tecnical traning report tata indicom rajkot

62
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 Ms. DHWANI SHAH, our project mentor, L.E.C., Institute of Technology, Nirma University for giving us invaluable guidelines and moral support. She, 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, Atmiya 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 the corporate culture.

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THIS IS TECNICAL REPORT ON TECNICAL TRANING IN TATA INDICOM IN RAJKOT IN 6th SEM.

TRANSCRIPT

Page 1: Tecnical Traning Report Tata indicom RAJKOT

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 Ms. DHWANI SHAH, our project mentor, L.E.C.,

Institute of Technology, Nirma University for giving us invaluable guidelines

and moral support. She, 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, Atmiya 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 the corporate culture.

Page 2: Tecnical Traning Report Tata indicom RAJKOT

INDEX

1. INTRODUCTION OF TATA TELESERVICE LTD.

2. INTRODUCTION OF CDMA SERVICE. 3. BASIC STRUCTURE OF CDMA NETWORK. 4. MOTAROLA BTS STRUCTURE.

5. PATCHING OF E1 ON DDF BLOCK.

6. DRIVE TEST.

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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 companies cover 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

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Profile

Tata Teleservices is part of the INR Rs. 2, 51,543 Crore Tata Group that has over 80 companies, over 3, 30,000 employees and more than 3.2 million shareholders. With a committed investment of INR 36,000 Crore (US$ 7.5 billion) in Telecom (FY 2006), the Group has a formidable presence across the 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 mobile services in India with the Andhra Pradesh circle.

Beginning with its acquisition of Hughes Telecom (India) Limited in December 2002 [now renamed Tata Teleservices (Maharashtra) Limited], which provides services in the Mumbai and Rest of Maharashtra telecom circles, the company has swung into expansion mode and currently has a pan-India state-of-the-art network.

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

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

The potential benefits and synergies from the alliance with DOCOMO cut across marketing, handset development and technical support, all of which are expected to create new opportunities for both companies. The alliance will also accelerate Tata Teleservices’ GSM plans and help the company penetrate the market with advanced technology and new VAS offerings.

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

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Some of the other products launched by the company include prepaid wireless desktop phones, public phone booths, new mobile handsets and new voice and data services such as BREW games, voice portal, picture messaging, facebook, M commerce applications, polyphonic ring tones, interactive applications like news, cricket, astrology, etc.

INTRODUCTION OF CDMA

CDMA/WIRELESS COMMUNICATION

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MULTIPLE ACCESS

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

1. FDMA2. TDMA3. CDMA

1)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 traditional analog cellular system. With FDMA, only one subscriber is assigned to a channel at a time. Other conversations can access this channel only after the subscriber's call has been terminated or after

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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 Communications System).

Fig. 26 FDMA

2)TDMA

TDMA is a common multiple access technique employed in digital cellular systems. It divides conventional radio channels into time slots to obtain higher capacity. Its standards include North American Digital Cellular, Global System for Mobile Communications, and PDC (Personal Digital Cellular). As with FDMA, no other conversations can access an occupied TDMA channel until the channel is vacated.

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Fig. 27TDMA

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3)CDMA

CDMA uses a radically deferent approach. It assigns each subscriber a unique "code" to put multiple users on the same wideband channel at the same 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 20 times the capacity of AMPS, and 4 to 7 times the capacity of TDMA.

Fig. 28 CDMA-A

FREQUENCY REUSE

Fig. 30 Freq. Reuse

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INTRODUCTION OF CDMA

DEFINITION OF CDMA

Designers and planners of the communication systems are often concerned with the efficiency with which the systems utilize the signal energy and bandwidth. In most communication systems these are the most important issues. In some cases, it is necessary for the system to resist external interference, to operate at low spectral energy, to provide multiple access capability without external control and secure channel not accessible to the outsiders. Thus, it is sometimes unavoidable to sacrifice some of the efficiency in order to enhance these features. Spread spectrum techniques allow accomplishing such objectives.

Fig. 31 CDMA-C

The theoretical aspects of using spread spectrum in a strong interference environment have been known for over forty years. It is only recently that practical implementations became feasible. In the beginning, the spread spectrum technology was developed and used for military purposes and their implementations were too expensive for the commercial applications. New technological advancements such as VLSI, and advanced signal processing techniques made it possible to develop less expensive spread spectrum equipment for civilian use. Applications of this technology include cellular, wireless data transmission and satellite communications.

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ALL OF THE SPREAD-SPECTRUM SYSTEMS HAVE TO SATISFY TWO CRITERIA:

The bandwidth of the transmitted signal must be greater then the transmittedSignal.

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

Bandwidth expansion in spread spectrum systems is achieved by using a function that is independent of the message, thus it is more susceptible to white noise as opposed to other communication techniques, such as FM and PCM. Spread spectrum techniques have other applications that make it unique 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 to provide increased bandwidth in a limited frequency system, but has also other advantages including extended range and more secure communications. In a CDMA system, a narrowband message signal is multiplied by a spreading signal, which is a pseudo-noise code sequence 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 CDMA system use the same carrier frequency and may transmit simultaneously. In this document I will be discussing about CDMA in detail.

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CDMA is a driving technology behind the rapidly advancing personal communications industry. Because of its greater bandwidth, efficiency, and multiple access capabilities, CDMA is becoming a leading technology for relieving the spectrum congestion caused by the explosion in popularity of cellular mobile phones, fixed wireless telephones, and wireless data terminals. Since becoming an officially recognized digital cellular protocol, CDMA is being rapidly implemented in the wireless communications networks of 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 uses mathematical codes to transmit and distinguish between multiple wireless conversations. Its bandwidth is much wider than that required for simple point-to-point communications at the same data rate because it uses noise-like carrier waves to spread the information contained in a signal of interest over a much greater bandwidth. However, because the conversations taking place are distinguished by digital codes, many users can share the same bandwidth simultaneously. The advanced methods used in commercial CDMA technology improve capacity, coverage and voice quality, leading to a new generation of wireless networks.

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

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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 communication869-894MHz 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 30KHz each. An actual CDMA carrier will be using a multiple of the 30KHz channels. That means for an actually utilized bandwidth of 1.23MHz we will need 41X30KHz channels.

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

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

Where N = CDMA channel number

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CDMA SPREAD SPECTRUM TERMINOLOGY

Fig. 32 SPREAD SPECTRUM-A

Fig. 33 SPREAD SPETRUM-B

Spread spectrum multiple access transmits the entire signal over a bandwidth that is much greater than that required for standard narrow band transmissions in order to gain signal-to-noise (S/N) performance. In channels with narrow-band noise, increasing the transmitted signal bandwidth results in an increased probability that the received information will be correct. Because each signal is an assembly of many smaller signals at the fundamental frequency and its harmonics, increasing the frequency results in a more accurate reconstruction of the original signal. The effective drawback of narrow-band data communications is the limitation of bandwidth; thus signals must be

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transmitted with enough power so the corruption by gaussian noise is not as effective and the probability that the data received is correct will remain low. This means that the effective SNR must be high enough so that the receiver should have no problem in recovering the transmitted code without error.

From a system viewpoint, the performance increase for very wideband systems is referred to as "process gain". This term is used to describe the received signal fidelity gained at the cost of bandwidth. Errors introduced by a noisy channel can be reduced to any desired level without sacrificing the rate 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 be decreased without decreasing the bit error rate. This means that the signal may be spread over a large bandwidth with smaller spectral power levels and still achieve the required data rate. If the total signal power is interpreted as the area under the spectral density curve, then signals with equivalent total power may have either a large signal power concentrated in a small bandwidth or a small signal power spread over a large bandwidth.

SPREAD SPECTRUM

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

DIRECT SEQUENCE SPREAD SPECTRUM

In direct sequence modulation the carrier frequency is fixed and the bandwidth of the transmitted signal is larger and independent of the bandwidth of the information signal. Some properties of direct sequence spread 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 CDMA modulation, it is helpful to know the relative length (time period) of these codes.

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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 different stages of the register. The output of the last stage and the output of one intermediate stage are combined and fed as input to the first stage. The register starts with an initial sequence of bits, or initial state, Stored in its stages. Then the register is clocked, and bits are moved through the stages. This way, the register continues to generate output bits and feed input bits to its first stage. The output bits of the last stage form the PN code. Let we demonstrate the code generation using the register shown in Figure. Let initial state is [1, 0, 1] for register. The output of stage 3 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

1. PN LONG CODE2. PN SHORT CODE

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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 Mcps) 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 is a 42-bit code which define the initial values used by the long code generator. Knowledge of this long code mask allows the base station or mobile user to generate the same PN Long Code. Generating the same long code (synchronized in time) at both end of the link allows information to be encrypted and decrypted. A unique and private, long code mask (thus, PN long code) is assigned to each 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), which allows 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 for encryption and decryption of Access and Paging information – more on this later.

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 Mcps) 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 Wash Functions. These codes are generated at 1.2288 Mbps (Mcps) giving them a period of approximately 52 µs. These are used to identify users on the forward link. For this reason they are loosely referred to as CDMA channels. All base stations and mobile users have knowledge of all Walsh codes.

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Orthogonal functions have zero correlation. Two binary sequences are orthogonal if the process of “XORing” them results in an equal number of 1’s and 0’s. Example:Example: 00000000

((XOR) 0101 0101 ------------ 0101 0101

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

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. CDMA traffic channels are different: they are dependent on the equipment platform on which the CDMA is implemented. Mostly channels are designated in three ways:

EFFECTIVE 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.

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1 1

1 0

ORTHOGONALITY OF WALSH CODES

0 0

0 1

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ACTUAL TRAFFIC CHANNELS

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

PHYSICAL TRAFFIC CHANNELS

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.)

Fig. 39 CHANNELS

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 andacknowledges 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 CHANNELS

ACCESS CHANNEL

When the mobile unit is not active on a traffic channel, it will communicate to the base station over the access channel. This communication includes registration requests, responses to pages, and call 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 the voice and mobile power control information from the mobile unit to the base station.

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 times that of TDMA:

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Power control helps the network dynamically expand the coverage area.

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

CAPACITY

CDMA capacity is ten to twenty times that of analog systems, and it's up 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

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CDMA’s better coverage and capacity result in cost benefits: Increased coverage per BTS means fewer are needed to cover a

given area. 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 both cellular and PCS applications.

COMPATIBILITY

CDMA phones are usually dual mode. This means they can work in both CDMA systems and analog cellular systems. Some CDMA phones are dual band as well as dual mode. They can work 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 provides better:

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 Frequencies824-849 MHz (US Cellular)

1850-1910 MHz (US PCS)

890-915 MHz (Europe)

1850-1910 MHz (US PCS)

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Downlink Frequencies869-894 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 Mchips/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 one cell to another as the user moves between cells. A CDMA cellular network handles mobile unit call processing transitions more subtly than the other technologies 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 through the system. CDMA offers the unique feature of allowing mobile users to process signals from multiple (up to 3) base stations simultaneously. The terminology and various types of Handoffs associated with CDMA are described below.

Fig. 43 HANDOFF-1

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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 is possible to make the connection to the new cell before leaving the current cell. This is known as a "make-before-break" or "soft" handoff. Soft handoffs require less power, which reduces interference and increases capacity.

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SOFT HANDOFF

The condition where two cells are in simultaneous communication with the mobile is called Soft Handoff. Soft Handoff will continue until the pilot signal from one of the contributing cells drops below a predefined threshold (TDROP). As the mobile moves from its current cell (source cell) to the next cell (target cell), a traffic channel connection is simultaneously maintained with both cells. Figure (a) and Figure (b) illustrate the simultaneous links during soft handoff. On the forward link (see Figure (a)), the mobile uses the rake receiver to demodulate two separate signals from two different base stations. The two signals are combined to yield a composite signal of better quality. On the reverse link (see Figure (b)), the mobile’s transmit signal is received by both base stations. The two cells demodulate the signal separately and send the demodulated frames back to the Mobile Switching Center (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 stations begin transmitting data to the mobile. The mobile receives information from the two forward links and uses the RAKE receiver to coherently combine the signals using the pilot sequence transmitted by each cell/sector as its reference. This combination of multiple forward link signals improves overall link performance.

ADVANTAGES OF CDMA HANDOFF

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

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

3. The signal measurement that triggers the handoff is performed by the mobile stations, not the base stations.

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Need Of CDMA

Designers and planners of the communication systems are often concerned with the efficiency with which the systems utilize the signal energy and bandwidth. In most communication systems these are the most important issues. In some cases, it is necessary for the system to resist external interference, to operate at low spectral energy, to provide multiple access capability without external control and secure channel not accessible to the outsiders. Thus, it is sometimes unavoidable to sacrifice some of the efficiency in order to enhance these features. Spread spectrum techniques allow accomplishing such objectives.

Fig. 1.1 CDMA-C

The theoretical aspects of using spread spectrum in a strong interference environment have been known for over forty years. It is only recently that practical implementations became feasible. In the beginning, the spread spectrum technology was developed and used for military purposes and their implementations were too expensive for the commercial applications. New technological advancements such as VLSI, and advanced signal processing techniques made it possible to develop less expensive spread spectrum equipment for civilian use. Applications of this technology include cellular, wireless data transmission and satellite communications.

Definition of CDMA 27

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CDMA is a wireless communications technology that uses the principle of spread spectrum communication. The intent of CDMA technology is to provide increased bandwidth in a limited frequency system, but has also other advantages including extended range and more secure communications. In a CDMA system, a narrowband message signal is multiplied by a spreading signal, which is a pseudo-noise code sequence 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 CDMA system use the same carrier frequency and may transmit simultaneously.

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 uses mathematical codes to transmit and distinguish between multiple wireless conversations. Its bandwidth is much wider than that required for simple point-to-point communications at the same data rate because it uses noise-like carrier waves to spread the information contained in a signal of interest over a much greater bandwidth. However, because the conversations taking place are distinguished by digital codes, many users can share the same bandwidth simultaneously.

The advanced methods used in commercial CDMA technology improve capacity, 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 channel numbers and the actual frequency.Forward Link Frequency = (870 + N0.03) MHzReverse Link Frequency = (825 + N0.03) MHzWhere N = CDMA channel number

BASIC STRUCTURE OF CDMA NETWORK

The basic structure of the network is shows in the figure 1.

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The components are describe below:1) Microwave Antenna2) ODU3) IDU4) MUX5) DDF6) BTS7) Sector antenna8) GPS antenna

1) Microwave Antenna: MW antenna is used to transmit MW signal in air.this antenna is directional antenna. It means it will transmit in one direction only. This is used to connect E1 link between two sites.Two MW antennas are there in each site to establish a ring network..It sends traffic to BSC.The transmitting frequency is in terms of GHz.Parabolic types of antenna are used in TTSL.

2) ODU: ODU stands for out door unit. ODU is attached to the MW antenna. Its function is modulates the incoming signal from IDU with higher carrier frequency signal. Means frequency up convertion is performed here.

3) IDU:

IDU stands for indoor unit.It convert RF signal in to optical signal.To establish ring network more then 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 data and voice traffic.MUX uses SDH(Synchronous Digital Hierarchy)technology.Different types are:

Type capacity

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a) STM-0 21E1b) STM-1 63E1c) STM-4 4*63E1 d) STM-16 16*63E1e) STM-64 64*63E1f) STM-256 256*63E1

Single E1 has a capacity of 2.048 Mbps.MSH11c(STM-1) and MSH41c(STM-4) are used TTSL.

5) DDF: DDF stands for DIGITAL DISTRIBUTION FRAME.DDF is a point were E1 is terminated. It provides only connectivity between two point.

6) BTS: BTS stands for BASE STATION TRANSCIEVER SUBSYSTEM.BTS is connected with GPS antenna via RF cable. The CDMA signal is processed by BTS.BTS include filter, amplifier and other control module. BTS receive and transmit signal via sector antenna.

7) Sector antenna: Sector antenna communicate with mobile.360 Degree is divided in to three parts Alpha Beta and Gamma. Also known as intra, metro and ultra. All three parts are separated by maximum up to 120 degree. Here because of sector the coverage is increase .Sector antenna is a directional antenna.

8) GPS system: A GPS stands for Globle positioning system. A GPS receiver is located in the BTS and is connected to antenna via RF cable.This provides synchronization signal and timing signal to CDMA network for channel coding.This antenna communicate with satellite continuously.

MOTOROLA BTS STRUCTURE

2.1 List of BTS Cards

1. BBX (BROAD BAND TRANSCEIVER)2. MCC-24/MCC-8E (MULTI CHANNEL CDMA)3. GLI (GROUP LINE INTERFACE) 4. CIO (COMBINER INPUT/OUTPUT)

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5. GPS (GLOBAL POSITION SYSTEM)6. CSM (CLOCK SYCHRONIZATION MANAGER)7. HSO (HIGH STABILITY OSCILLATOR)-

optional8. LFR (LOW FREQUENCY RECEVIE)-Optional9. C-CCP CDMA CHANNEL PROCESSOR10.LPA SHELF LINEAR POWER AMPLIFIER11.AMR ALARM MONITORING AND REPORTING12.DBPF DUAL BAND PASS FILETR

COMBINER (4:1 and 2:1)

2.2 Overview of Cards functionality

BBX:

The BBX provides the generation of the Pilot signal, the conversion from digital base band to RF for the forward link and RF to digital base band for the reverse link.

Controlled By: - Group Line Interface (GLI) card via Concentration Highway Interface (CHI)

The BBX receives clock and synchronization signals via the CCD from the CSM.

MCC-24/MCC-8E (MULTI CHANNEL CDMA)

The MCC card contain the circuitry necessary to implement like sync channel, paging channel, access channel and traffic channel. A single CDMA channel on an MCC card is referred to as a channel element.MCC-8E supports up to eight channel element, while MCC-24 supports up to 24 channel elements. Each channel element contains circuitry to provide the CDMA modulation and demodulation for a sync, paging, access or traffic channel. The MCC card also performs the necessary CDMA spreading and dispreading function.

The interface for the MCC-24 and MCC-8E include the GLI for control and traffic data and the BBX2 for the forward base band data, reverse base band and CCD for clocks.

GLI(GROUP LINE INTERFACE)

The GLI card function as the BTS controller and provide routing of traffic and control information and O&M function for all active devices in the C-CCP cage. It is the controller of the C-CCP cage

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and act as message router between the CBSC and the BTS equipment. The GLI2 interfaces to the CBSC via LAPD control link on a 64/56 kbps timeslot allocated on the digital span line connecting the cell site to the CBSC.Each SC4812T or SC4812ET has two GLI2 with on being Active and the other in standby mode. In active mode, the GLI2 provides traffic information to the MCCs, control information to the MCCs and BBXs,and control information to the other GLI2 via an Ethernet LAN.

The GLI is 2N redundant one C-CCP cage support up to two GLI2s.In standby mode, the GLI2 stays in sync with the active GLI2 so that it can be come the active GLI2 if necessary.

CIO (COMBINER INPUT/OUTPUT)

Each C-CCP shelf has one CIO.The CIO is a passive RF interface card that serves as an extension of the backplane.RX signals are routed from the MPC or EMPC then split to several levels to support up to 12 primary and one redundant BBX(via the switch card).In the forward link, the CIO combines each of the 12 primary TX paths with their redundant path(via BBX2 switch card),then routes the signals to the appropriate LPA cage. There are two different versions of the CIO board.1. 3 sector 2. 6 sector

GPS (GOBAL POSITION SYSTEM)

A GPS stands for Global Positioning System. A GPS receiver is located in the BTS and is connected to antenna via RF cable. This provides synchronization signal and timing signal to CDMA network for channel coding. This antenna communication with satellite continuously.

CSM(CLOCK SYNCHRONIZATION MANAGER)

The CSM maintain CDMA system time and generates the master clock and reference signals for other CDMA system modules. To provide the required synchronization for the CDMA frames, the CSM can phase lock up to two types of sources, a GPS receiver, or the LFR/HSO. The GPS receiver is the primary source and the LFR or HSO is the redundant source.

CCD (CDMA CLOCK DISTRIBUTION SUBSYSTEM)

The generation of the CDMA clock and synchronization signals is provided by the CSM.The CSM generates the CDMA clock

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(19.6608 MHz) ,even –second reference and the absolute time of day information .The CDMA clock and sync is routed to the C-CCP via the CCD.The CCD buffers the CDMA clock and sync and directs these signals out to the MCCs,BBXs,and the GLIs.Each CSM is linked to one and only one CCD card. The CCD card reports internal alarms back to its respective CSM.In case of failure, the active CSM then seamlessly switches to the redundant CSM and CCD pair.

HSO (HIGH STABILITY OSCILLATOR) – optional

The High Stability Oscillator (HSO) also is an optional card that provides backup for the GPS.The HSO module is and alternate source of the synchronization and absolute time information that is required at a CDMA BTS.It provides a precise oscillator as the backup source for timing reference where there is a loss of the GPS signal, A GPS failure, or a Primary CSM failure. The output of the HSO card is routed to the CSM cards, which derive the appropriate time references for the frame. The HSO is guaranteed to provide GPS timing for 24 hours, at minimum but cannot be used to bring a site into service.

LFR (LOW FREQUENCY RECEIVE) – optional

The LFR is an optional card that provides backup for the GPS.The LFR module is an alternate source of the synchronization and absolute time information that is required at a CDMA BTS. The LFR is used to provide a stable time reference when there is a loss of the GPS signal, a GPS failure, or a primary CSM failure. The output of the LFR card is routed to the CSM B card, which derives the appropriate time references for the frame. The LFR requires a dedicated LFR antenna. The LFR is a LoranC receiver, which uses the LoranC standard. This is not to be employed in any of he TTL BTS.

C-CCP POWER SUPPLY CONVERTER

The DC power supply converter cards installed in the C-CCP shelf convert the input voltage to the necessary DC voltages required to power the various modules in the C-CCP shelf. The primary input voltage is -48 volts DC. Power supply modules work on a load sharing basis. If one fails, the others will deliver full power to the rest of the modules in the shelves. They are hot swappable.

LPA SHELF

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The four linear power amplifiers(LPAs) per three sectors of one carrier are combined in “soft fail” redundancy.In”soft fail” redundancy, none of the sectors go out of service if an LPA module fails. In the event of an ST-LPA failure, the LPA module takes itself out of service sends an alarm to the GLI2, and the three sectors supported by that LPA module operate at 2.5db reduced power. Each trunked LPA set operates independently and is monitored separately. Monitoring and control of the LPAs is via the RS485 bus to the GLI2.The group line interface (GLI2) queries the LPAs for: Alarm status, Parameters involving Intermodulation Distortion (IM) suppression, Electronic ID, and the General state of device.

AMR (ALARM MONITORING AND REPORTING)

There will be a different type of problem in BTS like any of the card fail, main supply fail, rectifier system fail, LPA fail. To indicate this problem we use alarm system. By using this card the different types of alarm are sending to the OMC trough E1 so OMC can take necessary action. This card continuously monitoring and sending report to OMC.There are two AMR cards are available because if one of the AMR card fail then another one can take place.

DUAL BAND PASS FILTER

The TX dual Band pas filter is an option that can be employed if the frame has one or two adjacent or non-adjacent carriers in a 3-sector system. It allows the carriers to operate anywhere in the transmit band without tuning of the combiners. The TX DBPF module supports 2 carriers and has the same dimension as the 2:1 cavity combiner. The DBPF module offers transmit filtering but no combining of the CDMA signal. Maximum of 6 per -48 volt SC 4812T frame.

COMBINER (4:1 AND 2:1)

The LPA output are routed to either a 4:1 or 2:1 cavity combiner that is used to combine four or two non adjacent CDMA carriers onto a single TX antenna. A combiner can be used only when the carriers that need to be combined are not adjacent (alternate).Odd channels can be combined on one antenna and even channels on another. These combiners are installed internal to the frame with a maximum quantity of six 2:1 combiners and three 4:1 combiners per -48 volts SC 4812T frame.

2.3Function of BTS on the RF link.

FORWARD LINK

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The CBSC transmits a multiplexed digital data stream containing control signals and forward link traffic data for all subscribers communicating with the BTS over a high-speed Telco span line in T1(1.544 Mbps) or E1(2.048 Mbps) format. In circuit data system ,the digital signals are routed from the punchblock,Channel service Unit(CSU ), and span I/o block to the Group line interface(GLI) module via the digital signals are routed from the punchblock to the BTS Router(BTSRTR) .The BTSRTR converts the incoming span signals to digital LAN signals and its output are cabled to front of the Group Line Interface(GLI3) module by 100Base-T cables.

The GLI module routes the speech traffic and required control information to the MCC modules for processing. Traffic data for each subscriber in a sector is formatted and applied to a channel element on the Multi Channel CDMA card. Each CE encodes the traffic data and inserts power control information into a forward link data stream. The traffic data stream is converted into a CDMA baseband format, using a unique Walsh code assigned by the control information for that subscriber. The output from all CEs for a sector are summed together and routed to the Broadband Transceiver (BBX).The composite signal is spread by the assigned Interphase (I) and Quadrature (Q) Pseudo-random Noise (PN) mask codes to reduce I&Q components.A pilot signal is applied to Digital-to-Analog (D/A) converters to produce analog I and Q baseband signals and then up-converted to RF on the BBX.

The low-level RF drive signal is applied to the trunked Linear Power Amplifier (LPA)Assembly, which amplifies the signal to the level required for transmission via the site antenna. Three sectors share the resources of a composite power amplifier assembly consisting of four single carriers feed forward amplifier, LPA, modules.This trunking technique significantly increases the efficiency of the RF chain.

REVERSE LINK

Reverse link signals from subscriber mobile units enter the BTS through the RX path. Each of the sector has two receive branches, main and Diversity, with a dedicated antenna. The received signal at the RX port is routed through the DRDC (Duplexer, RX filter, Directional coupler)/TRDC (TX filter, RX filter, and Directional coupler) to the Multicoupler Preselector card (MPC), which provides low-noise amplification. Two MPC modules are used, one for the Main branches and one for the Diversity branches. The MPC output is routed to the combiner Input/Output (CIO) card through the C-CCP backplan.The CIO splits the signal

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and routes it to the BBX by the way of the C-CCP backplane. The BBX module for each sector contains two identical receiver strips, one each for the Main and Diversity signals. The main and Diversity signal outputs are amplified, down converted, demodulated and digitized.

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Patching of E1 cable on DDF Block.

Introduction

The aim of communication system has been to get more and more Information transmitted on a single cable. These involve gathering a number of sources to gather, transmitting them to gather and then send separating them and passing them to the individual receivers.

E1 was introduced in the 1960s.E1 is the digital communication link that enables the transmission of voice, data and video signals at the rate of 2.048 Mbps.

Why E1 in demands?:

o Simplification of Network:

E1 simplifies the task of Networking different types of communication equipment.E1 link carry both data and voice on a single digital communication link.

o Quality of Services:

E1 also provides a signal, which is superior in quality, then the analogue signal provides. In analogue signal, noise and distortion is also amplified so it degrades the quality of signal. While in E1 system because of signal regeneration we got exact signal at the receiver side.

Process of E1 Patching

Tools: Krone Tools, Wire cutter, LED, Loop Tester, DDF BlockProcedure:

o Pass E1 Cable Under Ground in Switch Room from DDF to MUX. o Open the Insulation of Cable Cat5.o Locate the Proper E1 slot on DDF Block. In TATA each DDF block

contain 4 E1 slot in One Row. DDF block has 12 rows.o Mount the Cable end in E1 slot on DDF and Punch using Krone

tool.o Use Proper side of Krone Tool & Tip.

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E1 patching

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Testing of E1

There are mainly two methods to check E1.

1)Using LED: Put external LED in E1 slot on DDF block. Note down that It’s glow or not. If it’s glow then it’s E1 connection is correct.

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2)Using Loop Cable: Put Loop cable in Tx and Rx slot of E1 and check By Computer in O&M Room.

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DRIVE TEST INTRODUCTION

A basic objective of CDMA RF performance engineering is to drive test the coverage area and investigate performance problems. CDMA is a common frequency system.

CDMA system is an inflexible, which requires area-wide or cluster testing of coverage. Adjustments made to coverage power, antenna geometry or RF call processing algorithm parameters will impact all sectors sharing the spectrum image. In addition, outside or distant noise sources must be surveyed, controlled or removed if possible.The tester must resist the localized changes but focus on changes that improve the overall cluster of cells – area wide coverage quality.CDMA drive testing is performed using a phone connected to a portable computer. Cellular and PCS subscribers view the performance of their service on the basis of the network coverage or the call quality. The drive-test tool uses a phone to re-create the problems that a subscriber is experiencing. For example, if a subscriber’s call is dropped while operating in a moving vehicle in a particular location; the drive-test should be able to duplicate this problem.

SET UP OF DRIVE TEST

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TWO CDMA PHONE AND ONE RECEIVER:1. Laptop Running E6474A Software, with Dongle attached2. GSM Receiver x 13. Receiver Cable (from USB to Receiver & Receiver Input Power) x1 4. RF Antenna + GPS Antenna x 15. Manifold Hub x 16. CDMA Kyocera QCP2235 phone x 27. CDMA Manifold Phone Cable (E6474-60139) x 28. USB Cable x 19. 9 pin - 9 pin Serial Cable x 110. Receiver power cable with 2 pin MOLEX power connector x 1

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GPS Antenna

Fig. 54 Setup for drive test

Dongle USB Cable CDMA Phone Cable CDMA Phone Receiver

Cable

Fig. 55 Drive test-A (GPS TRAKING FOR DRIVE TEST)

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Fig. Drive test-B

(IMPORTANT FOR WONDOWS)

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Fig. 57 Good call

Fig. 58 Dropped call and bad coverage

The drive-test system is placed in a vehicle and driven throughout the wireless service provider’s network coverage area.

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Fig. 59 Drive-test van in a CDMA wireless network

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THE PROCESS OF DRIVE TESTING INCLUDES

TESTING COVERAGE THE UNLOADED

In unloaded coverage test we include only measurement of CDMA parameters like sector coverage, neighbor list, proper channel transmission and this process is usually done when traffic is very low or in the night.

TESTING THE LOADED COVERAGE

In loaded coverage test we included hand off parameter in max traffic and received power level transmit power level and other parameter. It is done in daytime when traffic is high CDMA is a common frequency system; any RF configuration or feature parameter changes must be tested in the surrounding cluster of cells.

EQUIPMENT

Data Collection Tool (Examples: Agilent-Nitro, Qualcomm-CAIT) 1 or 2 Phones interconnected with the PC-Laptop GPS receiver interconnected with the PC-Laptop Attenuation Box to simulate penetration loss on the rev/fwd links

(RF) PC-Laptop with Data Collection and other software applications Power Supply to power up equipment Carrying case to fit every piece of equipment

DATA PROCESSING AND ANALYSIS

Data Processing Tool (Example: Agilent-Actics) PC to run the Data Processing software

DATA COLLECTION

Files logged using a data collection tool will have information on the following:

Mobile transmit power Mobile receive power Signal to noise ratio Frame error rate Handoff state Air interface Messaging Multi-paths Statistics

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Position and speed

Data Collection Laptops should be used as dedicated computers for data collection in the field. No additional user software should be installed on Data Collection Laptops.

POSSIBLE CAUSES OF NETWORK PROBLEMS

There are a number of causes for blocked calls (failed originations), dropped calls, and poor FER.These causes can include the following:

Poor RF coverage. Pilot pollution. Missing 47eighbour47. Search window setting problems. Timing errors.

Lack of RF coverage is often the cause of dropped calls and blocked calls. This may occur due to a localized coverage hole such as a low spot in the road), or it could be due to poor coverage at the extreme edge of the coverage area. Pilot pollution is the presence of too many CDMA pilot signals. The additional pilots act like interference to the subscriber’s call. The missing 47eighbour condition occurs when the phone receives a high-level pilot signal and it does not appear in the phone’s 47eighbour list. Again, it acts as an interfering signal and can cause dropped calls and high FER. Likewise, dropped calls can occur when the search window is not set properly. In this case, the phone cannot find pilots that are in its 47eighbour list. Finally, base station timing errors can lead to dropped calls, since CDMA systems depend on having synchronous timing between base stations.

DATA PROCESSING/ANALYSIS TOOL

The data processing tool processes and analyzes system data, and provides information about cell-site performance, mobile performance, and, RF coverage.

An output of the processing tool provides information to evaluate system performance and coverage, and to find faults. 

This tool allows the user to create performance metrics from mobile data. The same should be able to read an RF Call Trace (RFCT) file to be able to reproduce the RFER.

PILOT ANALYSIS

Pilot Ec/Io: Max Finger FCH47

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Provides information about the best multi-path Aggregate FCH Provides information about the best signal after soft-

handoff Dominant Pilot Ec/Io Provides information about the strength of the dominant (best)

pilot Number of Pilots above threshold Provides information about the amount of pilots above a certain

threshold (normally 15 dB) Ec/Io of Specific Pilot Provides information about the signal strength for a specific pilot Mobile transmit power Provides information about the amount of power the mobile is

transmitting to the base stations. Mobile receive power Provides information about the amount of power in band received

by the mobile. FWD/REV Frame Error Rate (FFER/RFER)

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CONCLUSION

Telecom field does know no bounds as the technology is developing and the customers are increasing manifold. After working in the practical environment we found that CDMA technology is very viable. It is reasonable at both the ends. It has proved its mettle till now and is showing its abilities incessantly. This technology has the ability to shape the future of mobile and Telecom Industry.

Purpose of Industrial Training:-The main aim of Industrial training is to understand the technology better on the practical basis. It tremendously helps an engineer to get an overview of corporate culture before joining a job. We get technical exposure to every old and new instrument and technical advances.

We also, after coming out of the modest environment of college, plunged into the realistic world. We understood the corporate ethics, culture and the working scenario of the company. Working day in and day out, along with new faces, where all wanted to prove their mettle, we learned a lot of things such as how to deal with people of various levels starting from a worker till the zonal manager and satisfying them excellently. We also found new friends aspiring the same dream and flocked together for a life-long companionship. We also learned to communicate efficiently, being particular, showing regularity and above all taking responsibilities and proving ourselves. We acquired team-spirit, leadership and soft skills working in such a splendid environment. We enjoyed taking our training at TATA TELESERVICES LIMITED, Gujarat.

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BIBLIOGRAPHY

[1] Introduction to Wireless © 2001 Scott Baxter

[2] Technical Introduction to CDMA v4.0 © 2005 Scott Baxter

[3] CDMA/CDMA2000 1X RF Planning Guide, Motorola

[4] SDH BASICS, NEC Guide

[5] Ring Architecture and Switching, NEC Guide

[6] CDMA TECHNOLOGY, Tata Teleservices Limited Guide

[7] 3G Network- An overview, BSNL Guide

[8] Wireless Communications, Theodore S. Rappaport, ©

2002, Prentice Hall, Inc.

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