(2)Diversity

Taking advantage of multiple levels of diversity: frequency diversity (spreading), spatial diversity (multiple antennas), path diversity (rake receiver) and time diversity (block interleaver), all of which reduce the interference and improve speech quality.

Variable Rate Vocoder Offering high speed coding and reducing

background noise and system interference based on the detection of the voice activity.

Coding Technique Enhancing the privacy and security.


IS-54/136 GSM IS-95

TDMA/FDMA CDMA Hard Handoff Soft Handoff

Open-loop and Slow Power Control

Close-loop and Faster Power Control

Fixed Rate Vocoder Variable Rate Vocoder

IS-95 Vs 2G Phone IS-95 Vs 2G Phone SystemsSystems


IS – 95 VocodersIS – 95 VocodersAMR: Adaptive multi-rate

◦Defined for UMTS (W-CDMA)◦Being retrofitted for GSM

SMV: Selectable mode vocoder◦Defined by 3GPP2 for CDMA2000

Many available coding rates◦AMR 8 rates: 12.2, 10.2, 7.95, 7.4, 6.7, 5.9,

5.15 & 4.75bps, plus silence frames (near 0 bps)

◦SMV 4 rates: 8.5, 4, 2 & 0.8kbpsLower bit rates allow more error

correction◦Dynamically adjust to radio interference

conditions04/11/23


Frequency Allocation GSM Vs Frequency Allocation GSM Vs CDMACDMA


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Mathematical Background – (1)Mathematical Background – (1)

Multiple users occupying the same band by having different codes is known as CDMA - Code Division Multiple Access system

Let W - spread bandwidth in HzR = 1/Tb = Date RateS - received power of the desired signal in WJ - received power for undesired signals like

multiple access users, multipath, jammers etc in W

Eb - received energy per bit for the desired signal in W

N0 - equivalent noise spectral density in W/Hz

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Mathematical Mathematical Background – (2)Background – (2)

00

0

NERW

NEWT

TEWN

SJ

bb

b

bb

min0max NERW

SJ

b

What is the tolerable interference over desired signal power?

)()((db) margin Jammingmin0max

dbNE

dbRW

SJ b

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In conventional systems W/R 1 which means, for satisfactory operation J/S < 1

Example Let R = 9600; W = 1.2288 MHz(Eb/N0)min = 6 dB (values taken from IS-95)

Jamming margin (JM) = 10log10(1.2288*106/9.6*103) - 6

= 15.1 dB 32

This antijam margin or JM arises from Processing Gain (PG) = W/R = 128

If (Eb/N0)min is further decreased or PG is increased, JM can be further increased

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JM can be used to accommodate multiple users in the same band

If (Eb/N0)min and PG is fixed, number of users is maximized if perfect power control is employed.

Capacity of a CDMA system is proportional to PG.

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Spreading CodesSpreading Codes

A noise-like and random signal has to be generated at the transmitter.

The same signal must be generated at the receiver in synchronization.

We limit the complexity by specifying only one bit per sample, i.e., a binary sequence.

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Desirable Randomness Desirable Randomness PropertiesProperties

Relative frequencies of “0” and “1” should be ½ (Balance property)

Run lengths of zeros and ones should be (Run property):◦ Half of all run lengths should be unity◦ One - quarter should be of length two◦ One - eighth should be of length three◦ A fraction 1/2n of all run lengths should be

of length n for all finite n

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Desirable Randomness Properties Desirable Randomness Properties (contd…)(contd…)

If the random sequence is shifted by any nonzeronumber of elements, the resulting sequenceshould have an equal number of agreements anddisagreements with the original sequence(Autocorrelation property)

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PN SequencesPN Sequences

A deterministically generated sequence that nearly satisfies these properties is referred to as a Pseudorandom Sequence (PN)

Periodic binary sequences can be conveniently generated using linear feedback shift registers (LFSR)

If the number of stages in the LFSR is r, P 2r - 1 where P is the period of the sequence

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PN Sequences (contd…)PN Sequences (contd…)

However, if the feedback connections satisfy a specific property, P = 2r - 1. Then the sequence is called a Maximal Length Shift Register (MLSR) or a PN sequence.

Thus if r=15, P=32767.MLSR satisfies the randomness properties

stated before

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Randomness Properties of PN Randomness Properties of PN SequencesSequences

Balance property - Of the 2r - 1 terms, 2r-1 are one and 2r-1–1 are zero. Thus the unbalance is 1/P. For r=50; 1/P10-15

Run length property - Relative frequency of run length n (zero or ones) is 1/ 2n for n r-1 and 1/(2r - 1) for n = r

One run length each of r-1 zeros and r ones occurs. There are no run lengths for n > r

Autocorrelation property - The number of disagreements exceeds the number of agreements by unity. Thus again the discrepancy is 1/p

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PN Sequences Specified in PN Sequences Specified in IS-95IS-95

A “long” PN sequence (r =42) is used to scramble the user data with a different code shift for each user

The 42-degree characteristic polynomial is given by:◦ x42+x41+x40+x39+x37+x36+x35+x32+x26+x25+x24

+x23+x21+x20+x17+x16+x15+x11+x9+x7+1

The period of the long code is 242 - 1 4.4*102 chips and lasts over 41 days

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PN Sequences Specified in IS-95 PN Sequences Specified in IS-95 (contd…)(contd…)

A short PN sequence (r = 15) is specific to a base station and its period is (215−1)Tc = 27ms.

Two “short” PN sequences (r=15) are used to spread the quadrature components of the forward and reverse link waveforms

Walsh CodeWalsh CodeThere are some issues with Walsh

Codes◦Synchronization of all users is required◦ In a multipath channel, delayed copies may

be received which are not orthogonal any longer!

◦Only J codes exist with a bandwidth expansion of J, so as far as capacity, we are right back where we started with TDMA and FDMA!

Advantages relative to TDMA and FDMA◦No guard bands or guard times are typically

required◦No equalizer is typically required, when a

RAKE receiver is used04/11/23


Spread SpectrumSpread SpectrumA modulation system in which the

modulated (spread spectrum) signal bandwidth is much greater than the message signal bandwidth.

The spectral spreading is performed by a code that is independent of the message signal. The same code is used at receiver to de spread the received signal and to recover the message signal.


Advantages of Spread Advantages of Spread SpectrumSpectrumIt is Secure, difficult to intercept A large number of codes can

support a large number of usersAs a large bandwidth is used

the system is less prone to distortion

Resistant to jammingAsynchronous multiple access

technology04/11/23


Types Of Spread Types Of Spread SpectrumSpectrumDirect Sequence Spread

SpectrumFrequency HopingHybrid System


Direct Sequence Spread Direct Sequence Spread SprectrumSprectrumDS-SS is one popular way to make

the noise-like waveforms for CDMAMaximal-length shift registers

make binary sequences that have noise-like properties

n-stage shift register produces a sequence with a period of length 2n-1.

Codes for different users


CDMA Forward LinkCDMA Forward Link The forward link uses the same frequency spectrum

as AMPS (824-849 Mhz) . Each carrier 1.25MHz Four types of logical channel

◦ Pilot, ◦ Synchronization, ◦ 7 Paging, and ◦ 55 Traffic channels

Channels are separated using different spreading codes

QPSK is the modulation scheme Orthogonal Walsh codes are used (64 total) After orthogonal codes, they are further spread by

short PN spreading codes Short PN spreading codes are M sequences generated

by LFSRs of length 15 with a period of 32768 chips.


CDMA Reverse ChannelCDMA Reverse ChannelFundamentally different from the

forward channelsUses OQPSK for power efficiencyQPSK demodulation is easy869-894 MHz range.No spreading of the data using

orthogonal codesSame orthogonal codes are used for

WAVEFORM encodingTwo types of logical channels:

◦ Access channels ◦ Reverse traffic channels


3G Vision3G VisionUniversal global roaming Multimedia (voice, data & video) Increased data rates

◦ 384 kbps while moving◦ 2 Mbps when stationary at specific

locationsIncreased capacity (more

spectrally efficient)IP architecture


IS 95 to CDMA 2000 3G IS 95 to CDMA 2000 3G Evolution Evolution


CDMA2000CDMA2000Evolution from original Qualcomm

CDMABetter migration story from 2G to 3G

◦cdmaOne operators don’t need additional spectrum

◦1xEVD0 promises higher data rates than UMTS, i.e. W-CDMA

Better spectral efficiency CDMA2000 core network less mature

◦cdmaOne interfaces were vendor-specific


W-CDMAW-CDMAWideband CDMA

◦Standard for Universal Mobile Telephone Service (UMTS)

Committed standard for Europe and likely migration path for other GSM operators◦Leverages GSM’s dominant position

Requires substantial new spectrum◦5 MHz each way (symmetric)

Legally mandated in Europe and elsewhere

Sales of new spectrum completed in Europe


Need For WCDMANeed For WCDMAWCDMA is a step further in the

CDMA technology. ◦Uses a 5 MHz wide radio signal and ◦chip rate of 3.84 Mcps, which is

about three times higher than the chip rate of CDMA2000 (1.22 Mcps)

◦QPSK ModulationMigration from 3G to 4G Higher spectrum efficiency Higher QoS



W-CDMA Vs cdma2000W-CDMA Vs cdma2000Parameter W-CDMA cdma2000Carrier spacing 5 MHz 3.75 MHz

Chip rate 4.096 MHz 3.6864 MHz

Data modulation BPSK FW – QPSK; RV - BPSK

Spreading Complex (OQPSK) Complex (OQPSK)

Power control frequency 1500 Hz 800 Hz

Variable data rate implement. Variable SF; multicode Repet., puncturing, multicode

Frame duration 10 ms 20 ms (also 5, 30, 40)

Coding Turbo and convolutional Turbo and convolutional

Base stations synchronized? Asynchronous Synchronous

Base station acquisition/detect 3 step; slot, frame, code Time shifted PN correlation

Forward link pilot TDM dedicated pilot CDM common pilot

Antenna beam forming TDM dedicated pilot Auxiliary pilot

TD-SCDMATD-SCDMATime division duplex (TDD)Chinese development - deployed in

ChinaGood match for asymmetrical traffic!Single spectral band (1.6 MHz) possibleCosts relatively low

◦Handset smaller and may cost less◦Power consumption lower◦TDD has the highest spectrum efficiency

Power amplifiers must be very linear◦Relatively hard to meet specifications

35MHz for downlink and uplink


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Rake ReceiverRake ReceiverMobile station receives multiple attenuated

and delayed replicas of the original signal (multipath diversity channels).

Two multipath signals are resolvable only if their relative delay exceeds the chip period Tc

Amplitudes and phases of multipath components are found by correlating the received waveform with multiple delayed versions of the signal (delay = nTc).

Searcher performs the above task for up to 3 different multipath signals.

3 parallel demodulators (RAKE fingers) isolate the multipath components and the RAKE receiver combines them.

Summary Summary Different mobile standard

organization ITU, IMT 2000, TIA, ISCDMA

◦IS 95 , IS95A,IS95B◦Codes –Walsh,Autocorrelation, PN◦Rake Receiver◦Forward and Reverse Link◦CDMA 2000◦WCDMA


ReferencesReferences

[1] T. S. Rappaport, “Wireless communications principles&practice”, Prentice Hall, 1996[2] C. Y. Lin and J. Shieh, “IS-95 North American standard-a CDMA based digital cellular system”, IEEE Website.[3] A. J. Viterbi, “CDMA principles of spread spectrum communication”, Addison-Wesley Publishing

Company, 1995.[4] R. Paul and K. V. Shah, “An objective comprison of

second generation cellular systems - GSM, IS-136 and IS-95”,

IEEE, 1997.[5] Dr.V.K Ananthashayana , “Lecture Notes on CDMA” [6] Motorola, Inc. “CDMA Technology & Benefits: An introduction to the benefits of CDMA for wireless technology”, 1996.

Cdma Anjan V1

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