Guided By Submitted By

Mr. Hardik Kothari Tejas V. Shah6th I.T.

C.U.SHAH COLLEGE OF ENGG. & TECH.WADHWAN CITY – 363 030

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WADHWAN CITYDIST: SURENDRANAGAR

CERTIFICATE

This is to certify that Mr. Tejas V. Shahis studying in SEM – VI of B.E. Information Technology having Roll No 46 has completed his seminar on the following topic successfully.

Topic Name: CODE DIVISION MULTIPLE ACCESS_____

Staff – Incharge Head of Dept.

(Miss Saroj Bodar)Date: ___________

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ACKNOWLEDGMENT

Here I acknowledged my deep sense of gratitude to our staff members of C.U. SHAH COLLEGE OF ENGG. & TECH. for providing me such opportunities to present seminar on:

“CODE DIVISION MULTIPLE ACCESS”

I also thank to the college library for providing me such magazines & books related to my subject for collecting good information about subject.

I also wish to express my sincere thanks to MR HARDIK KOTHARI who help me for guiding me in all the stage for preparing this seminar. & I also thank to whole I.T. department for assistance and co-operation.

With gratitude,

SHAH TEJAS V.

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CONTENT: PAGE-NO:

1. INTRODUCTION. 012. MAIN TYPES OF CDMA. 043. BIRTH OF CDMA. 054. EVOLUTION OF CDMA. 065. CDMA PRINCIPLE. 076. WORKING OF CDMA. 087. CDMA IMPLEMENTATION. 12

7.1 CDMA CHANNELS7.2 CDMA FORWARD CHANNELS7.3 CDMA REVERSE CHANNELS7.4 CDMA MODULATION

8.7.5 CDMA FOR CELLULAR

15DS-CDMA IN CELLULAR SYSTEMS.8.1 THE OBJECTIVES OF IMT-20008.2 DS-CDMA TECHNIQUE8.3 TRANSMITTER STRUCTURE8.4 RECEIVER STRUCTURE

9.8.5 PROPERTIES OF DS-CDMA

22FEATURES OF CDMA.10. CDMA VS GSM. 2311. ADVANTAGES OF CDMA. 2712. DISADVANTAGES OF CDMA. 29 13.APPLICATION OF CDMA TECHNOLOGY. 3014. CONCLUSION. 3115. BIBLIOGRAPHY. 32

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Generally a fixed amount of frequency spectrum is allocated to a cellular system by the national regulator (e.g. in the United States, the Federal communication commission). Multiple- access techniques are then deployed so that many users can share the available spectrum in an efficient manner. Multiple access systems specify how signals from different sources can be combined efficiently for transmission over a given radio frequency band and then separated at the destination without mutual interference. The three basic multiple access methods currently in use in cellular systems are:

• Frequency division multiple access (FDMA) • Time division multiple access (TDMA) • Code division multiple access (CDMA)

In case of FDMA, users share the available spectrum in the frequency domain, and user is allocated a part of the frequency band called the traffic channel.

In TDMA techniques that are utilized in many digital cellular systems, the available spectrum is partitioned into narrow frequency bands or frequency channels (as in FDMA), which in turn are divided into a number of time slots. An individual user is assigned a time slot that permits access to the frequency channel for the duration of the time slot.

The CDMA system utilizes the spread spectrum technique, whereby a spreading code (called a pseudo-random noise or PN code) is used to allow multiple users to share a block of frequency spectrum. In CDMA cellular systems (e.g. IS-95 in the United States) that use direct sequence spread (DSS) spectrum techniques, the(digital) information from an individual user is modulated by means of the unique PN code (spreading sequence) assigned to each user. All the PN –code-modulated signals from different users are then transmitted over the entire CDMA frequency channel (e.g.,1.23 MHZ in case of IS-95).Since the signal in the case of CDMA utilize the entire allocated block of spectrum, no guard bands of any kind are necessary within the allocated block.

CDMA permits a more uniform distribution of energy in the emitted bandwidth Short for Code Division Multiple Access, a digital cellular technology that uses spread-spectrum techniques. Unlike competing systems, such as GSM that use TDMA, CDMA does not assign a specific frequency to each user. Instead, every channel uses the full available spectrum. Individual conversations are encoded with a pseudo-random digital sequence. The older version of the CDMA technology and now it is now known as cdmaOne as well as IS-95. The other types of CDMA technology has CDMA2000,WCDMA (Wideband CDMA). The spread spectrum may be viewed as a kind of modulation scheme in which the modulated(spread spectrum) signal bandwidth is much greater than the message(baseband) signal bandwidth. Thus, spread spectrum is a wideband scheme.

The final assessment on the potential superiority of CDMA systems over TDMA systems,in terms of capacity,cost, and speech quality,will emerge only after both systems have been in operation in dense,urban areas with full complements of subscribers and services.

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A CDMA system is clearly not a collision avoidance system like FDMA and TDMA. The opposite is true and explains the differences in the behavior of CDMA systems compared to FDMA and TDMA. In general, the collisions at the channel is a disadvantage of CDMA system and can be mitigated by careful selection of the sequence and power control that is close to perfect. CDMA is restricted to a short distance charging area(SDCA). Currently, there are 2600 SDCAs within the country. A CDMA-based phone can thus ‘roam’ only within its SDCA. This is NOT a technological restriction. In India, Reliance Infocom and Tata Indicom use CDMA technology to provide WILL services. In remote rural areas, where installing cables is difficult as well as expensive, CDMA-based WILL networks can be deployed quickly. A CDMA doesn’t have a SIM card, which makes m-commerce difficult.

Daily application possible with CDMA is daily downloading, text communication such as chat,e-mail,sms,member search etc.sending photo on the air,entertainment and games.

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INTRODUCTION

This paper is intended to provide an introduction to CDMA use in wireless telephone systems. The focus is on explaining, in generally non-technical language, both the key aspects of CDMA technology, and the primary benefits the technology offers to wireless communication system operators and their subscribers. There is a tremendous amount of detailed technical information which is intentionally not covered in this forum.

It has been necessary, though, to assume at least a rudimentary familiarity with cellular telephone systems, including the basic characteristics of radio and the RF spectrum, as well as fundamental system design concepts such as frequency re-use.

Motorola welcomes your comments and feedback on this paper.

What is CDMA?

One of the most important concepts to any cellular telephone system is that of "multiple access", meaning that multiple, simultaneous users can be supported. In other words, a large number of users share a common pool of radio channels and any user can gain access to any channel (each user is not always assigned to the same channel). A channel can be thought of as merely a portion of the limited radio resource which is temporary allocated 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.

The CDMA Cellular Standard

With CDMA, unique digital codes, rather than separate RF frequencies or channels, are used to differentiate subscribers. The codes are shared by both the mobile station (cellular phone) and the base station, and are called "pseudo-Random Code Sequences." All users share the same range of radio spectrum.

For cellular telephony, CDMA is a digital multiple access technique specified by the Telecommunications Industry Association (TIA) as "IS-95".

In March 1992, the TIA established the TR-45.5 subcommittee with the charter of developing a spread-spectrum digital cellular standard. In July of 1993, the TIA gave its approval of the CDMA IS-95 standard.

IS-95 systems divide the radio spectrum into carriers which are 1,250 KHz (1.25 MHz) wide. One of the unique aspects of CDMA is that while there are certainly limits to the number of phone calls that can be handled by a carrier, this is not a fixed number. Rather, the capacity of the system will be dependent on a number of different factors. This will be discussed in later sections.

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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 Pseudorandom Noise (PN) sequences. As a result, DS CDMA uses much wider signals than those used in other technologies. Wideband signals reduce interference and allow one-cell frequency reuse.

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

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 "spread 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 "spread," 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, the digital 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 "noise floor" or interference level. With other 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

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be able to pick individual digital conversations out of the overall RF radiation in a frequency band.

Synchronization

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" to the 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 each other, CDMA stations must remain synchronized to a common time reference.

The primary source of the very precise synchronization signals required 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, it provides a readily available method for determining position and time to as many receivers as are required.

The Balancing Act

CDMA cell coverage is dependent upon the way the system is designed. In fact, three primary system characteristics - Coverage, Quality and Capacity - must be balanced off of each other to arrive at the desired level of system performance.

In a CDMA system these three characteristics are tightly inter-related. Even higher capacity might be achieved through some degree of degradation in coverage and/or quality. Since these parameters are all intertwined, operators can not have the best of all worlds: three times wider coverage, 40 time capacity, and "CD" quality sound. For example, the 13 kbps vocoder provides better sound quality, but reduces system capacity as compared to an 8 kbps vocoder.

Motorola is using system simulation and real world testing to identify and implement the correct balances in CDMA system application. Operators will have the opportunity to balance these parameters to best serve a particular area. The best balance point may change from cell site to cell site. Sites in dense downtown areas may trade off coverage for increased capacity. Conversely, at the outer edges of a system, capacity could be sacrificed for coverage area.

Motorola's system expertise, as demonstrated by its winning of the 1995 NCSA Industrial Grand Challenge Award for system simulation and testing achievements, is especially beneficial to operators in their efforts to balance system parameters.

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MAIN TYPES OF CDMA

CDMAONE:

This is the older version of the CDMA technology and now it is now known as cdmaone as well as IS-95.

CDMA 2000:

We now have cdma2000 and its variants like 1X EV, 1XEV-DO, and MC 3X. The reffer to variants of usage of a 1.25MHz channel. 3X uses a 5 MHz channel.

This first phase of cdma2000 - variously called 1XRTT, 3G1X, or just plain 1X - is designed to double current voice capacity and support always-on data transmission speeds 10 times faster than typically available today, some 153.6 kbps on both the forward and reverse links.

CDMA2000 Technical Detail:

Frequency band: Any existing band.Minimum frequency band required: 1x: 2x1.25MHz, 3x: 2x3.75Chip rate: 1x: 1.2288, 3x: 3.6864 McpsMaximum user data rate: 1x: 144 kbps now, 307 kbps in the future 1xEV-DO: max 384 kbps - 2.4 Mbps, 1xEV-DV: 4.8 Mbps.

WCDMA:

Wideband CDMA that forms the basis of 3G networks, Developed originally by Qualcomm, CDMA is characterized by high capacity and small cell radius, employing spread-spectrum technology and a special coding scheme. WCDMA uses 5 MHz bandwidth.

CDMA Phones at Glance:

¾ Samsung SCH-N191 ¾ LG RD2030 ¾ LG-Elect-TM910 ¾ LG Electronics TM510

THE Tata Indicom CDMA Mobile Cost Table

Activation Cost Rs.1050Monthly Rental Rs.450Deposit Rs.3,000

HandsetHyundai HGC-310E Rs.9,800Samsung SCH-620 Rs.10,800

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BIRTH OF CDMA

At World War II

CDMA is a military technology first used during World War II by the English allies to foil German attempts at jamming transmissions. The allies decided to transmit over several frequencies, instead of one, making it difficult for the Germans to pick up the complete signal.

History Of CDMA

Somewhere close to the Second World War, Hollywood actress-turned-inventor, Hedy Lamarr and co -inventor George Antheil, co-patented a way for controlling torpedoes by sending signals over multiple radio frequencies using random patterns. They called this “frequency hopping”.

After some hue and cry, the US Navy discarded their work as architecturally unfeasible. In 1957, Sylvania Electronic System Division, in Buffalo, New York , took up the same idea. After the expiry of the inventor’s patent, they used the same technology to secure communications for the US military.

In the mid-80s, the US military declassified what is now called CDMA technology, a technique based on spread-spectrum technology, for use in wireless communication. The spread-spectrum technology works by digitizing multiple conversations, attaching a code(known only to the sender and receiver), and then breaking the signals into bits and reassembling them.

Qualcomm, which patented CDMA, and other telecommunication companies, were attrached to the technology because it enabled many simultaneous conversations, rather than the limited stop-and-go transmissions of analogue technology and the previous digital option.

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EVOLUTION OF CDMA

1940s and 1950s Spread Spectrum technique for military anti-jam applications. 1949 Claude Shannon and Robert Pierce develop basic ideas of CDMA1970s Several CDMA developments for military systems (e. g. GPS)

In March 1992, the TIA (Telecommunications Industry Association) established the TR-45.5 subcommittee with the charter of developing a spread spectrum digital cellular standard. In July of 1993, the TIA gave its approval for the CDMA Technology standard.

1993 IS-95 CDMA standard finalized1995 Commercial operation of N-CDMA system (IS-95) in Hong Kong/KoreaOctober 1, 2000 SK Telecom of Korea launches the first commercial cdma2000 network April 17, 2001 Ericsson and Vodafone UK claim to have made the world's first WCDMA voice call over commercial network.October 1, 2001 NTT DoCoMo launched the first commercial WCDMA 3G mobile network. January 28, 2002 SK Telecom in Korea launched the world's first commercial CDMA2000 1xEV-DO.October 1, 2002 Qualcomm announces world's first Bluetooth WCDMA (UMTS) and GSM Voice Calls.

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CDMA PRINCIPLE

If we change our communication topology from point-to-point to point-to-multipoint, we have hanged the communication environment from single-link to a multiple-access link. The multiple-access scheme in a spread-spectrum system is termed code-division multiple-access (CDMA).

Each access to a common channel needs some form of orthogonality. For frequency-division multiple-access (FDMA), we achieve orthogonality in the frequency domain by selecting nonoverlapping unique frequency bands to each user. We achieve orthogonality in the time domain by selection nonoverlapping unique time segments to each user; this process is referred to as time- division multiple -access (TDMA). The spread-spectrum form of multiple access exploits the orthogonality in the code domain and is termed code-division multiple-access (CDMA).

The multiuser environment in the spread- spectrum case is set up for each user in assigning each user a unique spreading sequence out of a family of orthogonal sequences. Each user in a CDMA network occupies the same channel bandwidth.

A CDMA system is clearly not a collision avoidance system like FDMA and TDMA. The opposite is true and explains the differences in the behavior of CDMA systems compared to FDMA and TDMA. In general, the collisions at the channel is a disadvantage of CDMA system and can be mitigated by careful selection of the sequence and power control that is close to perfect.

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WORKING OF CDMA

The CDMA uses the spread spectrum technology. The spread spectrum refers to any system that satisfies the following conditions :

1. The spread spectrum may be viewed as a kind of modulation scheme in which the modulated(spread spectrum) signal bandwidth is much greater than the message(baseband) signal bandwidth. Thus, spread spectrum is a wideband scheme.

2.The spectral spreading is performed by a code that is independent of the message signal. This same ode is also used at the receiver to despread the received signal in order to recover the message signal (from spread spectrum signal). In secure communication, this code is known only to the person(s) for whom the message is intended.

The spread spectrum increases the bandwidth of the message signal by a factor N, called the processing gain. If the message signal bandwidth is B Hz and the corresponding spread spectrum signal bandwidth is Bss Hz, then Processing gain N = Bss / B

Thus, the key to CDMA is to be able to extract the desired signal while rejecting everything else as random noise. A somewhat simplified description of CDMA follows:

In CDMA each bit time is subdivided into m short intervals called chips. Typically, there are 64 or 128 chips per bit, but in the example given below we will use 8 chips/bit for simplicity.

Each station is assigned a unique m-bit code or chip sequence. To transmit a 1 bit, a station sends its chip sequence. To transmit a 0 bit, it sends the one’s complement of its chip sequence. No other patterns are permitted. Thus for m = 8, if a station A is assigned the chip sequence 00011011, it sends a 1 bit by sending 00011011 and 0 bit by sending 11100100.

If we have 1-MHz band available for 100 stations, with FDM each one would have 10 kHz and could send at 10 kbps (assuming 1 bit per Hz). With CDMA, each station uses the full 1 MHz, so the chip rate is 1 Megachip per second. With fewer than 100 chips per bit, the effective bandwidth per station is higher for CDMA than FDMA, and the channel allocation problem is also solved.

It is more convenient to use a bipolar notation, with binary 0 being –1 and binary 1 being +1. We will show chip sequences in parentheses, so a 1 bit for station A now becomes (-1-1-1+1+1-1+1+1). In Fig. (1), we show the binary chip sequence assigned to four example stations. In Fig. (2), we show them in our bipolar notation.

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A: 0 0 0 1 1 0 1 1 A: (-1-1-1+1+1-1+1+1)B: 0 0 1 0 1 1 1 0 B: (-1-1+1-1+1+1+1-1)C: 0 1 0 1 1 1 0 0 C: (-1+1-1+1+1+1-1-1)D: 0 1 0 0 0 0 1 0 D: (-1+1-1-1-1-1+1-1)

Fig. (1)Binary chip Fig. (2)Bipolar chip sequenceSequence for 4 stations

Six Examples:

_ _1_ C S1= ( -1 +1 –1 +1 +1 +1 –1 -1)_ 11_ B+C S2= ( -2 0 0 0 +2 +2 0 -2)1 0_ _ A+B S3= ( 0 0 –2 +2 0 -2 0 +2)1 0 1 _ A+B+C S4= ( -1 +1 –3 +3 –1 –1 –1 +1)1 1 1 1 A+B+C+D S5= ( -4 0 -2 0 +2 0 +2 -2)1 1 0 1 A+B+C+D S6= ( -2 –2 0 –2 0 –2 +4 0 )

Fig. (3) Six example of Transmission

S1C = (1+1+1+1+1+1+1+1)/8 = 1S2C = (2+0+0+0+2+2+0+2)/8 = 1S3C = (0+0+2+2+0-2+0-2)/8 = 0S4C = (1+1+3+3+1-1+1-1)/8 = 1S5C = (4+0+2+0+2+0-2+2)/8 = 1S6C = (2-2+0-2+0-2-4+0)/8 = -1

Fig. (4) Recovery of station C’s signal

Each station has its own unique chip sequence. Let’s use symbol S to indicate the m-chip vector for station S , and S for its negation. All chip sequences are pairwise orthogonal, by which we mean that the normalized inner product of any two distinct chip sequences, S and T (ST) is 0. In mathematical terms,

mST = 1/m ∑ Si * Ti = 0

i=1

in plain, English, as many pairs are same as are different. This orthogonality property will prove crucial. Note that if ST = 0 then ST= 0. The normalized inner product of any chip sequence with itself is 1:

m mSS = 1/m ∑ Si * Si = 1/m ∑(+1)²=1

i=1 i=1

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This follows because each of the m terms in the inner product is 1, so the sum is m. Also note

that SS = -1.

During each bit time, a station can transmit a 1 by sending its chip sequence, it can transmit a 0 by sending negative of its chip sequence, or it can be silent and transmit nothing. For the moment, we assume that all stations are synchronized in time, so all chip sequence begin at the same instant.

When two or more station transmit simultaneously, their bipolar signals add linearly. For example, if in one chip period three stations output +1 and one station outputs –1, the result is +2. One can think of this as adding voltages: three stations outputting +1 volts and 1 station outputting –1 volts gives 2 volts.

In Fig.(3), we see six examples of one or more stations transmitting at the same time. In the first example, C transmits a 1 bit, so we just get C’s chip sequence. In the second example, both B and C transmit 1 bits, so we get the sum of their bipolar chip sequences.

In the third example, station A sends 1 and station B sends a 0. The others are silent. In the fifth example, all four stations sends 1 bit. Finally, in the last example A, B, and D sends a 1 bit, while C sends a 0 bit. Note that each of the six sequences S1 through S6 given in Fig. (3) represents only one bit time.

To recover the bit stream of an individual station, the receiver must know that station’s chip sequence in advance. It does the recovery by computing the normalized inner product of the received chip sequence (the linear sum of all the stations that transmitted) and the chip sequence of the station whose bit stream it is trying to recover. If the received chip sequence is S and the receiver is trying to listen to a station whose chip sequence is C, it just computes the normalized inner product, SC.

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To see why this works, imagine the two stations, A and C, both transmit a 1 bit at the same time that B transmit a 0 bit. The receiver sees the sum: S = A+B+C and computes

SC = AC+ BC+ CC =0+0+1 = 1

The first two terms vanish because all pairs of chip sequence have been carefully chosen to be orthogonal. Now it should be clear why this property must be imposed on the chip sequence.

To make the decoding process more concrete, let us consider the six examples of fig.(4) again. Suppose that the receiver is interested in extracting the bit sent by station C from each of the six sums S1 through S6. It calculates the bit by summing the pairwise products of the received S and C vector of Fig.(2), and then taking 1/8 of the result (since m=8 here). As shown, each time the correct bit is decoded.

Assumptions in the above Example:

First, we assumed that all the chips are synchronized in time. In reality, doing so is impossible. What can be done is that the sender and receiver synchronize by having the sender transmit a long enough known chip sequence that the receiver can lock onto. All other (unsynchronized) transmissions are then seen as random noise.

An implicit assumption in the above example is that the power levels of all stations are the same as perceived by the receiver. CDMA is typically used for wireless systems with a fixed base station and many mobile stations at varying distances from it. The power levels received at the base station depends on how far away the transmitters are. A good heuristic here is for each mobile station to transmit to the base station at the inverse of the power level it receives from the base station, so a mobile station receiving a weak signal from the base will use more power than one getting a strong signal. The base station can also give explicit commands to the mobile stations to increase or decrease their transmission power.

We have also assumed that the receiver knows who the sender is. In principle, given enough computing capacity, the receiver can listen to all the senders at once by running the decoding algorithm for each of them in parallel. In real life, suffice it to say that this is easier than done.

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CDMA IMPLEMENTATION

CDMA Channels

Just when one grasps an understanding of the CDMA carrier which is 1.25 MHz wide, someone talks about "traffic channels" and confuses the issue. The fact is that with CDMA, the path by which voice or data passes is the entire carrier, as described previously.CDMA traffic channels are different: they are dependent on the equipment platform, such as Motorola's SC™ products, on which the CDMA is implemented. Motorola designates channels in three ways: effective traffic channels, actual traffic channels and physical traffic channels.

• The number of "Effective" traffic channels includes the traffic 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.

• The number of "Actual" traffic channels includes the effective traffic channels, plus

channels allocated for soft handoff.

• The number of "Physical" traffic channels includes the Pilot channels, the Sync channels, the Paging channels, the Soft Handoff Overhead channels and the Effective (voice and data) traffic channels.

CDMA uses the terms "forward" and "reverse" channels just like they are used in analog systems. Base transmit equates to the forward direction, and base receive is the reverse direction. ("Forward" is what the subscriber hears and "reverse" is what the subscriber speaks.)

CDMA Forward Channels

Pilot Channel

The pilot channel is used by the mobile unit to obtain initial system synchronization and to provide time, frequency, and phase tracking of signals from the cell site.

Sync Channel

This 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.

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Paging Channel

The 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 Channel

This channel carries the actual phone call and carries the voice and mobile power control information from the base station to the mobile unit.

CDMA Reverse ChannelsAccess 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 originations. The access channels are paired with a corresponding paging channel.

Reverse Traffic Channel

This channel carries the other half of the actual phone call and carries the voice and mobile power control information from the mobile unit to the base station.

CDMA Modulation

Both the Forward and Reverse Traffic Channels use a similar 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 to the speech or data activity. 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.

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CDMA starts with a basic data rate of 9600 bits per second. This is then spread to a transmitted bit rate, or chip rate (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 signals maintain 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.

CDMA for Cellular

When implemented in a cellular telephone system, CDMA technology offers numerous benefits to the cellular operator and their subscribers. These can be summarized as follows:

• Capacity increases: 8 to 10 times that of an AMPS analog system, and 4 to 5 times that

of a GSM system.

• Improved call quality: CDMA will provide better and more consistent sound as compared to AMPS. Cellular telephone systems using CDMA should be able to provide

higher quality sound and phone calls than systems based on other technologies.

• Simplified system planning: Engineers will no longer have to perform the detailed

frequency planning which is necessary in analog and TDMA systems.

• Enhanced privacy: Increased privacy over other cellular systems, both analog and

digital, is inherent in CDMA technology.

• Increased talk time and standby time for portables: Because of precise power control and other system characteristics, CDMA subscriber units normally transmit at only a fraction of the power of analog and TDMA phones

• Advanced Features: These include Multiple/High Quality Vocoders, Short Messaging

Services, Over-the-Air -Activation, Sleep Mode, and Data/Fax.

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DS-CDMA IN CELLULAR SYSTEMS

Originally, CDMA technique was employed in military applications. The purpose was to counteract intentional jamming. At 1980s, Qualcomm investigated the applicability of DS-CDMA on cellular communications. Finally, they introduced the narrowband CDMA IS-95 standard in 1993 in which year also the commercial operation started. Since 1990, wideband CDMA techniques have been studied and CDMA based cellular systems are now in use in USA and Korea and will hopefully start in Turkey by 2005. These third generation cellular systems known as IMT-2000 (International Mobile Telecommunications System 2000) in USA and UMTS (Universal Mobile Telecommunications System) in Europe will bring many superior services as compared to narrowband systems such as GSM.

Wideband cellular systems have many objectives to achieve which will be summarized next.

The objectives of IMT-2000

1. Obtaining higher bit rates as:

• Full coverage and mobility for 144kbps (ISDN Basic Rate), preferably 384kbps (ISDN Primary Rate)

• Limited coverage and mobility for 2Mbps

Hovewer market demand will determine the actual data rates. Figure 5 shows the data rates, different cellular systems offer at different mobility levels.

Figure 5 Data rates of different cellular systems

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More flexibility to introduce new services2. Simultaneous multiple services for one user 3. Services with different Qos. 4. High spectrum efficiency

DS-CDMA Technique

System Model

We will start with explaining how the CDMA system serves multiple users.Suppose there are N transmission sources which share the common air interface. Any of these sources ,say source i, intends to send narrowband information Sni. Sni in Figure 6 represents the narrowband signal. A spreading operation εi() turns the narrowband signal at point a into a wideband signal at point b which is the antenna output of the transmitter. In the channel, the wideband signal Swi is mixed with the other N-1 wideband signals and also with noise. A despreading operation εi() at the receiver turns the wideband information Swi into narrowband signal Sni and keeps the other wideband signals still wideband. The portion of these wideband signals’ spectrum and noise spectrum in the information bandwidth adds up as interference toSni.

SwSni

aεi( )

bchannel

cinv{εi ( )} =εi( ) d

n(t) i(t)

Figure 6: System model of spread spectrum CDMA communication

In the channel, all the wideband signals make the total wideband signal ∑ Swk k

∑ Swk = ∑ εk(Snk), k : kth user in the same frequency bandk k εk : spreading operation of user k.

In the receiver, the despreading operation is done :

εi-1(∑ Swk) = Sni + ∑ Swikk k,k≠i

Bandpass filtering F turns this equation into F(εi-1(∑ Swk)) = Sni + ∑ Srik

k k,k≠i

As a result the original signal Sni is reproduced.There is also an additional low-level interference component ∑ Srik.

k,k≠i

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Transmitter Structure

The transmitter is made up of a spreading module (multiplier) and a modulator. A transmitter block diagram is shown in Figure 7. The source data Sn(t) is a bipolar signal having a value ± 1 during one bit period Tb. It is multiplied with a higher frequency spreading signal C(t) which is also a bipolar signal with a value ± 1. C(t) has a period Tc which is called chip period.Tc is typically much smaller than Tb.

An example spreading operation is shown in Figure 8. The output signal is Sc(t) . Tb is a multiple of Tc. The multiplication factor is in fact the code length. In this example the code length is 12.

Sc(t) is a wideband signal whereas the original signal Sn(t) is a narrowband signal. From Figure 8 we understand that the bandwidth of Sc(t) is determined by C(t) but not Sn(t). Therefore, the more the multiplication factor Tb/Tc, the more the bandwidth Sc(t) has Sc(t) is fed to a modulator. The modulator can be any type such as BPSK, QPSK, MSK modulator. This modulator moves the baseband signal to a high frequency band.

SpreadingSc(t)

Data Modulator(BPSK,QPSK,M

Bipolar Data SK,...)Sw(t)Sn(t)

C(t) = +-1

CarrierGenerator

Figure 3 : Spread Spectrum Transmitter Block DiagramTb

Sn(t) Tc

1 1 -1 1 -1 1 1 1 -1 1 1 -1 C(t)

Sc(t)

Figure 8 : Spreading operation at the transmitter side

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Receiver Structure

The receiver does the reverse of what the transmitter does. It despreads and demodulates the received signal.It should also have a synchronization block. A receiver block diagram is shown in Figure 9.

At the output of the receiver the sum of original source signal Sn(t),low-correlation interference signal and noise is obtained.

r(t)Despreading

Data

C(t) = +-1DeModulator

Sn(t) + I(t)+n(t)

Code CodeSynch/Tracking Generator Carrier

Generator

Figure 9: Spread Spectrum Receiver Block Diagram

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Properties of DS-CDMA

Multiple Access Capability

If there are multiple users in the channel, then there will be many DS signals overlapping in both time and frequency. Provided that crosscorrelations between the code of the desired user and others’ are small, the interfering power at the receiver output will be much smaller than the desired information power.

An example of multiple access capability under the light of the previously described DS-CDMA technique is shown in Figure 10.

Snini(f)

f

1 . Source Output :Source output signal Sni(t) is a narrowband signal. PSD of Sni(t) occupies a BW Bi .

Sww(f)

f

3. In the channel :The wideband signal Swi(t) is mixed with other users’ wideband signals in the channel.

Swiwi(f)

f

2. After Spreading:The signal occupies a much higher bandwidth after it is spread. Its PSD is as small.

Snini(f)+ Sii(f)

fBi

4. After despreading :Despreading recovers the desired narrowband signal. Other rejected wideband signals interfere only in the information band Bi.

Figure 10 : An Example Multiple Access Capability Representation in Frequency Domain

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Antijamming Capability in Case of Narrowband Interference

If there is an intensive narrowband jammer in the channel, this is rejected by the receiver despreading block. As the name implies, the despreading block turns the wideband desired user data into narrowband form. However,since the despreading operation, which is in fact the multiplication, is exactly the same as the spreading operation, it spreads the narrowband jammer data. Consequently the effect of the jammer data is reduced. This antijamming capability of CDMA is shown in Figure 11.

InIn the channel :In the channel exists the widebanduser data and the intentional

Sw narrowband jammer data. As seen ,the jammer is able to distort only asmall portion of user spectrum.

f

SnAfter despreading:

-1 -1Despreading : ε (Sw+In) =ε (Sw) +ε(In)

= Sn + IwAfter despreading narrowband desired user

Iw signal and a wideband jammer signal isobtained.

fBw

Sn + Iwr

Bn

After Bandpass Filtering :Filtering : F(Sn+Iw) = Sn + IwrOnly a small portion of the interfering signal power passes the filter. The ratio of the overall jammer power to the effective jammer power can be found as Gp=Bw/Bn. This is called the processing gain.

f

Figure 11 : Antijamming Capability in Case of Narrowband Interference

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The processing gain Gp is a measure of how much the interfering signal is suppressed. If the level of interference is too high, the scheme shown in Figure 11 may not be enough to suppress the effect of interfering signal. In this case, preliminary bandstop filtering operation should be applied before despreading. This is possible, if the narrow frequency band of interfering signal is known by the receiving end. Unfortunately, when this filtering is applied, the desired user signal in this band is also lost. This can be tolerated if the ratio of this frequency band to the total wideband user frequency band is less than 1/5.

In the past prefiltering was mostly used in military applications, it is also used in CDMA overlay type networks. In these networks, CDMA signals coexist with the narrowband signals. The high level narrowband signals are suppressed at the receiver by prefiltering and spreading.

Multipath Interference Rejection

Ideally a good code sequence should have the following properties:

� Almost zero cross- correlation with the other codes. This is the golden key of the CDMA system that we based all our claims while discussing multi access capability and narrowband interference rejection.

• A good autocorrelation property which means that the code sequence should have an autocorrelation of zero outside the interval [-Tc,Tc] where Tc is the chip duration.

If the second property is satified, then the receiver treats the incoming different path signals which are delayed more than 2Tc as interfering signals and rejects them.

Low Probability of Interception

Since the DS-CDMA system utilizes a wide spectrum with low PSD at the levels of noise floor, it is difficult to detect DS signal.

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FEATURES OF CDMA

CDMA and WiLL

For many years now, India has been a GSM subscriber. In 1999, when MTNL decided to provide the CDMA-based WiLL(Wireless in Local Loop) service in India, quite a few eyebrows were raised. The biggest reason why mobile operators opposed the entry of WiLL is that it is uncertain to allow mobility in the local loop.

CDMA is restricted to a short distance charging area(SDCA). Currently, there are 2600 SDCAs within the country. A CDMA-based phone can thus ‘roam’ only within its SDCA. This is NOT a technological restriction.

In India, Reliance Infocom and Tata Indicom use CDMA technology to provide WiLL services. In remote rural areas, where installing cables is difficult as well as expensive, CDMA-based WiLL networks can be deployed quickly.

3G (3rd Generation)

3G, as it is popularly called, refers to the 3rd generation of wireless networks. The 3 rd

generation provides higher frequency bands (of 2Ghz and more) and a bandwidth of around 5 MHz. The Bandwidth and frequency is matched by speeds of 384 Kbps in a mobile environment.

Will CDMA be the path towards 3G” The world seems to be divided on this. While the standard choosen by Reliance-CDMA2000 1x-is the 3G avatar of CDMA, the restrictions imposed by the TRAI(Telecom Regulatory Authority of India) doesn’t let it explore the 3G realms. Plus, some Wide CDMA supporters(W-CDMA) aren’t helping the situation by claiming CDMA 1x is not 3G. Third-generation applications includes WCDMA, 1x and High Data Rate (HDR).

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CDMA Vs GSM (The Old Horse)

In India, clutching a cell phone is still sometimes a status symbol. And if the phone uses technology that is said to be far superior to the one used in America, well, that calls for a celebration. That is how it was with GSM technology. But just as the drinks were being served, Reliance entered the party, bringing with it ‘outclassed technology’. Suddenly, the phones stopped ringing. Because the ‘outclassed technology’ had become ‘the’ technology. The same people who had said CDMA had no takers were suddenly fascinated with it. What happened? Why did GSM lose its appeal? Or, did it?

The Basics

Let’s begin by learning what these two acronyms stand for. TDMA stands for "Time Division Multiple Access", while CDMA stands for "Code Division Multiple Access". Three of the four words in each acronym are identical, since each technology essentially achieves the same goal, but by using different methods. Each strives to better utilize the radio spectrum by allowing multiple users to share the same physical channel. You heard that right. More than one person can carry on a conversation on the same frequency without causing interference. This is the magic of digital technology.

Where the two competing technologies differ is in the manner in which users share the common resource. TDMA does it by chopping up the channel into sequential time slices. Each user of the channel takes turns transmitting and receiving in a round-robin fashion. In reality, only one person is actually using the channel at any given moment, but he only uses it for short bursts. He then gives up the channel momentarily to allow the other users to have their turn. This is very similar to how a computer with just one processor can seem to run multiple applications simultaneously.

CDMA on he hand really does let everyone transmit at the same time. Conventional wisdom would lead you to believe that this is simply not possible. Using conventional modulation techniques, it most certainly is impossible. What makes CDMA work is a special type of digital modulation called "Spread Spectrum". This form of modulation takes the user's stream of bits and splatters them across a very wide channel in a pseudo-random fashion. The "pseudo" part is very important here, since the receiver must be able to undo the randomization in order to collect the bits together in a coherent order. If you are still having trouble understanding the differences though, perhaps this analogy will help you. This my own version of an excellent analogy provided by Qualcomm:

Imagine a room full of people, all trying to carry on one-on-one conversations. In VDMA each couple takes turns talking. They keep their turns short by saying only one sentence at a time. As there is never more than one person speaking in the room at any given moment, no one has to worry about being heard over the background din. In CDMA, each couple talk at the same time, but they all use a different language. Because none of the listeners understand

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any language other than that of the individual to whom they are listening, the background din doesn't cause any real problems.

Voice Encoding

At this point many people confuse two distinctly different issues involved in the transmission of digital audio. The first is the WAY in which the stream of bits is delivered from one end to the other. This part of the "air interface" is what makes one technology different from another. The second is the compression algorithm used to squeeze the audio into as small a stream of bits as possible.

This latter component is known at the "Voice Coder", or Vocoder for short. Another term commonly used is CODEC, which is a similar word to modem. It combines the terms "COder" and "DECoder". Although each technology has chosen their own unique CODECs, there is no rule saying that one transmission method needs to use a specific CODEC. People often lump a technology's transmission method with its CODEC as though they were single entities. We will discuss CODECs in greater detail later on in this article.

Voice encoding schemes differ slightly in their approach to the problem. Because of this, certain types of human voice work better with some CODECs than they do with others. The point to remember is that all PCS CODECs are compromises of some sort. Since human voices have such a fantastic range of pitch and tonal depth, one cannot expect any single compromise to handle each one equally well. This inability to cope with all types of voice at the same level does lead some people to choose one technology over another.

All of the PCS technologies try to minimize battery consumption during calls by keeping the transmission of unnecessary data to a minimum. The phone decides whether or not you are presently speaking, or if the sound it hears is just background noise. If the phone determines that there is no intelligent data to transmit, it blanks the audio and reduces the transmitter duty cycle (in the case of TDMA) or the number of transmitted bits (in the case of CDMA). When the audio is blanked, your caller would suddenly find themselves listening to "dead air", and this may cause them to think the call has dropped.

To avoid this psychological problem, many service providers insert what is known as "Comfort Noise" during the blanked periods. Comfort Noise is synthesized white noise that tries to mimic the volume and structure of the real background noise. This fake background noise assures the caller that the connection is alive and well.

However, in newer CODECs such as EVRC (used exclusively on CDMA systems), background noise is generally suppressed even while the user is talking. This piece of magic makes it sound as though the cell phone user is not in a noisy environment at all. Under these conditions, Comfort Noise is neither necessary, nor desirable. You can read my article on EVRC by clicking here.

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Spectral Efficiency

Channel capacity in a TDMA system is fixed and indisputable. Each channel carries a finite number of "slots", and you can never accommodate a new caller once each of those slots is filled. Spectral efficiency varies from one technology to another, but computing a precise number is still a contentious issue. For example, GSM provides 8 slots in a channel 200 kHz wide, while IS-136 provides 3 slots in a channel only 30 kHz wide. GSM therefore consumes 25 kHz per user, while IS-136 consumes only 10 kHz per user.

One would be sorely tempted to proclaim that IS-136 has 2.5 times the capacity of GSM. In a one-cell system this is certainly true, but once we start deploying multiple cells and channel reuse, the situation becomes more complex. Due to GSM's better error management and frequency hopping, the interference of a co-channel site is greatly reduced. This allows frequencies to be reused at closer range without a degradation in the overall quality of the service.

Capacity is measured in "calls per cell per MHz". An IS-136 system using N=7 reuse (this means you have 7 different sets of frequencies to spread out around town) the figure is 7.0. In GSM we get figures of 5.0 for N=4 and 6.6 for N=3. It was hoped that IS-136 could use tighter reuse than N=7, but its inability to cope with interference made this impossible.

Computing this figure for CDMA requires that certain assumptions are made. Formulas have been devised, and using very optimistic assumptions, CDMA can provide a whopping 45 users per cell per MHz. However, when using more pessimistic (and perhaps more realistic) assumptions, the value is 12. That still gives CDMA an almost 2:1 advantage over the TDMA competition.

In-building Coverage

Now let's deal with another issue involving CDMA and TDMA. In-building coverage is something that many people talk about, but few people properly understand. Although CDMA has a slight edge in this department, due to a marginally greater tolerance for weak signals, all the technologies fair about the same. This is because the few dB advantage CDMA has is often "used up" when the provider detunes the sites to take advantage of this process gain.

Buildings come in many configurations, but the most important aspect to their construction is the materials used. Steel frame buildings, or those with metal siding, shield their interiors more thoroughly than building made of wood. Large window openings allow signals to penetrate more deeply into buildings, so malls with glass roofs will generally provide better service than fully enclosed ones. More important than the type of building however, is the proximity of the nearest site. When a site is located just outside a building, it can penetrate just about any building material. When a site is much further away however, the signals have a much harder time of getting past the walls of a structure when it comes to distance, remember that signals are subject to the "distance squared law". This means that signals decrease by the square of the distance. A site at 0.25 kilometers away will have 4 times the signal strength of a

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site at 0.50 kilometers away, and 16 times that of a site 1.0 kilometers away. Distance squared however, is the rate of signal reduction in free space.

Recent studies have shown that terrestrial communications are usually subject to rates as high as "Distance cubed", or even "Distance to the 4th". If the latter is true, then a site 1.0 kilometers away will actually be 256 times weaker than a site 0.25 kilometers away.

In-building penetration is therefore less a technology issue than it is an implementation issue. Service providers who have sites close to the buildings you commonly visit will inevitably look better those who don't. Never use someone else's in-building experiences unless you expect to go in the same buildings as they do. You cannot make useful generalizations about in-building coverage based upon one person's experience.

CDMA does however have one peculiarity concerning in-building penetration that does not affect TDMA. When the number of users on a channel goes up, the general level of signal pollution goes up in tandem. To compensate for this the CDMA system directs each phone to transmit with slightly more power. However, if a phone is already at its limit (such as might be the case inside a building) it cannot do anything to "keep up with the pack". This condition is known as "the shrinking coverage phenomenon" or "site breathing". During slow periods of the day you might find coverage inside a specific building quite good. During rush hour however, you might find it exceedingly poor (or non-existent).

Some Final Observations

CDMA really comes into its element when you are out in the countryside with few sites covering large expanses of land. Under these conditions CDMA provides extremely stable audio with few frame errors to mess things up. This is because Channel Pollution is almost unknown in these situations. Under similar conditions TDMA suffers too readily from interference and it will often blank the audio. Many people who use CDMA systems in sparsely populated areas have given this technology extremely high marks.

TDMA systems also have great difficulties in open regions just outside densely populated areas. In this situation your phone is exposed to signals coming from countless sites in the densely populated areas, but there are no dominant signals from a close-by site. CDMA can suffer under these conditions too (due to channel pollution), but not quite so badly. Valleys don't present a big problem for TDMA, but high ground is a killer. You can experience choppiness in the audio even when your signal indicator is reading 2 or 3 bars.

So in the end, can we really proclaim a winner in the CDMA Vs TDMA war? For the time being I think not. Perhaps in the future when newer technologies built around the W- CDMA standard (wideband CDMA) come into existence, the issue will warrant another look. By that time, even GSM will have moved to CDMA as its air interface of choice, but don't let that fool you into believing that they think the current TDMA air interface is inadequate for its purpose. Future standards are being built around high speed data.

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ADVANTAGES OF CDMA

♦No SIM card is required.

♦Improved call quality: CDMA provides better and more consistent sound quality than systems based on other technologies.

♦Enhanced privacy when compared to systems using other technologies.

♦Increased talk time and standby time for mobiles.

♦They are difficult to intercept for an unauthorized person.

♦They are easily hidden. For an unauthorized person, it is difficult to ever detect their presence in many cases.

♦They are resistant to jamming.

♦Capacity increases of 8 to 10 times that of an AMPS Analog system, and 4 to 5 times GSM , because of CDMA’s unique spread spectrum technology.

♦Many users can share the same carrier frequency, and without time-sharing. This means that mobile phone service providers can handle more customers on a CDMA network than on a GSM network.

♦Improved call quality, with better and more consistent sound , CDMA systems use precise power control—that is, the base station sends commands to every mobile phone currently involved in a call, turning down the power on the nearby ones, and increasing the power of those further away. The result is a nice, even noise level across the carrier, with lower overall power levels and no spiky interference.

♦In this civilized atmosphere, each station can easily pick out its own coded data frames, decode them and deliver a clean end result. Dropped calls are minimized by CDMA's unique ability to keep every sector of every cell on the same frequency, so handoffs are "soft" as the mobile phone moves from one area to the next. (There is no hole in the signal as one cell is dropped and another is acquired.)

♦CDMA decoders interpret constant sounds, such as road noise, as having no useful content, and ignore them as much as possible.

♦Simplified system planning through the use of the same frequency in every sector of every cell. Other types of systems (analog, GSM, etc.) need to break up their frequency spectrum allotments so that each cell uses a different frequency. And since no two adjoining cells can use the same frequency, a given cell has to be surrounded by a circle of six other cells, all of which have to be on different frequencies. This translates to frequency re-use of only 1 in 7, and if you change one (by adding a cell for example), the effects ripple through the system.

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♦To an eavesdropper, the call looks like unintelligible noise. CDMA was originallydeveloped by the military for this very reason.

♦CDMA providers have no such planning earaches, since every sector of every cell uses the same frequency. Enhanced Privacy is inherent in the way CDMA works. Each call is spread over the entire 1.25 MHz carrier—much wider bandwidth than is needed for a single call.

♦The data bits used to convey real information are mixed with digital coding that is known only to the base station and the individual mobile phone.

♦Improved coverage characteristics, allowing for the possibility of fewer cell sites This comes from the accurate power control of all mobile phones using the site, and the fact that individual sites don't interfere with each other, since they are all on the same frequency.

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DISADVANTAGES

Collision :

In general, the collisions at the channel is a disadvantage of CDMA system and can be mitigated by careful selection of the sequence and power control that is close to perfect.

Roaming :

Since most countries have chosen the GSM standard, “roaming” on CDMA is limited.

M-commerce :

A CDMA doesn’t have a SIM card, which makes m-commerce difficult.

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APPLICATION OF CDMA TECHNOLOGY

Daily applications possible with CDMA

Daily Downloads :ringers

charactersimages

horoscopes

Real time stock quotes :

of different stock exchanges

Text Communication :

¾ Chat ¾ instant messaging ¾ SMS ¾ e-mail ¾ message board ¾ member search

Sending photos over the air :

MMS messages

Position Location Services :

¾ nevigation assistance ¾ friend finder

Games and Entertainment :

¾ magazine ¾ comic book store

All these services are already being offered in South Korea and Japan.

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CONCLUSION

After these wonderful particulars of CDMA technology I arrive at the conclusion as follows:

Where CDMA scores Where CDMA needs to scores

Where CDMA scores :

¾ Voice Quality :

CDMA reduces background noise and cross talk, ensuring better voice quality, which is further enhanced by the microprocessors inside the phones.

Call Security:

By design, CDMA is more secure against evasdropping.

Talk Time:

A CDMA phone consumes very little power, and has a longer talk time.

Bandwidth:

CDMA 2000 1x offers 144kbps, which makes it capable for multimedia tasks.

Weight:

CDMA phones due to their low-power requirements can do with smaller-sized batteries, which decrease the overall weight of a CDMA phone.

Where CDMA needs to score :

¾ Roaming :

Since most countries have chosen the GSM standard, “roaming” on CDMA is limited.

M-commerce:

A CDMA doesn’t have a SIM card, which makes m-commerce difficult.

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BIBLIOGRAPHY

Reference Books :

1.CRESPO, P.M., HONIG, M.L., and SALEHI, J.A. : “Spread-Time Code- Division

Multiple Access” IEEE Trans. On Commun., vol 43, pp. 2139-2148, June 1995.

2.COMPUTER NETWORKS, 3rd Ed. - By Andrew S. Tanenbaum

3.VITERBI, A.J.: CDMA Principle of Spread Spectrum Communications, Reading ,MA: Addison-Wesley, 1995.

Websites :

www.cdg.or g www.umts.or g www.palowireless.co m www.ieee.or g www.yahoo.co m www.google.co m

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