53673006 Tata Traning Report

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TATA TELESERVICE LTD.

Srinagar.

TRAINING REPORT

2011

PREPARED BY:

Hakim Yasir Ali.



PREFACE

I know the general rule of world that

―reading makes man ready, writing makes man everyday but practice makes man

perfect.‖ Only theoretical knowledge is not enough for a B-tech student. An

industrial training is one in which we have to develop hardware with software

practical knowledge, where we not theoretically analyze the system but also designsoftware and implement the same. The final phase is to test the functionally of

project action. From this subject student can get opportunity of real activities of our

theoretically. Here programming, system is testing and quality checking and control

this documentation the report of industrial training from this documentation we can

understand the hardware and software engineering concept can be implemented to

a real problem.



ACKNOWLEDGEMENT

We would like to express our heartfelt gratitude to TATA TELESERVICES

LIMITED for equipping us with the platform to enhance our skills in the field of

Mobile Communication. The entire team proved to be very accommodating and

cooperative to us without whom the project would not have been accomplished.

We would like to thank Mr. HARMOHINDER for giving us invaluable guidelines

and moral support. He being very enthusiastic and genial gave us orientation and

motivation to gain more hands-on experience and hence get an edge over.

We would also like to thank all our colleagues in Tata Teleservices Ltd. who

provided us their priceless time and companionship during the entire training

period.

Last but not the least, we are most thankful to our institute, DESH BHAGAT

GROUP OF INSTITUE OF MANAGEMENT AND COMPUTER SCIENCE for

providing us this opportunity and platform to explore our horizons in the practical

field and gain professionalism and etiquettes along with technical abilities in thecorporate culture.



INDEX

• INTRODUCTION OF TATA TELESERVICE LTD.

2. INTRODUCTION OF CDMA SERVICE.

TATA TELE SERVICES

COMPANY PROFILE:

Communications is the Tata Group’s largest investment and the Group’s objective is

to provide end-to-end telecommunications solutions for business and residential

customers across the nation, and internationally. The Group’s communications

activities are currently spread primarily over four companies—Tata Teleservices

Limited (TTSL) and its associate Tata Teleservices (Maharashtra) Limited (TTML),

Tata Communication (erstwhile VSNL) and Tata Sky. Together, these companiescover the full range of communications services, including:

• Telephony Services: Fixed and Mobile

• Media and Entertainment Services: Satellite TV

• Data Services: Leased Lines, Managed Data Networks, IP/MPLS VPN, Dial-up

Internet, Wi-Fi and Broadband



• Value-Added Services: Mobile and Broadband Content/Applications, Calling

Cards, Net Telephony and Managed Services

• Infrastructure Services: Submarine Cable Bandwidth, Terrestrial Fiber

Network and Satellite Earth Stations and VSAT Connectivity

Profile

Tata Teleservices is part of the INR Rs. 2, 51,543 Crore Tata Group that hasover 80 companies, over 3, 30,000 employees and more than 3.2 millionshareholders. With a committed investment of INR 36,000 Crore (US$ 7.5billion) in Telecom (FY 2006), the Group has a formidable presence acrossthe telecom value chain.

Tata Teleservices spearheads the Group’s presence in the telecom sector.

Incorporated in 1996, Tata Teleservices was the first to launch CDMA mobileservices in India with the Andhra Pradesh circle.

Beginning with its acquisition of Hughes Telecom (India) Limited inDecember 2002 [now renamed Tata Teleservices (Maharashtra) Limited],

which provides services in the Mumbai and Rest of Maharashtra telecomcircles, the company has swung into expansion mode and currently has apan-India state-of-the-art network.

Having pioneered the CDMA 2000 technology platform in India, TataTeleservices has established a 3G-ready robust and reliable telecominfrastructure in partnership with Motorola, Ericsson and Lucent. Thecompany has also received the license from the Department of Telecommunications to launch GSM services as well. With this launch set forearly 2009, TTSL is on the threshold of emerging as a true-play dualtechnology telecom operator.

In November 2008, Tata Teleservices entered into an agreement withJapanese telecom major NTT DOCOMO, as part of which the Japanesecompany acquired a 26% stake in TTSL for USD 2.7 billion. The transactionmarks a key step in the strategic evolution of Tata Teleservices, as it movestowards a pan-India dual network presence. On a broader level, thetransaction is also expected to mark the beginning of a relationship of broader co-operation between Tata companies and the Nippon Telegraphand Telephone Corporation (NTT).



The potential benefits and synergies from the alliance with DOCOMO cutacross marketing, handset development and technical support, all of whichare expected to create new opportunities for both companies. The alliancewill also accelerate Tata Teleservices’ GSM plans and help the companypenetrate the market with advanced technology and new VAS offerings.

Tata Teleservices’ bouquet of telephony services includes mobile services,wireless desktop phones, and public booth telephony and wire line services.Other services include value-added services such as voice portal, roaming,post-paid Internet services, 3-way conferencing, group calling, Wi-FiInternet, USB Modem, data cards, calling card services and enterpriseservices.

Some of the other products launched by the company include prepaidwireless desktop phones, public phone booths, new mobile handsets andnew voice and data services such as BREW games, voice portal, picturemessaging, face book, M commerce applications, polyphonic ring tones,

interactive applications like news, cricket, astrology, etc.



INTRODUCTION OF CDMA

CDMA/WIRELESS COMMUNICATION

MULTIPLE ACCESSES

Why there is requirement of multiple access schemes? The answer is thatthe international authority for frequency management has allocated 25 MHzband to the cellular telephony. As we know that today there are manycellular users and to provide service to all of them a large frequency band isrequired. But the band is limited to 25MHz.So different multiple accessschemes are used. It means that multiple access scheme allow number of

users to use the same band. The different multiple access schemes arementioned below:

• FDMA• TDMA• CDMA



FDMA

FDMA is the acronym of Frequency Division Multiple Access. FDMA divides

radio channels into a range of radio frequencies and is used in the traditionalanalog cellular system. With FDMA, only one subscriber is assigned to achannel at a time. Other conversations can access this channel only after thesubscriber's call has been terminated or after the original call is handed off to a different channel by the system. FDMA cellular standards include AMPS(Advanced Mobile Phone Service) and TACS (Total Access CommunicationsSystem).



Fig. 26 FDMA

TDMA

TDMA is a common multiple access technique employed in digital cellularsystems. It divides conventional radio channels into time slots to obtainhigher capacity. Its standards include North American Digital Cellular, GlobalSystem for Mobile Communications, and PDC (Personal Digital Cellular). As



with FDMA, no other conversations can access an occupied TDMA channeluntil the channel is vacated.

Fig. 27TDMA

CDMA



CDMA uses a radically deferent approach. It assigns each subscriber aunique "code" to put multiple users on the same wideband channel at thesame time.

Both the mobile station and the base station to distinguish between

conversations use the codes, called ―pseudo-random code sequences‖.Depending on the level of mobility of the system, it provides 10 to 20times the capacity of AMPS, and 4 to 7 times the capacity of TDMA.

Fig. 28 CDMA-A

FREQUENCY REUSE

Fig. 30 Freq. Reuse

INTRODUCTION OF CDMA

DEFINITION OF CDMA

Designers and planners of the communication systems are often concernedwith the efficiency with which the systems utilize the signal energy and

bandwidth. In most communication systems these are the most importantissues. In some cases, it is necessary for the system to resist externalinterference, to operate at low spectral energy, to provide multiple accesscapability without external control and secure channel not accessible to theoutsiders. Thus, it is sometimes unavoidable to sacrifice some of theefficiency in order to enhance these features. Spread spectrum techniquesallow accomplishing such objectives.



Fig. 31 CDMA-C

The theoretical aspects of using spread spectrum in a strong interferenceenvironment have been known for over forty years. It is only recently thatpractical implementations became feasible. In the beginning, the spreadspectrum technology was developed and used for military purposes and theirimplementations were too expensive for the commercial applications. Newtechnological advancements such as VLSI, and advanced signal processingtechniques made it possible to develop less expensive spread spectrumequipment for civilian use. Applications of this technology include cellular,wireless data transmission and satellite communications.

ALL OF THE SPREAD-SPECTRUM SYSTEMS HAVE TO SATISFY TWOCRITERIA:

The bandwidth of the transmitted signal must be greater than thetransmittedSignal.

Transmitted bandwidth must be determined by some function that isindependent of the message and is known to the receiver.

Bandwidth expansion in spread spectrum systems is achieved by using afunction that is independent of the message, thus it is more susceptible towhite noise as opposed to other communication techniques, such as FM andPCM. Spread spectrum techniques have other applications that make itunique and useful.



THESE APPLICATIONS INCLUDE:

1. Anti-jam capability-particularly for narrow-band jamming.2. Interference rejection.

3. Multiple-access capability.4. Multi-path protection.

5. Convert operations or low probability of intercept (LPI).

6. Secure communications.7. Improved spectral efficiency-in special circumstances.8. Ranging.

CDMA is a wireless communications technology that uses the principle of spread spectrum communication. The intent of CDMA technology is toprovide increased bandwidth in a limited frequency system, but has alsoother advantages including extended range and more securecommunications. In a CDMA system, a narrowband message signal ismultiplied by a spreading signal, which is a pseudo-noise code sequence thathas a rate much greater than the data rate of the message. CDMA usesthese code sequences as a means of distinguishing between individualconversations. All users in the CDMA system use the same carrier frequencyand may transmit simultaneously. In this document I will be discussingabout CDMA in detail.

CDMA is a driving technology behind the rapidly advancing personalcommunications industry. Because of its greater bandwidth, efficiency, andmultiple access capabilities, CDMA is becoming a leading technology forrelieving the spectrum congestion caused by the explosion in popularity of cellular mobile phones, fixed wireless telephones, and wireless dataterminals. Since becoming an officially recognized digital cellular protocol,CDMA is being rapidly implemented in the wireless communications networksof many large communications corporations.

CDMA stands for "Code Division Multiple Access." It is a form of spread-spectrum, an advanced digital wireless transmission technique. Instead of using frequencies or time slots, as do traditional technologies, it usesmathematical codes to transmit and distinguish between multiple wirelessconversations. Its bandwidth is much wider than that required for simplepoint-to-point communications at the same data rate because it uses noise-like carrier waves to spread the information contained in a signal of interestover a much greater bandwidth. However, because the conversations taking



place are distinguished by digital codes, many users can share the samebandwidth simultaneously. The advanced methods used in commercial CDMAtechnology improve capacity, coverage and voice quality, leading to a newgeneration of wireless networks.

Old-fashioned radio receivers separate stations and channels by filtering inthe frequency domain. CDMA receivers, conversely, separate communicationchannels by a pseudo-random modulation that is applied and removed in thedigital domain. Multiple users can therefore occupy the same frequencyband. This universal frequency reuse is crucial to CDMA's distinguishing highspectral efficiency. CDMA has gained international acceptance by cellularradio system operators as an upgrade because of its universal frequencyreuse and noise-like characteristics. CDMA systems provide operators andsubscribers with significant advantages over analog and conventional TDMA-

based systems.

THE 850MHZ CDMA BAND IS MOST POPULARLY USED ALL OVER THEWORLD. THIS BAND AS MENTIONED IN THE PREVIOUS SLIDEWORKS BETWEEN

824-849MHz Used for the Reverse link communication

869-894MHz Used for the Forward link communication

The CDMA band is divided into sub bands as shown above. The Total Band of 25MHz is divided into small channels of 30 KHz each. An actual CDMA carrierwill be using a multiple of the 30 KHz channels. That means for an actuallyutilized bandwidth of 1.23MHz we will need 41 X 30 KHz channels.

THE FOLLOWING EQUATION GIVES THE RELATIONSHIP BETWEEN THECHANNEL NUMBERS AND THE ACTUAL FREQUENCY.

Reverse Link Frequency = (825 + N0.03) MHzForward Link Frequency = (870 + N0.03) MHz

Where N = CDMA channel number



CDMA SPREAD SPECTRUM TERMINOLOGY

Fig. 32 SPREAD SPECTRUM-A

Fig. 33 SPREAD SPETRUM-B

Spread spectrum multiple access transmits the entire signal over abandwidth that is much greater than that required for standard narrow bandtransmissions in order to gain signal-to-noise (S/N) performance. Inchannels with narrow-band noise, increasing the transmitted signalbandwidth results in an increased probability that the received informationwill be correct. Because each signal is an assembly of many smaller signals



at the fundamental frequency and its harmonics, increasing the frequencyresults in a more accurate reconstruction of the original signal. The effectivedrawback of narrow-band data communications is the limitation of bandwidth; thus signals must be transmitted with enough power so thecorruption by Gaussian noise is not as effective and the probability that the

data received is correct will remain low. This means that the effective SNRmust be high enough so that the receiver should have no problem inrecovering the transmitted code without error.

From a system viewpoint, the performance increase for very widebandsystems is referred to as "process gain". This term is used to describe thereceived signal fidelity gained at the cost of bandwidth. Errors introduced bya noisy channel can be reduced to any desired level without sacrificing therate of information transfer using Claude Shannon's equation describing

channel capacity:

C=W log 2 (1+S/N)

Where,

C = Channel capacity in bits per second,W = Bandwidth,S/N = Energy per bit/Noise power.

The benefits of increasing bandwidth become clearer. The S/N ratio may bedecreased without decreasing the bit error rate. This means that the signalmay be spread over a large bandwidth with smaller spectral power levelsand still achieve the required data rate. If the total signal power isinterpreted as the area under the spectral density curve, then signals withequivalent total power may have either a large signal power concentrated ina small bandwidth or a small signal power spread over a large bandwidth.



SPREAD SPECTRUM

CDMA is a spread spectrum modulation scheme. This implies that thetransmission bandwidth is much larger than the information bandwidth.

DIRECT SEQUENCE SPREAD SPECTRUM

In direct sequence modulation the carrier frequency is fixed and thebandwidth of the transmitted signal is larger and independent of thebandwidth of the information signal. Some properties of direct sequencespread spectrum systems are listed in table.

Fig. 35 DS CDMA

TABLE 10: SUMMARY OF DIRECT SEQUENCE SPREAD SPECTRUM QUALITIES



CDMA CODES

In discussing CDMA modulation, several different PN sequences or ―codes‖ are bantered about incessantly. In attempting to make sense out of CDMAmodulation, it is helpful to know the relative length (time period) of thesecodes.

GENERATION OF PN CODES

PN code sets can be generated from linear feedback shift registers. One such

example is shown in Figure. Binary bits are shifted through the differentstages of the register. The output of the last stage and the output of oneintermediate stage are combined and fed as input to the first stage. Theregister starts with an initial sequence of bits, or initial state,Stored in its stages. Then the register is clocked, and bits are movedthrough the stages. This way, the register continues to generate output bitsand feed input bits to its first stage. The output bits of the last stage formthe PN code. Let we demonstrate the code generation using the registershown in Figure. Let initial state is [1, 0, 1] for register. The output of stage3 is the output of the register.After clocking the bits through the register:



Fig. 36 PN CODE GENERATION THROUGH SHIFT REGISTER

TYPES OF PN CODES

• PN LONG CODE• PN SHORT CODE

PN LONG CODE

The Long Code is a PN sequence that is 242 - 1 bits (chips) long. It is

generated at a rate of 1.2288 Mbps (or MCPc) giving it a period (time before

the sequence repeats) of approximately 41.4 days. The long code is used to

encrypt user information. Both the base station and the mobile unit have

knowledge of this sequence at any given instant in time based on a specified

private ―long code mask‖ that is exchanged.

Long Code Mask governs the generation of a Long Code. A long code mask is42-bit codes which define the initial values used by the long code generator.Knowledge of this long code mask allows the base station or mobile user togenerate the same PN Long Code. Generating the same long code(synchronized in time) at both end of the link allows information to beencrypted and decrypted.



A unique and private, long code mask (thus, PN long code) is assigned toeach CDMA user. This code is referred to as a ―user mask‖. The user mask is

exchanged between the mobile and the serving cell(s)/sector(s), whichallows user traffic data to be encrypted on both the forward and reverse

links. A different long code mask is used to generate the long code forencryption and decryption of Access and Paging information – more on thislater.

PN SHORT CODES

The Short Code is a PN sequence that is 215 bits (chips) in length. This

code is generated at 1.2288 Mbps (or MCPc) giving a period of 26.67 ms.

this code is used for final spreading of the signal and is transmitted as a

reference known as the ―Pilot Sequence‖ by the base station. All base

stations use the same short code. Base stations are differentiated from one

another by transmitting the PN short code at different ―offsets‖ in absolute.

This time offset is known as a ―PN Offset‖. All base stations and mobiles

have knowledge of this code; however, mobile units do not have initial

knowledge of absolute time. Mobile units initially search (in time) until they

synchronize with a pilot code transmitted by a base station. The base station

then conveys timing information to the mobile – more on this stuff later.

WALSH CODES

CDMA defines a group of 64 orthogonal sequences, each 64 bits long,known as Walsh Codes. These sequences are also referred to as WashFunctions. These codes are generated at 1.2288 Mbps (MCPc) giving them aperiod of approximately 52 µs. These are used to identify users on theforward link. For this reason they are loosely referred to as CDMA channels.All base stations and mobile users have knowledge of all Walsh codes.

Orthogonal functions have zero correlation. Two binary sequences areorthogonal if the process of ―XORing‖ them results in an equal number of 1’s

and 0’s.

Example: 0000(XOR) 0101

------0101



• Generation Sequence:- Seed - Repeat right & below- Invert: diagonally

ORTHOGONALITY OF WALSH CODES

CDMA CHANNELS

Just when one grasps an understanding of the CDMA carrier, which is 1.25MHz 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. CDMA traffic channels are different: they are dependent onthe equipment platform on which the CDMA is implemented. Mostly channelsare designated in three ways:

EFFECTIVE TRAFFIC CHANNELS

The number of "Effective" traffic channels includes the traffic carryingchannels less the soft handoff channels. The capacity of an effective trafficchannel is equivalent to the traffic carrying capacity of an analog trafficchannel.

ACTUAL TRAFFIC CHANNELS

The number of "Actual" traffic channels includes the effective trafficchannels, plus channels allocated for soft handoff.

PHYSICAL TRAFFIC CHANNELS

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

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

Fig. 39 CHANNELS

CDMA FORWARD CHANNELS



PILOT CHANNEL

The pilot channel is used by the mobile unit to obtain initial systemsynchronization 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 thecell site pilot pseudo-random (PN) phase offset information. With thisinformation the mobile units can establish the System Time as well as theproper transmits power level to use to initiate a call.

PAGING CHANNEL

The mobile unit will begin monitoring the paging channel after it has set itstiming to the System Time provided by the sync channel. Once a mobile unithas been paged and acknowledges that page, call setup and traffic channelassignment 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 CHANNELS

ACCESS CHANNEL

When the mobile unit is not active on a traffic channel, it will communicateto the base station over the access channel. This communication includesregistration requests, responses to pages, and call origination. 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 thevoice and mobile power control information from the mobile unit to the basestation.

ADVANTAGES OF CDMA

CDMA technology has numerous advantages including:• Coverage• Capacity• Clarity• Cost• Compatibility• Customer satisfaction

COVERAGE

CDMA's features result in coverage that is between 1.7 and 3 timesthat of TDMA:

• Power control helps the network dynamically expand the coveragearea.

• Coding and interleaving provide the ability to cover a larger area forthe same amount of available power used in other systems.

CAPACITY

CDMA capacity is ten to twenty times that of analog systems, and it'sup to four times that of TDMA. Reasons for this include:

• CDMA's universal frequency reuse• CDMA users are separated by codes, not frequencies.

• Power control minimizes interference, resulting in maximized capacity.CDMA's soft handoff also helps increase capacity. This is because a soft

handoff requires less power.



CLARITY

Often CDMA systems can achieve ―wire line‖ clarity because of CDMA’s

strong digital processing. Specifically:• The rake receiver reduces errors• The variable rate vocoder reduces the amount of data transmitted per

person, reducing interference.• The soft handoff also reduces power requirements and interference.• Power control reduces errors by keeping power at an optimal level.• CDMA’s wide band signal reduces fading.

• Encoding and interleaving reduce errors that result from fading.

COST

CDMA’s better coverage and capacity result in cost benefits:

• Increased coverage per BTS means fewer are needed to cover a givenarea. This reduces infrastructure costs for the providers.

• Increased capacity increases the service provider’s revenue potential.



CDMA costs per subscriber have steadily declined since 1995 for bothcellular and PCS applications.

COMPATIBILITY

CDMA phones are usually dual mode. This means they can work inboth CDMA systems and analog cellular systems.

Some CDMA phones are dual band as well as dual mode. They canwork in CDMA mode in the PCS band, CDMA mode in the cellular band,or analog mode in an analog cellular network.

CUSTOMER SATISFACTION

CDMA results in greater customer satisfaction because CDMA providesbetter:

• Voice quality• Longer battery life due to reduced power requirements

• No cross-talk because of CDMA's unique coding• Privacy--again, because of coding.

TABLE 11: CDMA-GSM PARAMETERS

PARAMETERS CDMA GSM



Uplink Frequencies 824-849 MHz (US Cellular)

1850-1910 MHz (US PCS) 890-915 MHz (Europe)

1850-1910 MHz (US PCS)

Downlink Frequencies 869-894 MHz (US Cellular)

1930-1990 MHz (US PCS)

935-960 MHz (Europe)

1930-1990 MHz (US PCS)

Multiple Access Tech. CDMA TDMA

Carrier Separation 1.25 MHz 200 KHz Channel Data Rate 1.2288 chips/sec 260.833 Kbps

Frequency Planning Not required Required Mobile Handset Power 23mW max 2 W max Handoff Soft/Softer Hard

CDMA HANDOFF

The act of transferring support of a mobile from one base station to another

is termed handoff. Handoff occurs when a call has to be handed off from onecell to another as the user moves between cells. A CDMA cellular networkhandles mobile unit call processing transitions more subtly than the othertechnologies used for mobile communications networks.

CDMA Handoffs require that the mobile unit maintain an ongoing list of possible base station sites that it may use for Handoffs as it travels throughthe system. CDMA offers the unique feature of allowing mobile users toprocess signals from multiple (up to 3) base stations simultaneously. Theterminology and various types of Handoffs associated with CDMA aredescribed below.



Fig. 43 HANDOFF-1

Fig. 44 Handoff 2

TYPES OF HANDOFFS

There are basically two types of Handoff mechanism.

Hard Handoff

• Soft Handoff

HARD HANDOFF

In a traditional "hard" handoff, the connection to the current cell is broken,and then the connection to the new cell is made. This is known as a "break-

before-make" handoff. Since all cells in CDMA use the same frequency, it ispossible to make the connection to the new cell before leaving the currentcell. This is known as a "make-before-break" or "soft" handoff. Softhandoffs require less power, which reduces interference and increasescapacity.



SOFT HANDOFF

The condition where two cells are in simultaneous communication with themobile is called Soft Handoff. Soft Handoff will continue until the pilot signalfrom one of the contributing cells drops below a predefined threshold

(TDROP). As the mobile moves from its current cell (source cell) to the nextcell (target cell), a traffic channel connection is simultaneously maintainedwith both cells. Figure (a) and Figure (b) illustrate the simultaneous linksduring soft handoff. On the forward link (see Figure (a)), the mobile uses therake receiver to demodulate two separate signals from two different basestations. The two signals are combined to yield a composite signal of betterquality. On the reverse link (see Figure (b)), the mobile’s transmit signal is

received by both base stations. The two cells demodulate the signalseparately and send the demodulated frames back to the Mobile SwitchingCenter (MSC). The MSC contains a selector that selects the best frame out of

the two that are sent back.

On Forward Link, when the Soft Handoff is initiated, the two base stationsbegin transmitting data to the mobile. The mobile receives information fromthe two forward links and uses the RAKE receiver to coherently combine thesignals using the pilot sequence transmitted by each cell/sector as itsreference. This combination of multiple forward link signals improves overalllink performance.

ADVANTAGES OF CDMA HANDOFF

1. It is "soft", meaning that communication is not interrupted by thehandoff. This is sometimes called "make before break." This means fewerdropped calls for users and higher customer satisfaction for operators.

2. The handoff is not abrupt, but rather it is a prolonged call state duringwhich there is communication via two or more base stations. The multi-waycommunication diversity improves the link performance during the handoff.The diversity gain partially compensates for the large path loss at the cellboundary.

3. The signal measurement that triggers the handoff is performed by the

mobile stations, not the base stations.

Need of CDMA

Designers and planners of the communication systems are oftenconcerned with the efficiency with which the systems utilize the signal



energy and bandwidth. In most communication systems these are themost important issues. In some cases, it is necessary for the systemto resist external interference, to operate at low spectral energy, toprovide multiple access capability without external control and securechannel not accessible to the outsiders. Thus, it is sometimes

unavoidable to sacrifice some of the efficiency in order to enhancethese features. Spread spectrum techniques allow accomplishing suchobjectives.

Fig. 1.1 CDMA-C

The theoretical aspects of using spread spectrum in a stronginterference environment have been known for over forty years. It isonly recently that practical implementations became feasible.

In the beginning, the spread spectrum technology wasdeveloped and used for military purposes and their implementationswere too expensive for the commercial applications. New technologicaladvancements such as VLSI, and advanced signal processingtechniques made it possible to develop less expensive spreadspectrum equipment for civilian use. Applications of this technologyinclude cellular, wireless data transmission and satellitecommunications.

Definition of CDMA

CDMA is a wireless communications technology that uses the principleof spread spectrum communication. The intent of CDMA technology is



to provide increased bandwidth in a limited frequency system, but hasalso other advantages including extended range and more securecommunications. In a CDMA system, a narrowband message signal ismultiplied by a spreading signal, which is a pseudo-noise codesequence that has a rate much greater than the data rate of the

message. CDMA uses these code sequences as a means of distinguishing between individual conversations. All users in the CDMAsystem use the same carrier frequency and may transmitsimultaneously.

CDMA stands for "Code Division Multiple Access." It is a form of

spread-spectrum, an advanced digital wireless transmission technique.Instead of using frequencies or time slots, as do traditionaltechnologies, it uses mathematical codes to transmit and distinguishbetween multiple wireless conversations. Its bandwidth is much wider

than that required for simple point-to-point communications at thesame data rate because it uses noise-like carrier waves to spread theinformation contained in a signal of interest over a much greaterbandwidth. However, because the conversations taking place aredistinguished by digital codes, many users can share the samebandwidth simultaneously.

The advanced methods used in commercial CDMA technology improvecapacity, coverage and voice quality, leading to a new generation of wireless networks.

The 850MHz CDMA band is most popularly used all over the world.This band as mentioned in the previous slide works between,

• 824-849MHz Used for the Reverse link communication.

• 869-894MHz Used for the Forward link communication.

The Following equation gives the relationship between the channelnumbers and the actual frequency.Forward Link Frequency = (870 + N0.03) MHzReverse Link Frequency = (825 + N0.03) MHz

Where N = CDMA channel number

BASIC STRUCTURE OF CDMA NETWORK



The basic structure of the network is shows in the figure 1.The components are described below:1) Microwave Antenna2) ODU3) IDU

4) MUX5) DDF6) BTS7) Sector antenna8) GPS antenna

1) Microwave Antenna:

MW antenna is used to transmit MW signal in air. Thisantenna is directional antenna. It means it will transmit in one directiononly. This is used to connect E1 link between two sites. Two MW antennasare there in each site to establish a ring network. It sends traffic to BSC. Thetransmitting frequency is in terms of GHz. Parabolic types of antenna areused in TTSL.

2) ODU:

ODU stands for outdoor unit. ODU is attached to the MWantenna. Its function is modulates the incoming signal from IDU with higher

carrier frequency signal. Means frequency up conversion is performed here.

3) IDU:

IDU stands for indoor unit. It convert RF signal in to opticalsignal. To establish ring network more than one IDU can be required.

4) MUX:

Here MUX are used to carry E1 from one site to another

site.BTS is connected to the MUX via DDF. Here MUX can carry both dataand voice traffic.MUX uses SDH (Synchronous Digital Hierarchy) technology.Different types are:



Type capacity

• STM-0 21E1

• STM-1 63E1• STM-4 4*63E1• STM-16 16*63E1• STM-64 64*63E1• STM-256 256*63E1

Single E1 has a capacity of 2.048 Mbps.MSH11c (STM-1) andMSH41c (STM-4) are used TTSL.

5) DDF:

DDF stands for DIGITAL DISTRIBUTION FRAME.DDF is a point wasE1 is terminated. It provides only connectivity between two points.

6) BTS:

A BTS stand for BASE STATION TRANSCIEVER SUBSYSTEM.BTS isconnected with GPS antenna via RF cable. The CDMA signal is processed byBTS.BTS include filter, amplifier and other control module. BTS receive andtransmit signal via sector antenna.

7) Sector antenna:

Sector antennas communicate with mobile.360 Degree is dividedin to three parts Alpha Beta and Gamma. Also known as intra,metro andultra. All three parts are separated by maximum up to 120 degree. Herebecause of sector the coverage is increase .Sector antenna is a directionalantenna.

8) GPS system:

A GPS stands for Global positioning system. A GPS receiver islocated in the BTS and is connected to antenna via RF cable. This providessynchronization signal and timing signal to CDMA network for channelcoding. These antennas communicate with satellite continuously.

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