CHAPTER 1

INTRODUCTION TO TELECOMMUNICATION

1.1 DEFINITION OF TELECOMMUNICATION

Telecommunication is the transmission of information over significant distance to

communicate. In earlier times, telecommunications involved the use of visual signals, such as

beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio

messages via coded drumbeats, lung-blown horns, or sent by loud whistles, for example. In

the modern age of electricity and electronics, telecommunications now also includes the use

of electrical devices such as the telegraph, telephone, and teleprinter, as well as the use of

radio and microwave communications, as well as fiber optics and their associated electronics,

plus the use of the orbiting satellites and the Internet.

In modern times, this process almost always involves the sending of electromagnetic waves

by electronic transmitters but in earlier years it may have involved the use of smoke signals.

Today, telecommunication is widespread and devices that assist the process, such as the

television, radio and telephone, are common in many parts of the world. There is also a vast

array of networks that connect these devices, including computer networks, public telephone

networks, radio networks and television networks. Computer communication across the

Internet, such as e-mail and instant messaging, is just one of many examples of

telecommunication.

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

tion and offer service to many subscribers without requiring extensive frequency planning.

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

tinguished 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 trans-

mitted power required by CDMA is much lower than what is required by analog, FDMA and

TDMA technologies.

1

1.2 CLASSIFICATION

Figure 1.1 Classification of Telecommunication

1.2.1 GSM

GSM (Global System for Mobile communication) is a digital mobile telephony system that is

widely used in Europe and other parts of the world. GSM uses a variation of time division

multiple access (TDMA) and is the most widely used of the three digital wireless telephony

technologies (TDMA, GSM, and CDMA). GSM digitizes and compresses data, then sends it

down a channel with two other streams of user data, each in its own time slot.

GSM networks operate in a number of different frequency ranges (separated into GSM

frequency ranges for 2G and UMTS frequency bands for 3G). Most 2G GSM networks

operate in the 900 MHz or 1800 MHz bands. Some countries in the Americas (including

Canada and the United States) use the 850 MHz and 1900 MHz bands because the 900 and

1800 MHz frequency bands were already allocated. Most 3G GSM networks in Europe

operate in the 2100 MHz frequency band.

1.2.2 CDMA

CDMA (Code-Division Multiple Access) refers to any of several protocols used in so-called

second-generation (2G) and third-generation (3G) wireless communications. As the term

2

Telecommunication

Wireline Wireless

CDMA

GSM

DLCPRIBRIILL

MPLSLL

NPLC

implies, CDMA is a form of multiplexing, which allows numerous signals to occupy a single

transmission channel, optimizing the use of available bandwidth. The technology is used in

ultra-high-frequency (UHF) cellular telephone systems in the 800-MHz and 1.9-GHz bands.

CDMA employs analog-to-digital conversion (ADC) in combination with spread spectrum

technology. Audio input is first digitized into binary elements. The frequency of the

transmitted signal is then made to vary according to a defined pattern (code), so it can be

intercepted only by a receiver whose frequency response is programmed with the same code,

so it follows exactly along with the transmitter frequency. There are trillions of possible

frequency-sequencing code, which enhances privacy and makes cloning difficult.

The CDMA channel is nominally 1.23 MHz wide. CDMA networks use a scheme called soft

handoff, which minimizes signal breakup as a handset passes from one cell to another. The

combination of digital and spread-spectrum modes supports several times as many signals

per unit bandwidth as analog modes. The original CDMA standard, also known as CDMA

One and still common in cellular telephones in the U.S., offers a transmission speed of only

up to 14.4 Kbps in its single channel form and up to 115 Kbps in an eight-channel form.

CDMA uses a radically different 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

codes”.

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.

Figure 1.2 CDMA technique

3

Figure 1.3 CDMA users separated by codes

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

tion and offer service to many subscribers without requiring extensive frequency planning.

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

tinguished 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 trans-

mitted power required by CDMA is much lower than what is required by analog, FDMA and

TDMA technologies.

1.3 CDMA TECHNOLOGY

CDMA technology is most developing technology in nowadays world. Earlier it was only

used for military purpose because of its message security property but now we are using it for

commercial use also. RELIANCE and TATA, both service providers are using this

technology. We are using CDMA technology because of its great advantages which are listed

here under.

CDMA technology has numerous advantages including:

1. Coverage

2. Capacity

3. Clarity

4. Cost

5. Compatibility

Here we will take brief description of each advantage of the CDMA technology:

1.3.1 CDMA Coverage

4

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.

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

of available power used in other systems.

1.3.2 CDMA 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 re-

quires less power.

Figure 1.4 Comparison of various techniques

1.3.3 CDMA 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.

1.3.4 CDMA Cost

5

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

Increased coverage per BTS means fewer BTS 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.

1.3.5 CDMA Compatibility

CDMA phones are usually dual mode. This means they can work in both CDMA systems and

analog cellular systems. Some CDMA phones are dual band as well as dual mode. They can

work in CDMA mode in the PCS band, CDMA mode in the cellular band, or analog mode in

an analog cellular network.

1.4 CDMA WORKING

As the name suggest this technique uses mathematical codes to allow multiple access Instead

of using frequencies or time slots, as do traditional technologies. However, because the con-

versations 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.

CDMA receivers, conversely, separates communication channels by a pseudo-random modu-

lation 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. Central to the cellular concept is frequency reuse, which is critically

dependent upon the fact that the carrier wave power decreases with increasing distance. With

this information, a cellular division of frequency channels can be implemented. The channel

is allocated to another radio station far enough apart where signals won't interfere with each

other. By reusing channels in multiple cells, the system can grow without geographical lim-

its.

6

F2

F1 F3

F4

F5 F6

F7

Figure 1.5 Frequency Reuse Pattern-7 Frequency Reuse Pattern-1

CDMA assigns one distinct spreading code to each user. As long as the codes are or-

thogonal or almost orthogonal all users can send and receive their signal through the

same wide band channel.

Other users’ signals appear like noise.

A CDMA system allows multiple access using a single CDMA channel.

The same channel can be used in adjacent cells. Thus CDMA allows a universal reuse

pattern, or reuse of one.

Because of spread spectrum nature of signals all co-channel interference appear like

noise to intended user.

Since different base stations or users use different codes with almost zero correlation,

the receivers can reject co-channel interference as part of De-spreading.

1.5 CDMA BENEFITS

When implemented in a cellular telephone system, CDMA technology offers numerous bene-

fits to the cellular operators and their subscribers. The following is an overview of the bene-

fits of CDMA.

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

that of a GSM system.

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Improved call quality, with better and more consistent sound as compared to AMPS

systems.

Simplified system planning through the use of the same frequency in every sector of

every cell.

Enhanced privacy.

Improved coverage characteristics, allowing for the possibility of fewer cell sites.

1.6 CDMA CODES

As the technology, it is known as spread spectrum technology so for spreading the

information we have to consider some points, they are as followed:

A CDMA signal uses many chips to convey just one bit of information.

Each user has unique pattern, in fact a code channel.

To receive or recover a bit, integrate a large number of chips known by the code pat-

tern.

Other user’s code pattern appears random and integrates in a self-canceling fashion;

don’t disturb the decoding decision being made with the proper code pattern.

Uplink Identification

On the uplink, the base station uses the long code to identify the mobile unit that is using a

particular CDMA channel. The long code also provides spreading and encryption.

The uplink signal uses the short code for quadrature spreading and to allow the base station

to obtain bit synchronization. The Walsh functions are used on the uplink to provide for

better signal reception through spreading gain.

Downlink Identification

Now consider downlink identification. On the downlink, the mobile unit must identify the

base station as well as the call itself. The following are used on the downlink:

Long code for encryption

Short code for base station identification

Walsh functions for channel assignment

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1.7 PN CODES

Forward link of IS-95 CDMA has pilot and sync channels to aid synchronization, but the

reverse link does not have pilot and sync channels. Thus, Walsh codes cannot be used on the

reverse link. The incoherent nature of the reverse link calls for the use of another class of

codes, PN codes, for Channelization. PN codes have very sharp autocorrelation.

Generation of PN Codes

PN code sets can be generated from linear feedback shift registers. Binary bits are shifted

through the different stages of the register. The output of the last stage and the output of one

intermediate stage are combined and fed as input to the first stage. The register starts with an

initial sequence of bits, or initial state, stored in its stages. Then the register is clocked, and

bits are moved through the stages. This way, the register continues to generate output bits and

feed input bits to its first stage. The output bits of the last stage form the PN code.

Here we show the code generation using the register Figure 1.6. Let initial state is [1, 0, 1]

for register. The output of stage 3 is the output of the register.

Figure 1.6 PN code generation through shift registers

1.8 HANDOFF IN CDMA

The act of transferring support of a mobile from one base station to another is termed ‘Hand-

off’. Handoff occurs when a call has to be handed off from one cell to another as the user

moves between cells.

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Figure 1.7 Handoff between two cells

Types of Handoff

Hard Handoff

Soft Handoff

Handover occurs when a call has to be passed from one cell to another as the user moves

between cells. The connection to the current cell is broken, and then the connection to the

new cell is made. This is known as a "break-before-make" handover. This is also known as

“hard” hand over. Since all cells in CDMA use the same frequency, it is possible to make the

connection to the new cell before leaving the current cell. This is known as a "make-before-

break" or "soft" handover. Soft handovers require less power, which reduces interference

and increases capacity. Mobile can be connected to more than two BTS at the time of

handover. This is sometimes called "softer" handover.

HARD HANDOFF Figure 1.8 SOFT HANDOFF

Break before make (a) Make-before-break (b)

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One of the main advantages of CDMA systems is the capability of using signals that arrive in

the receivers with different time delays. This phenomenon is called multi path. FDMA and

TDMA, which are narrow band systems, cannot discriminate between the multi path arrivals,

and resort to equalization to mitigate the negative effects of multi path.

Due to its wide bandwidth and rake receivers, CDMA uses the multi path signals and com-

bines them to make an even stronger signal at the receivers. CDMA subscriber units use rake

receivers. This is essentially a set of several receivers. One of the receivers constantly

searches for different multi paths and feeds the information to the other three fingers. Each

receiver then demodulates the signal corresponding to a strong multi path. The results are

then combined together to make the signal stronger.

Figure 1.9 Use of Rake receiver

Soft Handoff

This handoff requires the mobile to constantly search for multi paths from different base sta-

tions even while actively receiving and sending traffic. Soft handoff can be costly for net-

work capacity if not implemented properly, as each base station that the mobile is in simulta -

neous contact with must allocate resources for the communications link.

To make Handoff Mobile Station maintains four types of different sets.

Active Set: It contain pilot offset of sector whose channel is currently monitored by

mobile.

Candidate Set: It contain pilot that are not in the active set, but have sufficient signal

strength for demodulation.

Neighbor Set: It contain pilot of base station of neighboring cell that are indicated by

network through paging channel.

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Remaining Set: This set contains all pilot offset in system excluding active and

neighbor set.

The active set is the set of base stations that the mobile may be in simultaneous contact. The

base station based on measurement information relayed by the mobile controls this set. The

candidate set entails pilots that are not in the active set but can be successfully demodulated

by the mobile. The maximum number of pilots in either the active or candidate sets is 6.

The neighbor set is based on predetermined pilots that are in the vicinity of the base station

or base stations the mobile is currently in contact with. This may have as many as 20 pilots in

it. The remaining set covers all other pilots.

The base station must drop pilots from the active set whose strength has dropped below a cer-

tain threshold, T_DROP. This is also another event that can trigger the mobile to send a

PSMM. Threshold comparisons to drop a pilot are timer based, meaning that the pilot must

be below T-DROP for a certain amount of time (given by T_TDROP) before the pilot is de-

moted. In addition, the mobile may search for multi paths at certain PN offsets given the net-

work deployment. For instance, if the base station knows the PN offsets of neighboring base

stations, it may provide the mobile with search windows.

Hard Handoff

The third is the hard handoff. The CDMA system uses two types of hard handoffs. CDMA-

to-CDMA handoff occurs when the mobile is transitioning between two CDMA carriers (i.e.,

two spread-spectrum channels that are centered at different frequencies). This hard handoff

can also occur when the mobile is transitioning between two different operators’ systems.

CDMA-to-CDMA handoff is sometimes called D-to-D handoff. On the other hand, CDMA-

to-analog handoff occurs when a CDMA call is handed down to an analog network. This can

occur when the mobile is traveling into an area where there is analog service but no CDMA

service. CDMA-to-analog handoff is sometimes called D-to-A handoff.

Other CDMA Handoff

CDMA uses soft handoff whenever possible because the performance is very much superior

to other forms of handoff. However, there are several forms of handoff that cannot be done

“softly”.

Inter Frequency Handoff

If there are multiple CDMA carrier frequencies active, then handoffs between them must be

hard. Inter-frequency hard handoffs are probably best accomplished by doing so within one

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geographical site, rather than trying to handoff to a neighboring site. The inter-frequency

handoff can first be executed intra-site, where the mobile’s timing is already known, followed

immediately by a soft handoff to the neighbor without frequency change on the new

frequency.

Softer Handoff

Each BTS sector has unique PN offset & pilot. If multiple sectors of one BTS simultaneously

serve a handset, this is called Softer Handoff.

CDMA Handoff Advantage over AMPS Handoff

It is “soft” meaning that communication is not interrupted by the handoff. This means

fewer dropped calls for users and higher customer satisfaction for operators.

The handoff is not abrupt, but rather it is a prolonged call state during which there is

communication via two or more base stations. The multi-way communication diver-

sity improves the link performance during the handoff, the diversity gain partially

compensates for the large path loss at the cell boundary.

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CHAPTER 2

DIGITAL TRANSMISSION

2.1 TRANSPORT NETWORK

The network that carries communication and information signals from one place to another

is called the Transport Network.

TABLE 2.1

Comparison between Early & Modern Transmission Network

Modern definition of Transmission network:

The purpose of a transmission network is to multiplex together multiple low bit rate digital

traffic streams into higher bit rate traffic streams for efficient transport between access points.

Medium: Carries signals from one place to another. Eg. air, copper, optical fiber, etc.

14

Early Transmission Network Modern Transmission Network

1. Supports Voice only

2. Analog

3. Covered short distances

4. Operate at very slower speed

5. Could only accommodate few

users.

6. Network availability is not

ensured.

1. Provide multiple services like

digital voice, video and data.

2. digital

3. Cover long distances

4. Operate at very high speed

5. Accommodate millions of users

6. Ensure 99.999% network

availability.

2.2 EVOLUTION OF DIGITAL TRANSMISSION NETWORKS

Main principles:

1. Pulse Code Modulation

2. Time Division Multiplexing

3. Standard Multiplexing Hierarchies (E.g. PDH, SDH).

2.2.1 Pulse Code Modulation

PCM is the method to convert analog signals into digital signals by means of sam-

pling according to Nyquist criteria , quantizing and then encoding analog signal and

transmitting it at a bit rate of 64 Kbit/s.

A transmission rate of 2.048 Mbit/s (known as E1) results when 30 such coded chan-

nels are collected together into a frame along with the necessary signaling informa-

tion. This so-called primary rate is used throughout the world.

Only the USA, Canada and Japan use a primary rate of 1.544 Mbit/s, formed by com-

bining 24 channels (known as T1 carrier system) instead of 30.

2.2.2 Time Division Multiplexing

Multiplexing is the assembly of a group of lower bit rate individual channels into a higher bit

rate aggregate.

32 channels x 64Kbps = 2048 Kbps = 2 Mbps

2.2.3 Introduction to E1 Interface

A communication line that was developed by European standards is, that multiplexes thirty

voice channels and two control channels onto a single communication line. The E1 line uses

256 bit frames and transmits at 2.048 Mbps. The E1 interface is independent standardized

TDM technology. This technology enables transmission of several (multiplexed) voice/data

channel simultaneously on the same transmission facility. The E1 standard is mostly

deployed in Europe.

15

Fig 2.1 E1 frame structure

Figure 2.2 A communication network without E1

E1 Link

16

PhoneSystem

FAX FAX

PC PC

PhoneSystem

Phone System

PhoneSystem

FAX FAX

PC PC

MUX M

UX

Figure 2.3 A communication network with E1

Suppose we have 32 channels, each with a rate of 64Kbs that we wish to transfer to the other

end. The multiplexing takes from each of the 32 lines a single byte and sends then one after

the other. After doing so; it takes the next byte from every channel, and so on. The

multiplexer must be able to send all the 32*8 bits from the 32 channels without the second

byte of the first channel getting lost.

This implies that output rate of the multiplexer should be at least 32*64 Kbps or 2048Kbps.

This method is called Time Division Multiplexing (TDM). Because the multiplexer took

there 1/8000 second for transferring a single byte of a single channel, and divided it between

the 32 channels by increasing the rate so that each byte of a channel will take 1/ (8000*32)

second to send.

2.2.4 Multiplexing Hierarchies

Traffic over the past decade has demanded that more and more of these basic E1s be

multiplexed together to provide increased capacity.

PDH (Plesionchronous Digital Hierarchy):

As bandwidth demand grew, the technology called Plesionchronous Digital Hierarchy

(PDH) was developed by ITU-T G.702, whereby the basic primary multiplexer 2.048 Mb/s

trunks were joined together by adding bits (bit stuffing) which synchronized the trunks at

each level of the PDH. This hierarchy is based on multiples of 4 E1s.

E2, 4 x E1 - 8Mb/s

E3, 4 x E2 - 34Mb/s

E4, 4 x E3 - 140Mb/s

E5, 4 x E4 - 565Mb/s

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Figure 2.4 PDH (Plesionchronous Digital Hierarchy)

Limitations of PDH:

Data sources are nominally synchronous.

Tributary signals can only be accessed at the level from which they were multiplexed.

The use of Justification bits (added bits which tell the multiplexers which bits are

data and which are spare) at each level at PDH, means that identifying the exact loca-

tion of the frames from a single 2 Mb/s line within a 140 Mb/s channel is impossible.

In order to access a single 2 Mb/s line, the 140 Mb/s channel must be completely de-

multiplexed to its 64 constituent 2 Mb/s lines via 34 and 8Mb/s.

Once the required 2 Mb/s has been identified and extracted, the channels must be then

be re-multiplexed back up to 140 Mp/s for onward transmission.

SDH (Synchronous Digital Hierarchy):

As management in PDH is very inflexible, SDH was developed. Synchronous Digital Hierar-

chy (SDH) originates from Synchronous Optical Network (SONET) in the US. Telecom-

munications technologies are generally explained using so called layer models. SDH can also

be depicted in this way. SDH networks are subdivided into various layers that are directly re -

lated to the network topology.

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The lowest layer is the physical layer, which represents the transmission medium. This is

usually a glass fiber or possibly a radio-link or satellite link. The regenerator section is the

path between regenerators. Part of the overhead (RSOH, regenerator section overhead) is

available for the signaling required within this layer.

The remainder of the overhead (MSOH, multiplex section overhead) is used for the needs of

the multiplex section. The multiplex section covers the part of the SDH link between

multiplexers.

Fig 2.5 SDH layer model

The carriers (VC, virtual containers) are available as payload at the two ends of this section.

The two VC layers represent a part of the mapping process. Mapping is the procedure

whereby the tributary signals, such as PDH and ATM signals are packed into the SDH

transport modules. VC-4 mapping is used for 140 Mbit/s or ATM signals and VC-12 mapping

is used for 2 Mbit/s signals.

2.3 SDH FRAME STRUCTURE

STM-1 frame

In SDH the basic rate is 155.52 Mb/s. This is called the Synchronous Transport Module

Level 1(STM-1). Higher rates are designated by STM-M where values of M by the ITU-T

recommendations are M=1, 4, 16 and 64.

Overheads bytes (first 3*3 columns of frame) carry Network Management Informa-

tion such as:19

– Trail Trace - misconnection of the physical media most common

– Error Monitoring

– Automatic Protection Switching

– Framing, Multiplexing

Fig 2.6 SDH STM-1 Frame Format

Synchronous Payload Envelope (SPE) (261(87*3) columns) carry User Data i.e.

PDH frames plus 27(9*3) bytes of path overhead.

Path overhead

In transmission, a path is defined as a circuit joining two nodes that may pass trough a

number of intermediate nodes. In SDH, extra capacity is reserved to carry monitoring and

management information associated with the path. This extra information associated with the

path is called Path Overhead.

It allows the checking of aspect such as,

Quality of the overall end to end transmission.

Existence of path between two termination points.

Section Overhead

A section can be considered as one stage of an end path. It is defined as node to node

transmission. A path may be a number of sections .One section may be a path. The SDH also

reserves some extra capacity within the defined bit rates to carry information relating to the

section. This extra information associated with a section is called Section Overhead.

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It contains data to control node-to-node transmission.

Protection switching

Error monitoring

Network management

Fig 2.7 Logical mapping of signals

How Is The Frame Composed ?

PDH Payload = Container (C)

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

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

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TABLE 2.2

SDH denominations

22

PDH Standard

(Bit rates)

SDH

Denomination

SDH Transport

Capacity

Corresponding

SDH Bit rate

64 kbps VC-0 -  

1.5 mbps VC-1 -  

2 mbps VC-1 -  

6 mbps VC-2 -  

34/45 mbps VC-3 -  

140 mbps VC-4 STM-1 155 mbps

  VC-4x4 STM-4 620 mbps

  VC-4x16 STM-16 2500 mbps

  VC-4x64 STM-64 10 gbps

Figure 2.8 SDH Hierarchy - TUG Structure

2.4 BENEFITS OF SDH TRANSMISSION

High transmission rates

Transmission rates of up to 10 Gbit/s can be achieved in modern SDH systems. SDH is

therefore the most suitable technology for backbones.

Simplified add & drop function

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

channels from or into the high-speed bit streams in SDH. It is no longer necessary to de-

multiplex and then re-multiplex the plesiochronous structure, a complex and costly

procedure at the best of times.

High availability and capacity matching

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

customers. For example, leased lines can be switched in a matter of minutes. The network

provider can use standardized network elements that can be controlled and monitored

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C-12 VC-12 TU-12

C-3 VC-3 TU-3

C-4

TUG-2

TUG-3

VC-4

AU-4

STM-1

X 3

X7

X1

X 3

X1

POINTERS

MULTIFLEXING

ADDITION OF OVERHEADS

ALIGNMENT

from a central location by means of a telecommunications network management (TNM)

system.

Reliability

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

cope with system faults. Failure of a link or a network element does not lead to failure of

the entire network which could be a financial disaster for the network provider. These

back-up circuits are also monitored by a management system.

Future-proof platform for new services

Right now, SDH is the ideal platform for services ranging from POTS, ISDN and mobile

radio through, to data communications (LAN, WAN, etc.), and it is able to handle the

very latest services, such as video on demand and digital video broadcasting via ATM

that are gradually becoming established.

Interconnection

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

SONET systems. The SDH interfaces are globally standardized, making it possible to

combine network elements from different manufacturers into a network. The result is a

reduction in equipment costs as compared with PDH.

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CHAPTER 3

NETWORK MANAGEMENT

3.1 NETWORK TOPOLOGIES

Basic topologies possible in SDH are shown in figure below.

Figure 3.1 Possible topology in SDH architecture

Point-to-point:

The simplest topology is a permanent link between two endpoints. Switched point-to-point

topologies are the basic model of conventional telephony. The value of a permanent point-to-

point network is the value of guaranteed, or nearly so, communication between the two end-

points. This topology doesn’t provide redundancy. If the path is broken then the communica-

tion will be over.

Ring:

The type of network topology in which each of the nodes of the network is connected to two

other nodes in the network and with the first and last nodes being connected to each other,

forming a ring – all data that is transmitted between nodes in the network travels from one

node to the next node in a circular manner and the data generally flows in a single direction

only. But if any fault occurs in the transmission, then data will flow through the reverse

direction and provide redundancy.

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Dual-ring

The type of network topology in which each of the nodes of the network is connected to two

other nodes in the network, with two connections to each of these nodes, and with the first

and last nodes being connected to each other with two connections, forming a double ring –

the data flows in opposite directions around the two rings, although, generally, only one of

the rings carries data during normal operation, and the two rings are independent unless there

is a failure or break in one of the rings, at which time the two rings are joined (by the stations

on either side of the fault) to enable the flow of data to continue using a segment of the

second ring to bypass the fault in the primary ring.

Mesh

In this topology each node is connected to every node in the network. This topology gives

redundancy path but the network becomes very complex as the no. of nodes increases.

3.2 OPTICAL ADD DROP MULTIPLEXER

The main function of optical multiplexers is to couple two or more wavelengths into the

same fiber. It is clear that if a de-multiplexer is placed and properly aligned back to back with

a multiplexer, one could remove an individual wavelength and also insert an individual

wavelength. Such a function is called an optical add-drop multiplexer (OADM.).

The OADM selectively removes (drops) a wavelength from a multiplicity of wavelength in

the fiber, and thus traffic on this channel. It then adds in the same direction of dataflow the

same wavelengths, but with different data content.

Fig 3.2 OADM

OADMs are classified as fixed wavelength and as dynamically wavelength selectable

OADMs. In a fixed wavelength OADM, the wavelength has been selected and remains the

26

same until human intervention changes it. In dynamically selectable wavelength OADM, the

wavelengths between the optical de-multiplexer/multiplexer may be dynamically directed

from the outputs of the de-multiplexer to any of the inputs of the multiplexer.

3.3 COMPONENTS OF A SYNCHRONOUS NETWORK

Figure 3.3 Components of Synchronous network

Figure shows a schematic diagram of a SDH ring structure with various tributaries. The

mixture of different applications is typical of the data transported by SDH. Synchronous

networks must be able to transmit plesionchronous signals and at the same time, be capable

of handling future services such as ATM.

Current SDH networks are basically made up from four different types of network element.

3.3.1 Regenerators

Fig 3.4 Regenerators

Regenerator regenerates the clock and amplitude relationships of the incoming data signals

that have been attenuated and distorted by dispersion. They derive their clock signals from

the incoming data stream. Messages are received by extracting various 64 Kbit/s channels

27

(e.g. service channels E1) in the RSOH (regenerator section overhead). Messages can also be

outputed using these channels.

3.3.2 Terminal Multiplexers

Terminal multiplexers are used to combine plesionchronous and synchronous input signals

into higher bit rate STM-N signals.

Fig 3.5 Terminal multiplexers

3.3.3 Add/Drop Multiplexers (ADM)

Plesionchronous and lower bit rate synchronous signals can be extracted from or inserted into

high speed SDH bit streams by means of ADMs. This feature makes it possible to set up ring

structures, which have the advantage that automatic back-up path switching is possible using

elements in the ring in the event of a fault.

Fig 3.6 ADM

3.3.4 Digital Cross Connects (DXC)

28

This network element has the widest range of functions. It allows mapping of PDH tributary

signals into virtual containers as well as switching of various containers up to and including

VC-4.

Fig 3.7 DXC

The telecommunications management network (TMN) is considered as a further element in

the synchronous network. All the SDH network elements mentioned so far are software-

controlled. This means that they can be monitored and remotely controlled, one of the most

important features of SDH.

3.4 PROTECTION IN RING ARCHITECTURE

Two basic types of protection architecture are distinguished in APS (Automatic Protection

Switching). One is the linear protection mechanism used for point-to-point connections. The

other basic form is the so-called ring protection mechanism which can take on many

different forms. Both mechanisms use spare circuits or components to provide the back-up

path. Switching is controlled by the overhead bytes K1 and K2.

3.4.1 Linear Protection

The simplest form of back-up is the so-called 1 + 1 APS. Here, each working line is

protected by one protection line. If a defect occurs, the protection agents in the network

elements at both ends switch the circuit over to the protection line. The switchover is

triggered by a defect such as LOS. Switching at the far end is initiated by the return of an

acknowledgment in the backward channel. 1+1 architecture includes 100% redundancy, as

there is a spare line for each working line.

Economic considerations have led to the preferential use of 1: N architecture, particularly for

long-distance paths. In this case, several working lines are protected by a single back-up line.

If switching is necessary, the two ends of the affected path are switched over to the back-up

line.

29

The 1+1 and 1: N protection mechanisms are standardized in ITU-T Recommendation G.783.

The reserve circuits can be used for lower-priority traffic, which is simply interrupted if the

circuit is needed to replace a failed working line.

Fig 3.8 1:3 Linear Protection

3.4.2 Ring Protection

The greater the communication bandwidth carried by optical fibers, the greater the cost

advantages of ring structures as compared with linear structures. A ring is the simplest and

most cost-effective way of linking a number of network elements. Various protection

mechanisms are available for this type of network architecture, only some of which have

been standardized in ITU-T Recommendation G.841. A basic distinction must be made

between ring structures with unidirectional and bi-directional connections.

Unidirectional rings

Figure shows the basic principle of APS for unidirectional rings. Let us assume that there is

an interruption in the circuit between the network elements A and B. Direction y is unaffected

by this fault. An alternative path must, however, be found for direction x. The connection is

therefore switched to the alternative path in network elements A and B.

The other network elements (C and D) switch through the back-up path. This switching

process is referred to as line switched. A simpler method is to use the so-called path

switched ring. Traffic is transmitted simultaneously over both the working line and the

30

protection line. If there is an interruption, the receiver (in this case A) switches to the

protection line and immediately takes up the connection.

Fig 3.9 Two fiber unidirectional path switched ring

Bi-directional rings

Fig 3.10 Two fiber bi-directional line switched ring

In this network structure, connections between network elements are bi-directional. This is

indicated in the figure by the absence of arrows when compared with above figure. The

overall capacity of the network can be split up for several paths each with one bi-directional

working line, while for unidirectional rings, an entire virtual ring is required for each path. If

a fault occurs between neighboring elements A and B, network element B triggers protection

switching and controls network element A by means of the K1 and K2 bytes in the SOH.

Even greater protection is provided by bi-directional rings with 4 fibers. Each pair of fibers

transports working and protection channels. This results in 1:1 protection, i.e. 100 %

redundancy. This improved protection is coupled with relatively high cost.

31

Retentive and Non Retentive Switch

Retentive Switch: Automatically takes its original path after recovery of the path in case of

breakup.

Non Retentive Switch: In case of break up alternate path will work and it will continue to

work in spite of original path is now ready to work.

CHAPTER 4

STRUCTURE OF BTS

32

4.1 BTS (BASE TRANSCEIVER STATION)

The Base Transceiver (BTS) belongs to the radio part of a base station system. Controlled by

BSC, it serves the radio transceiving equipment of a certain cell, implements the conversion

between BSC and radio channels, radio transmission through air interface between BTS and

MS and related control, and communicates with BSC through the Abis interface.

4.1.1 Overview of the HUAWEI BTS3900

A cellular Base Transceiver Subsystem (BTS) is one part of a cellular infrastructure system.

The Basic functions of cellular infrastructure equipment are to provide the fixed end of the

Radio interface to subscribe cellular phones and to route voice and data traffic up to the

Public Switched Telephone Network (PSTN). The BTS3900 is an indoor macro base station

developed by Huawei. The BTS3900 mainly consists of the BBU3900 and the RFUs.

Compared with traditional BTSs, the BTS3900 features simpler structure and higher

integration.

The BTS3900 has the following features:

1. It is developed on the basis of the unified BTS platform for Huawei wireless products

and enables the smooth evolution from 2G to 3G.

2. It supports the Abis IP/FE interface in hardware and enables Abis over IP through

software upgrade if required.

3. It shares the BBU3900 sub rack, which is the central processing unit, with the

DBS3900 to minimize the number of spare parts and reduces the cost.

4. It can be flexibly installed in a small footprint and can be easily maintained with low

cost.

5. It supports 2-way and 4-way RX diversity (not supported by the GRFU) to improve

the uplink coverage.

6. It supports the GPRS and the EGPRS.

7. It supports Omni directional cells and directional cells.

8. It supports multiple topologies, such as star, tree, chain, ring, and hybrid topologies.

9. It supports the cell broadcast SMS and point-to-point SMS.

4.1.2 Structure of the BTS Cabinet

The BTS3900 cabinet adopts the module structure. It consists of the BBU3900, CRFU, FAN,

DCDU-01, and SLPU (optional). A space is reserved at the bottom of the cabinet for the

installation of user devices such as the transmission equipment.33

Figure 4.1 Internal structure of the BTS3900 cabinet

4.1.3 Configuration of the BTS Cabinet

The BTS3900 cabinet supports the typical configuration with three CRFUs and the full

configuration with six CRFUs. The SLPU is an optional component of the BTS3900 cabinet.

Typical configuration of BTS 3900 is as shown in figure 4.2 below. Different cards for BTS

are as shown below used in BTS configuration.

34

Figure 4.2 Typical configuration of the BTS3900 cabinet

TABLE 4.1

Describes the functions of the main components of the BTS3900 cabinet.

Component Description

CRFU CRFU is the CDMA RF unit of the BTS3900. It receives and sends

radio signals for communication between network system and MS.

FAN The FAN is the fan unit of the BTS3900. It houses fans for heat

dissipation in the BTS3900 cabinet.

BBU3900 The BBU3900 is the baseband unit of the BTS3900. It performs

resource management, operation maintenance, and environment

monitoring for the BTS.

DCDU-01 The DCDU-01 is the direct current distribution unit of the BTS3900.

It supports one DC input and multiple DC outputs.

SLPU

(optional)

It is the protection unit of the BTS3900 cabinet, and it houses the

UELP and UFLP board for protecting the E1/T1 and FE signals from

lightning

4.1.4 Logical Structure of the BTS

This describes the logical structure of the BTS. Logically, the BTS consists of the baseband

system, RF system, power system, and antenna system.

35

Figure 4.3 Logical structure of the BTS3900

4.1.5 Baseband System

The baseband system consists mainly of BBU3900s and performs the following functions:

1. Providing the physical interface for data exchange between the BTS and the BSC.

2. Modulating and demodulating baseband data and CDMA channel signals.

3. Providing system synchronization clock signals.

4. Implementing resource management, operation and maintenance, and environment

monitoring.

4.1.6 RF System

The RF system consists mainly of CRFUs and performs the following functions:

1. On the forward link, implementing up-conversion and power amplification for modu-

lated transmitted signals and filtering the transmitted signals to make them meet the

requirements of the Um interface protocol.

2. On the reverse link, filtering the signals received by the antenna to suppress out-band

interference and performing low noise amplification, channel division, down-conver-

sion, and channel-selective filtering.

4.1.7 Power Supply System

The power supply system consists mainly of DCDUs and performs the following functions:

1. The DCDU is a DC power distribution unit and provides -48 V DC power input for

the components in the cabinet.

4.1.8 Antenna System

36

The antenna system consists of the RF antenna system and satellite antenna system. The

antenna system performs the following functions:

Satellite antenna system

Through the satellite synchronization antenna, the BTS receives signals from the GPS or

GLONASS system and performs wireless synchronization.

RF antenna system

The RF antenna system transmits modulated RF signals and receives the signals from the

MS.

4.1.9 Clock Synchronization Modes of BTS

The BTS supports various clock sources, such as the GPS clock source, interface clock

source, Abis interface clock source, and internal clock source.

TABLE 4.2

Clock synchronization modes supported by the BTS

Clock

Synchronization

Type

Description

GPS clock source The BTS provides the GPS clock input port and obtains

clock signals through the external GPS equipment.

Abis interface clock

Source

The BBU3900 supports the extraction of clock signals

directly from ports such as the E1/T1 port. The clock module

performs frequency division, phase locking, and phase

adjustment for the clock signals. In this way, precise 2 MHz

and 8 KHz clock signals are obtained and used for frame

synchronization and bit synchronization inside the BTS.

Internal clock signals When external clock sources are not available, the crystal

oscillators of the BBU3900 boards provides 10 MHz clock

signals to guarantee the normal running of the BTS.

4.1.10 Performance Specification of the BTS

This describes the performance specifications of the BTS in terms of transmitter and receiver

specifications, CRFU cascading specifications, and BERs on transmission links.

Transmitter and Receiver Specifications:

37

The transmitter and receiver specifications refer to the technical parameters of the transceiver

of the BTS. The receiver and transmitter specifications of the BTS in different band classes

are as follows:

TABLE 4.3

Transmitter specifications (800 MHz)

Item Specification

Working frequency band 869 MHz to 889 MHz

Channel bandwidth 1.2288 MHz

Channel precision 30 kHz

Frequency tolerance ≤ ±0.05 ppm

Transmit power ≤ 80 W

TABLE4.4 Receiver specifications (800 MHz)

Item Specification

Working frequency band 824 MHz to 844 MHz

Channel bandwidth Channel bandwidth

Channel precision 30 kHz

Signal receiving sensitivity Better than -130 dBm (main and diversity

receiving at RC3)

CHAPTER 5DIFFERENT TYPES OF MULTIPLEXERS

5.1 CLASS OF MUX’S USED BY TTSL

38

Micro SDM BG 20B/E/C XDM 100 XDM 300 XDM 500 XDM 1000

Common Functionality

Most cross-connect, timing, and control functionality is integrated and internal to the main card in BG-20, the MXC20. No separate card is used to control these operational aspects of the unit. Besides this common functionality, the MXC20 also supports vari-ous traffic interfaces, such as STM-1/4 aggregates, E1, and FE interfaces.

MXC20 functionality includes:

Integrated cross connection, timing, system control, and overhead processing (includ-ing DCC and Clear Channel)

Communication with and control of a daughterboard in the Dslot and extension cards in the BG-20E shelf through the backplane

Control-related functions

Communications and control (by the CPU)

Alarms and maintenance

Fan control

SDH-related functions

SDH timing and synchronization

5.2 µSDM-1E

39

Figure 5.1 MicroSDM MUX

These are third generation Broad gate multiplexers, optimally designed for installation in

street cabinets and customer premises locations. This type of equipment enables the

implementation of small and simple Access network topologies that are fully managed,

flexible, and very cost-effective. With Lights cape Networks new µSDM-1E multiplexers,

telecom operators can achieve a high level of service and increased revenues, as they benefit

from the following advantages:

1. Low cost per line

2. Advanced fiber and copper technologies

3. Integrated management system

4. Support of a wide range of services.

5. Flexible configuration and easy upgradability.

The maximum capacity of this mux is 63 E1 and it does not provide Ethernet interface.

MAC CARD

The MAC card houses one or two O/E modules which are piggyback mounted mini-boards.

The O/E modules provide the SDH line interfaces (optical or electrical). An additional card

mounted on the MAC is the Timing Module Unit (TMU).

The CDB Card

The CDB provides control and processing functions to the MAC card and the TEX card 40

(when fitted). It houses the power supply as well as various memory modules (including the

NVM, which is mounted on the CDB). The central processing unit is a state-of-the-art

PowerPC RISC processor.

The TEX Card

The TEX card is an optional expansion card fitted into the µSDM-1E which provides tributaries

interfaces expansion as follows TEX 2_42 support Up to 42 E1.

5.3 BG-20B (BROADGATE-20)

Figure 5.2 BG-20B

ECI Telecom’s BG-20 miniature MSPP delivers a cost-effective and affordable mix of

Ethernet, SDH, PDH, and PCM services, resulting in new revenue-generating opportunities.

It offers a wide variety of features and benefits, including:

1. Ultra-high scalability based on coupling the BG-20E to the BG-20B to make a

build-as-you-grow solution.

2. Gradual capacity expansion based on service provisioning needs. More STM-1

interfaces can be added very conveniently and ADM-1s can be upgraded to

ADM-4s without affecting traffic. This highly adaptable and flexible architecture

translates into significant savings in both operational and capital expenditures

(OPEX and CAPEX).

3. Provides a carrier class Ethernet-over-WAN/MAN solution (including Ethernet

over SDH and Ethernet over PDH) with SDH reliability, security, and

management of data services.

41

4. PCM service interfaces and 1/0 digital cross-connect functions to facilitate the

construction and maintenance of various private networks.

5. Multi-ADM and cross-connect functionality, ideal for deployment in flexible

network topologies like ring, mesh, and star.

6. Compactness and resiliency, perfectly suited for both indoor and outdoor

enclosures. Due to its extended operating temperature range, it is also most

suitable for harsh environmental conditions.

7. The maximum capacity of BG-20 is STM-4. When the capacity increase beyond

the STM-4 than we directly use the XDM-100

MXC20 Card

The MXC20 supports the following interfaces: 21xE1, 6 Ethernet port, 2 ports forSTM-1/4,

MNG for local login, RS-232, housekeeping alarms. In addition to these interfaces, the

MXC20 has LED indicators and one push button. It also consist one D-slot for providing

more interface. As the BG-20 is a front-access shelf, all its interfaces, LEDs, and push button

are located on the front panel of the MXC20. Now we discuss about the cards that are

inserted into the D-slot.

ME1_21H card

ME1_21H is a D-slot module with 21 x E1 (2.048 Mbps) balanced electrical interfaces. The

cabling of the ME1_21H module is directly from the front panel with a twin 68-pin VHDCI

female connector.

ME1_42H Module

The ME1_42 is a D-slot module with 42 x E1 (2.048 Mbps) balanced electrical interfaces.

The cabling of the ME1_42 module is directly from the front panel with two twin 68-pin

VHDCI female connectors.

SMD1H Module

The SMD1H is an SDH D-slot module with two STM-1 (155 Mbps) interfaces (either optical

or electrical).

OMS4H Module

The OMS4H is an SDH D-slot module with one STM-4 (622 Mbps) optical interface.

MEoP_4 Module

42

The MEoP is an L1 data Dslot module with four 10/100BaseT interfaces on the LAN side

and four EoP interfaces on the WAN side. The total WAN bandwidth is 32xE1.

5.4 BG-20E (BROADGATE-20)BG-20E is same as the BG-20B but the only difference is that we expand the cards in the

BG-20E. Remaining all the things are same in both cases. Three extension slots are available

in the BG-20E to accommodate the various types of extension cards. These cards are:

PE1_63 Card

The PE1_63 is an electrical traffic card with 63 x E1 (2 Mbps) balanced electrical interfaces.

A maximum of three PE1_63 cards can be installed in one BG-20E shelf. The cabling of the

PE1_63 card is directly from the front panel with three twin 68-pin VHDCI female

connectors.

S1_4 Card

The S1_4 card is an SDH extension card with four STM-1 (155 Mbps) interfaces (either

optical or electrical).

ESW_2G_8F_E Card

The ESW_2G_8F_E is an EoS Metro Ethernet L2 switching card with 8 x 10/100BaseT

LAN interfaces, 2 x GbE LAN interfaces, and 16 EoS WAN interfaces. The total WAN

bandwidth is up to 4 x VC-4. A maximum of three ESW_2G_8F_E cards can be installed in

one BG-20E shelf.

5.5 BG-20C (BROADGATE-20)It is same as the BG-20B but the only difference is that it does not have the D-slot and it contains only four Ethernet port.

5.6 XDM-100

43

Figure 5.3 XDM-100

ECI Telecom's XDM-100 miniature MSPP delivers a cost-effective and affordable mix of

Ethernet, SDH and PDH services, resulting in new revenue-generating opportunities. It offers

a wide variety of features and benefits, including:

1. Gradual in-service capacity expansion based on service provisioning needs. An

optical connection operating at a specific STM rate can be upgraded from STM-1

to STM-4/16 without affecting traffic. This high adaptability and "build-as-you-

grow” architecture means significant savings in both OPEX and CAPEX.

2. Multi-ADM and cross-connect functionality makes XDM-100 ideal for deploy-

ment in flexible network topologies, such as ring, mesh and star.

3. The XDM-100 is compact and resilient, making it perfectly suited for both indoor

and outdoor enclosures, as well as for harsh environmental conditions, due to its

extended operating temperature range.

All electrical connections are located directly in the tributary modules; therefore, the XDM-

100 does not need additional electrical interface connections.

To support system redundancy, each MXC card contains an integrated xINF (XDM Input

Filter) unit with connectors for two input power sources.

The xFCU-100 fan control unit at the right side of the shelf provides cooling air to the

system. It contains nine separate fans for added system redundancy. Air is drawn in by the

fans from the right side of the chassis and exhausted through the horizontally mounted cards

and modules and through the left side of the chassis. Redundant controllers, located on the

two MXC cards, activate the fans. The xFCU-100 can be extracted and replaced without

44

interrupting the multiplexer operation, provided the replacement does not exceed a few

minutes.

The basic XDM-100 cage contains slots for I/O interface modules, and dedicated slots for the

MXC cards and the ECU. The cage’s design and mechanical practice conform to

international mechanical standards and specifications. The modules and cards are distributed

as follows:

1. Eight (8) slots, I1 to I8, optimally allocated for I/O interface modules.

2. Two (2) slots, A and B respectively, allocated for the MXC cards (main and pro-

tection). Each MXC card has two slots (A1 and A2 and B1 and B2) to accommod-

ate SDH aggregate modules.

3. One (1) slot allocated for the ECU card.

The ECU is located beneath the MXC cards. Its front panel features several interface

connectors for management, external timing, alarms, order wire and overhead (future

release). It also includes alarm severity colored LED indicators and selectors plus a display

for selecting specific modules and ports for monitoring purposes.

MXC(MAIN CROSS-CONNECT AND CONTROL) CARD

The basic and expanded versions of the XDM-100 shelf accommodate two identical

MXC cards. By default, the MXC-A is the main card and MXC-B is the protection card.

Both cards perform the following functions simultaneously in a 1+1 protection

configuration:

1. Communications and control

2. Alarm and maintenance

3. Cross-connect

4. Timing and synchronization

5. Distribution of power supply to all modules (xINF function)

6. Routing and handling of 32 DCC channels

In addition, the MXC accommodates the NVM compact flash memory card and houses SDH

aggregate modules (SAM). The additional MXC card provides 1+1 protection to the cross

connect matrix and full 1:1 protection to all other functions, since the standby MXC has an

identical database to the active MXC.

45

In case of a hardware failure in the active MXC or its traffic interconnection, the I/O

interface modules switch to the protection MXC within 50 ms. Similarly, in case of a

hardware failure in the Timing Unit (TMU) of the operational MXC card, the backup TMU

takes over the timing control with no disruption in traffic.

ECU(EXTERNAL CONNECTION UNIT) CARD

The ECU connects management, alarms, overhead access, and order wire interfaces to the

active MXC card. This card also provides the physical connections for these interfaces. Two

types of ECU cards are available for the XDM-100: ECU-F and ECU (reduced cost). The

ECU-F supports the following management and alarm interfaces and functions:

1. Ethernet interface to XDM element management system

2. Ethernet hub for multiple NE connections

3. USB interface (future option)

4. Synchronization inputs and outputs

5. Alarm severity outputs (Critical, Major, Minor, Warning)

6. External alarm outputs and inputs

7. Operation and alarms LEDs

8. Selection and display of traffic interfaces for monitoring purposes

9. Multiplexer reset.

AGGREGATE MODULES

Two SDH aggregate modules (SAM) plug into each MXC. The MXC provides the aggregate

modules with power and control. The traffic buses of each SAM are connected to both MXC

cards. A variety of aggregate modules with electrical, optical and mixed interfaces, and at bit

rates from STM-1 to STM-16 are available.

I/O MODULES

Eight slots are available in the XDM-100 shelf to accommodate the various types of I/O

modules. Each type of module (PIM, SIM or EIS-M) can be inserted in any of the I1 through

I8 positions without limitation (the EIS-M module occupies two slots). PIM and SIM

modules, with electrical interfaces, fully supports direct connection to the module without

other external connection modules.

46

TABLE 5.1

List of the XDM-100 I/O modules

47

CHAPTER 6

ANTENNAS

6.1 PATCH ANTENNA

Figure 6.1 Patch Antenna

GMS offers variety of Patch (Panel) antennas in bands from 1.7-6 GHz. They are light-

weight and housed in a weather-proof housing. The Messenger Antenna Patch (MAP) is

a precision, high gain antenna designed for broadband receivers and transmitters where wide

bandwidth and high efficiency are key system parameters.  They are designed to either output

RF directly, or can be configured to include an internally-mounted GMS LNA or Block-

Down Converter. GMS also supplies this Antenna in a 360 degree array configuration called

Messenger Antenna Array (MAA) for tracking applications with the Messenger Smart Re-

ceiver (MSR).

6.2 OMNI DIRECTIONAL ANTENNA

GMS offers variety of Omni antennas in bands from 1.7-16 GHz. They are light-weight and

housed in a strong weather-proof PVC housing.

48

Figure 6.2 Omni Directional Antenna

6.3 HELICAL ANTENNA

Figure 6.3 Helical Antenna

GMS Helical (Rod) antennas Right Hand Circular Polarization (RHCP) and range in gain

from 6, 12 and 16 dBic. They are lightweight and constructed from strong, gel-coated fiber-

glass and have an aluminum mounting plate.

6.4 DISK ANTENNA

GMS offers high accuracy parabolic spun aluminum dishes that are designed with rugged

portability in mind. The dish sizes are 24 or 30 inches in diameter and come with tripod or

pole-mount hardware. A wide selection of Linear or Circular feeds that cover 1.7-16 GHz

with quick-release option are also available. 

49

Figure 6.4 Disk Antenna

6.5 YAGI ANTENNA

Figure 6.5 Yagi Antenna

GMS offers variety of Yagi antennas in bands from 1.7-5 GHz with typical gain of 10 or 14

dBic. They are light-weight and housed in a weather-proof radome.

50

CHAPTER 7

DIFFERENT CONNECTERS AND CORDS

7.1 PATCH CORDS

A patch cable or patch cord is an electrical or optical cable used to connect ("patch-in") one

electronic or optical device to another for signal routing. Devices of different types (e.g., a

switch connected to a computer, or a switch to a router) are connected with patch cords.

Patch cords are usually produced in many different colors so as to be easily distinguishable.

Types of patch cords include microphone cables, headphone extension cables, XLR

connector, Tiny Telephone (TT) connector, RCA connector and ¼" TRS connector cables (as

well as modular Ethernet cables), and thicker, hose-like cords (snake cable) used to

carry video or amplified signals. However, patch cords typically refer only to short cords

used with patch panels.

Patch cords can be as short as 3 inches (ca. 8 cm), to connect stacked components or route

signals through a patch bay, or as long as twenty feet (ca. 6 m) or more in length for snake

cables. As length increases, the cables are usually thicker and/or made with more shielding,

to prevent signal loss (attenuation) and the introduction of unwanted radio frequencies and

hum (electromagnetic interference).

Patch cords are often made of coaxial cables, with the signal carried through a shielded core,

and the electrical ground or earthed return connection carried through a wire mesh

surrounding the core. Each end of the cable is attached to a connector so that the cord may be

plugged in. Connector types may vary widely, particularly with adapting cables.

Various Patch Cords are:

LC

SC

FC

E2000

ST

51

Figure 7.1 Various Patch Cords

7.2 CONNECTORS

An electrical connector is an electro-mechanical device for joining electrical circuits as

an interface using a mechanical assembly. The connection may be temporary, as for portable

equipment, require a tool for assembly and removal, or serve as a permanent electrical joint

between two wires or devices.

There are hundreds of types of electrical connectors. Connectors may join two lengths of

flexible copper wire or cable, or connect a wire or cable or optical interface to an

electrical terminal.

In computing, an electrical connector can also be known as a physical

interface (compare Physical Layer in OSI model of networking). Cable glands, known

52

as cable connectors in the U.S., connect wires to devices mechanically rather than

electrically and are distinct from quick-disconnects performing the latter.

Figure 7.2 Different types of Connectors

53

CHAPTER 8

WIRELESS LINKS

8.1 MICROWAVE LINK

8.1.1 Overview of Microwave Link

Microwaves in a descriptive term, is used to identify electromagnetic waves in the frequency

spectrum ranging from 1 GHz to 30 GHz (telecom). Microwaves frequency characteristics

are very similar to light, depending upon propagation in different ways causing attenuation to

the original wave. Microwave communication systems require high frequency signals for

effective transmission of information. There are several factors that lead to this requirement.

For example, an antenna radiates effectively if its size is comparable to the signal

wavelength, since the signal frequency is inversely related to its wavelength, antennas

operating at higher radiation efficiencies. Further their size is relatively small and hence

convenient for mobile communication. Another factor that favours RF and microwaves is

that the transmission of broadband information requires high frequency signal.

The ionosphere does not reflect microwaves and the signals propagate at line of sight. Hence,

curvature of earth limits the range of microwave communication link to less than 50 km. One

way of increasing the range of microwave link is to place the repeater intervals. This is

known as terrestrial communication.

As TTSL communication is using two Types of technology for transportation of data and

voice traffic. It is not possible to make OFC network everywhere at city areas because fiber is

very costly. Two types of network technology is responsible for making connectivity between

one BTS (base transceiver station) to its next BTS. Such a ring connectivity network reaches

to MSC (mobile switching centre). Microwave antennas 0.6m to 0.8m are generally used to

make point to point connection between two BTS.

54

Figure 8.1 Real time Microwave connectivity

When there is a customer group available in some area out of the radiation coverage then all

the times it will not be economical to install another BTS with fiber ring connectivity and use

all transport equipment again. In such cases we can install nearby BTS with Microwave

connectivity. This will be point to point link provided by drum antennas. It will use

appropriate ODU and IDU for conversion from RF signals to E1 lines. Then using this E1s,

again we can serve customers as mentioned above.

8.1.2 Frequency Allocation

6 and 7 GHz frequency bands are used for intercity backbone routes. Nominal hop

distances are 5-50 Kms.

15, 18 and 23 GHz frequency bands are used for access network. Hop distances are 1-

10 Kms.

Frequency spots in 6 and 7 GHz are extremely crowded. Hence frequency allocation

in this band is subjective from place to place. The Tx/Rx separation is fixed at 152

and 154 MHz.

The frequency spectrum in 15 GHz is from 14.25 to 15.35 GHz. The frequencies are

further classified into various sub bands with channel numbers.

In long run OFC would be the right choice, as it will attract no recurring license cost.

55

IDU alarms

ODU alarms

Power alarms

maintenance alarms

Reset switch

Router connection Optional

Ethernet connection optional

Engineering order wire connection ( EOW)

Buzzer

Wayside optional

IF connection to ODU

Earthing Point

Red LED Indicates Alarm

Figure 8.2 IDU

8.1.3 Pasolink System Features

Single chip modulator/ demodulator (fully digital)

High reliability

Low power consumption

Allows smaller antenna and reduced system cost

With PASOLINK PDH (QPSK) and PASOLINK PLUS SDH (32 QAM)

Forward error correction (FEC)

Transmit power controlled in two ways: Automatic transmit power control(ATPC)

and Manual transmit power control(MTPC)

Common IDU for different RF frequencies.

Remote monitoring of ODU operation.

Local and remote supervision function on IDU.

Local monitor and maintenance using Local Craft Terminal (LCT).

8.1.4 IDU (Indoor Unit)

IDU is an Indoor Unit placed inside the shelter and connected to ODU (Outdoor Unit) with

help of IF cable, with maximum distance of approx. 300 mts. IDU is connected to electric

cable called E1.

56

PRINCIPLE

Principle of IDU is to convert IF signal into optical or electrical signal. There are two types

of IDU:

1. SDH pasolink IDU

2. PDH pasolink IDU

In SDH IDU, we do not get directly electric E1 but first the optical output of IDU is given to

MUX which converts optical output to electric and from Mux we get electrical output from

DDF (Digital Distribution Frame), then the output is given to customer. So, SDH gives

optical output which is converted to electric with help of DDF. In PDH we directly get the

electric output and there is no need to use DDF. But the capacity of PDH IDU is less then

SDH IDU. It supports up to 16 E1 only, whereas SDH IDU can support upto STM-1

capacity.

8.1.5 ODU (Outdoor Unit)

PRINCIPLE

Principle of ODU is to convert IF (Intermediate Frequency) into RF and vice versa. Its design

depends on requirement. Microwave frequency ranges from 6 GHz to 18 GHz.

Figure 8.3 Outdoor Unit

The actual TX frequency of the ODU should be within the TX radio frequency band of the

ODU and is entered using the local craft terminal (LCT). The corresponding RX frequency is

automatically set after the TX frequency is entered. For 6/7/8 GHz band ODU, the frequency

setting should be the same as that written on the ODU label.

PASOLINK provides point-to-point wireless solution that fit in a variety of network applica-

tions. All the PASOLINK systems feature simple installation and fast rollout, reliable opera-

tion, and offer high-speed transmission, scalable future.

57

8.1.6 Antenna (ODU) Alignment

During alignment of the antenna always refer NDD for alignment planning and an-

tenna angles. (Latitude, Longitude, Azimuth, Elevation, Height of antenna etc.)

Make a short check of adjustability and free rotation in all directions.

For the azimuth adjustment of short (urban) distance links, use of a geographic map is

most efficient.

Use compass for coarse direction finding.

If the opposite antenna is not visible, define a remarkable / noticeable object (e.g.

building, tree, street-crossing, etc) which is in line with the opposite site and can be

found with the above mentioned tools (maps, compass).

Install the antenna at proper height for LOS clear visible.

Proper route IF cable and check the cable connector connection is proper.

Install IDU in Rack and give -48v dc input voltage

Connect DDF with IDU if PDH site or with MUX if SDH site.

8.1.7 System Configuration

System protection is required to ensure robustness and survivability of the data link in the

case of any radio link’s problem:

Equipment problems (hardware / software failure)

Propagation problems (fading / obstruction)

The protected configuration would assure the link is up in case of hardware failure and allow

maintenance and repair of the redundant (standby) units.

8.1.8 Non Protected System

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Figure 8.4 Non-Protected System

One IDU with modulation / demodulation channel

One ODU

One antenna

The system has no protection channel (no switching over)

8.1.9 Protected System: Single Antenna Configuration

Figure 8.5 Protection by two ODUs

One IDU with two modulation / demodulation module

Two ODU working at the same spot frequency

One antenna

On each side only one ODU sends TX power and both ODUs receive the RX power

Only one system is selected to carry the traffic and the other system is standby

TX & RX switching is available manually and automatically to control switch over

function

TX & RX switching over does not affect the traffic.

8.2 FREE BAND RADIO LINK

8.2.1 Introduction

FBR (Free band radio) can be used to provide services like, leased line, PRI etc. Bandwidth

up to 8 Mbps (two ways) can be provided using FBR. Varieties of customer services can be

provided using FBR. It can also be used for DLC. FBR are actually useful at the place where

59

fiber cannot be deployed and hence communication is required to be done through air

interface.

Figure 8.6 Structure of FBR

The free band radio delivers up to 8 Mbps of total data rate for Ethernet and E1/T1 traffic.

The system supports a variety of spectrum bands and can be configured to operate in any

channel on the band with a carrier step resolution of 20 MHz.

The unlicensed band radio employs Time Division Duplex (TDD) transmission. This

technology simplifies the installation and configuration procedure. There is no need to plan

and to allocate separate channels for the uplink and downlink data streams. Operation over

2.4GHz and 5.8GHz bands is not affected by harsh weather conditions, such as fog, heavy

rain etc.

8.2.2 Need of FBR

FBR is called free band because we don’t have to pay for this band (2.4Ghz and 5.8Ghz). In

other words, if one wants, one can start service almost immediately using unlicensed band

radios and one need not wait for one year for frequency clearance. This presents great

opportunities for service providers.

Free Band Radio offers advantages such as

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Immediate and hassle free deployment of services as no clearance from WPC are re-

quired.

Radios are very cost effective.

Fast realization of revenue (as a result of rapid deployment)

Demand-based build-out.

Cost shifts from fixed to variable components (with traditional wire-line systems,

most of the capital investment is in the infrastructure, while with radio a greater per-

centage of the investment is shifted to CPE, which means an operator spends money

only when a revenue-paying customer signs on)

No stranded capital when customers churn

Cost-effective network maintenance, management, and operating costs.

Limitations Of free band radio

Since radio operates in unlicensed band, protection from interference is not guaran-

teed. Since it is intended to be deployed in very remote areas, where not much inter-

ference is expected and also the parabolic antennas have very narrow beam, which

provides an additional protection against interference.

Lack of standards.

8.2.3 Physical Installation of the FBR

Installation of antennas.

Install ODU at both sites of the link.

Install ODU cable and connecting ODU to IDU at both sites.

Connect power.

Install the management program on the network management station.

Run the Installation wizard from the management program.

Alignment of the antennas.

Connect network and customer equipment to the local and remote IDUs respectively.

Proper grounding of all equipments.

8.2.4 IDU (Indoor Unit)

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Indoor unit is installed in the customer premise. This is the unit, which interfaces with

customer equipment, which in most of the cases is a router. This unit receives modulated

digital signal over Cat5 cable from ODU. It then de-multiplexes payload, FEC, Management

data etc from the digital steam and reconstructs and retimes E1s or similar signals, which are

then send to customer equipment. IDU is independent of frequency and hence ODU. IDU can

work with any frequency band ODU like 2.4 GHz or 5.8 GHz.

Figure 8.7 IDU

Different types of IDUs and their applications,

2E1+FE IDU

This IDU provides 2E1 and One Fast Ethernet ports. This can be used where up to 2E1 ports

are required. In such cases, FE port at Hub can be used for monitoring.

2E1+2FE IDU

This IDU provides Two E1s and Two Fast Ethernet ports. This IDU will replace the old

2E1+FE for all the new cases. This can be used where up to 2E1+ One FE services are

required.

4E1+2FE IDU

This IDU provides Four E1s and Two Fast Ethernet solution. This can be used where up to

4E1+ One FE services are required. Note that more than 2 E1, in normal circumstances is not

recommended because of high S/I requirement.

8.2.5 ODU (Outdoor Unit)

This is radio frequency unit, which is mounted on a pole on the rooftop of the building or on

the tower. This unit receives radio signal, down converts and after demodulation recovers the

62

digital signal. The recovered digital signal is send to IDU over Cat5 cable. In the transmit

direction the similar reverse process is done by the ODU.

In TTSL network now two type of ODU are deployed:

1. 2.4GHz

2. 5.8GHz

Figure 8.8 ODU

8.2.6 Various Connections

CONNECTION BETWEEN THE ODU AND IDU

The ODU-IDU cable is Ultraviolet Proof CAT-5e, 4 twisted-pair 24 AWG FTP. It is

terminated with RJ-45 connectors on both ends. It is covered by a cable gland on the ODU

side for hermetic sealing. It conducts all the user traffic between the IDU and the ODU and

also provides -48 VDC supply to the ODU. The maximum length for one leg of the cable is

100m (328ft) in accordance with10/100BaseT standards.

The cable should be clamped directly on the surface with cable ties at 600mm interval. The

cable will be laid inside the building through PVC channel. Make sure that some spare length

is left for future maintenance purpose.

CONNECTION BETWEEN THE ODU AND ANTENNA

The external antenna is connected to the ODU using a co-axial RF cable. An N type RF

connector is provided on the ODU for this. Both ends of the RF cable are to be tightly sealed

with weather proofing tape.

DATA CABLE

ODU and IDU are connected by Cat5 cable. This cable carries not only the IF signal but also

DC Voltage to power ODU. It means that IDU is also used for POE ( Power over Ethernet).

Thus a separate power cable for ODU is not required.

8.2.7 How Interface can be Overcome?

KEEP THE LINK DISTANCE SMALL IN URBAN AREAS

63

Small link distance is possible in TSL network, as the numbers of CDMA BTS, which are the

take-off point for FBR, are large. Thus probability of finding a BTS in reasonable radius,

around potential customer site, is very high. C/I will not get affected adversely unless there is

very close source interference near the prospective UBR site.

EMPLOY HIGH GAIN ANTENNAS

High gain parabolic antennas provide dual protection. By virtue of high gain they increase

the signal quality and by small beam width they reject interfering signals.

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Shrinking Area

In Shrinking AreaGood Rx levelWeak Ec/IoNo dominate pilotHigh call drop rateFrequent Hand-off

CHAPTER 9

REPEATER

9.1 INTRODUCTION

Repeaters are bi-directional amplifiers used with highly directional antennas to increase the

coverage area of a base station. Repeaters are not designed to increase the base station capac-

ity but will improve signal strength out past the normal operating area for both uplink and

downlink traffic.

Repeaters are normally located at the outer limit of the base station coverage area and re-

transmit both the base station downlink signal to mobiles and the mobile’s uplink signal back

to the base station. Repeaters can also be used to boost signal strength inside a building

where mobile users are operating in a highly attenuated area behind coated windows that re-

flect RF energy or lossy cement and steel walls.

What is need of Repeater?

Cell enhancing solution with lower cost.

Many kinds of cell enhancing applications are available from small room to large

coverage.

Lower cost cell coverage extension solution than BTS.

Flexible cell coverage planning.

Easy maintenance of Repeater than BTS

Figure 9.1 shrinking area

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Figure 9.2 To remove above Shrinking Area, Repeater installed

9.2 TYPES OF REPEATERS

RF Repeaters:

RF stands for Radio Frequency as the transmission path between the donor BTS and the

Repeater is used in RF Repeater system. No wires are used for this path. RF repeaters can be

divided into two types with respect to whether donor link frequency is same to service signal

frequency or not, On-frequency and frequency conversion type.

On-Frequency Repeaters:

A repeater is, in a simplified view, a bi-directional amplifier with filters that amplifies weak

signal in both paths, down link and up link. There is no change between input and output

frequencies of on-frequency repeater. Type of repeaters are classified as broadband, band

selective or channel selective by method of the filtering processes for limiting frequency

bandwidth and removing spurious.

On-frequency repeater plays a role of extending the outdoor coverage of a Macro-cell. The

repeater is installed at the coverage border of the donor BTS cell where the mobile user re-

ceives signals close to the acceptable level and re-transmits the amplified signal to additional

coverage to extend.

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Figure 9.3 Setup of On-frequency repeater:

In the downlink path, an antenna receives signals from a donor BTS. The link antenna is

connected to the input of the repeater. The signals are filtered, amplified and transmitted into

the service area via a service antenna. The uplink path of the repeater works in the same way.

The service antenna takes up signals from mobile stations within the service area and re-

radiates the amplified signals through the link antenna to the donor BTS.

Broadband RF Repeaters:

The filters in a broadband RF repeater are designed to cover the whole actual operating RF

band. The filtering and amplification are on the RF band. Band pass filters of RF band are

used of which filtering characteristic meets minimum requirements for operating. The

broadband RF repeaters are installed in areas with low traffic and where the risk for

interference with users directly outside the band is low. The broadband RF repeaters have

generally lower gain and lower output power. Propagation delay time in RF band pass filter is

short as less than 1 microsecond.

Band Selective RF Repeaters:

The incoming RF signals are down-converted to an intermediate frequency (IF) with filters

that more sharply and effectively blocks signals directly outside the actual band. The band

selective RF repeater handles a defined specific band within the total operating band, and any

frequency or any numbers of FA can be handled in specific band without changes on

hardware. The SAW filter is used as filtering and time delay is generally around 5

microseconds.

67

Channel Selective RF Repeaters:

A channel selective RF repeater is equipped with a number of one channel up-down

converter units. The incoming RF signals are down-converted to an intermediate frequency

(IF) with filters that more sharply and effectively blocks any signals directly outside the

specified channel’s bandwidth in operating band. IF SAW filter is used as filtering process

and time delay is generally around 5 microseconds. The number of channel up-down

converter units shall be equal to (or more than) the number of carriers that the operator wants

to use.

Example of Repeater solution with low o/p power repeater:

Figure 9.4 Repeater installation for low o/p power

Another type of repeater is low power and low cost repeater. This type of repeater is avail-

able with 15 dBm, 17dbm and 27 dBm gains and is employed for providing in-building solu-

tions. Premises such as basement, tunnel, go down, operating rooms in industries and some

type of closed offices remain uncovered from coverage of BTS due to the shadow effect.

In such type of buildings it is necessary to provide coverage inside the premises by means of

low power repeater. Low power repeater receives signals from nearby donor BTS and ampli-

fies it and then provides it inside the building with the help of panel antenna. The panel an-

tenna and repeater module are mounted on the wall inside the structure where the coverage is

to be provided. Depending on the area and geographic condition the antenna with suitable

gain in selected ex. 15 dBm, 17 dBm.

To install the yogi antenna intensity of the coverage is checked on the terrace with CDMA

monitor and then yogi is located at proper point.

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9.3 FIBER OPTIC REPEATER

Another basic type of repeater is the Fiber Optical repeater. The transmission path between

the donor BTS and the repeater is fiber optic cables. Optical repeater first convert RF BTS

signal into fiber optic signal & transmit the converted signal afterwards retransmit the RF

signal at remote.

Fiber Optical repeater system also provides,

effective solution for extending cell coverage,

Solving multi PN problem and eliminating shadow areas instead of BTS.

Seamless service provided into the rural area and on highway.

The system consists of Master unit and Slave unit, and installation of fiber optic cable

between Master unit and Slave unit is required. The forward link signal of BTS is coupled to

the master unit and translated into optic wave in Master Unit. The optic wave goes through

optical cable to the Slave unit. Slave unit translates optic signal to service RF signal again

and radiates the RF signal to desired service area. Reverse link signal from mobile handset is

picked up by service antenna of Slave Unit and translated into optic wave. The optic wave

goes through optical cable to the Master Unit. Master unit recovers optic signal to reverse

link RF signal and feeds RF signal to Receiver stage of BTS. By using different Medias for

service and link signal, RF and optic wave.

Fiber optical repeater system can have extreme isolation between input and output stage.

Stable and high power of repeater system can be achieved by such a concept of optic

conversion. Time delay of optic wave propagation in optic cable is longer than that of air.

Consideration should be taken carefully to deploy this type of repeater system.

Merits:

No limit of FAs

Long link distance

Not degrade the BTS performance

High reliability which has excellent electrical characteristic

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Figure 9.5 Set up of optical repeater:

Demerits:

High rental cost using Optical Fiber

FOR Configuration:

MU (Master Unit)

OFD (Optical Fiber Distributor)

SU (Slave Unit)

FOR Total Path Connection:

Forward Path

MU ~ Patch chord ~ OFD ~ Optical Link ~ OF ~Patch chord ~ SU

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Reveres Path

SU ~ Patch chord ~ OFD ~ Optical Link ~ OFD ~ Patch chord ~ MU

9.4 FREQUENCY SHIFT REPEATER

Frequency Conversion Repeater system provides effective solution for extending cell

coverage, solving multi PN problem and eliminating shadow areas. The system consists of

Donor unit and Remote unit, and assignment of additional link channel between Donor unit

and Remote unit is required.

The down link signal of service channel frequency from BTS is translated to the link channel

frequency and transmitted to the Remote unit by Donor Unit. Remote unit translates link

channel signal to original service channel frequency and radiates the signal to the mobile

handset.

The reverse link signal of service channel frequency from mobile station is converted to the

link channel frequency and transmitted to the Donor unit by Remote unit. And Donor unit

translates link channel signal to service channel frequency and feeds to the BTS coupling

port. The empty channel in the Permitted band is used for assigning link channel.

By using different frequencies for link and service channel, frequency shifting repeater

system can have higher isolation and higher gain than on-frequency repeaters. Stable, longer

distance and higher power of repeater system can be achieved by such a concept of frequency

conversion. The system handles the signal processing by channel conversion unit and low

frequency SAW filter is adapted for filtering channels of which delay time is around 5 to 13

microseconds

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Figure 9.6 Set up of frequency Shift Repeater:

Merits:

Utilize unoccupied FA as link FA

High antenna isolation between a link antenna & service antenna is not required

Demerits:

Limited service FA

Likely to degrade performance of a BTS due to using adjacent FA

SR Total Path Connection:

Forward Path

DU ~ Link antenna cable ~ Link antenna (Donor site) ~ RF link ~Link antenna

(Remote site) ~ Link antenna able ~ RU.

Reverse Path

RU ~ Link antenna cable ~ Link antenna (Remote site) ~ RF link ~ Link antenna (Donor

sit) ~ Link antenna able ~ RU.

Site Selection condition for FSR:

Recommendation to choose installation location as below; Ensure that link loss between

Donor Unit site and Remote Unit site is no more than 17kms.

Easily installed antenna with proper height

Less interference from other BTS Cells

Easy access and maintenance of the equipment

Avoiding direct sunlight to protect equipment

72

Easy access to electrical power

Figure 9.7 connection between BTS and FSR

9.5 IBS (IN BUILDING SOLUTION)

Introduction:

IBS is stands for IN BUILDING SOLUTION, as the name implies we are using IBS for to

recover poor coverage in the congested indoor areas. We are providing IBS service to those

service users whose monthly revenue of used service is very much high. So generally, we are

providing this service to the small scale and big scale based companies, in which all of the

users use mobile phone service, which are provided by us.

Three basic equipments are used for IBS, which are Out Door pick up antenna, Repeater and

Indoor antenna. Here Yagi antenna used as outdoor picks up antenna. And Panel antenna,

Omni antenna used as an indoor antenna. Panel used for a small cabin while omni antenna

used in large hall. IBS connection flow is shown in below diagram.

73

Figure 9.8 repeater block

Survey:

If the company decided to establish the new BTS tower than before that, survey of the

particular area is required.

In the survey, we use the GPS antenna, by which we can note down the latitude and lon-

gitude position of the particular point.

We have to determine height of tower, orientation of antenna to be mounted on that tower

according to clutter of area.

During the survey, we must keep in mind that the distance between the two BTS tower is

not too large or to small.

If the distance between the two towers is so large than the signal can be weak and cover-

age might be poor in between and if distance is less than the it will be wastage of re -

sources in addition to interface between two channels can be possible.

Equipments used in IBS:

Indoor antenna

Outdoor antenna

74

Yagi Antenna

Repeater

RF cable

Connectors

Splitter

C

Figure 9.9 Outdoor Yagi antenna

Figure 9.10 Omni Directional, Panel

antenna

These are the two types of antenna which is

used as a indoor antenna:

Panel antenna generally used in small

cabin or small room type area,

Omni antenna used generally used at large hall type area. Above figure shows both

type of antenna. For IBS the setup is as shown in below figure. At the field we use

following set up. The procedure for the same is as follows:

75

Figure 9.11 Set up Of IBS (In Building Solution)

Procedure:

Step1:

First by using calibrated CDMA phone we check which are PN we getting at that particular

place where we are going to use IBS solution, then we check that which PN giving us better

CDMA parameter performance. According to that conclusion we clamp our Yagi pick up

antenna on the terrace to fetch that particular PN coverage.

Step2:

After getting better coverage signals through pick up antenna we route those signals through

RF cable to the repeater, here repeater amplifies those signals up to required level and then

fed it to the indoor panel antenna.

Step3:

76

Here panel indoor antenna re radiate it in the indoor locations where we need to give good

coverage.

Step4:

Sometimes we keep more than one panel indoor antenna inside the building to give better

coverage at different places, so at that time we are using splitter to split signals for to give

each indoor antenna.

CHAPTER 10

WIRELINE PRODUCTS

Wireline Line products are:

Primary Rate Interface (PRI).77

Basic Rate Interface (BRI).

Leased Line (LL).

Internet Lease Line (ILL).

Digital Loop Carrier (DLC).

National Private Lease Circuit (NPLC).

Multi Protocol Label Switching (MPLS).

10.1 PRIMARY RATE INTERFACE (PRI)

This is a special service provided to commercial customers. It is a high value service. Call

centers, Hostels, and all the big offices need many phones with intercom facility. So PRI

provides this service.

To provide the PRI service, one special card called a PRI card is kept in the DLC. It also uses

the E1 technology for communication. At the customer end, this E1 line gets terminated in

their EPBX (Electronic Private Branch Exchange). There are 8 maximum possible customers

in one card, and each can get a maximum band width of 2 Mbps.

In E1, 2 slots are reserved. So we are left with 30 slots. So PRI can connect 30 fixed line

phones at a time.

If a customer needs more than 30 numbers, 2 slots of a card is given to customer. But pilot

number is kept same as much as possible.

When a user takes PRI service, he is allotted a pool of numbers containing 30 numbers in a

pool ideally. There is one master number, which is common for all the phones. The first 4

digits are master number. Then the number varies inside the group.

Facts:

1. When any call is made inside the group, we just have to dial the digits after master

number. And only the digits, after master number appears on the receiver’s phone.

2. When we make a call outside the group, we have to dial the whole number. But, on

the receiver’s side, he will get the first number of the pool.

3. When any user calls from outside, he will have to dial the precise number, in order to

reach to a particular user.

10.2 BASIC RATE INTERFACE (BRI)

78

This service is used for customers who, has less equipments to be connected, but importance

of each is high.

To give BRI service, one BRI card is kept in the RT. It can serve up to 8 customers. It also

uses E1 technology to get the connectivity. The range of this is also 300 meters, since E1’s

range is 300 meters only.

The ISDN Basic Rate Interface (BRI) service offers two B channel and one D channel

(2B+D). BRI channel service operates at 64 kbps and is meant to carry user data; BRI D

channel service operates at 16 kbps and is meant to carry control and signaling information,

although it can support user data transmission under certain circumstances. So for BRI

service 144 kbps bandwidth is given. From this bandwidth, 16 kbps is used for signaling and

synchronization and remaining 128 kbps is divided into 2 slots of 64 kbps. We can connect

either 2 computers with it to get the data service, or can connect one computer and one phone

or 2 phones also.

10.3 LEASED LINE (LL)

It is used for point to point link.

Typically, leased lines are used by businesses to connect geographically distant

offices.

Unlike dial-up connections, a leased line is always active.

The primary factor affecting the monthly fee is distance between end points.

79

Figure 10.1 Leased Line

10.4 NATIONAL PRIVATE LEASE CIRCUIT (NPLC)

Features are same with Leased line but it will connect inter circle locations.

Figure 10.2 NPLC

10.5 MULTI PROTOCOL LABEL SWITCHING (MPLS)

MPLS is a highly scalable, protocol independent, data-carrying mechanism.

MPLS network, data packets are assigned labels. Packet-forwarding decisions are

made completely on the contents of this label, without the need to examine the packet

itself.

When you have multiple branches across a state or a country, you would definitely

want to connect all these branches together to facilitate data transfer/ access between

them in order to accelerate the speed of business transactions.

10.6 INTERNET LEASED LINE (ILL)

It provides permanent, reliable, high-speed connectivity as compared to the temporary

connectivity of dial up access.

The quality of the connection is far superior to what is normally available through

dialup, because of the digital signaling, less noise, fewer exchanges etc. 80

10.7 DIGITAL LOOP CARRIER (DLC)

Digital loop carrier (DLC) is equipment that bundles a number of individual phone

line signals into a single multiplexed digital signal for local traffic between a telephone

company central office and a business complex or other outlying service area. Analog voice

calls are combined into a single signal and transmitted over a single copper T-carrier system

or E-carrier line, an optical fiber cable, or a wireless connection. In a home, business, or

other installation using digital loop carrier, the analog phone lines of individual users are

connected to a local DLC box which then converts the analog signals into digital and

combines (multiplexes) them into one signal that it sent to the phone company's central office

on the single line. Thus DLC serves bridge between Backbone network and customer’s

premises.

In competitive era, for a telecommunication provider to remain a provider of choice, require

end to end infrastructure must be reliable and survivable while providing the required band

width / services & should be cost effective.

Digital loop carrier (DLC) technology was started in the early 1970s as a cost-effective

method for providing voice services.

Also known as Access Node (Network).

CT’s are in Control of the Local Exchange.

RT’s are in Control of the CT.

Type (Wall Mount, Indoor, Outdoor)

Currently, the DLC market is evolving rapidly with new DLC

Broadband Loop Carriers (BLCs)

As well as third-generation (3G) DLCs

Basic Connectivity

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Figure 10.3 Basic Connectivity

Responsibility

CT ….

Physical connect to each subscriber

It has maintenance and testing capability

Signaling detections for RT’s

Signaling generations for RT’s

Message/Alarm receiving and display.

Responsible for Link Status (NMS)

LE ….

Incharge of call processing. (LE to COT)

Resp. for forwarding dial tone to subscriber.

Resp. for billing/charging mechanism of each subscriber.

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LE

COT 1

RT 2

RT 1

RT 3

RT 4

RT 5

E1 (V5.2)

E1

E1

E1E1

E1

Control Protocol Protection ProtocolLink ProtocolBarer Ch. Cont. ProtocolPSTN Protocol

Resp. for Sub Database and Facility management.

Resp. for Announcement generation.

Effects

Benefits….

To reduce copper cable pair requirements.

Overcome electrical constraints.

Save Expense due to cable cost and the associated labour, installation work.

Quick provisioning of multiple service.

Cost + Space effective solutions.

Effective use of available resources.

Issues can be….

Dependent on Local Exchange. (Sub Data, Centrex, Dial tone, etc)

Can lead to multiple subscriber outage.

10.8 POINTS OF DIFFERENCE BETWEEN DLC AND EPBX

OPTIONS DLC EPBX

Dial Tone No Dial Tone (dep. LE) Possible

Centrex / Internal

Calling Not Possible (dep. LE) Possible

External Calling Not Possible (dep. LE) Not Possible (dep. LE)

Sub. Line Provision Possible (dep. LE) Possible (dep. LE )

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During Link Failure Calling get's stop Only outer calling get's stop

Time Slot Usages Require while Int. & Ext calling Only while external calling

Individual Line Feature

(call waiting, fw, div etc) Possible (dep. LE)

Not Possible

(Apply to whole Range (DID)

CHAPTER 11

CONFIGURATION OF MUX

11.1 BG-20 CONFIGURATION PROCEDURE

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Fig 11.1 BG 20 B

Change IP address of your PC to last four digit of serial no. (make sure it is 1 less or

more then original)

E.g. if your IP is 192.100.45.37 and last four digit of your serial no is 6296 then

change your IP to 192.100.62.97 or 192.100.62.95

Enter in BOOT CONFIGURATION TOOL.

Enter IP (last four digit are serial no) e.g. if serial no is 6296 then IP is

192.100.62.96

And before Click on OK, power OFF the mux and then ON when orange LED blink

which is called minor mode and at that time click OK.

Click on BASIC PARAMETER CONFIGURATION then enter GET and APPLY so

we get the NEID number and IP, if we want to change the IP and NEID to use the

mux at different location we change it from here.

Click on DOWNLOAD EMBEDED SOFTWARE

Select UPPER BANK.

Select latest embedded version file and then DOWNLOAD and APPLY.

Select LOWER BANK.

Enter DOWNLOAD and APPLY.

Exit.

Now, for Login in mux we have to change IP of PC to 194.194.194.194.

Enter in LCT-BGF software for BG-20 mux.

Enter IP 194.194.194.193 is the default IP of mux and password (sdh123456).

Click on ADVANCE->REQUEST LOGIN AS MASTER

Click CONFIGURATION -> NE TIME, enter GET and APPLY.

Click CONFIGURATION -> NE ATTRIBUTE

Change NAME, LOCATION etc and then APPLY.

Click CONFIGURATION -> NE CONNECTION SETTING, Enter GET and

APPLY.

Click CONFIGURATION -> SLOT ASSIGNMENT.

Select PHYSICAL and then click on GET PHYSICAL CARD and then click on AP-

PLY.

Select LOGICAL and then click on GET & APPLY.

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Click on XC -> DCC XC

In A1 SAM select MDCC & COM_MDCC1 then click on ADD ITEM

In A2 SAM select MDCC & COM_MDCC2 then click on ADD ITEM

Then click on ACTIVATE

Click on CONFIGURATION -> ANY CONFIGURATION DATA MANAGER ->

FULLY UPLOAD

Right click on MXC CARD -> DOWNLOAD EMBEEDED SOFTWARE, Enter

GET (version should be same).

11.2 SNAPSHOTS OF THE CONFIGURATION PROCEDURE:

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CHAPTER 12

MEASURING EQUIPMENTS

There are many measuring equipments used in transport, such as, OTDR (Optical Time

Domain Reflecto meter), Multi meter, E1 tester, Power meter etc.

12.1 OTDR (OPTICAL TIME DOMAIN REFLECTOMETER):

This equipment is mainly used when there is a cut in fiber. In this equipment a laser is

transmitted through fiber and the distance is calculated where the cut is there with the help of

time delay between transmission and received reflected wave.

Fig 12.1 Optical Time Domain Reflectometer (OTDR)

The OTDR is used for making single ended measurements of optical link characteristics such

as:

1. Fiber attenuation

2. Connector and splice losses

3. Reflectance levels from link components

4. Chromatic dispersion

5. Locate fiber breaks quickly and accurately.92

OTDR Trace:

Fig 12.2 Screen indicating various parameters

Vertical axis is logarithmic and measures the returning (back reflected) signal in deci-

bels.

Horizontal axis denotes the distance between the instrument and the measurement

point in the fiber.

Performance Parameters of an OTDR:

Dynamic range:

Difference between the initial back scatter power level and noise level after 3 min-

utes of measurement time.

Provide information on the maximum fiber loss that can be measured and denotes

the time required to measure a given fiber loss.

Expressed in decibel of one way fiber loss.

Measurement range:

Identifies number of events in the link, such as splice points, connection points, or

fiber breaks.

Defined as maximum allowable attenuation between an OTDR and an event that stills

enable the OTDR to measure the event accurately.

0.5 dB splice is the acceptable event.

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12.2 OPTICAL POWER METER (OPM)

This equipment is used when there is power related problem. This is mainly used for power

measurement, attenuation testing, if any fiber loss is there etc. It has four parts:

1. Protective cover

2. Adapter, where patch code is connected for measuring power.

3. Display, displays power in dB or dBm.

4. Keypad, used for on/off, changing wavelength, changing in dB or dBm.

Fig 12.3 Power meter

It supports two wavelength, one of 1310 nm and other of 1550 nm.

Fig 12.4 Power measurement Fig 12.5 Attenuation measurement

For measuring power this equipment is connected with the equipment for which the power

measurement is carried. In this adapter is connected to the equipment TX, from where we get

the power received by equipment.

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In attenuation measurement, equipment sensitivity is measured. In this test, a variable

attenuator is used to find sensitivity. A variable attenuator is connected between power meter

and equipment. Now power is transmitted through patch code and received power is

measured at equipment. This process is carried until we get loss at equipment. When loss is

found, the power is noted and accordingly equipment sensitivity is measured.

12.3 E1 SERVICE TESTER (EST)

This equipment is designed to provide all the test functions required by engineers installing

and maintaining SDH systems in the Access Network. It can be fitted with the optical and

electrical interfaces listed below. It has independent transmitters & receivers for connection

to the following interfaces:

SDH:

STM-1 electrical line interface

Optional STM-1 optical interfaces, 1310nm and/or 1550nm wavelengths

Optional STM-4 optical interfaces, 1310nm and 1550nm wavelengths

Figure 12.6 E1 Service Tester (EST)

PDH:

E4 electrical line interface, 140 Mbit/s

DS3 electrical line interface, 45 Mbit/s

E3 electrical line interface, 34 Mbit/s

E1 electrical line interface, 2048 Kbit/s (balanced and unbalanced)

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When any E1 is established it is tested with this equipment. If the E1 is working properly, it

will show OK on screen. If not then it will give error accordingly. Other parameter such as

LOS, LOF, data rate, Power level etc can also be measured with help of this equipment.

12.4 VSWR METER

The VSWR meter measures the standing wave (a single-frequency mode of vibration of a

body or physical system in which the amplitude varies from place to place) ratio in a

transmission line in order to check the quality of radio equipment. The meter refers to the

match between the antenna and the transmission line. A VSWR meter should be installed

near the antenna to avoid loss of transmission, which happens because transmission lines

have a certain amount of loss. The reflected power travels back to the cable, producing a low

reading on a VSWR meter.

"VSWR" stands for “Voltage Standing Wave Ratio.” It is an RF (radio frequency) signal

source, a coaxial cable (i.e., a transmission line that consists of a tube of electrically conduct-

ing material surrounding a central conductor held in place by insulators) with some sort of

mechanism to allow access to the center conductor at various lengths, load impedance for the

other end of the coaxial cable, and some kind of meter to be able to measure the RF voltage

as a probe selecting various points along the coaxial cable. The VSWR is a measure of im-

pendence mismatch between the transmission line and its load. A transmission line can be de-

fined as a device which transmits or leads energy from one point to another. The desired out-

come is the highest efficiency. The intention is to diminish the loss through heat and radiation

at its maximum.

The voltage component of a standing wave in a transmission line consists of forward wave

superimposed on the reflected wave. The signal source is generally set to a fixed frequency

and is tuned up for a good output voltage.

An ideal system would transmit energy without any loss along the way. This requires an ex-

act match between the source impedance, the characteristic impedance of the transmission

line and all its connectors as well as the load’s impedance. The signal’s AC (alternate current)

voltage will be the same from end to end since it runs through without interference.

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Figure 12.7 VSWR Meter

12.5 ETHERNET TESTERWhenever customer requires Ethernet output then we use Ethernet Tester. In this we set data

rate as per the requirement of customer and machine transmits set data rate signal. We have

to give soft loop at another end. Our NMS team does this activity of giving soft loop and we

can receive data as per transmitted data rate if our transmission media is ok. Else we get

some data loss. In this way we check if Ethernet link is working properly or not.

Figure 12.8 Ethernet Tester

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CHAPTER 13TROUBLESHOOTING

1. PROBLEM:

Coverage issue

SOLUTION:

We had visited a site at Vapi where a yarn company had demanded for the coverage as the

coverage was very weak i.e. next to negligible in that area. The company was situated at a far

away distance from the main city location so signal strength was very poor. We asked if we

can install a BTS site in their premises, so that the nearby area can also be served. But they

refused for this.

Other option was to install a repeater in that premise. So we checked the RSSI and PN using

CDMA mobile phone. RSSI strength was proper and then PN was checked. The received PN

was verified and it was deduced that the received signal was of Maharashtra BTS. PN is a

pilot number which is unique for each BTS and from the PN code we can know about the

donor BTS of the received signal. CDMA mobile was also receiving other signals of different

PN’s which were of Gujarat BTS’s. But their RSSI was very poor. So we checked RSSI and

PN outside of the compound and we got nearly sufficient RSSI with PN of BTS of Haria

Park (site situated at Vapi).

We installed a Yagi antenna as a receiving antenna and connected it to the repeater, which

was installed inside the building. Then the received signal from the repeater was divided

using splitter. The splitted signal was used to provide coverage in four different rooms using

panel antenna. Panel antenna is used as transmitting antenna.

2. PROBLEM:

Link was down and all the services were closed down.

SOLUTION:

We have a ODU and IDU unit. IDU is at the base and ODU is connected at the top of the

building. Alarm was seen at IDU that was ODU link alarm. So we logged into the software

named “RADWIN”. In this we saw that frequency was changed from previously being set so

we reset the frequency by using this software. But problem was not yet solved so we went to

another BTS site to check the connection between ODU and BTS.

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This site was located at LOS of the customer end where problem had occured. There we

found the cable broken between ODU and BTS. It was repaired. Then here also the frequency

was reset. And the link came up.

3. PROBLEM:

Problem in AC to DC convertor.

SOLUTION:

Here, at this site we had given 3-E1’s through PRI. Due to large increase in voltage, the

convertor was short circuited. So the services were interrupted. The converter unit was

replaced with another. And the services started again.

4. PROBLEM:

LOS was not clear

SOLUTION:

We had provided Lease Line (LL) service at a site in Daman. It was a leading bank. This site

was not getting proper service as LOS was not clear. Initially when the site was installed,

there were no obstacles between BTS site and Customer site. But as the time elapsed,

obstructions like long trees had grown up. They could not be cut down. So another option

was to rotate antenna a little or rather shift antenna so that it can receive microwave signal

from the BTS site. NEC IDU was connected here. We logged into it and then shifted antenna

and checked for various angles of rotation. The angle for which maximum RSSI was

achieved, at that angle we kept the antenna. And the service started again as it was working

previously.

5. PROBLEM:

Signal received was weak.

SOLUTION:

TTSL’s main fiber is running from Surat to Valsad. At the main site at Valsad in Gundlav, the

received signal through fiber was weak due to long distance between fiber ends. So for

amplification of the signal, we had inserted a booster card. This card works same as a

repeater. This card is named as MO_DC_BAS. After this card was inserted, signal strength

was measured by Optical Power Meter (OPM). It was within the acceptable range.99

6. DEMAND FOR PRI SERVICE:

At another site a customer had demanded for PRI services. So we had to install a new site

over there. This site was demanding for a SDH service. So we had to install the whole

hardware including MUX also.

PRI service is basically providing E1 for voice calls only. So there we first installed the

whole hardware consisting of MUX, DDF, FMS etc. FMS port which has to be connected to

the input of the MUX, is predefined by NMS. So we connect the FMS port to the MUX by

patch code which is optical input to the MUX. Then electrical output from MUX is given to

DDF. From there PRI service is provided.

We also use AC to DC converters to provide power supply to the equipments.

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CONCLUSION

During the duration of my training at TATA TELESERVICES LTD., I was involved in

TRANSMISSION Department. I have learned many things as my first step towards Telecom

industries, regarding mobile communication and Internet.

It is really a great advantage for me that I got opportunity to work on a live system in such a

good organization. I learned about the telecom network and how practically the telecom in-

dustry works. I have learned different equipments used in TRANSMISSION such as MUX,

Microwave IDU, ODU, installation of link between two end, DLC (Digital Loop carrier) and

Lease Line services. I have also learned how to configure and manage these equipments us-

ing software. I have also seen how this whole system is monitored using software Lightsoft. I

got opportunity to practically get interacted with BTS. Most of the knowledge I gained was

because of troubleshooting at various sites and obtained practical experience from this itself.

I also become familiar with industrial environment. I really enjoyed working with this team. I

have learnt many new things here. This development helped me to improve in me qualities

such as time management, sincerity and scheduling. 

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REFERENCES

Books

Wireless Communications, Principles and Practice, by Theodore S. Rappaport

Modern Analog and Digital Communication, by B. P. Lathi

Benefits of Soft Switch Concept by TATA product Description Manual

Websites

1. www.ecitelecom.com/ouroffering/products/pages/BG-20b.aspx2. www.nec.com/en/global/prod/nw/pasolink3. www.ceragon.com/product_category.asp?ID=164. www.ericssion.com/ourportfolio/products/microwave-networks5. http://en.wikipedia.org/wiki/Wavelength-division_multiplexing6. http://products.nortel.com

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