Tata Tele Services Training Report

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CHAPTER 1

INTRODUCTION TO

TATA TELESERVICES LTD

1.1 Introduction

1.2 Brief History of the company

1.3 Service offered by TTSL

1.3.1 Voice

1.3.2 Data

1.4 Partners of TTSL



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1.1 Introduction

Tata Teleservices Ltd (TTSL) offers its products and services to customers across

India under the name of "Tata Indicom".

TATA Teleservices limited is India's leading Private Basic Service Operator. TATA

Teleservices is an integral part of the TATA Group's holistic venture in the telecom

industry. The Group has a significant presence in all sectors of the telecom industry -

Basic, ISP, NLD and Broadband.

The company signed its license and inter-connects agreement with the Government of

India on November 4 1997, when the Government opened up the Basic Services business

to Private Operators.

TATA Teleservices brings the benefits of convergence to the customer's doorstep.

TTSL's wire line connections are a mix of both copper and fiber, which enable clear

voice transmission and faster data transmission. The Company is upgrading its wireless

network to 3G 1X with capabilities of handling speeds up to 144 kbps and has a full-

length managed network with centralized Network Management System. The network is

highly reliable and supports monitoring and maintenance.

TTSL's Pay Telephone Booths offer significant consumer benefits, including privacy &

comfort. Operators and customers also benefit through accurate billing. TTSL has clearly

demonstrated its leadership in Pay Telephony by setting up over 5000 Pay telephone

booths in Andhra Pradesh. The Company has successfully replicated these value added

services in the other five proposed circles of Delhi, Gujarat, Tamil Nadu, Karnataka &

Maharashtra, thus effectively servicing its customer base of 13,17,000 customers across

all the six circles it currently provides it services in.

1.2 Brief history of the Company

TATA Teleservices Limited is a customer-focused company, and aims to provide the

latest network supported by specialized IT systems, thereby ensuring an efficient and

cost-effective network and business operations. TTSL has entrusted Tata Consultancy

Services (TCS) with the task of complete IT provisioning, operation and maintenance.

Leading IT vendors like Keenan (for billing systems) and Oracle (for Enterprise Resource

Planning) are associated with TTSL for the provision of world class back office support.

TTSL's portfolio of products and services vary from basic features such as alarm service

and STD locking to value added services in call management such as call waiting, three-

way conference, call forwarding (immediate busy and no reply) and caller line

identification to advanced services such as Centrex, ISDN, leased lines and E1s. TTSL

was the first telecom service provider in the country to offer corporate telecom solutions

such as Centrex to its customers. TTSL also offers ISDN PRI to its customers and intends

to offer a wide range of telecommunication services.

TTSL is used the products of Lucent, Marconi, and Motorola.



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1.3 Services offered by TTSL

TTSL offered services in Voice as well as in Data as mentioned below.

1) Voice

TATA Indicom Mobile is based on the latest CDMA 3G-1X technology that offers

superior voice clarity and congestion-free networks. You can make and receive calls from

any landline, GSM cell phone or CDMA mobile phone from any other network in any

part country or the world.

Our handsets can of the work if you wish to switch your service provider to other CDMA

networks, but not with GSM networks. And indeed, GSM handsets will not work if the

service provider is on the CDMA platform. Calls can be made to or received from all

networks.

Current telecom regulation permits mobile phones based on Wireless in Local Loop

(WLL) technology (like TATA Indicom) to be provided within a specific geographic

limit termed as Short Distance Charging Area (SDCA), which usually corresponds to a

taluka or city like Mumbai, Delhi, Bangalore, Hyderabad, Chennai, Ahmedabad, etc. This

means that the handset will work only within the SDCA you are registered in (and hence

the phrase 'limited mobility'). Within the SDCA, calls including STD and ISD can be

made to or received from anywhere.

1.1 Landline phone connections

If you take a wire line connection, your telephone is connected to the TATA Indicom

exchange by a combination of high technology fiber - optic cables and copper cables. A

global standard today, fiber - optic cables enable our network to handle higher capacities

of load as compared to ordinary cables and at much higher transmission speeds. This

gives you trouble-free and faster connectivity.

1.2 Wireless Connections

When you take a wireless connection, your telephone is linked to the TATA Indicom

network via CDMA Wireless in Local Loop technology. In Wireless Local Loop (WLL)

technology, there are no cables connecting your telephone to the telephone exchange.

Instead, a Network Interface Unit (NIU) is installed within your premises and your phone

instrument is connected to it.

1.3 ISDN Lines



4

ISDN, which stands for Integrated Services Digital Network, is a system of digital phone

connections that has been available for over a decade. This system allows data to be

transmitted simultaneously across the world using end-to-end digital connectivity. used to

analog connectivity so far) to your phone line for various applications such as data and

image transfer amongst others, in addition to normal voice telephone on the same line.

This system allows data to be transmitted simultaneously across the world using end-to-

end digital connectivity. With ISDN, two bearer channels carry voice and data.

1.4 Centrex

Centrex (Central Exchange) is a facility that enables a customer to utilize all the facilities

provided by an EPBX from TTSL’s wire line switch. It is a productivity booster that

helps the customer to utilize facilities similar to those offered by an EPBX while also

retaining the benefits of a direct line. With Centrex facility, one can access other

members of their group through 3 or 4 digit dialing. It is offered to corporate who have

multiple connections. It allows the caller to be directly routed to the received or the

extension without going through an exchange. It also serves as an intercom with

extension numbers for internal calls.

2) Data

2.1 E1 Links

This is an ideal solution for large business users who require a large number of telephone

lines to their EPABX. An E1 link is a 2 Mbps data circuit, which can carry 30 voice /

data channels. The benefits are:

1. Faster connectivity

2. Confidentiality

3. Guaranteed uptime levels

4. Optimal utilization of lines and resources

2.2 Basic/Primary Rate ISDN

2.2.1 Basic Rate ISDN

Basic Rate ISDN is what would typically be provided to the residential user. But that

does not mean to say a business would not use Basic Rate, it could be used in a small

office environment or as some form of backup for other services. In this overview we will

look at Basic Rate ISDN or BRI as it is sometimes called. In BRI there are 2 B channels

and 1D channel that operate at 128 Kbps. A maximum of 2 applications can run

simultaneously.

2.2.2 Primary Rate ISDN



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Primary rate ISDN is based on the same frame format as an E1 trunk using Common

Channel Signaling. Typically a business customer would have Primary Rate ISDN. In

PRI there are 30 B channels and 1D channel that operates at 2 Mbps. A maximum of 8

applications can run simultaneously.

2.3 Leased Line

There are three types of leased line used in modern digital communication system:

1. Managed Leased Line

2. Leased Line

3. Digital Leased Line

2.3.1 Managed Leased Line

These are point-to-point dedicated pipes starting from 64 Kbps to 2 Mbps lines. They can

also be used for Internet bandwidth access as point to ISP connectivity. Managed Leased

Line is connected to the Concentrator (Any Media). The fault in this type of Leased Line

can be detected through a terminal that is connected to the Concentrator. This terminal is

placed at the TTSL premises. This terminal has a ESM (Element Service Manager). ESM

has the details of all the Concentrator Sites, which monitors the equipment (LL). Through

ESM, it is detected which Any Media port has a problem. This type of Leased line is not

currently being offered by TTSL. Managed leased line is a costly affair. Managed Leased

Line services can be offered to the customers in n X 64 Kbps form varying from 64 Kbps

to 2 Mbps

2.3.2 Leased Line

This type of leased line does not give scope to detect the problem. An Engineer has to

check the end to end connectivity to identify the fault. A standard bandwidth of 2 Mbps is

offered to the customers. This facility is being offered by TTSL. The downtime is very

low and is a planned outage which means TTSL informs the customer about the period

when the Leased Line doesn't function.

2.3.2 Digital Leased Line (DLL)

In case of DLL, the bandwidth is offered in multiples of 64 Kbps. The bandwidth offered

is unlimited in this scenario. Digital Leased Line (DLL) offers a transmission media

between two points falling within the same or different CSA. The points A and B

respectively can be within a maximum distance of 3 kms from the CSA. The DLL

solution consists of one ISDN-NT1 and one Multicom ISDN router as customer premises

equipment (CPE) and customer does not require any modem or router at his premises.

The circuit so offered can present the Ethernet interface to the customer equipment.

The Ethernet interface from Multicom router is used to interface to Hub / Switch in

customer LAN.



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2.4 Virtual Private Network (VPN)

A Virtual Private Network (VPN) provides you the most cost-effective solution for

keeping your offices, staff and customers over multiple locations stay connected with

each other with maximum speed, convenience and security. VPNs allow a free flow of

information and quick data transfers and are highly secure because they are accessible

only through an authorized identified.

1.4 Partner of TTSL

To ensure superior transmission quality for our customers, we use the best technology

available.

To achieve this, TTSL has entered into partnership with various international leaders like:

1) Lucent, the world’s leading manufacturer of telecom Network equipment, to set up the

core network Infrastructure.

2) DMC, for microwave and Marconi for optical transmission network

3) TATA Consultancy Services, to help implement and integrate IT systems.

4) Kenan, USA for effective customer management.

5) Oracle Financials, for enterprise resource planning and small world, for Geographical

Information System (GIS).



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CHAPTER 2

INTRODUCTON

TO E1 LINE

2.1 Introduction

2.2 Why E1 is Demand?

2.3 How E1 Works. Making voice & data

Compatible

2.4 Alarms

2.1 Introduction

The aim of communication system has been to get more and more Information



8

transmitted on a single cable. This involves gathering a number of sources together,

transmitting them together and then separating them and passing them to the individual

receivers.

E1 is a digital communication link that enables the transmission of voice, data, and video

signals at the rate of 2.048 Mbps. It was introduced in the 1960s.

2.2 Why is E1 in demand?

The current demand for E1 services can be linked to a number of tangible benefits.

1) Simplification

E1 simplifies the task of networking different types of communication equipment. To

illustrate, figure 1 show what your company’s communication network might be look like

without E1 and figure 2 Shows Company’s communication network with E1 link.

Figure 1 shows that telephone, fax, and computer applications would all require separates

lines. Typically, voice and low speed data serviced by analogue line, while high-speed

data application like computer are serviced by digital line. In figure 2 same things is

shown with E1 link installed.

E1 link carry both data and voice on a single digital communication link. In this way we

can reduce the task of managing many different networks.

2) 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.

Phone

System

Phone

System



9

� �

� �

Figure 2.1

A communication network without E1

� �

E1 Link

� �

Figure 2.2

A communication network with E1

2.3 How E1 works – Making voice and data compatible

Many benefits of E1 are attributable to the fact that voice and data transmitted over a

single digital communication link. Since computer data consists of ones and zeros (the

symbol of the binary system), it is already compatible with E1’s digital format. However,

because voice signals are actually complex analogue waveform, they must be digitized to

achieve compatibility with E1.

FAX FAX

PC

PC

Phone

System

Phone

System

FAX FAX

PC

PC

M

U

X

M

U

X



10

1) Pulse Code Modulation (PCM)

The most common method of Digitalized analog voice signals is a technique called PCM.

It is a sampling process that compresses a voice conversation into a 64 kbps standard rate

known as digital signal-level zero (DS0).

PCM is actually a two-step process. In the first step, the incoming analog signal is

sampled at 8,000 samples per second. The voice signal has a frequency of 300 Hz to 3400

KHz. And Shannon’s sampling theorem said that a sampled signal contains all the

information if the sampling frequency is at least twice of the highest frequency of the

analog signal to be sampled. Let the highest frequency of the voice signal is 4000Hz. So

Sampling rate = 2 * 4000

= 8000

So we have to sample the analog signal at this rate. These sample values are then

converted in the pulses using technique called Pulse Amplitude Modulation (PAM) as

shown in figure 3.

Figure 2.3

Pulse Amplitude Modulation.

In the second step, the height of each pulse is assigned an equivalent eight–bit binary

value. The resulting output is a digital representation of the pulse and, by extension, the

sampled analog voce signal. As shown in figure 4.

01110111

01010101

01000100

00110011

00100010

00010001

00000000

10011001

10101010



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Figure 2.4

Quantization

Rate is obtained as explained below.

Rate = 8000 samples/second * 8 bit /sample

Rate = 64000 bits/second (single channel-DS0)

2) Time Division Multiplexing (TDM)

Once digitized, voice and data signals from many sources can be combined (i.e.

multiplexed) and transmitted over a single E1 link. This process is made possible by a

technique called TDM.

TDM divides the E1 link into 32 discrete 64 kbps timeslots. An identical number of DS0

signals is assigned to each time slots for transmission within the link as shown in figure.

� �

� �

Figure 2.5

Time Division Multiplexing (TDM)

3) 2.048 Mb/s Explained

In E1, the eight samples created in the PCM step (for voice traffic only) are grouped into

the 32 discrete DS0 timeslots created by TDM. Each group of 32 timeslots is called a E1

frame. Since each timeslot contains eight bits, the total number of information bits within

each frame totals 256 (32x8).

PCM

Data Data

PCM

TDM

TDM



12

Since the DS0 signals are sampled 8,000 times per second, it means that 8,000 256 – bit

information frames are created during that period. So total BW comes,

BW = 8000 x 256

= 2048 kbps

= 2.048 Mbps

1 8

1 ………………………………………….. 31 32

Figure 2.6

E1 Frame = 256 bit

4) Signal Regeneration

Any newly created signal begins strongly, but degrades as it progresses along the E1 line.

Such attenuation is usually the results of line noise caused by interference from other

electrical sources. To compensate for these negative effects, devices called regenerative

repeaters sample and recreate the original signal at the periodic interval along the link as

shown in figure.

Figure 2.7

Regenerative Repeater

The number of regenerative repeaters that may be required along the path of E1 link

varies with the type of transmission media used.

5) Frame Type

Timeslots

TDM

Regenerative

Repeaters

Signal



13

The primary frame consists of 32 timeslots numbered from 0 to 31. Two types of primary

frame are PCM30 and PCM31.

5.1 PCM30

In this type of frame 1 to 15 and 17 to 31 timeslots are used for traffic. While 0 slot is

used for synchronization and 16 is used for signaling purposes.

5.2 PCM31

In this type of frame slot 0 is used for synchronization while slot 1 to 31 is used for

traffic. As shown below

Figure 2.8

PCM 30 & PCM 31

6) Synchronization

The transmitter and receiver are synchronized to the PCM frame with the aid of Frame

Alignment Signal (FAS) which is transmitted in timeslot 0 of every second frame. The

Not Frame Alignment Signal (NFAS) is transmitted in timeslot 0 of the alternate

frames. Two types of frame are shown below which is transmitted along the 0 slot.

0 1 to 15 timeslots 16 17 to 31 timeslots

32 Timeslots

Synchronization slot Signalling slot

0 1 to 31 timeslots

32 Timeslots

Synchronization slot

0 1 to 31 Timeslots

X 0 0 1 1 0 1 1

8 bit



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Figure 2.9

Synchronization

6.1 FAS (Frame Alignment Signal)

Frame Alignment Signal (FAS) is transmitted at every even frame ( i.e. 2,4,6,8,… ).

Bit 1 is Si (C) where.

Si = reserved for international use.

C = CRC division remainder with PCM30 and PCM31

The receiving side of the PCM system determines the timeslot of the PCM frame on the

basis of the received frame alignment signals, so that received bits can be assigned to the

various channels in the correct sequence.

6.2 NFAS (Not Frame Alignment Signal)

The Not Frame Alignment Signal is used to carry information about the status of the link

and provide control signals for primary rate multiplexers.

Not Frame Alignment Signal (NFAS) is transmitted at every odd frame ( i.e.

1,3,5,7,9,…..)

Bit 1 is Si (M) where….

Si = reserved for international use.

M is used for transmitting the CRC - Multiframe alignment signal in

PCM30 or PCM31

Bit 2 is set to 1

Bit 3 (A-bit) shows remote alarm indication

FAS In even frames

NFAS In Odd frames



15

Bit 4 to 8 are spare bits which are used in specific point-to-point applications within

national borders.

Bit Sa4 may be used for as a message-based data link for operations, maintenance and

performance monitoring.

6.3 Frame Synchronization

Figure 2.10

Frame Synchronization

PCMX 30: Primary Multiplex for 30 speech/data channels.

LTE: Line Termination Equipment

LR: Line Regenerator

PCM multiplex B will synchronize on to incoming bit stream from mux A under the

following condition:

1. Correct FAS, Si 0 0 1 1 0 1 1, is received in timeslot 0 of a frame.

2. Bit 2 in timeslot 0 (NFAS) of the next frame received must be 1, Si 1 A Sa4 Sa5

Sa6 Sa7 Sa8 is received in timeslot 0.

3. FAS, Si 0 0 1 1 0 1 1, is received in timeslot 0 of the subsequent frame.

The multiplex is synchronized on to the incoming frames only if all three conditions are

fulfilled.

6.4 Signalling

In PCM30 and PCM31C system timeslot 16 is used channel-associated (CAS).

The information necessary for switching and routing all 30 telephone channels (signaling

and status codes) are interleaved and transmitted in this timeslot.

The interchange of signaling between the multiplexers in the forward and backward

channel takes place using pulse signals comprising four bits (a, b, c, d) which are formed

by signaling multiplex equipment from the signals originating in the exchange.

6.5 Channel-associated signaling (CAS)



16

Interchange of signaling in the forward and backward directions is accomplished using

bits that only change state slowly. It is therefore sufficient to transmit these relatively

static signaling bits at a rate of 2 kbps for each subscriber.

As a result, the 64 kbps capacity of timeslot 16 is divided between the 30 subscriber

channels and 2 auxiliary channels for synchronization and alarms. A signaling multiframe

is formed which comprises 16 normal PCM frames.

Each signaling timeslot of the multiframe has a transmission capacity of 4 kbps (64 kbps

divided into 16.

6.6 Cyclic Redundancy Check (CRC)

With the introduction of ISDN (Integrated Services Digital Network), subscribers are

provided with transparent 64 kbps channels for speech or data transmission. Transparent

in this sense means that the binary signal transmitted by the subscriber is transmitted over

the entire signal path without being altered is in any way by analogue/digital conversion

or other means, with the bit sequence integrity preserved.

There is a danger with this type of data communication that the subscriber may

intentionally or unintentionally transmit the bit pattern 10011011 which corresponds to

the FAS. This may lead to the PCM multiplexer re-synchronizing to this apparent FAS,

with the result that all of the PCM channels will be incorrectly assigned.

2.4 Alarms

1) Remote Alarms

Multiplexers are connected together so the PCM transmissions take place in both

directions, it also follows that messages are also transmitted bi-directionally.

Figure 2.11

Remote Alarm



17

The NFAS is used to transmit service information. Bit 3 of the NFAS indicates a remote

(or distant) alarm:

If Bit 3 is 0 – No alarm

1 – Following situations has occurred.

• Power failure

• Codec failure

• Failure of incoming 2048 kbps signal

• Frame alignment error

2) HDB3

HDB3 stands for high density bipolar code in which a max of 3 zeros may occur in

sequence.

The following rules are used to convert a binary signal into a HDB3 coded signal:

Rule 1: If four 0-bits consecutively, the fourth zero is replaced by a violation bit or V-bit.

The substitution is thus: 0000 becomes 000V

Rule 2: If there is an even number of 1-bits between the violation bit to be inserted and

the previous violation bit, the first zero of the sequence of four zeros is replaced by the so

called B-bit.

The substitution is thus: 0000 becomes B00V.

CHAPTER 3

INTRODUCTION

TO CDMA



18

3.1 What is CDMA?

3.2 Overview of Multiple Access

Technology

3.3 Frequency Re-use

3.4 CDMA Spread Spectrum Technology

3.5 Generation of CDMA Signal

3.6 Code Channels used in CDMA

3.7 Call Processing Stages

3.8 CDMA Physical and Logical Channels

3.1 What is CDMA?

Code Division Multiple Access (CDMA) is a digital technology pioneered by

QUALCOMM that provides crystal clear voice quality in a new generation of wireless

communications products and services. Using digital encoding and "spread spectrum"

Radio Frequency (RF) techniques, CDMA provides better and more cost effective:

• Voice quality

• Privacy

• System capacity

• Flexibility

than other wireless technologies. CDMA also provides enhanced services such as:

• Short messaging

• E-mail



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• Internet access

CDMA and other wireless communication have become very popular in the last few

years, but people have been trying to accomplish the goals of wireless telecommunication

since shortly after the invention of the telephone.

Figure 3.1

Multiple Access System

3.2 Overview of Multiple Access Technology

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 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).



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Figure 3.2

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.

Figure 3.3

TDMA

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.



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Figure 3.4

CDMA-A

Figure 3.5

CDMA-B

CDMA is the only one of the three technologies that can efficiently utilize spectrum

allocation and offer service to many subscribers without requiring extensive frequency

planning.

All CDMA users can share the same frequency channel because their conversations are

distinguished only by digital code, while TDMA operators have to coordinate the

allocation of channels in each cell in order to avoid interfering with adjacent channels.

The average transmitted power required by CDMA is much lower than what is required

by analog, FDMA and TDMA technologies.

3.3 Frequency Re-use



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Figure 3.6

Frequency Re-use

1) Introduction 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.

Figure 3.7

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. All of the spread-spectrum systems have to

satisfy two criteria:



23

• The bandwidth of the transmitted signal must be greater then the transmitted

Signal.

• 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.

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



24

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.

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 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) MHz

Forward Link Frequency = (870 + N0.03) MHz

Where N = CDMA channel number

3.4 CDMA Spread Spectrum Technology



25

Figure 3.8

CDMA Spread Spectrum-A

Figure 3.9

CDMA Spread Spectrum-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

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



26

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.

1) The main issues in a communication system

The three issues in a communication system are:

• Capacity

• Delay

• Error detection/correction.

Capacity concerns how much information you can deliver from the source to the

destination.

Delay issues are those involving delivery of information in the shortest time.

Error detection/correction is a method to reduce errors in the delivery of information.

Think about problems you may have experienced due to these issues. For example, there

may be a capacity problem in your carrier's system if you experience trouble placing a

call

2) How CDMA works?

The words “Code” and “Division” are important parts of how CDMA works. CDMA

uses codes to convert between analog voice signals and digital signals. CDMA also uses

codes to separate (or divide) voice and control data into data streams called “Channels”.

These digital data streams channels should not be confused with frequency channels.

3.5 Generation of CDMA Signal



27

1) Analog to Digital conversion. 2) Vocoding. 3) Encoding and interleaving. 4) Channelizing the signal. 5) Conversion of the digital signal to RF signal.

The use of codes is the key part of this process. The block diagram and the required

components for generating the CDMA signal are as shown in figure .

1) Analog to Digital Conversion

The first step of CDMA signal generation is analog to digital conversion. CDMA uses a

technique called pulse code modulation (PCM) to accomplish A/D conversion.

2) Vocoder

The second step of CDMA signal generation is voice compression. CDMA uses a device

called a vocoder to accomplish voice compression. The term “Vocoder” is a contraction

of the words “voice” and “code”. Vocoder is located at the BSC and in the phone. People

pause between syllables and words when they talk. Thus CDMA takes advantage of these

pauses in speech activity by using a variable rate vocoder.

Figure 3.10

Generation of CDMA Signal-A

2.1 Variable Rate Vocoder

A CDMA vocoder varies compression of the voice signal into one of four data rates

based on the rate of the users speech activity. The four rates are:

Full rate 9.6Kbps

A/D

D/A

Code

generator

+ spreader

Vocoder Antenna



28

1/2 rate 4.8Kbps

1/4 rate 2.4Kbps

1/8 rate 1.2Kbps

Table 3.1

Variable Rate Vocoder

The vocoder uses its full rate when a person is talking very fast. It uses the 1/8 rate when

the person is silent.

2.2 Vocoder Types

CDMA systems can use either an 8Kbps or 13kbps vocoder to maximize capacity. The

13Kbps vocoder was later developed to provide a more baud line quality voice signal.

The improvement in quality was worth the slight reduction in capacity.

Recently the CDMA community adopted a new 8kbps vocoder. This new vocoder is

usually referred as the EVRC (Extended Variable Rate Coding). It combines the quality

of 13Kbps vocoding with the capacity of the 8Kbps data rate.

Figure 3.11

Generation of CDMA Signal-B

3) Encoding and Interleaving

Encoders and interleaves are built into the BTS and the phones. The purpose of the encoding and interleaving is to build a redundancy into the signal so that information lost

in transmission can be recovered.

The type of encoding done at this stage is called “Convolution Encoding”. A simplified

encoding scheme is shown below:

Bit A B C D

Encoded Symbol A A A B B B C C C D D D

Error A A A B B ? ? ? C D D D

A/D VOCODER

PCM

1011011

Vocoded Signal

or Voice



29

Decoded Bits A B ? D

Table 3.2

Bit Encoding

A digital message consists of four bits (A, B, C, D) of vocoded data. Each bit is repeated

three times. These encoded bits are called symbol.

The decoder at the receiver uses a majority logic rules.

3.1 Interleaving

Interleaving is a simple but powerful method of reducing the effect of burst errors and

recovering lost bits. In this example shown here the symbols from each group are

interleaved in a pattern that the receivers know.

Bit A B C D

Symbol A A A B B B C C C D D D

Interleaved Symbol ABC DAB CDA BCD

Errors ABC D?? ??A BCD

Deinterleaved A?A B?B C?C D?D

Decoded bits A B C D

Table 3.3

Bit Interleaving

4) Channelizing the signal

The encoded voice data is further encoded to separate it from other encoded voice data.

The encoded symbols are then spread over the entire bandwidth of the CDMA channel.

This process is called Channelization.

CDMA uses two types of Codes:

1. Walsh Codes

This type of coding is used in forward link. Walsh codes provide a means to uniquely

identify each user on the forward link. Walsh codes have a unique mathematical property

– “they are orthogonal”. In other words ,Walsh codes are unique enough that the voice

data can only be recovered by a receiver applying the same Walsh code. All other signals

are discarded as background noise.



30

1.1 Generation of Walsh Codes

Starting with a seed of 0 and same bit in horizontally and same bit vertically while

complements in diagonally generates orthogonal codes. This process is to be continued

with newly generated block until the desired codes with proper length are generated. So

in this way we will get total 64-walsh codes each have 64 bit long. Walsh codes are used

in the forward CDMA link to separate users. In any given sector, each forward code

channel is assigned a distinct Walsh code. The process is shown on below.

0 0 0 00 00 0000 0000 00000000 00000000

01 01 0101 0101 01010101 01010101

0 1 00 11 0011 0011 00110011 00110011

01 10 0110 0110 01100110 01100110

00001111 00001111

0000 1111 01011010 01011010

0101 1010 00111100 00111100

0011 1100 01101001 01101001

0110 1001 00000000 11111111

01010101 10101010

00110011 11001100

01100110 10011001

00001111 11110000

01011010 10100101

00111100 11000011

01101001 10010110

Figure 3.12

Generation of Walsh Codes

64 bit Walsh codes (providing 64 bit orthogonal codes) are used to provide 64 channels

within each frequency band. They are used for spreading in the forward link. In the

reverse link it is used to provide orthogonal modulation but not spreading to the full

1.2288 Mcps rate. The specific Walsh function on to which the data is modulated defines

the forward link Channelization.

• Pilot Channel (always used Walsh code W0)

• Mobile acquires phase, timing and signal strength via the pilot channel.

• Paging Channel (use Walsh codes W1-W7)

• Mobile gets system parameters via the paging channel.

• Sync Channel (always uses Walsh code W32)

• Mobile synchronizes via the sync channel. Traffic Channel (use Walsh codes

W8-W31 and W33- W63)

• Mobile and BTS communicate over the traffic channels during a connection.



31

Walsh sequences are also referred to as Wash Functions. These codes are generated at

1.2288 Mbps (Mcps) with a period of approximately 52 µs as illustrates below. These are

used to identify users on the forward link. For this reason they are also referred to as

either Walsh Channels or TCH. All base stations and mobile users have knowledge of all

Walsh codes.

Walsh Code generator Rate = 1.2288 Mcps

Time duration for the one Chip = 1/1.2288 Mcps

= 0.813 micro second

Total 64 chips are in one Walsh code so time between two Walsh code generations

= 0.813* 10-6 * 64

= 52.08 * 10-6 Second.

2. Pseudorandom Noise (PN)

This type of coding is used in reverse link. PN codes uniquely identify users on the

reverse link. A PN code is one that appears to be random. The PN codes used in CDMA

yield about 4.4 trillion combination of code. This is a key reason why CDMA is so

secure.

5) Conversion of Digital signal to RF signal

The BTS combines channelized data from all calls into one signal. It then converts the

digital signal to a RF signal for transmission.

3.6 Code Channels used in CDMA

A code channel is a stream of data designated for a specific user or person. This channel

may be voice or data or overhead control data. There are two basic links from BTS to

mobile unit and from mobile to BTS i.e. forward link and reverse link respectively. These

links use different types of channels.

CDMA

1 Chip of 813 ns



32

Figure 3.13

Code Channels of CDMA

1) Forward Link Channels

The forward link uses four types of channels to transmit voice and control data to the

mobile. The types of forward link channels are:

1. Pilot Channel

The BTS constantly transmits the pilot channel. The mobile uses the pilot signal to

acquire the system. It then uses the pilot signal to monitor and adjust the power needed in

order to transmit back to the BTS.

2. Sync Channel

The BTS constantly transmits over the sync channel so the mobile can synchronize with

the BTS. It provides the mobile with the system time and the identification number of

the cell site. The mobile ignores the sync channel after it is synchronized.

3. Paging Channel

CDMA uses up to seven paging channels. The paging channel transmits overhead

information such as commands and pages to the mobile. The paging channel also sends

commands and traffic channel assignment during call setup. The mobile ignores the

paging channel after a traffic channel is established.

4. Forward Link Traffic Channels

REVERSE

CHANNELS FORWARD

CHANNELS



33

CDMA uses between 55 and 61 forward traffic channels to send both voice and overhead

control data during a call. Once the call is completed, the mobile tunes back in to the

paging channel for commands and pages.

2) Reverse Link Channels

The reverse link uses two types of channels to transmit voice and control data to the BTS.

The types of reverse link channels are:

1. Access Channel

The mobile uses the access channel when not assigned to a traffic channel. The mobile

uses the access channel to:

• Originate the calls

• Respond to pages and commands from the base station

• Transmit overhead messages to the base station.

2. Reverse Link Traffic Channel

The reverse traffic channel is only used when there is a call. The reverse traffic channel

transmits voice data to the BTS. It also transmits the overhead control information during

the call.

3.7 Call Processing Stages

There are four stages or modes in CDMA call processing:

1) Initialization Mode

During initialization, the mobile:

- Acquires the system via the Pilot Code Channel

- Synchronizes with the system via the Sync Code Channel.

2) Idle Mode

The mobile is not involved in a call during idle mode, but it must stay in communication

with the base station

- The mobile and the base station communicate over the access and paging

code channels.

- The mobile obtains overhead information via the paging code channel.

3) Access Mode



34

The mobile accesses the network via the Access code channel during call origination. The

Access channel and Paging channel carry the required call setup communication between

the mobile phone and the BTS until a traffic channel is established.

4) Traffic Mode

• During a Land To Mobile (LTM) call:

a. The mobile receives a page on the paging channel

b. The mobile responds on the access channel.

c. The traffic channel is established and maintained throughout the call.

• During a Mobile To Land (MTL) call:

d. The call is placed using the Access channel.

e. The base station responds on the paging channel.

f. The traffic channel is established.

3.8 CDMA Physical and Logical Channels

1) Physical Channel

Physical channels are described in terms of a wideband RF channel and code sequence.

As defined in IS-95, each RF channel is 1.2288 MHz wide. For each RF channel, there

are 64 Walsh sequences (W0 through W63) available for use on the forward link. These

Walsh sequences are commonly referred to as CDMA code channels.

2) Logical Channel

The physical channel that carry specific types of information are known as logical

channels. Logical channels in CDMA are divided into two categories: Traffic Channels

and Control Channels. For the forward link there are three types of Control/Signaling

channels and one Traffic Channel (per user). For the Reverse Link there is one type

Signaling Channel and one Traffic Channel per user.

It is important to note that signals on the forward link are identified by Walsh codes;

however, signals on the reverse link are identified by Long Codes.

1. Orthogonal Codes

Orthogonal codes have a zero correlation. Walsh code has a property of orthogonality.

Two orthogonal codes will never interfere with each other. CDMA system there are 64

unique Walsh codes, each have 64 bits long. When we X-OR two codes and we get equal

numbers of 0 and 1 then these two codes are orthogonal to each other and have a zero

correlation.

Orthogonality = Equal Number of Matches and Mismatches



35

2. Pseudo random Noise (PN) code

PN code has randomness properties. If the current state and the generating function of the

PN code are known, the Future state of the code can be predicted. In CDMA One system

each base stations and all mobile in that base station use same set of three PN sequence

(two short codes and one long code).

The summary of all codes is given below:

Generation Rate: 1.2288Mcps

Length: 64 bits

Total No. of Code: 64

Repetition Rate: 64/1.2288Mcps = 52.08 micro second

Forward Link: Spreading the logical channel

Reverse Link: Orthogonal Modulation


Length: 242 = 4398046511104 bits

Repetition Rate: 41 days

Forward Link: Scrambling of Paging and Traffic channel, Encryption

Reverse Link: Spreading, Encryption


Length: 215 = 32768bits

Repetition Rate: 26.67 ms

Forward Link: Scrambling (Cell Identification), Synchronization

Reverse Link: Scrambling (Cell identification), Synchronization

CHAPTER 4

FUNCTION OF THE

Walsh

Code

Long

Code

Short

Code



36

CELL - SITE

4.1 Function of the Cell-Site

4.2 Converting Digital Signal to RF Signal

4.3 Architecture of CDMA

4.4 Types of Call

4.5 Features of CDMA

4.6 Hand-Offs in CDMA

4.7 Advantages of CDMA

4.8 Site Structure

• How does the cellular system work?

Cellular service providers used a network of cells in a geographic area. This reduced the

power requirements of the transceivers and accommodated more users. The main

components of an analog cellular network are:

• Public Switched Telephone Network

• Mobile Telephone Switching Office (MTSO)

• Cell site (also called "Base Station" or "BTS")

Everything from your telephone to the PSTN is considered part of the standard wire line

service.



37

4.1 Function of the cell site

The cell site contains a transmitter and receiver (or transceiver) to connect cellular

phones to the network. The cell site is also called the Base Station or the Base Station

Transceiver Subsystem (BTS).

Figure 4.1

Function of Cell Site

1) MTSO

The Mobile Telephone Switching Office (MTSO) provides control and commands to the

mobile telephones. It also provides connectivity to the PSTN.

2) PSTN

The Public Switched Telephone Network (PSTN) provides connection to wire line

telephones in homes and businesses.

3) Roaming

Wireless phones are programmed to operate in a specific network, called the home

network. A phone operating in a non-home network is called a roamer. Roaming users

are usually charged additional fees for accessing the non-home network. Digital

communications functions as follows:

1. Analog voice signals are converted to digital signals.

2. The digital signals are converted to Radio Frequency (RF) signals.



38

3. The RF signals are transmitted over the air.

4. The RF signals are received then converted to digital signals.

The digital signals are used to reconstruct the analog voice signals.

Figure 4.2

Digital Communication

4) Human Speech

Voice is an analog signal. A person involved in a two-way conversation usually only

transmits 40% of the time. The other 60% of the time includes pauses and listening to the

other person. Digital telecommunications exploits these and other properties of the

human voice.

4.2 Converting digital signals to RF signals

Digital information must be converted to a Radio Frequency (RF) signal in order to be

transmitted over the air. An RF signal may carry the information on the phase, frequency

and/or amplitude of the wave.

1) Digital wireless systems

Key elements of digital wireless systems include:

• Network components and equipment

• The interrelationship between the components

2) Network Components



39

A digital wireless system has two basic components:

• Mobile phones

• Infrastructure equipment

Figure 4.3

Converting Digital Signal to RF Signal

3) Infrastructure equipment

The equipment that provides the interconnection between the phones and PSTN is called

"infrastructure." A CDMA system requires two pieces of infrastructure equipment. The

first is the "Base Station Transceiver Subsystem" (BTS). The other is the "Base Station

Controller" (BSC).

4) Base Station Transceiver Subsystem

The Base Station Transceiver Subsystem is most commonly just called the "BTS."

However, you will sometimes hear it referred to more simply as the Base Station (BS).

Sometimes it's called the "cell site," but don't confuse it with an analog cellular cell site.

The two function very differently. The BTS comes in both an indoor and an outdoor

model. The outdoor BTS is sometimes called an "OBTS."

4.3 Architecture of CDMA



40

Figure 4.4

Architecture of CDMA

4.3.1 BTS functions

The BTS includes an antenna for transmitting and receiving Radio Frequency signals.

The BTS also performs the CDMA processing of all signals.

1) Cell Site Antenna

The BTS attaches to an antenna. The antenna's three-sided design includes three sectors

called alpha, beta, and gamma, each of which can be further subdivided.

2) BTS Sectorization Hardware

Adding sectors to a BTS increases its capacity. Each sector operates like an independent

BTS. BTS Sectorization requires additional hardware within the BTS unit.



41

Figure 4.5

BTS Sectorization Hardware

4.3.2 BSC functions

The Base Station Controller (BSC) is part of the link between the BTS and the MTSO. It:

• Performs vocoding of the voice signal

• Routes calls to the MTSO

• Handles call control processes

• Maintains a database of subscribers



42

Figure 4.6

Base Station Controller (BSC)

1) Network Interconnects

There are three types of interconnects in a CDMA network:

• Mobile to BTS. These include both forward and reverse radio links

• BTS to BSC. This is called the backhaul. This connection is usually via T1 or E1

lines.

• BSC to MTSO. This connection uses standard wire line methods.

4.3.3 MSC functions

The primary node in a CDMA network is the MSC. It is the node which controls calls

both to MSs and from MSs. The primary functions of an MSC include the following:

1) Switching and Call Routing

An MSC controls call set-up, supervision and release and may interact with other nodes

to successfully establish a call. This includes routing of calls from MSs to other networks

such as a PSTN.

2) Charging

An MSC contains functions for charging mobile calls and information about the

particular charge rates to apply to a call at any given time or for a given destination.

During a call it records this information and stores it after the call, e.g. for output to a

billing centre.

3) Service provisioning

Supplementary services are provided and managed by an MSC. In addition, the SMS

service is handled by MSCs.

4) Communication with HLR

The primary occasion on which an MSC and HLR communicate is during the set-up of a

call to an MS, when the HLR requests some routing information from the MSC.

5) Communication with the VLR

Associated with each MSC is a VLR, with which it communicates for subscription

information, especially during call set-up and release.



43

6) Communication with other MSCs

It may be necessary for two MSCs to communicate with each other during call set-up or

handovers between cells belonging to different MSCs.

7) Control of connected BSCs

As the BSS acts as the interface between the MSs and the SS, the MSC has the function

of controlling the primary BSS node: the BSC. Each MSC may control many BSCs,

depending on the volume of traffic in a particular MSC service area. An MSC may

communicate with its BSCs during; for example, call set-up and handovers between two

BSCs.

4.3.4 Gateway MSC (GMSC)

Gateway functionality enables an MSC to interrogate a HLR in order to route a mobile

terminating call. It is not used in calls from MSs to any terminal other than another MS.

For example, if a person connected to the PSTN wants to make a all to a CDMA mobile

subscriber, then the PSTN exchange will access the CDMA network by first connecting

the call to a GMSC. The GMSC requests call routing information from the HLR which

provides information about which MSC/VLR to route the call to. The same is true of a

call from an MS to another MS.

4.3.5 HLR functions

Each operator has a database with information about all subscribers belonging to that

specific service provider. It is used for the following purposes:

1. Registering subscriber’s MDN and IMSI numbers.

2. Storing subscriber’s categories and services.

3. Keeping track of which MSC/VLR is serving the subscriber.

4. Ordering a serving MSC/VLR to delete its record about a Subscriber.

4.3.6 VLR Functions

The VLR is implemented in the same switch as the MSC, which is then referred to as an

MSC/VLR.

It contains temporary information about the mobile subscriber visiting this specific

MSC/VLR Service Area.

It also performs location updating of the HLR.

The VLR contains a copy of the subscriber information from the HLR where it is

registered, means subscriber’s home location.



44

Since VLR has a set of information about the mobile subscriber in its Service Area, the

HLR does not need to be consulted about subscriber data very often. This considerably

reduces the signaling to HLR.

Figure 4.7

VLR-HLR Interface

4.3.7 Authentication Centre (AUC)

PLMNs need a higher level of protection than traditional telecommunication networks.

Therefore, to protect CDMA systems, the following security functions have been defined:

1) Subscriber Authentication

By performing authentication, the network ensures that no unauthorized users can access

the network, including those which are attempting to impersonate others.

2) Radio Information Ciphering

The information sent between the network and an MS is ciphered. An MS can only

decipher information intended for it self.

3) Mobile Equipment Identification

Because the subscriber and equipment are separate in CDMA, it is necessary to have a

separate authentication process for the MS equipment. This ensures, e.g. that a mobile

terminal which has been stolen is not able to access the network.

4) Subscriber Identity Confidentiality

During communication with an MS over a radio link, it is desirable that the real identity

(IMSI) of the MS is not always transmitted. Instead a temporary identity (TLDN) can be

used. This helps to avoid subscription fraud.



45

4.3.8 Equipment Identity Register (EIR)

In CDMA there is a distinction between subscription and mobile equipment. As

mentioned above, the AUC checks the subscription at access. The EIR checks the mobile

equipment to prevent a stolen or non-type-approved MS from being used.

1) Equipment Identification Procedure

The equipment identification procedure uses the identity of the equipment itself (IMEI) to

ensure that the MS terminal equipment is valid.

1. The MSC/VLR requests the IMEI from the MS.

2. MS sends IMEI to MSC.

3. MSC/VLR sends IMEI to EIR.

4. On reception of IMEI, the EIR examines three lists:

• A WHITE LIST containing all number series of all equipment identities that have

been allocated in the different participating CDMA countries.

• A BLACK LIST containing all equipment identities that have been barred.

• A GRAY LIST (on operator level) containing faulty or non approved mobile

equipment.

5. The result is sent to MSC/VLR, which then decides whether or not to allow network

access for the terminal equipment.

Figure 4.8

Equipment identification

The decision to identify equipment remains with individual operators. CDMA

specifications recommend identification for each attempted call set-up.

4.4 Types of calls

Calls are defined by their point of origin and point of destination. There are three basic

types of calls:

1) Mobile to Landline (MTL)

2) Landline to Mobile (LTM)



46

3) Mobile to Mobile (MTM)

Figure 4.9

Types of Calls

1) Mobile to Landline calls (MTL)

This call path proceeds from the mobile phone to BTS to respective BSC to the main

MTSO. From there it is diverted towards the PSTN, then to the CO, as shown in the

figure.

Figure 4.10

Mobile to Landline Calls (MTL)



47

2) Landline to Mobile calls (LTM)

This call path proceeds follows from the Land line phone to its CO to the PSTN . from

there it is given to the MTSO which in turn directs it towards the BSC to BTS and finally

given to the mobile phone as shown in the figure below.

Figure 4.11

Landline to Mobile Calls (LTM)

3) Mobile to Mobile calls (MTM)

3.1 Mobile to Mobile calls within the same network

The call path proceeds as shown in the figure for calls within the same network:

Figure 4.12

Mobile to Mobile Calls (MTM) Within the Same Network

3.2 Mobile-to-Mobile calls to a separate network



48

For calls to a separate network, the call path proceeds from Mobile phone #1 to BTS #1

to MTSO #1 via BSC #1, towards the PSTN to MTSO #2 to BSC #2 to BTS #2 as

illustrated in the fig

Figure 4.13

Mobile to Mobile Calls (MTM) to a Separate Network

4.5 Features of CDMA

The following features are unique to CDMA technology:

• Universal frequency reuse

• Fast and accurate power control

• Rake receiver

• Different types of handoff

1) Frequency reuse

The frequency spectrum is a limited resource. Therefore, wireless telephony, like radio,

must reuse frequency assignments. For example, two radio stations might transmit at 91.3

FM. There is no interference as long as the radio stations are far enough apart

2) Cell interference

Cell A and B of a conventional, analog system are using the same frequency. The area of

overlap, area C, has a frequency conflict and interference. This is similar to what you

experience when you are driving between the broadcast zones of two radio stations

transmitting at the same frequency.



49

Figure 4.14

Cell Interference

3) FDMA and TDMA frequency re-use planning

A frequency (channel) can be used again within an FDMA or TDMA network, but cells

using the same frequency must be separated by an appropriate distance. Adjacent cells

must be assigned a different set of frequencies. For example, a cell using frequency A

must not be adjacent to another cell using frequency A. As a result, each cell site in the

site is able to use only 1/7 of the possible frequencies.

Figure 4.15

FDMA and TDMA Frequency Re-use Planning

4) CDMA frequency re-use planning

Each BTS in a CDMA network can use all available frequencies. Adjacent cells can

transmit at the same frequency because users are separated by code channels, not

frequency channels. This feature of CDMA, called "frequency reuse of one," eliminates

the need for frequency planning.



50

Figure 4.16

CDMA Frequency Re-use Planning

5) Power control

Power control is a CDMA feature that enables mobiles to adjust the power at which they

transmit. This ensures that the base station receives all signals at the appropriate power.

The CDMA network independently controls the power at which each mobile transmits.

Both forward and reverse links use power control techniques.

Figure 4.17

Power Control

5.1 Why power control is needed?

If all mobiles transmitted at the same power level, the base station would receive

unnecessarily strong signals from mobiles nearby and extremely weak signals from



51

mobiles that are far away. This would reduce the capacity of the system. This problem is

called the near-far problem.

Figure 4.18

Need For Power Control

5.2 Reverse link power control

Reverse link power control consists of two processes:

5.2.1 Open loop power control

5.2.2 Closed loop power control

Open loop is an initial estimate of the power the mobile needs to transmit to the BTS.

Closed loop is a refinement of the open loop estimate.

5.2.1 Open loop power control

Open loop is the mobile's estimate of the power at which it should transmit. The open

loop estimate is based on the strength of the pilot signal the mobile receives. As the pilot

signal gets weaker or stronger, the mobile adjusts its transmission strength upwards or

downwards. Open loop is used any time the mobile transmits



52

Figure 4.19

Open Loop Power Control

5.2.2 Closed loop power control

In closed loop, the BTS sends a command to the mobile to increase or decrease the

strength at which it is transmitting. The BTS determines this command based on the

quality of the signal it receives from the mobile. Closed loop is only used during a call.

Closed loop commands are sent on the forward traffic channel.

Figure 4.20

Close Loop Power Control

5.3 Forward link power control

The BTS independently adjusts the power for each forward traffic channel based on the

information it receives from the mobile.



53

Figure 4.21

Forward Link Power Control

5.4 Rake Receiver

The rake receiver is a CDMA feature that turns what is a problem in other technologies

into an advantage for CDMA. Signals sent over the air can take a direct path to the

receiver, or they can bounce off objects and then travel to the receiver. These different

paths, called multi-paths, can result in the receiver getting several versions of the same

signal but at slightly different times. Multi-paths can cause a loss of signal through

cancellation in other technologies.

Figure 4.22

Rake Receiver



54

CDMA's rake receiver is multiple receivers in one. The rake receiver identifies the three

strongest multi-path signals and combines them to produce one very strong signal. The

rake receiver therefore uses multipath to reduce the power the transmitter must send.

Both the mobile and the BTS use rake receivers.

4.6 Handoff in CDMA

Handoff is the process of transferring a call from one cell to another. This is necessary to

continue the call as the phone travels. CDMA is unique in how it handles handoff.

CDMA has three primary types of handoff:

1) CDMA Soft handoff

2) CDMA Hard handoff

3) CDMA Idle handoff

The type of handoff depends on the handoff situation.

1) CDMA Soft handoff

A soft handoff establishes a connection with the new BTS prior to breaking the

connection with the old one. This is possible because CDMA cells use the same

frequency and because the mobile uses a rake receiver. The CDMA mobile assists the

network in the handoff. The mobile detects a new pilot as it travels to the next coverage

area. The new base station then establishes a connection with the mobile. This new

communication link is established while the mobile maintains the link with the old BTS.

Soft handoffs are also called "make-before-break."



55

Figure 4.23

CDMA Soft Handoff

• Variations of the soft handoff

There are two variations of soft handoffs involving handoffs between sectors within a

BTS:

1.1 Softer

1.2 Soft-softer

The softer handoff occurs between two sectors of the same BTS. The BTS decodes and

combines the voice signal from each sector and forwards the combined voice frame to the

BSC. The soft-softer handoff is combination handoff involving multiple cells and

multiple sectors within one of the cells.



56

Figure 4.24

CDMA Softer Handoff

2) CDMA hard handoff

A hard handoff requires the mobile to break the connection with the old BTS prior to

making the connection with the new one. CDMA phones use a hard handoff when

moving from a CDMA system to an analog system because soft handoffs are not possible

in analog systems. A Pilot Beacon Unit (PBU) at the analog cell site alerts the phone that

it is reaching the edge of CDMA coverage. The phone switches from digital to analog

mode as during the hard handoff. Hard handoffs are also called "break-before-make."

Figure 4.25

CDMA Hard Handoff



57

The CDMA hard handoff may be used when moving from a CDMA network to an analog

one. It may also be used when moving to a different:

• RF channel

• MTSO

• Carrier

• Market

Analog to CDMA handoff is not available due to the limitations of analog technology.

3) CDMA Idle handoff

An idle handoff occurs when the phone is in idle mode. The mobile will detect a pilot

signal that is stronger than the current pilot. The mobile is always searching for the pilots

from any neighboring BTS. When it finds a stronger signal, the mobile simply begins

attending to the new pilot. An idle handoff occurs without any assistance from the BTS.

• TDMA and FDMA handoff

TDMA and FDMA systems use a hard handoff when the mobile is moving from one cell

site to another. These technologies do not allow for any type of make-before-break

handoff. A hard handoff can increase the likelihood of a dropped call.

Figure 4.26

FDMA and TDMA Handoff

4.7 Advantages of CDMA



58

1) Coverage

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

� Power control helps the network dynamically expand the coverage area.

o Coding and interleaving provide the ability to cover a larger area for the same

amount of available power used in other systems.

2) 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.

3) 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

4) Cost

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.

5) Compatibility



59

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.

6) 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.

7) Wireless local loop (WLL)

Wireless local loop phones in homes, offices or even boats connect with a wireless

system in a manner similar to that of CDMA cell phones. The difference is that WLL

phones usually stay in a relatively fixed location. WLL phones often connect to AC

current rather than using batteries. They can be used to provide voice, fax, and data

connections.

Figure 4.27

Wireless Local Loop (WLL)

4.8 Site Structure



60

The basic structure of the network is shown in the figure. The components are described

below:

1) Microwave Antenna

2) ODU (Out Door Unit)

3) IDU (In Door Unit)

4) MUX

5) DDF (Digital Distribution Frame)

6) BTS (Base station Transceiver Subsystem)

7) Sector antenna

8) GPS antenna

1) Microwave antenna

MW antenna is used to transmit MW signal in air. This antenna is a directional antenna

(DA). 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 (Base Station Controller). The transmitting frequency is in terms of

GHz. Parabolic types of antenna are used in TTSL.

2) ODU (Out Door Unit)

ODU is attached to the MW antenna. Its function is to modulate the incoming signal

from IDU with higher carrier frequency signal. Means frequency up conversion is

performed here.

3) IDU (In Door Unit)

IDU converts between RF (Radio Frequency) signal and 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 the other 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 Data Rate

STM-0 21E1 51.54 Mbps



61

STM-1 63E1 155.520 Mbps

STM-4 4x63 E1 622.080 Mbps

STM-16 16x63 E1 2488.320 Mbps

STM-64 64x63 E1 9953.280 Mbps

STM-256 256x63 E1 39813.120 Mbps

Table 4.1

Types of MUX

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

used in TTL.

5) DDF

DDF stands for Digital Distribution Frame. DDF is a point where E1 is terminated. It

provides only connectivity between two points.

6) BTS

BTS stands for Base Station Transceiver Subsystem. BTS is connected with GPS antenna

via RF cable. The CDMA signal is processed by BTS. BTS include filters, amplifier and

other control module. BTS receive and transmit signal via sector antenna.

Following Functions are performed by BTS:

Radio/Antenna Interconnect, RF Modem

Power control

Handoff (soft/softer)

7) Sector antenna

Sector antenna communicates 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 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 communicates with satellite

continuously.



62

CHAPTER 5

PDH – SDH

FUNDAMENTALS

5.1 Plesiochronous Digital Hierarchy

5.2 Dis-Advantages of PDH

5.3 Why SDH?

5.4 SDH Frame Architecture

5.5 Overhead Analysis

5.6 Virtual Container

5.1 Plesiochronous Digital Hierarchy

Plesio means = similar

Chronous means= Timing



63

Plesiochoronous - "almost synchronous, because bits are stuffed into the frames as

padding and the calls (signal) location varies slightly - jitters - from frame to frame".

The basis of analog to digital conversion is Shannon’s theory. The theory states that after

transmission the original signal can be reproduced within certain limits from digital

signal obtained by Sampling an analog at regular intervals and at a rate at least twice the

highest significant message frequency.

5.2 Disadvantages of PDH

Plesiochoronous Hierarchy based on 2Mbps primary rates permits multiplexing up to

140Mbps respectively.

• Changing from one hierarchical level to another requires additional equipment.

• Transmitting a multiplexed signal (34/140 Mb, etc) requires specialized

equipment.

• Redirection (cross-connection) of channels must be done by hand on DDFs.

• Administrative connections require separate equipment to support Supervision,

EOW and protection switching.

• Compatibility of transmission and administrative signals between different

vendors may give trouble.

Figure 5.1

Pre-SDH (System Monitoring Only)

5.3 Why SDH Require?

To cope up the demand of higher bit rate SDH technology is introduced.



64

Figure 5.2

SDH (System Monitoring and Management Possible)

• Advantages of SDH over PDH

1) Higher Transmission rate

Transmission rate up to 10 Gbps can be achieved by the modern SDH system. SDH is

therefore considered to be more suitable for backbone.

2) Simplified Add/Drop function

Compared with older PDH system, it is much easier to insert and extract low bit rate

channels from or into the high-speed bit streams in SDH.

3) High availability and capacity matching

With SDH network providers can react quickly and easily to the requirements of their

customers.

4) Reliability

Modern SDH networks include various back-up and repair mechanisms to cope up with

system faults.

5) Interconnection

SDH makes it much easier to set up gateways between different network providers and to

SONET systems.



65

5.4 SDH frame Architecture

A frame with a bit rate of 155.52 Mbps is defined in ITU-T recommendation G.707. This

frame is called synchronous Transport Module (STM), since it is first level in hierarchy it

is called STM-1.

It is made up from a byte matrix of 9 rows and 270 columns.

Transmission is row by row, starting with the byte in the upper left corner and ending

with the byte in the lower right corner.

The frame repetition rate is 125us. Each byte in the payload represents a 64 kbps channel.

Figure 5.3

SDH Frame Structure-A

PAYLOAD CONTAINER 9 (Rows) * 260 (Column) * 64Kbps = 149.76 Mbps

POH 9 (Rows) * 1 (Column) * 64 Kbps = 0.576Mbps

RSOH 3 (Rows) * 9 (Columns) * 64 Kbps = 1.728 Mbps

MSOH 5 (Rows) * 9 (Columns) * 64 Kbps = 2.880 Mbps

Table 5.1

SDH Frame Architecture

1) How Is The Frame Composed? PDH Payload = Container (C)

Container + Path Overhead (POH) = Virtual Container (VC)

PAYLOAD CONTAINER

P

O

H

RSOH

POINTER

MSOH

1

3

4

9

1 9 10 270



66

Virtual Container + TU Pointer = Tributary Unit (TU)

More than 1 Tributary Unit = Tributary Unit Group (TUG)

Biggest Tributary Unit Group = Administrative Unit (AU)

Tributary Unit Group + AU Pointer = Administrative Unit (AU)

More than 1 Administrative Unit = Administrative Unit Group

Administrative Unit Group + Section Overhead (SOH) = SDH Frame

Figure 5.4

SDH Hierarchy – TUG Structure

2) PDH: Plesiochoronous Digital Hierarchy (PDH) consists of E1, E2, E3 and E4

communication standard.

3) SDH

It is a high speed – high capacity optical telecommunication network.

C-12 VC-12 TU-12

C-3 VC-3 TU-3

C-4 VC-4

AU-4

STM-

1

X 3

POINTER

MULTIFLEXING

ADDITION OF VERHEADS

ALIGNMEN

TUG

-2

TUG

-3



67

Plesiochoronous multiplexing technology left no room in the signal structure for network

management and maintenance functions. In a Plesiochoronous network accessing one

individual tributary req the whole signal to be demultiplexed.

Synchronous Digital Hierarchy (SDH) consists of STM-1, STM-4, STM-16 and STM-64.

SDH overcomes the problems of Plesiochoronous networks.

The lowest level SDH signal is called the “Synchronous Transport Module”

SDH line rates.

STM – 1 155.52 Mbps

STM – 4 622.08 Mbps

STM – 16 2488.32 Mbps

SDH is a technology which supports a single telecommunication network infrastructure

based on synchronous multiplexing.

SONET in North America is equivalent of SDH. The STM – 4 also have 9 rows but have

1080 columns. 4 STM – 1 can be multiplexed up to STM – 4.

4) Frame structure

Figure 5.5

SDH Frame Structure-B



68

Figure 5.6

STM-1 & STM-4 Frame Structure

5.5 Overhead analysis

The path overhead supports end-to-end management of the virtual container.

The multiplex section overhead is used to manage transmission between network nodes

i.e. between adjacent multiplexers and cross-connect switches.

The regenerators section overhead is used to manage transmission between regulators.

The bytes in the SDH frame are transmitted from left to right & top to bottom.



69

Figure 5.7

Overhead Analysis

Figure 5.8

Bytes Transmitted in SDH Frame

5.6 Virtual Container

The virtual container is where the actual data is.

The VC is subdivided into smaller units like palettes or crates.

These are known as individual tributary units.

Examples of which are standard rates E1 and E3.



70

The path overhead is always provided in the first column of a VC – 4, the remaining

capacity (the C-4 container) can be loaded with 63 TU-12’s (which carry mapped E1

services or TU-3’s (used to carry mapped E3)

Figure 5.9

Virtual Container-A

The stuff bytes in this case are simply used to fill the unused space in VC-4, thus

maintaining the VC-4 signal structure.

Figure 5.10

Virtual Container-B

The path overhead (POH) provides the facilities to manage the transport of the VC-4

between path terminating equipment (i.e. where the VC-4 is assembled and

disassembled.)

It is worth noting that this process of assembling and disassembling the VC-4 happens

only once, at end locations, known as “High Order Path Terminations”.

The VC-4 remains intact even though it may be transferred from one transferred from one

transport system to another many times through the network.



71

Figure 5.11

The Completed Virtual Container-4

1) Virtual Container Capacity

The STM-1 frame is made up of 270 columns 9 rows of 8 bytes. There is a frame

repetition rate of 8000 Hz.

This gives us a total of

270 * 9 * 8 * 8000 = 155.52 Mbps

However 9 columns are used as section overhead, leaving us with the VC-4 capacity

261 * 9 * 8 * 8000 = 150.33 Mbps

1 column is used for the Path Overhead, so actual payload capacity (C-4) of the VC-4 is

260 * 9 * 8 * 8000 = 149.76 Mbps

Actual customer data is transported in the payload area of the Virtual Container (e.g. C-4

is the ‘Container’ of a VC-4.)

Figure 5.12



72

Virtual Container Capacity-A

The container can be split up into Tributary units which are like palettes to be loaded onto

our trucks.

The Virtual Container is completed by adding the Path Overhead which is like a baggage

label for our container.

Figure 5.13

Virtual Container Capacity-B

The VC-4 is allowed to start at any position within the payload area. Most often it begins

in one frame and ends in another. This ability of the VC-4 to move relative to STM frame

is known as ‘floting’.

It is important to understand the VC-4 can start at any byte location within the STM

frame’s payload area. No matter the start location the order of bytes within the VC-4

remains unchanged.

Different network operators will have their own independent master timing references.

These clocks will operate at slightly different rates.

SDH transport must therefore, be able of operate effectively between network nodes

which are operating asynchronously.

Pointers are used to

1. Compensate for frequency offsets between a received STM-N signal and the

network element’s clock.

2. Identify the location of individual VCs for efficient cross connecting and

demultiplexing.

2) Sub STM-1 Payloads

STM-1 payload (VC-4) was designed to provide transport for a 139 Mbps tributary

signal.



73

Transport for a lower rate tributary signals, such as 2 Mbps is provided by a Tributary

Unit (TU) structure. The TU represents a mini frame with a fixed number of TUs

assembled within a VC-4.

3) Range of TUs

Each TU-12 frame consists of 36 bytes, structured as 4 columns of 9 bytes.

At a frame rate of 8000 Hz, these bytes provide a transport capacity of 2.304 Mbps

4 columns * 9 rows * 8 bits * 8000 frames/sec = 2.304 Mbps

This will accommodate the mapping of a 2.048 Mbps (E1) signal.

63 TU-12’s may be multiplexed into the VC-4.

4) TU packaging

How many TU-12 are carried in a VC-4?

The TU-12’s go through two levels of intermediate multiplexing before being loaded into

the VC-4. These intermediate multiplexing levels are known as Tributary Unit Groups

(TUG).

CHAPTER 6



74

INTRODUCTION TO

MODCELL 1.0 BTS

6.1 BTS (Base Transceiver Station)

6.2 BTS Modules

6.3 Radio Link

Filters

Facilities

Interface

Module

(FIM)

Power Distribution

Assembly (PDA)



75

Figure 6.1

Primary Outdoor Modcell 1.0

6.1 BTS (Base Transciever Station)

Base Transceiver System is the first node in the path of call flow from MS to MSC.

The basic structure of mobile network is as follows:

1) CDMA ANTENNAS

CDMA antennas are mounted on the tower according to the RF planning, which includes

height, electrical and mechanical tilt and the number of antennas.

The area is segmented in 120 degrees in three sectors with the aid of 3 antennas, which

are polarized +45 and -45 degrees.

Each antenna has 2 cables, a) Diversity cable for receiving signals and b) TRX i.e. Tx

and Rx cable which transfers the call request to BTS. This makes a total of 6 cables

emerging from the antenna and converging to BTS. The TRX cables go to the duplexers

and segregate the 3 Tx and Rx cables.

CTRM

Amplifier Fans

Smart Switch

Crystal OM (Xo)

ULAMs

Rubidium OM (Rb)

Digital Fans

CDM

1 CDM

2 CDM

3

Remote Maintenance

Panel (RMP)

Digital Module

(CCUs, CRCs,

CBRs, TFUs,

PCUs)

Fan Controller

ULAM Interface

Panel (UIP)

Type 1



76

2) MOTOROLA BTS

The –48 Volt Motorola BTS can accommodate up to four separate carriers in a three-

sector configuration or up to two carriers in a six-sector configuration.

The TX base band path begins at the MCC card. The MCC card generates traffic channel

information, and data is routed to the BBX module for combining and filtering of

transmitted digital I and Q signals. Each MCC has a direct connection to each BBX. The

TX RF path begins at the output of the BBX modules. The BBX generates the CDMA RF

signal, which will be amplified by the CLPAs. A redundant BBX is combined with all

sectors and is automatically switched into service in the event of a primary BBX failure.

When a CCCP shelf includes a IS 2000 1X carrier, the BBX cards that support the

respective 1X sector carriers must be a BBX1X card, and the redundant BBX must be a

BBX1X. The BBX output is routed through the CIO card in the C–CCP cage to the

CLPA trunking backplane of each carrier via a cabled connection. The Trunked CLPA

Sets amplify the modulated transceiver transmit signal. The CLPA output connects to the

TX band pass filter, or cavity combiner modules and is routed to the TX antenna ports

(N-type connectors) on the I/O Panel at the top of the –48 Volt Motorola BTS frame. Up

to four sector carrier outputs can be combined together via cavity combiner(s) to

minimize the number of TX antennas.

For the –48 Volt Motorola BTS the RX signal path in the frame begins at the N–type RX

antenna inputs located on the I/O Panel at the top of the frame. The signals are routed

through the RX Tri–filters, located on the I/O Panel, to the Multicoupler Preselector cards

(MPC), or Expansion MPC (EMPC) on the C–CCP Shelf via coax. A frame is equipped

with two MPCs, one supporting the main signals and the other supporting the diversity

signals. The MPC module provides low noise amplification for the incoming RX signals.

The MPC outputs are routed to the Combiner Input/Output (CIO) card via the C–CCP

backplane and to the BBX cards. The CIO routes the RF receive signals to the expansion

connector and the respective BBX card or the BBX Switch cards, and provides the

expansion output.

6.2 BTS Modules

The –48 Motorola BTS CDMA frames contain all of the CDMA functions in the CCCP

Cage and the CDMA ST-CLPA Shelf. These functions are implemented in the modules

listed below:

1) C-CCP CAGE

• MCC24 or MCC-8E or MCC1X

• BBX2 or BBX1X

• GLI2

• CIO

• CSM w/RF GPS



77

• CSM w/Remote GPS (Available with R9)

• CCD

• HSO

• AMR

• MPC or EMPC

• +27 Volt C-CCP Power Supply

• Switch Card

2) CDMA ST-CLPA SHELF

CDMA ST-CLPAs

• Trunking Module(s)

• Combiners/Filters

3) -48V POWER SUPPLY SYSTEM

• –48V Power Supply Module

• Power and Alarms Card (PAC)

4) +27 VOLT C-CCP CAGE

The single +27 Volt SC™4812T Combined CDMA Channel Processor (C-CCP) shelf

provides the span line interfaces, channel processing, shelf control, and CDMA

transceivers (purchased separately). The +27 Volt BTS C-CCP cage supports up to a total

of twelve sector carriers(e.g., 3-sector, 4-carrier or 6-sector, 2-carrier) and up to 576

Physical Channels (assuming use of MCC1X-48 cards). A fully loaded C-CCP shelf

houses 13 (one per sector per carrier with one redundant) Broad Band Transceiver boards

(BBX2s or BBX1X), 12 Multi- Channel CDMA cards (i.e., MCC1X or MCC-24 or

MCC-8E), one Switch card, two Group Line Interface-2 boards (GLI2), the Combiner

Input/Output (CIO) board, two Multi-Coupler Preselector (MPCs), two Alarm Module

Reporting (AMR) boards, two Clock Synchronization Manager (CSMs), the Rubidium

High Stability Oscillator (HSO), two Clock Distribution Modules (CCD), and two or

three power supply boards.

These are CCCP cage cards.

1. MPC 1, MPC 2

2. Power 1, Power 2, Power 3

3. BBX2 - Redundant Switch

4. MCC 1 to 12

5. HSO

6. BBX1 to 12

7. GLI -1 GLI -2

8. AMR-1 AMR-2

9. CSM 1, CSM 2



78

10. CCD1/CCD2 11. Modem

1. The MCC card contains the circuitry necessary to implement CDMA channels of any

Type except the pilot.

• The MCC-1X cards contain the circuitry necessary to implement all the

1X channel types in IS-2000.

• For overhead channel redundancy, a three sectors or Omni configuration

requires a minimum of two MCCs, and a six-sector configuration requires

a minimum of three MCC cards. A C-CCP cage can be populated with up

to twelve MCC cards.

• If redundancy is required for the new IS-2000 channels, a minimum of

two MCC-1X cards will be required.

• For 6-sector BTS’s, the MCC-1X cards will need to be dedicated per

carrier.

2. The BBX provides the generation of the Pilot signal, the conversion from digital base

band to RF for the forward (transmit) link, and RF to digital base band for the reverse

(receive) link.

• Each BBX will support any single CDMA RF channel per sector at any

frequency in the IS-95 800 MHz frequency band at a cell site.

• The BBX is controlled by the Group Line Interface (GLI2) card via the

Concentration Highway Interface (CHI) within the CDMA Channel

Processor (C–CCP) backplane.

• The BBX receives clock and synchronization signals via the CCD from

the CSM.

• An Omni site requires one BBX2 or BBX1X card plus a redundant BBX2

or BBX1X card

• A 1 carrier, 3 sector site requires three BBX2 or BBX1X cards plus a

redundant BBX2 or BBX1X card

• A 2 carrier, 3 sector site requires six BBX2 or BBX1X cards plus a


• A 3 carrier, 3-sector site requires nine BBX2 or BBX1X cards plus a




79

• A 4 carrier, 3-sector site requires twelve BBX2 or BBX1X cards plus a


• A 1 carrier, 6-sector site requires six BBX2 or BBX1X cards plus a


• A 2 carrier, 6-sector site requires twelve BBX2 or BBX1X cards plus a


3. The GLI2 card functions as the BTS controller and provides routing of traffic and

control information, and O&M functions for all active devices in the C-CCP cage. It is

the controller of the C-CCP cage and acts as a message router between the CBSC and the

BTS equipment.

4. The CSM (Clock Synchronization Manager) maintains 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 HSO.

• The GPS receiver is the primary source and the HSO is the redundant

source.

• The CSM generates three clock/synchronization signals, which are

distributed to the C-CCP cage.

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

CSM. The CSM generates the CDMA clock (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 (Clock

Distribution Subsystem).

• 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.

6. The HSO (High Stability Oscillator) also is an optional card that provides backup for

the GPS.

• The HSO module is an alternate source of the synchronization and

absolute time information that is required at a CDMA BTS.



80

• It provides a precise oscillator as the backup source for timing reference

when 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.

7. The AMR (Alarm Monitoring and Reporting) cards collect alarms from the C-CCP

fans, MPCs, and the CSM.

• Each card also detects up to eighteen user-defined alarms and has eight

relay outputs for connection to external customer equipment. With two

cards available, this doubles the number of user equipable alarms and

relay outputs to thirty-six and sixteen, respectively.

• The AMR cards are connected to the GLI via a redundant RS-485 bus.

Upon polling from the GLI2, the AMR sends the status and alarm

information to the active-master GLI2 where it is multiplexed into the

network interface. The AMR also provides output to the Fan Modules and

Frame LED’s.

8. The MPC (Multicoupler Preselector Card/Expansion MPC (EMPC) Card) card

provides low-noise amplification of independent RX path signals.

• There are four types of MPCs. The frame sectorization determines which

type of MPC must be installed.

o MPC for 3 Sector BTS

o EMPC for 3 Sector Expansion BTS

o MPC for 6 Sector BTS o EMPC for 6 Sector Expansion BTS

9. The primary function of BBX Switch card is to provide RF switching circuitry to allow

the redundant BBX to take the place of any primary BBX in the event of BBX failure.

6.3 Radio Link

Radio link mainly consists of parabolic antenna, IDU (Indoor Unit), ODU (Outdoor

Unit), RF cables and multiplexers.

MSC lays out fiber cables to the different BTS. According to the traffic requirement of

BTS, the density of the Link is decided and STM paths are allocated henceforth.



81

The connectivity can be 1) Microwave or 2) Fiber. Microwave can be either PDH or SDH

while Fiber is having STM standard.

The call which originates from MS travels through BTS, for modulation, channel

allocation and synchronization, and enters IDU via BTS E1 cable link.

The call then flows from the main path, which is pre-decided. If it is fiber link it will go

through the same connectivity to MSC and if it is microwave then it will pass through

ODU via RF cables, which will further be passed to parabolic antennas and then

transmitted to the next link.

In case of fiber link, Optical Multiplexers are used so as to convert the Optical signal to

Electrical signal and vice-versa.

CHAPTER 7

BASIC MICROWAVE

RADIO SYSTEM



82

7.1 Introduction

7.2 Advantages and Disadvantage of

Microwave

7.3 Wave Propagation

7.4 Fresznel zone

7.5 Surveying

7.6 Microwave Antenna

7.7 Free space loss & power budget

7.8 Precipitation

7.9 Fading margin

7.10 Diversity

7.11 Error performance & object

Availability

7.1 Introduction

In recent, there are no. of ways to communicate within network. Mostly it dependents on

which type of technology we use. There are some medium which listed below.

WAYS OF Communication Telecom industry:

1. Cable

2. Microwave radio

3. Optical fiber

4. Satellite

7.2 Advantages and Disadvantage of Microwave

1) Advantages of Microwave

1. Easy installation



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2. Medium is free

2) Disadvantage of Microwave

1. Medium is exposed to much uncertainty

7.3 Wave propagation

Figure 7.1

Wave Propagation

1) Snell’s law

Ray bends towards the denser medium of the two media

2) Atmosphere Multipath Propagation

Formation of duct due to convection

- Ground based duct

- Elevated duct

3) Terrain Profiles

1. Line of sight

2. Fresznel zone

Line of sight between transmitter and receiver is a straight line and ray bending due to K-

value variation is added to the terrain heights.

With atmosphere For no atmosphere



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The modification of terrain heights is given by (d1.d2) / (12.74.k), where

k=1.33 for (5 to 15 kms) and 0.6 for longer path lengths (15-30 kms)

There must be a clearance for the first Fresznel zone to avoid diffraction loss in addition

to free space loss.

7.4 Fresznel zone

First Fresznel zone is defined as the locus of Points having maximum energy lobe from

Transmitter.

Antenna to Receiver Antenna

d3 - (d1+d2) = λ/2, where d3 = D1 + D2 refer to figure.

λ = wavelength

Figure 7.2

Fresznel Zone

For practical application the radius F1

May be approximated by the formula:

F1=17.3 (d1.d2/f.d), where f is the freq in GHz

D=d1+d2 the total path length in km

7.5 Surveying

1) Field work

1. Confirmation of LOS (checking critical obstacles)

2. Verification of position and altitudes of the sites

3. Soil investigation

4. Checking of site, road access

5. Availability of power (Exiting shelters and towers)

6. Propagation condition

7. Make interference measurements

8. Finally prepare a report with required optimum tower heights

F1

d1

D1 D2

d2



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2) Difficult areas for Microwave link

1. Over water paths

2. High reflection coefficient.

3. High ducting probability.

4. Rice and wheat fields

5. Strong ground reflection

6. Desert area

7. Multipath fading

8. Hot and Humid coastal areas

9. High ducting probability

7.6 Microwave Antennas

The parabolic Antenna is the most commonly used antenna in Microwave Radio-relay

systems.

1) Antenna parameters

1. Antenna gain

Gain is approximated by the formulae,

Gain = 17.8 + 20 log (D.f) dBi

Where D = Antenna diameter [m], f = Frequency in GHz

2. VSWR

Standard type Antenna 1.06 to 1.15 typically

High performance Antenna 1.04 to 1.06 typically

3. Cross polarization

A good cross-polarization enables full utilization of the frequency band by using.

4. Beam width

The half power beam width of an antenna is defined as the angular width of the main

beam at – 3 dB point.

7.7 Free space loss and Power Budget

Power received at any point from a radiated antenna is inversely proportional to square of

distance between them and radiating frequency.

It can be defined by formula:



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Lfs = 92.45 +20 log (f.d)

Power budget

Figure 7.3

Free Space Loss and Power Budget

Tx power o/p +21 dBm

Losses (feeder + branching) 3.0 dB

Tx Antenna Gain 36.5 dB

Free space loss 130 dB

Rx Antenna Gain 36.5 dB

Feeder loss Rx 1.2 dB

Nominal input level -40.2 dB

Receiver Threshold -80 dBm

Fading margin 39.8 dB

Table 7.1

Free Space Loss and Power Budget

7.8 Preception

Transmission of microwave signal above 10 GHz is vulnerable to precipitation. The

energy is attenuated due to radiation (scattering) and absorption (heating).

1) Scattering

Radio waves are a time varying electromagnetic field; the incident field will induce a

dipole moment in the raindrop. The rain drop will also have the same time Variation as

the radio waves and will act as an antenna and reradiate the energy. As rain drop-antenna

has low directivity it will radiate energy arbitrary direction and add to loss.

2) Absorption

When the wavelength becomes small (High freq. < 18GHz) relative to the raindrop size

more energy is absorbed by heating of the raindrop.

3) Why vertical polarization favorable at high frequency?

As the rain-drop increases in size they depart spherical shape and extended in the

horizontal direction. For freq. Higher than 18 GHz the wavelength is generally in mm. So

Tx Rx



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these rain-drops attenuate horizontally polarized waves than the vertical Polarized.

Raindrop shapes

Figure 7.4

Vertical Polarization

7.9 Fading Margin

Figure 7.5

Fading Margin

Fading events are mainly caused by multipath fading and fading due to precipitation. So

larger the fading margin better the system performance.

This can be achieved by higher Tx o/p, larger (Gain) antennas, lower threshold level and

reduced path length etc.

1) Multipath Fading

Fading due to layering of the atmosphere is the dominating factor of degradation of radio-

relays transmitted waves that receives at the receiver refracted from the troposphere or

reflected from the ground other than wanted signals are added to it. The phase and

amplitude relationship determines the resulting I/p signal at the receiver.

1. Flat fading

2. Selective fading

7.10 Diversity

The common forms of diversity in LOS link frequency and space or combination of both.

Lately angle diversity is also introduced.

1) Space Diversity

Rx

I/P

Level

-40dBm

-80dBm Outage

Receiver

Threshold

Atmospheric

Disturbance

1mm 1.5mm 2mm 2.5mm



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Placing two antennas vertically separated at the receiver tower. So only one antenna is

located in a power minimum range. The optimum antenna separation is half of the pitch

distance.

H

LR(x)

Figure 7.6

Space Diversity

2) Frequency Diversity

This protection technique takes advantage of the frequency selectivity of the multipath

fading. But the as the freq. Bandwidth is costlier in India this technique is rarely being

used.

3) Switching sections

By switching or combining the different channels (in freq. Diversity)/ Rx. Signals (from

main antenna and space diversity antenna) carrying the same signal, it is possible to attain

an improvement.

4) Hot Standby configuration

Reduces the system outage due to equipment failures.

5) Hybrid Diversity

1+1 hot standby system having space diversity at one of the radio sites.

6) Combined Diversity

When using space diversity and frequency diversity at the same time.

Pitch distance (V)



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7.11 Error Performance and object Availability

These are based on the definition of the network for different microwave systems.

ITU-T and ITU-R recommendations.

G.801, G.821 and G.826

1) Some Definitions

1. SES

A BER of (10)¯³ is measures with an integration time of one second. BER of (10)¯³ is the

point where the signal is unacceptable to most of services.

2. ES

An ES is a second that contains at least one error. ES may result from causes other than

fading.

3. DM

A BER of 10¯6 is measure with an integration time of one minute.

4. Unavailable Time

If the 10 consecutive seconds are SES than that period is Unavailable period/Time.

2) Performance objectives (G.821 [2])

SES 0.2 % of one second interval in any month.

DM 10 % of one minute intervals in any month.

ES 8% of one second intervals of any errors.



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CHAPTER 8

PRACTICAL WORK



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1) Everyday at 9.30 am I have to go company & start my training by visiting

different site in Ahmedabad city. Some cities of North Gujarat.

2) At that site I do some work like:

• Alarms checking

• Cable routing

• E1 patching / removing

• Checking connectivity between IDU & ODU

• Replace the LPA

• To insert login cable & check link to other site

• Antenna alignment

• Make site in working condition

3) Types of Alarms:

Alarms -1. Minor: - No incoming signal

2. Major: - No outgoing signal

3. OMU block

4) At the Science City we have to install the Cow BTS. At there first install CDMA

antenna and then install the Microwave antenna. And alignment nearest

Microwave antenna.

5) We have to replace the faulty LPA and install the new LPA at Kalupur Chokha

Bazaar. And unlock LPA by the MSC at S.G.Highway.



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6) Power plant & Battery bank installation at SHAPATH due to loss of voltage.

7) Went to the site, Viramgam, to route traffic. Connect the higher capacity

multiplexer [XDM-500] & Disconnect the cable from [XDM-100].

8) Connect the higher capacity multiplexer in SR-HOUSE.

9) Survey of line of sight of nearer BTS at Santej, Shymal using GPS system

10) We went to NEWYORK TOWER, SG Highway there TTSL provides wireless

Services. It has intercom in ford show room. By using PRI meter we detected the

signal from BTS the line was clear. The problem was in EPBX (switching).

11) We have to replace the faulty LPA and install the new LPA at Narol. And unlock

LPA by the MSC at S.G.Highway.

12) AT NANO project, science city install COW BTS, first install CDMA antenna,

and MW link antenna, also alignment nearer MW antenna (BTS).

13) Visited at Paldi given DC power supply (-48 v), purpose standby Ethernet line

(FOC line) in DLC.

14) At some site I have (Juhapura, Nawab complex) done antenna TILTING

(Electrical & Mechanical alignment) to solve the coverage problem.

15) With help of OTDR (Optical Time Domain Reflectometer) we can locate the

OPTICAL fault within particular FIBRE link by radiating LASER from the

source.

16) We have done a VSWR measurement at VRUDAVAN SHOPPING CENTRE at

Manekchawk.

17) To give the INTERCOM facilities at CAMBAY I have check LOS by using GPS

device.

18) Mandali CDMA antenna was replaced. At site, BTS alarm cable replaced.

19) We have to Patching the E1 at the MUX at the kalash due to a guidance of the sir.

For that we have to use kronch. And also hoe that the E1 is dropped that we have

to check at there.

20) At Kalash sir gives us the knowledge of the MUX, E1.

21) We have also replaced the Cards at the different sites.



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22) At Kalash O&M department we observe that which company instrument that

TTSL used.

Documents

Tata Tele Services Training Report