New Cdma Report

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A

SEMINAR REPORT

ON

CDMA TECHNOLOGY

SUBMITTED BY:

ANKUR BANSAL

Roll No. 0722631011

DEPARTMENT OF ELECTRONICS AND

COMMUNICATION ENGINEERING

BACHLOR OF TECHNOLOGY

(ECE, VII SEM)

SESSION ± 2010-2011

D.J COLLEGE OF ENGINEERING & TECHNOLOGY

MODINAGAR-201204(U.P.)

U.P. TECHNICAL UNIVERSITY, LUCKNOW

2010-2011





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ACKNOWLEDGEMENT

³Appreciation can make a day, even change a life. Your willingness to put it into words is all that is necessary´.

I thank God Almighty for the successful completion of my seminar.

I express my sincere gratitude to Mr. Sumit Gupta, Head of the Department,Electronics & Communication Engineering. I am deeply indebted to Mr.

Prabhat Mishra, for their valuable advice and guidance. I am also grateful to

all other members of the faculty of Electronics & Communication department

for their co-operation.

I am grateful to DJCET, Modinagar for giving me the opportunity to undergo

this Seminar Program..

Last but not the least; I would like to thank my friends for their valuable inputs

without which this seminar would not have been complete.

ANKUR BANSAL



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CONTENT

What is CDMA

Multiple Access Comparison

y FDMA

y TDMA

y CDMA CDMA Technology

y Spread Spectrum

y Introduction to Spread Spectrum Communication

y Three types of Spread Spectrum

y Direct Sequence Spread Spectrum Coding

y Generating Pseudo-Random Code

y Code Correlation

y Pseudo-Noise Spreading

y System Capicity

The Spreading Process

CDMA Benefits

CDMA Implementation

y CDMA Channel

y CDMA forward Channel

Pilot Channel

Sync Channel

Paging Channel

Forward Traffic Channel

y CDMA Reverse Channel

Access Channel

Reverse Traffic Channel CDMA Modulation

Transmitting Data

Receiving Data

y Demodulation

y Code acquisition lock

y Correlation & data dispreading

y Automatic power control

Receiving an incoming call in CDMA

Conclusion

Refrence



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WHAT IS CDMA?

(Code Division Multiple Access) A method for

transmitting realtime signals over a shared portion of the

spectrum. The foremost application of CDMA is the digital

cellular phone technology that operates in the 800MHz band and

1.9GHz . Unlike GSM and TDMA, which divides the spectrum

into different time slots CDMA uses a spread spectrum technique

to assi gn a code to each conversati on. After the speech codecconverts voice to digital, CDMA spreads the voice stream over

the full 1.25MHz bandwidth of the CDMA channel coding each

stream separately so it can be decoded at the receiving end. Therate of the spreading signal is known as the ³chip rate,´ as each

bit in the spreading signal is called a ³chip´ voice conversationsuse the full bandwidth at the same time. One bit from each

conversation is multiplied into 128 coded bits by the spreadingtechniques, giving the receiving side an enormous amount of data

it can average just to determine the value of one bit.

CDMA phones are noted for their excellent call quality

and low current draw CDMA is less costly to implement,requiring fewer cell sites than the GSM and TDMA digital cell

phone systems and providing three to five times the calling

capacity. It provides more than 10 times the capacity of the

analog cell phone system (AMPS). CDMA is also expected to

become the third-generation (3G) technology for GSM.

CDMA transmission has been used by the military for

secure phone calls. Unlike FDMA and TDMA methods, CDMA¶s

wide spreading signal makes it difficult to detect and jam.

One of the most important concepts to any cellular telephone system is that of ³multiple access´, meaning that

multiple, simultaneous users can be supported. In other words, alarge number of users share a common pool of radio channels and

any user can gain access to any channel (each user is not alwaysassigned to the same c hannel). A channel can be thought of as

merely a portion of the limited radio resource which is temporaryallocated for a specific purpose, such as someone¶s phone call. A

multiple access method is a definition of how the radio spectrum

is divided into channels and how channels are allocated to the

many users of the system.



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MULTIPLE ACCESS COMPARISON

It is easier to understand CDMA if it is compared with other multiple

access technologies. The following sections describe the fundamental

differences between a Frequency Division Multiple Access Analog technology

(FDMA), a Time Division Multiple Access Digital technology (TDMA) and a

Code Division Multiple Access Digital technology (CDMA).

FDMA - Frequency Division Multiple Access

FDMA is used for standard analog cellular. Each user is

assigned a discrete slice of the RF spectrum. FDMA permits onlyone user per channel since it allows the user to use the channel

100% of the time. Therefore, only the frequency ³dimension´ isused to define channels.

TDMA - Time Division Multiple Access

The key point to make about TDMA is that users are still

assigned a discrete slice of RF spectrum, but multiple users now

share that RF carrier on a time slot basis. Each of the users

alternate their use of the RF channel. Frequency division is still

employed, but these carriers are now further sub -divided into

some number of time slots per carrier.

A user is assigned a particular time slot in a carrier and

can only send or receive information at those times. This is true

whether or not the other time slots are being used. Information

flow is not continuous for any user, but rather is sent and

received in ³bursts.´ The bursts are re-assembled at the receiving

end, and appear to provide continuous sound because the p rocessis very fast.



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CDMA - Code Division Multiple Access

IS-95 uses a multiple access spectrum spreading technique

called Direct Sequence

(DS) CDMA.

Each user is assigned a binary, Direct Sequence code

during a call. The DS code is a signal generated by linear

modulation with wideband Pseudorandorn Noise (PN) sequences.As a result, DS CDMA uses much wider signals than those used

in other technologies. Wideband signals reduce interference andallow onecell frequency reuse.

There is no time division, and all users use the entirecarrier, all of the time.

Figure 3: DS-CDMA



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CDMA TECHNOLOGY

Though CDMA application in cellular telephony is relatively new, it is not a

new technology. CDMA has been used in many military applications, such as

anti- jamming (because of the spread signal, it is difficult to jam or interfere

with a CDMA signal), ranging (measuring the distance of the transmission to

know when it will be received), and secure communications (the spread

spectrum signal is very hard to detect).

Spread Spectrum

CDMA is a ³spread spectrum´ technology, which means

that it spreads the information contained in a particular signal of interest over a much greater bandwidth than the original signal.

The standard data rate of a CDMA call is 9600 bits per

second (9.6 kilobits per second). This initial data is ³spread,´including the application of digital codes to the data bits, up to

the transmitted rate of about 1.23 megabits per second. The data

bits of each call are then transmitted in combination with the

data bits of all of the calls in the cell. At the receiving end, thedigital codes are separated out, leaving only the original

information which was to be communicated. At that point, each

call is once again a unique data stream with a rate of 9600 bits

per second. Traditional uses of spread spectrum are in military

operations. Because of the Wide bandwidth of a spread spectrum

signal, it is very difficult to jam, difficult to interfere with, and

difficult to identify. This is in contrast to technologies using a

narrower bandwidth of frequencies. Since a wideband spread

spectrum signal is very hard to detect, it appears as nothing more

than a slight rise in the ³noise floor´ or interference level. Wit hother technologies, the power of the signal is concentrated in a

narrower band, which makes it easier to detect.

Increased privacy is inherent in CDMA technology. CDMA phone calls will be secure from the casual eavesdropper since,

unlike an. analog conversation, a simple radio receiver will not be able to pick individual digital conversations out of the overall

RF radiation in a

frequency band.

Introduction to Spread Spectrum Communications

CDMA is a form of Direct Sequence Spread Spectrum

communications. In general, Spread Spectrum communications is

distinguished by three key elements:

1. The signal occupies a bandwidth much greater than that

which is necessary to send the information. This results i n

many benefits, such as immunity to interference and

jamming and multi-user access



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2. The bandwidth is spread by means of a code which isindependent of the data. The independence of the code

distinguishes this from standard modulation schemes inwhich the data modulation will always spread the spectrum

somewhat.

3. The receiver synchronizes to the code to recover the data.

The use of an independent code and synchronous

reception allows multiple users to access the same

frequency band at the same time.

In order to protect the signal, the code used is

pseudo-random. It appears random, but is actually

deterministic, so that the receivefcan reconstruct the code

for synchronous detection. This pseudo-random code is

also called pseudo-noise (PN).

Three Types of Spread Spectrum Communications

There are three ways to spread the bandwidth of the signal:y Frequency hopping. The signal is rapidly switched

between different frequencies within the hopping

bandwidth pseudorandomly, and the receiver knows

before hand where to find the signal at any given time.

y Time hopping. The signal is transmitted in short bursts

pseudo-randomly, and the receiver knows beforehand

when to expect the burst.

y Direct sequence. The digital data is directly coded at amuch higher frequency. The code is generat ed pseudo -

randomly, the receiver knows how to generate the samecode, and correlates the received signal with that code to

extract the data.

Direct Sequence Spread Spectrum

CDMA is a Direct Sequence Spread Spectrum system. The

CDMA system works directly on 64 kbit/sec digital signals.

These signals can be digitized voice, ISDN channels, modem

data, etc.

Signal transmission consists of the following steps:

1.

A pseudo-random code is generated, different for eachchannel and each successive connection.

2. The Information data modulates the pseudo-random code

(the Information data is ³spread´).

3. The result ing signal modulates a carrier.

4. The modulated carrier is amplifi ed and broadcast.



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Signal reception consists of the following steps:

1. The carrier is received and amplifi ed.2. The received signal is mixed with a local carrier to

recover the spread digital signal.

3. A pseudo-ra ndom code is generated, matching the

anticipated signal.

4. The receiver acquires the received code and phase

locks its own code to it.

5. The received signal is correlated with the generated

code, extracting the Information data.

The main Problem with Direct Sequence is the Near -Far

effect. If there are more then one users active, the transmitt ed

power of nonreference users is suppressed by a factor dependent

on the (partial) cross correlation between the code of thereference user and the code of a non -ref erence user. However

when a non- reference user is closer to the receiver then th ereference-user, it is possible that the interference caused by this

non-reference user (however suppressed) has more power thereference user. Now only the non-reference user will be received,

this nasty property is called the near -far effect.

One way to beat the near -far effect can be exploit ed in

cellular systems. In such systems the base station takes care that

all users.have such a power that the received power at the base

station is equal for all users.

In non-cellular systems the influence of the near-far effect

can be reduced by using the frequency-hopping spread spectrum

technique.

CDMA uses a form of direct sequence. Direct sequence is,

in essence, multipli cation of a more conventional ommunication

waveform by a pseudonoise (PN) ±1 binary sequence in the

transmitter.



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Spreading takes place prior to any modulation, entirely inthe binary domain, and the transmitted signals are carefully

bandlimited.

A second multiplication by a replica of the same +1

sequence in the receiver recovers the original signal.

The noise and interference, being uncorrelated with the PN

sequence, become noise-like and increase in bandwidth when

they reach the detector. The signal-to- noise ratio can be

enhanced by narrowband filtering that rejects most of the

interference power. The SNR is enhanced by the so-called

processing gain W/R, where W is the spread bandwidth and R is

the data rate.



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CODING

CDMA uses unique spreading codes to spread the basebanddata before transmission. The signal is transmitted in a channel,

which is below noise level. The receiver then uses a correlator to

despread the wanted signal, which is passed through a narrow

bandpass filter. Unwanted signals will not be despread and will

not pass through the filter. Codes take the form of a carefully

designed one/zero sequence produced at a much higher rate thanthat of the baseband data. The rate of a spreading code isreferred to as chip rate rather than bit rate.

Generating Pseudo-Random Codes

For each channel the base station generates a unique code

that changes for every connection. The base station adds together

all the coded transmissions for every subscriber. The subscriber

unit correctly generates its own matching code and uses it toextract the appropriate signals. Note that each subscriber uses

several independent channels.



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In order for all this to occur, the pseudo-random code musthave the following properties:

1. It must be deterministic. The subscriber station must be

able to independently generate the code that matches the

base stat ion code.

2. It must appear ra ndom to a l istener without prior

knowledge of the code (i.e. it has the statistical properties

of sampled white noise).

3. The cross-corr elation bet ween any two codes must b e

small (see below for more information on code

correlation).

4. The code must have a long period (i.e. a long time before

the code repeats itself).

Code Correlation

In this context, correlation has a specific mathematical

meaning. In general the correlation function has these properties:

y It equals 1 if the two codes are identical

y It equals 0 of the two codes have nothing in commony Intermediate values indicate how much the codes have in

common. The more they have in common, the harder it is

for the receiver to extract the appropriate signal. There are

two correlation functions:

y Cross-Correlation: The correlation of two different codes.As we¶ve said, this should be as small as possible.

y Auto-Correlation: The correlation of a code with a time -delayed version of itself. In order to reject multi-path

interference, this function should equal 0 for any time

delay other than zero.

The receiver uses cross-correlation to separate theappropriate signal from signals meant for other receivers, and

auto-correlation to reject multi-path interference.

Pseudo-Noise Spreading

The FEC coded Information data modulates the

pseudorandom code,, : - -

Some terminology related to the pseudo-random code:

y Chipping Frequency (fe): the bit rate of the PN code.

y Information rate (f): the bit rate of the digital data. -

y Chip: One bit of the PN code.

y Epoch: The length of time before the code starts repeating

itself (the period of the code). The epoch must be longer

than the round trip propagation delay (The epoch is on the

order of several seconds).

The bandwidth of a digital signal is twice its bit rate. The



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bandwidth of the combination of the two, information data (f)and the PN code, for fc>fi, can be approximated by the

bandwidt h of the PN code.

System Capacity

The capacity of a system is approximated by

WhereCmax Is the maximum number of simultaneous calls

G p Is the processing gain

E b / No Is the total signal to noise ratio per bit, and

Is the cell interference factor

The capacity is directly proportional to the processing gain. Capacity is also

inversely proportional to the signal to noise ratio of the received signal. So, the

smaller the transmitted signal, the larger the system capacity. Both the RCS

and FSU control the power transmitted by the other so that the received signal

is as small as possible while maintaining a minimum signal to noise ratio. This

maximizes system capacity.



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THE SPREADING PROCESS

WCDMA uses Direct Sequence spreading, where spreading process is done by directly combining the baseband information

to high chip rate binary code. The Spreading Factor is the ratio

of the chips (UMTS = 3. 84Mchips/s) to baseband information

rate. Spreading factors vary from 4 to 512 in FDD UMTS.

Spreading process gain can in expressed in dBs (Spreading factor

128 = 21dB gain).

CDMA spreading



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CDMA BENEFITS

BENEFIT 1: CDMA CAPACITY INCREASES

CDMA anti Cell Reuse

Eb/No and Interference Threshold

Examples of Capacity Improvements

Other influence on Capacity

BENEFIT 2: IMPROVED CALL QUALITY

Advanced Error Detection and! Error Correction Sophisticated Vocoders

Multiple Levels of DiversitySoft Handoff

Precise Power Control

BENEFIT 3: SIMPLIFIED SYSTEM PLANNING

BENEFIT 4: ENHANCED PRIVACY

BENEFIT 5: IMPROVED COVERAGEBENEFIT 6: INCREASED PORTABLE TALKTIMEBENEFIT 7:BANDWIDTH ON DEMAND



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CDMA IMPLEMENTATION

CDMA Channels

CDMA traffic channels are different: they are dependenton the equipment platform. Channels are designated in three

ways-effective traffic channels, actual traffic channels and physical traffic channels.

y The number of ³Effective´ traffic channels includes thetraffic carrying channels less the soft handoff channels.

The capacity of an effective traffic channel is equivalent

to the traffic carrying capacity of an analog traffic

channel.

y The number of ³Actual´ traffic channels includes the

effective traffic channels, plus channels allocated for soft

handoff.

y The number of ³Physical´ traffic channels includes thePilot channels, the Sync channels, the Paging channels, the

Soft Handoff Overhead channels and the Effective (voiceand data) traffic channels.

CDMA Forward Channels

Pilot Channel

The pilot channel is used by the mobile unit to obtaininitial system synchronization and to provide time, frequency,

and phase tracking of signals from the cell site.

Sync ChannelThis channel provides cell site identification, pilot

transmit

power, and the cell site pilot pseudo-random (PN) phase offset

information. With this information the mobile units can establish

the System Time as well as the proper transmit power level to

use to initiate a call.

Paging ChannelThe mobile unit will begin monitoring the paging channel

after it has set its timing to the System Time provided by the

sync channel. Once a mobile unit has been paged and

acknowledges that page, call setup and traffic channel

assignment information is then passed on this channel to the

mobile unit.

Forward Traffic ChannelThis channel carries the actual phone call and carries the

voice and mobile power control information from the basestation to the mobile unit.



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CDMA Reverse Channels

Access Channel

When the mobile unit is not active on a traffic channel, it

will communicate to the base station over the access channel.

This communication includes registration requests, responses to

pages, and call originat ions. The access channels are paired w it h

a corresponding paging channel.

Reverse Traffic ChannelThis channel carries the other half of the actual phone call

and carries the voice and mobile power control information fromthe mobile unit to the base station.



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CDMA Modulation

Both the Forward and Reverse Traffic Channels use asimilar control structure consisting of 20 millisecond frames. For

the system, frames can be sent at either 14400, 9600, 7200, 4800,

3600, 2400, 1800, or 1200 bps. For example, with a Traffic

Channel operating at 9600 bps, the rate can vary from frame to

frame, and can be 9600, 4800, 2400, or 1200 bps. The receiver

detects the rate of the frame and processes it at the correct rate.This technique allows the channel rate to dynamically adapt tothe speech or data activit y. For speech, when a talker pauses, the

transmission rate is reduced to a low rate. When the talker speaks, the system instantaneously shifts to using a higher

transmission rate. This technique decreases the interference to

other CDMA signals and thus allows an increase in system

capacity. CDMA starts with a basic data rate of 9600 bits per

second. T his is then spread to a transmitted bit rate, or chip rat e

(the transmitted bits are called chips), of 1.2288 MHz. The

spreading process applies digital codes to the data bits, which

increases the data rate while adding redundancy to the system.

The chips are transmitted using a form of QPSK

(quadrature phase shift keying) modulation which has been

filtered to limit the bandwidth of the signal. This is added to the

signal of all the other users in that cell. When the signal is

received, the coding is removed from the desired signal,returning it to a rate of 9600 bps. When the decoding is applied

to the other users¶ codes, there is no despreading; the signalsmaintain the 1.2288 MHz bandwidth. The ratio of transmitted

bits or chips to data bits is the coding gain. The coding gain for the IS-95 CDMA system is 128, or 21 dB.

Input data

CDMA works on Information data from several possible

sources, such as digitized voice or ISDN channels. Dat rates canvary, here are some examples:



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The system works with 64 kBits/sec data, but can acceptinput rates of 8, 16, 32, or 64 kBits/sec. Inputs of less than 64

kBits/sec are padded with extra bits to bring them up to 64kBits/sec. For inputs of 8, 16, 32, or 64 kBits/sec, the system

applies Forward Error Correction (FEC) coding, which doubles

the bit rate, up to 128 kbits/sec. The Complex Modulation

scheme (which we¶ll discuss in more detail later), transmits two

bits at a time, in two bit symbols. For inputs of less than 64

kbits/sec, each symbol is repeated to bring the transmission rate

up to 64 kilosymbols/sec. Each component of the complex signal

carries one bit of the two bit symbol, at 64 kBits/sec, as shown

below



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Transmitting Data

The resultant coded signal next modulates an RF carrier

for transmission using Quadrature Phase Shift Keying (QPSK).

QPSK uses four different states to encode each symbol. The four

states are phase shifts of the carrier spaced 90_ apart. By

convention, the phase shifts are 45, 135, 225, and 315 degrees.

Since there are four possible states used to encode binary

information, each state represents two bits. This two bit ³word´

is called a symbol.

Receiving Data

The receiver performs the following steps to extract the

Information:

Demodulation

Code acquisition and lock

Correlation of code with signal

Decoding of Information data

Demodulation

The receiver generates two reference waves, a Cosine wave

and a Sine wave. Separately mixing each with the received

carrier, the receiver extracts 1(t) and Q(t). Analog to Digital

converters restore the 8-bit words representing the I and Q chips.

Code Acquisition and Lock

The receiver, as described earlier, generates its owncomplex PN code that matches the code generated by the

transmitter. However, the local code must be phase- locked tothe encoded data.

Correlation and Data Despreading

Once the PN code is phase-locked to the pilot, the received

signal is sent to a correlator that multiplies it with the complex

PN code, extracting the I and Q data meant for that receiver. The

receiver reconstructs the Information data from the I and Q data.

Automatic Power Control

The RCS gets bombarded by signals from many FSUs.

Some of these FSUs are close and their signals are much stronger

than FSUs farther away. This results in the Near/Far problem

inherent in CDMA communications. System .Capacity is also

dependant on signal power. For these reasons, both the RCS andFSU measure the received power and send signals to control the

other¶s transmit power



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Receiving an Incoming Call in CDMA

y All idle mobiles monitor the paging channel to receiveincoming calls.

y When an incoming call appears, the paging channelnotifies the mobile in a General Page Message.

y A mobile which has been paged sends a Page Response

Message on the access channel.

y The system sets up a traffic channel for the call, thennotifies the mobile to use it with a Channel Assignment

Message.

y The mobile and the base station notice each other¶s trafficchannel signals and confirm their presence by exchanging

acknowledgment messages.

y The base station and the mobile negotiate what type of call

this will be -- I.e., 13k voice, etc.

y The mobile is told to ring and given a ³calling line ID´ to

display.

y When the human user presses the send button, the audio

path is complet ed and the call proceeds.



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cdmaOne: The Family of IS-95 CDMA Technologies

cdmaOne describes a complete wireless system based ontheTIA/EIA IS-95 CDMA standard, including IS-95A and IS-95B

revisions.

It represents the end-to-end wireless system and all the

necessary specifications that govern its operation. cdmaOne

provides a family of related services including cellular, PCS and

fixed wireless (wireless local loop).

CDMA2000: Leads the 3G revolution

CDMA2000 represents a family of ITU-approved, IMT-

2000 (3G) standards and includes CDMA2000 l and CDMA20001xEV technologies. They deliver increased network capacity to

meet growing demand for wireless services and high-speed dataservices. CDMA2000 lx was the world¶s first 3G technology

commercially deployed (October 2000).

CDMA is the fastest growing wireless technology and itwill continue to grow at a faster pace than any other technology.

It is the platform on which 2G and 3G advanced services are

built.



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CONCLUSION

The world is demanding more from wirelesscommunication technologies than ever before. More people

around the world are subscribing to wireless services and

consumers are using their phones more frequently. Add in

exciting Third-Generation (3G) wireless data services and

applications - such as wireless email, web, digital picture

taking/sending and assisted-GPS position location applications -and wireless networks are asked to do much more than just a fewyears ago. And these networks will be asked to do more

tomorrow.

This is where CDMA technology fits in. CDMA

consistently provides better capacity for voice and data

communications than other commercial mobile technologies,

allowing more subscribers to connect at any given time, and it is

the common platform on which 3G technologies are built.

In a world of finite spectrum resources, CDMA enables

many more people to share the airwaves at the same time than doalternative technologies. The CDMA air interface is used in both

2G and 3G networks. 2G CDMA standards are branded cdmaOne

and include IS-95A and IS-95B. CDMA is the foundation for 3G

services: t he two dominant IMT-2000 standards, CDMA2000 and

WCDMA, are based on CDMA.



REFERENCE

Wireless Networked Communication - Jay Ranade

Principles of Communication - Taub & Schilling

Principle of Wireless Network - Kaveh Pahlavan

Prashant Krishnamurthi

www.rf.rfglobalnet.com

www.bee.netwww.cas.et.tudelft.nl

www.unstsworld.com

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