Kamal Kiran

7/29/2019 Kamal Kiran

1/86

SIX MONTHS INDUSTRIAL TRAINING

COMPLETED AT

TELCOMA TECHNOLOGIES Pvt. Ltd

Submitted in the partial fulfillment of the requirement for the award of degree of

Bachelors of Technology

in

Electronics & communication Engineering

Department of Electronics & communication Engineering

Swami Vivekanand Institute of Engineering & Technology

Ramnagar, Banur

Under the Guidance ofEr. Gaganpreet Singh

Submitted byNavjeet Singh

7320407922


2/86

ACKNOWLEDGEMENT

The successful completion of any task would be incomplete without accomplishing the

people who made it all possible and whose constant guidance and encouragement secured

us the success

This seems to be a fitting moment for me to express my heartfelt gratitude towards all those who

helped me tirelessly and patiently in my training work. It gives me a great sense of pleasure to

present this report on my Two month industrial training. Training in an organization like A

TRAFFIC LIGHT which is fuelled by the individuals with so much zest & energy, teaming up

to form a formidable force, was in itself a true learning experience which is going to help usimmensely in our career.

To begin with, I express my sincere thanks to Mr. Gagandeep Singh Walia(Managing

Director).)to my training coordinators for allowing me to avail all the available amenities in the

division. They kept faith in me and made me an active member of my team. I am thankful to

them for sharing their vast resource of knowledge and experience with me.

Last but not the least I would like to express my heartfelt thanks to my teammates, who with

their thought provoking views, veracity and whole hearted co-operation supported me throughout

the duration of the training. I am thankful to The Institution of Electronics and

Telecommunication Engineers (IETE) for giving me an opportunity to undertake my Two

Months Industrial Training.

ABOUT ORGANISATION


3/86

Telcoma Technologies Pvt. Ltd (ISO 9001:2008 Certified) is a provider ofTelecommunication and IT based solutions, including software, equipment and systemsintegration services.

Telcoma Technologies develops and provides products, solutions, and professional services

primarily for Telecommunications/IT companies.

The business paradigm of Telcoma Technologies includes the following areas

Telecommunications

Network Solutions

Next Generation Networks

Wireless Broadband Service

Data TransmissionMobile Networks

Value-added Systems and Intelligent Networks

Network Deployment and Integration

New Technologies

Operation & Business Support

Network Monitoring

Network and Service Management Fulfillment

Billing and Customer Care Management

Customized software development

Telcoma Technologies develops customized software solutions for its clients. Our expertise

includes Java programming, Apple iPhone/Google Android applications, PHP/MySQL, Ajax and

Ruby on Rails.

Web development and Internet/Intranet based Solutions

Telcoma Technologies has completed many web projects catering to niche segment of internet

fraternity, which include social networking sites, content management portals, dynamic websites,

multimedia rich interactive websites with Flash and Intranet based solutions for Business


4/86

Automation. The sites and portalsgenerate a run-of-the-network traffic and a significantbusiness every month for our clients

Corporate Training and IT/Telecom Education

Telcoma Technologies has also launched various initiatives in the area of corporate trainingand IT education introducing the emerging technologies training solutions at affordable price.

The team at Telcoma Technologies is well-qualified and strongly motivated and committed to

providing the high level of personal service and customer satisfaction. All processes withinTelcoma Technologies are aligned towards the highest quality standards and formally certified

to ISO 9001:2008. We "Believe in the Best", be it people, products or services. Our approach toeverything emanates from this corporate philosophy. With every new day the quest for acquiring

new competencies continues. Forever searching, experimenting, innovating, learning, movingahead with our sincere efforts and dedication, shaping the future, and challenging our

competencies to create new opportunities, is a never-ending proces

100% PlacementsThe company has tie-ups with all the major companies of India such asNOKIA-SIEMENS, TATA, IDEA, ZTE, CONNECT, TATA-DOCOMO, VODAFONE, etc. The

company assures 100% placement assistance

Personality Development

The company recently collaborated with IIPM, Mohali for overall personality development andcommunication skills

ORGANIZATION PROFILE

Company Name: Telcoma Technologies.Faculty Members: Mr.Gagandeep Singh Walia

Mr. Pawanjeet singh

Mr.Kapil Bhutani

Mrs.Rashi Gupta.Company Address: Telcoma Technologies pvt. limitedSCO 123, Phase 3B2, Mohali.

Contact: Phone: 0172-4010731, 09814145471Website: Web:http://www.telcoma.inEmail: info@telcoma
http://www.telcoma.in/http://www.telcoma.in/http://www.telcoma.in/


5/86

PREFACE

With the ongoing telecom revolution where the innovations are taking place at the blink of an

eye, it is impossible to keep pace with the emerging trends. Excellence is an attitude that whole

of the human race is born with. It is the environment that makes sure that whether the result of

this attitude is visible or otherwise. A well planned properly executed and evaluated Industrial

Training helps a lot in inculcating a professional attitude.

During this period, the students get the real, firsthand experience for working in the actual

environment. Most of the theoretical knowledge that has been gained during the course of their

studies is put to test here. I had the opportunity to have a real experience, which increased my

sphere of telecom knowledge to a great extent. I was entrusted with projectDRIVE TEST.

I was entrusted with a real life project, working on which had finally made me step into the

ongoing telecom revolution and gradually become a part of it. And all the credit goes to

organization TELCOMA TECHNOLOGIES PVT. LIMITED which in true self made the

telecom revolution happen.

GSM FUNDAMENTALS


6/86

Brief History

The Global System for Mobile communication (GSM) is an ETSI (European Telecommunication

Standard Institute) standard for 2G pan European digital cellular with international roaming.

The main purpose of the group was to develop a 2G standard to resolve the roaming problem in

the six existing different 1G analog systems in Europe. In 1986, the task force was formed, and

in 1987 a memorandum of understanding (MoU) was signed. In 1989, ETSI included GSM in its

domain. In 1991, the specification of the standard was completed, and in 1992, the first

deployment started. By the year 1993, thirty two operators in 22 countries adopted the GSM

standard, and by 2001, close to 150 countries had adopted GSM for cellular adaptation

Frequency BandsThis GSM system is a frequency and time division system. Each physical channel is characterized

by a carrier frequency and a time slot number. GSM system frequencies include two bands at

900 MHZ and 1800 MHz commonly referred to as the GSM 900 and DCS 1800 systems.

For the primary band in the GSM 900 system, 124 radio carriers have been defined and

assigned in two sub-bands of 25 MHz each in the 890 915 MHz and 935-960 MHz ranges with

channel width of 200 kHz (these sub-bands are always referred as downlink as well as uplink

respectively, we will see this concept in detailed in channel concepts later in this module).

Each carrier (a total channel width of 200 KHz) is divided into frames of 8 time slots.

For DCS1800, there are two sub bands of 75 MHz in the 1710 1785 MHz and 18051880

MHz ranges

GSM Services

To study any system, it is very important to know the services, which the system supports or

provides. Analog cellular systems were developed for a single application that is voice and in a

manner similar to analog access to PSTN, other data services such as fax and voice-band

modems were defined as overlay services on top of the analog voice service. GSM is an

integrated voice-data service that provides a number of services beyond cellular telephone.


7/86

These services are divided into three major categories. They are Teleservices, Bearer services

and supplementary services.

Features of GSM

1. The GSM system provides a greater subscriber capacity than analogue systems.

2. GSM allows 25 kHz per user, that is, eight conversations per 200 kHz channel pair (a pair

comprising one transmit channel and one receive channel).

3.Digital channel coding and the modulation used makes the signal resistant to interference from

cells where the same frequencies are re-used (co-channel interference); a Carrier to Interference

Ratio (C/I) level of 12 dB is achieved, as opposed to the 18 dB typical with analogue cellular.

4. This allows increased geographic reuse by permitting a reduction in the number of cells in the

reuse pattern.

Teleservices

It provide communication between two end user applications according to a standard protocol.

These services are telephony, emergency, speech calls, group 3 facsimile, telex, short messages,

and videotext. The upper most layer of the protocol stack of the standard should be specified so

that it could communicate with protocols used in these applications.

Bearer services

It provide capabilities to transmit information among user network interfaces. Traditional bearer

services include a variety of asynchronous and synchronous data access to PSTN/ISDN and

packet switched public data network. To implement bearer services, the lower layers and the

frame format of the standard should specify how these transmission would be implemented over

the air-interface

Supplementary services

GSM supports a wide range of supplementary (complementary and is not mandatory) services.

These services belong to both telephony as well as data services. These services are considered

as revenue generating features. These are not stand-alone services but they are services that


8/86

supplement a bearer or teleservice. These services are call forwarding, call barring, call waiting,

call hold, calling line identification, connected line identification, multiple communication (like

conferencing, up to five ongoing calls can be included in one conversation), closed user group,

Advice of charge, operator determined call barring etc.

The important supplementary services are:-

1. Call forwarding : gives the subscriber the ability to forward incoming calls to

another number (either to the same network or even other network) with conditional or

unconditional. The conditions are when the MS is not reachable, if it is busy or if there is

no reply. While unconditional call forwarding is active, calls are forwarded without any

condition that is the MS will be treated as a passive device.

2. Barring of outgoing calls : This function makes it possible for a mobile subscriber

to prevent all outgoing calls.

3. Barring of incoming calls : This service exists with two conditions: barring of all

incoming calls and barring of incoming calls when roaming outside the home PLMN.

4. Advice of Charge (AoC): This service provides the mobile subscriber with an

estimate of the call charges. There are two types of Aoc information: one provides the

subscriber with an estimate of the bill and one that can be used for immediate charging

purposes.

5. Call hold: This service enables the subscriber to interrupt an ongoing call and then

subsequently reestablish the call.

6. Call waiting : This service enables the mobile subscriber to be notified of an incoming

call during a conversation. The subscriber can answer, reject or ignore the incoming

call. This functionality is applicable to all GSM telecommunications services using a

circuit switched connection.

7. Multiparty service: This service enables a mobile subscriber to establish a multiparty

conversation. That is the subscriber can establish multiple conversations at a time (max

five).


9/86

8. Calling line identification (CLI) presentation/restriction: These services

supply the called party with the ISDN number of the calling party. These restriction

services enable the calling party to restrict the presentation. The restriction overrides the

presentation.

INTEGRATION OF BASE STATION SYSTEM (BSS)


10/86

The information contained in the file is solely property of ZTE corporation. Any kind of disclosing without permission is prohibited.ZTE University univ.zte.com.cn

Antenna

7/16 Din Connector

7/8 Cable

Grounding

1/2 Jumper

Cabinet

EMP

Grounding clip

Grounding bar

1/2 Clamp

Tower Top

Amplifier

7/8 Cable

Machine house

1/2 Jumper

Microwave


11/86

Feeder and J umper Cables

Mount, Mechnical Tilt and GSM antenna


12/86

Electrical Tilt


13/86

Feeder and jumper cable

When a new site is to be installed, firstly the right place for the site is planned by the planning

department. It includes right height, TX and RX frequency of the microwave antenna. The site is

installed mainly on top of the building so that the total height may be achieved by subtracting the

height of the building from the total height from where the antenna is to be installed i.e. if we

have planned to mount an antenna at a height of 30 meters and the height of the building selected

is 18 meters, so we have to built an tower of (30mts -18mts) 12 meters.

BLOCK DIAGRAM OF PROJ ECT AREA

BASE STATION LAYOUT

MainsPower

Panel

DC

PowerSupply

Unit BatteryBackup

Abis

BTS

MW

BTS Cabin/Shelter/Room

A C

MINILINK

GSM Antenna System


14/86

All the hardware installation (Tower, Antennas, DG, BTS, Shelter AC,) during site installation is

done by different vendors (NOKIA, Kirloskar, Zeppelin etc). When they complete their job, the

O&M Engineer comes and checks whether the installations are done properly or not. He checks

the jumpers coming from antennas very carefully. After he is completely satisfied, he starts his

job of integrating the site .

A site mainly consists of following:

1.Shelter

2.DC Generator(DG)

3.Tower (including antenna)

Shelter :

For the shelter, we use four cemented base which is raised from ground to a height

approximately one and a halffeet with two metal rails running over this base. The shelter is

mounted over this by metal nails. The Back side of the shelter has an AC exhaust fans mounted

over by two metal nails. As the shelter is at a height of one and a half feet, we use 3 to 4 stairs

for getting into the shelter conveniently.

Shelter


15/86

Diesel Generator :

It is one of the important components used in a site. It is used in case of power breakdown, in

that case it starts automatically and when the mains are ok, it stops automatically. The

specifications of the DG are :

AC generator: 50Hz 1500 RPM, 240 V, 10 KVA or 15KVA or 25KVA

DC Generator

Tower

For constructing the tower, firstly a concrete square wall of 3 -4 feet is made. The thickness is

such that it can withhold the weight of the antenna. It is painted by orange and white color as it

the standard for any antenna using microwave frequency. The two antennas i.e. the GSM and the

microwave antenna are installed on top of the tower using moulds. The jumper cables are

connected from top of BTS &hen connected to the feeder cable which is routed through the cable

tray on to the top of the tower, then further connected by the jumper to the antenna.

There are basically two types of towers :

1.Roof Top(RT) towers .


16/86

2.Ground Based towers.

The main advantage of Roof Tower (RT) tower is that it reduces the height of the tower and

therefore not only reduces the material required for constructing the tower but automatically

saves the time required to erect a tower as well as reduces the cost required for construction.

Ground Base Tower


17/86

Roof Top Tower

GSM BASICS

Introduction to GSM (Global System for Mobile Communications)

INTRODUCTION

1.The Global System for Mobile Communications (GSM) is a set of recommendations and

specifications for a digital cellular telephone network (known as a Public Land Mobile Network,

or PLMN).

2.These recommendations ensure the compatibility of equipment from different GSM

manufacturers, and interconnectivity between different administrations, including operation

across international boundaries.3.GSM networks are digital and can cater for high system capacities.

4.They are consistent with the world-wide digitization of the telephone network, and are an

extension of the Integrated Services Digital Network (ISDN), using a digital radio interface

between the cellular network and the mobile subscriber equipment.


18/86

GSM (Global System for Mobile Communication)

Definition :

Global system for mobile communication (GSM) is a globally accepted standard for digital

cellular communication. GSM is the name of a standardization group established in 1982 to

create a common European mobile telephone standard that would formulate specifications for a

pan-European mobile cellular radio system operating at 900 MHz. It is estimated that many

countries outside of Europe will join the GSM partnership.

FEATURES OF GSM

INCREASED CAPACITY

1. The GSM system provides a greater subscriber capacity than analogue systems.

2. GSM allows 25 kHz per user, that is, eight conversations per 200 kHz channel pair (a pair

comprising one transmit channel and one receive channel).

3.Digital channel coding and the modulation used makes the signal resistant to interference from

cells where the same frequencies are re-used (co-channel interference); a Carrier to InterferenceRatio (C/I) level of 12 dB is achieved, as opposed to the 18 dB typical with analogue cellular.

4. This allows increased geographic reuse by permitting a reduction in the number of cells in the

reuse pattern.

AUDIO QUALITY

1. Digital transmission of speech and high performance digital signal processors provides good

quality speech transmission.

2. Since GSM is a digital technology, the signals passed over a digital air interface can be

protected against errors by using better error detection and correction techniques.

3. In regions of interference or noise-limited operation the speech quality is noticeably better

than analogue.

IMPROVED SECURITY AND CONFIDENTIALITY


19/86

1. GSM offers high speech and data confidentiality.Subscriber authentication can be performed

by the system to check if a subscriber is a valid subscriber or not..

2. The GSM system provides for high degree of confidentiality for the subscriber. Calls are

encoded and ciphered when sent over air.

3. The mobile equipment can be identified independently from the mobile subscriber. The mobile

has an identity number hard coded into it when it is manufactured. This number is stored in a

standard database and whenever a call is made the equipment can be checked to see if it has

been reported stolen.

CLEANER HANDOVERS

1. GSM uses Mobile assisted handover technique.

2. The mobile itself carries out the signal strength and quality measurement of its server and

signal strength measurement of its neighbors.

3. This data is passed on the Network which then uses sophisticated algorithms to determine the

need of handover.

SUBSCRIBER IDENTIFICATION

1. In a GSM system the mobile station and the subscriber are identified separately.

2. The subscriber is identified by means of a smart card known as a SIM.

3. This enables the subscriber to use different mobile equipment while retaining the same

subscriber number.

ENHANCED RANGE OF SERVICES

1. Speech services for normal telephony.

2. Short Message Service for point ot point transmission of text message.


20/86

3. Cell broadcast for transmission of text message from the cell to all MS in its coverage area.

Message like traffic information or advertising can be transmitted.

4. Fax and data services are provided. Data rates available are 2.4 Kb/s, 4.8 Kb/s and 9.6 Kb/s.

5. Supplementary services like number identification, call barring, call forwarding, charging

display etc can be provided.

FREQUENCY REUSE

1. There are total 124 carriers in GSM ( additional 50 carriers are available if EGSM band is

used).

2. Each carrier has 8 timeslots and if 7 can be used for traffic then a maximum of 868 (124 X 7)

calls can be made. This is not enough and hence frequencies have to be reused.

3. The same RF carrier can be used for many conversations in several different cells at the same

time.

4. The radio carriers available are allocated according to a regular pattern which repeats over

the whole coverage area.

5. The pattern to be used depends on traffic requirement and spectrum availability.

6. Some typical repeat patterns are 4/12, 7/21 etc.

CELLULAR TELEPHONY

1. A cellular telephone system links mobile subscribers into the public telephone system or to

another cellular subscriber.

2. Information between the mobile unit and the cellular network uses radio communication.

Hence the subscriber is able to move around and become fully mobile.


21/86

3. The service area in which mobile communication is to be provided is divided into regions

called cells.

4. Each cell has the equipment to transmit and receive calls from any subscriber located within

the borders of its radio coverage area.

WHY CELLULAR:

Radio spectrum is very limited, thats why we have only 10-25MHz dedicated to wireless

communication. Such narrow bandwidth allows 100-400 channels of reasonable quality, which

is not rational and commercially not profitable to develop network for such small number of

mobile subscribers. Genius idea lead to division of the whole geographical area to relatively

small cells, and each cell may reuse the same frequencies by reducing power of transmission.

Each cell has its own antenna (base station), and all base stations are interconnected using

microwave or cable communication.

Every telephone network needs a specific structure to route incoming calls to the correct

exchange and then on to the subscriber. In a mobile network, this structure is very important

because the subscribers are mobile.

Radio

Mobilesubscriber

Cell


22/86

CELL

A cell is the basic unit of a cellular system and is defined as the area where radio coverage is

given by one base station. Different cells are identified by a unique number called Cell Global

Identity (CGI). In a complete network the number of cells is large.

There are a limited number of frequencies available within the frequency band specified for

cellular systems. Each operator licensed to run a cellular network, has been provided with a

number of frequencies. A cell has one or several frequencies, depending on traffic load. To cover

a country, for example, the available frequencies must be reused. The same frequency cannot be

used in neighboring cells due to interference.

Neighbouring cells cant have the same frequency.

LOCATION AREA

The Location Area (LA) is defined as a group of cells. The system uses LA to search for

subscribers in active state. When there is a call for a mobile station, a paging message is

broadcast to all cells belonging to a specific LA.


23/86

A LA is the part of the network in which a mobile station may move around freely without

reporting its location to the network. Different location areas can be identified by the system

using the Location Area Identity (LAI).

Location Areas

MSC/VLR SERVICE AREAThe mobile station is registered in a database called Visitor Location Register (VLR). MSC and

VLR are always implemented in the same node in all Ericsson GSM networks, thus the area is

often called MSC/VLR Service Area. A MSC/VLR Service Area is made up of a number of LAs. It

represents the geographical part of the network that is covered by one MSC. To route a call to

an MS, the subscribers MSC service area is also recorded and monitored.

Network Areas

PLMN SERVICE AREAThe Public Land Mobile Network (PLMN) is a geographical area served by one network

operator and is defined as the area in which an operator offers radio coverage and possibility to

access its network.


24/86

PLMN Service Area

GSM SERVICE AREA

The GSM service area is the entire geographic areas in which a subscriber can gain access to

the GSM network. The GSM service area increases as more operators sign contract agreeing to

work together. As shown in Figure, these areas include cells, location areas (LAs), MSC/VLR

service areas, and public land mobile network (PLMN) areas.


25/86

The GSM network can be divided into four main parts:

1.Mobile Station (MS).

2.Base Station Subsystem (BSS).

3.The Network and Switching Subsystem (NSS).

4.Operation and Support Subsystem (OSS).

Mobile Station

A Mobile Station consists of two main elements:

1.The mobile equipment or terminal.

2.The Subscriber Identity Module (SIM).

MOBILE EQUIPMENT

There are different types of terminals/mobile equipment distinguished principally by their power

and application:

1.The `fixed' terminals are the ones installed in cars. Their maximum allowed output power is 20

W.

2.The GSM portable terminals can also be installed in vehicles. Their maximum allowed output

power is 8W.

3.The handheld terminals have experienced the biggest success thanks to their weight and

volume, which are continuously decreasing. These terminals can emit up to 2 W. The evolution of

technologies allows decreasing the maximum allowed power to 0.8W.

MOBILE STATION

The MS includes radio equipment and the man machine interface (MMI) that a subscribe needs

in order to access the services provided by the GSM PLMN. MS can be installed in Vehicles or

can be portable or handheld stations. The MS may include provisions for data communication as

well as voice. A mobile transmits and receives message to and from the GSM system over the air

interface to establish and continue connections through the system.

Different type of MSs can provide different type of data interfaces. To provide a common modelfor describing these different MS configuration, reference configuration for MS, similar to

those defined for ISDN land stations, has been defined.

Each MS is identified by an IMEI that is permanently stored in the mobile unit. Upon request,

the MS sends this number over the signaling channel to the MSC. The IMEI can be used to

identify mobile units that are reported stolen or operating incorrectly.


26/86

Just as the IMEI identities the mobile equipment, other numbers are used to identity the mobile

subscriber. Different subscriber identities are used in different phases of call setup. The Mobile

Subscriber ISDN Number (MSISDN) is the number that the calling party dials in order to reach

the subscriber. It is used by the land network to route calls toward an appropriate MSC. The

international mobile subscribe identity (IMSI) is the primary function of the subscriber within

the mobile network and is permanently assigned to him. The GSM system can also assign a

Temporary Mobile Subscriber Identity (TMSI) to identity a mobile. This number can be

periodically changed by the system and protect the subscriber from being identified by those

attempting to monitor the radio channel.

Functions of MS

The primary functions of MS are to transmit and receive voice and data over the air interface of

the GSM system. MS performs the signal processing function of digitizing, encoding, error

protecting, encrypting, and modulating the transmitted signals. It also performs the inverse

functions on the received signals from the BS.

In order to transmit voice and data signals, the mobile must be in synchronization with the

system so that the messages are the transmitted and received by the mobile at the correct instant.

To achieve this, the MS automatically tunes and synchronizes to the frequency and TDMA

timeslot specified by the BSC. This message is received over a dedicated timeslot several times

within a multiframe period of 51 frames. The exact synchronization will also include adjusting

the timing advance to compensate for varying distance of the mobile from the BTS.

MS keeps the GSM network informed of its location during both national and international

roaming, even when it is inactive. This enables the System to page in its present LA.

Finally, the MS can store and display short received alphanumeric messages on the liquid

crystal display (LCD) that is used to show call dialing and status in formation. These messages

are limited to 160 characters in length (varies from mobile to mobile).

Power Levels

These are five different categories of mobile telephone units specified by the European GSM

system: 20W, 8W, 5W, 2W, and 0.8W. These correspond to 43-dBm, 39-dBm, 37-dBm, 33-dBm,


27/86

and 29-dBm power levels. The 20-W and 8-W units (peak power) are either for vehicle-mounted

or portable station use.

The MS power is adjustable in 2-dB steps from its nominal value down to 20mW (13 dBm). This

is done automatically under remote control from the BTS, which monitors the received power

and adjusts the MS transmitter to the minimum power setting necessary for reliable

transmission.

The SIM

The SIM is a smart card that identifies the terminal. By inserting the SIM card into the terminal,

the user can have access to all the subscribed services. Without the SIM card, the terminal is notoperational.

The SIM card is protected by a four-digit Personal Identification Number (PIN). In order to

identify the subscriber to the system, the SIM card contains some parameters of the user such as

its International Mobile Subscriber Identity (IMSI).

Another advantage of the SIM card is the mobility of the users. In fact, the only element that

personalizes a terminal is the SIM card. Therefore, the user can have access to its subscribed

services in any terminal using its SIM card.

Equipment identification

The purpose of equipment identification is to ensure that no stolen or otherwise unauthorized

mobiles are used in the network. To this end, every mobile is provided with a tamper-proof

equipment number in the manufacturing process, in GSM an international mobile equipment


28/86

identity (IMEI). During the set-up phase, the MSC can request this number from the mobile and

then send it on for checking in the network element called EIR (in GSM). If the number is barred

or unknown, the set-up attempt is rejected.

Subscriber identity confidentiality

Subscriber identity confidentiality means that the operator tries to protect the user's telephone

number (the IMSI) from unauthorized tapping. A temporary mobile subscriber number (TMSI in

GSM) is used in the dialogue between the mobile and the network, except for the first contact

attempt in a set-up phase. The MSC gives the mobile a random TMSI for each set-up.

LOCATION AREA IDENTITY (LAI)

It identifies the current location of the subscriber.

LAI=MNC+MCC+LAC

Where:

MCC= Mobile Country Code

MNC= Mobile Network Code (2 digit). Identifies the GSM PLMN in that country and takes the

same value as the MNC in IMSI.

LAC= Location Area Code (max. 16 bits). Identifies a location area within a GSM PLMN

Network & enabling 65536 different location areas to be defined in one GSM PLMN.

SUBSCRIBER AUTHENTICATION KEY (Ki)

It is used to authenticate the SIM card.

PERSONAL IDENTITY NO.

It is used to unlock the MS. If one enters the wrong PIN three times it will lock the SIM. The SIM

can be protected by use of PIN password.

PIN UNBLOCKING KEY (PUK)

In case of PIN, the PUK is needed for unlocking the SIM again. PUK is numeric only, with eight

digits. If a correct PUK is entered, an indication is given to the user. After 10 consecutive

incorrect entries the SIM is blocked. Either the IMSI or the MSISDN Number may access the

subscriber data. Some of the parameters like IAI will be continuously updated to reflect the

current location of the subscriber. The SIM is capable of storing additional information such as

accumulated call charges. This information will be accessible to the customer via handset key

entry.


29/86

TECHNICAL DEPARTMENT HIERARCHY

Technical department has four main streams:

1. Network Switching System (NSS) & Base Station Subsystem (BSS)

3. Network Planning

4. Operation Maintenance & controlling (OMC)

5. Operation and Maintenance (O&M)

Base Station Subsystem (BSS)

The BSS connects the Mobile Station and the NSS. It is in charge of the transmission and

reception. The BSS can be divided into two parts:

1.The Base Transceiver Station (BTS) or Base Station.

2.The Base Station Controller (BSC).

Base Transceiver Station (BTS)

The BTS controls the radio interface to the MS. The BTS comprises the radio equipment such as

transceivers and antennas which are needed to serve each cell of the network. A BTS is usually

placed in the centre of a cell. Its transmitting power defines the size of a cell. Each BTS has

between one and sixteen transceivers depending on the density of users in the cell.

BTS has 4 functional parts:

1. Transmission unit

2. Control functions

3. TRX

TECHNICAL DEPARTMENT

OPERATION AND MAINTENENCE(O&M)

NETWORK PLANNING

OPERATIONMAINTAINENCE &CONTROLLING (OMC)

NSS & BSS


30/86

4. Combiner

1.Transmission unit

The task of the transmission unit is to connect the BTS to the Abis interface and, in doing so,

create different types of transmission configuration possibilities. All of the Nokia BTSs have

integrated transmission units. Certain Talk-family models offer additional integrated radio relay

links. Transmission units are monitored by the operation and maintenance unit by means of an

internal Q1 bus.

2.Control functions

Control functions can be split into four individual functions:

1. Operation and maintenance

2. Master clock function

3. Frequency hopping control

4. External alarms and controls

That being said, depending on the type of BTS this could mean from one integrated unit to up to

four individual plug-in units.

a.Operation and maintenance

The O&M processor controls and supervises the operation of all BTS units alone or in co-

operation with other processors. It is the main interface for local O&M and controls and

supervises the other units as well as delivers all status information to the BSC by means of the

O&M signalling link , which it manages. It stores SW as well as downloads SW to the other

units. It also downloads the software and configuration information received from the BSC or

the MMI to other processors.

b. External alarms and controls

External alarms and controls are programmable interfaces to other devices in the BTS , which

can be used to monitor environmental conditions at the BTS site as well as monitor the state of

units, which do not have a processor of their own. An example of external alarm might be an

intruder alarm or a smoke detector.


31/86

C. Frequency hopping control

The frequency hopping control processor controls the frequency hopping functions of the BTS by

calculating the frequency hopping algorithm and controls the transceivers through a specific

parallel bus.

3.Transceiver (TRX)

The TRX can also contain a varying number of plug-in units depending on the type of BTS. The

TRX can basically be thought of in terms of two functional parts: the base band part and the

radio part. The radio part can also be split into a transmitter part(Tx) and a receiver part(Rx).

The Rx part may also be configured to support antenna diversity , which is supported by all of

the BTS products.

The functions of the TRX can be divided into two categories: O&M and telecommunication

control. One of the most important functions relative to O&M is to download the software and

configuration information received from the main O&M processor to its slave processors

(DSPs).

In terms of telecommunication control, we can apply many of the functions examined in the

previous section directly to the TRX.

Apart from digitising and source coding, all of these are in fact performed in the TRX, speech

coding being performed in the transcoder. It is important to remember that in the uplink

direction the mobile will perform the same functions as well as digitising and speech coding.

Relative to the other functions of the TRX, we could also mention channel equalisation, adaptive

frame alignment, RACH channel detection and measurements as TRX functions.

TRX software is also designed to handle a number of signalling scenarios including call set-up

and release, handovers, TX power control, Air-interface measurements and short messages.

Functionality of the BSC

The BSC manages a variety of tasks ranging from channel administration to short messaging

service. Furthermore the BSC provides interfaces to other network elements. The main

functionalities are explained in brief below.

The following BSC functionalities consist of basic and optional functionalities. These

functionalities and options are described in more detail in BSS feature descriptions.


32/86

General functionalities

A. Management of terrestrial channels

1. Indication of blocking on the A interface channels between the BSC and the MSC

2. Allocation of traffic channels between the BSC and the BTSs3. Pool support for A interface circuits

4. concept support for flexible channel assignments, for example, half rate and high speed circuit

switched data

B. Management of radio channels

1.Management of channel configurations, that is, how many traffic channels and signallingchannels can be used in the BSS. This is done in connection with radio network configuration.

2.Management of traffic channels (TCH) and stand-alone dedicated control channels (SDCCH).

This function can be subdivided into the following tasks:

- resource management

- channel allocation

- link supervision

- channel release

- power control

3. Management of broadcast control channels (BCCH) and common control channels (CCCH).

This function can be subdivided into the following tasks:

- channel management

- random access

- access grant

- paging

- Management of PCCCH/PBCCH for (E)GRPS

C. Management of frequency hopping:

The BSC is in charge of frequency hopping management which enables effective use of radio

resources and enhanced voice quality for a GSM subscriber.


33/86

1. Handovers

The frequency of the mobile is changed in connection with handovers which are executed and

controlled by the BSC. Such a handover can be one of the following three types:

a. Intra-BSC, intra-cell (both intra-TRX and inter-TRX), which means that the handover takes

place within the area controlled by the BSC and the mobile stays in the same cell

b. Intra-BSC, inter-cell, which means that the mobile stays in the area of the BSC but moves from

one cell to another

c. Inter-BSC, both outgoing and incoming, which means that the mobile moves into the area of

another BSC

Management of signalling channels between the BSC and the BTSs

The BSC supervises all 16, 32 or 64 kbit/s permanent point-to-point LAPD signalling

connections, consisting of one connection per Transceiver Unit (TRX) and BTS Operation and

Maintenance Unit (OMU).

Maintenance

The BSC offers the possibility for the following maintenance procedures:

Fault localization for the BSC

Reconfiguration of the BSC

Reconfiguration support to the BTS

Updating of the software in the BSC, TCSM2 and BTS

Operation

During normal operation, the BSC offers various possibilities for the operator:

modification of the parameters of the BSC and the BTS

modification of the radio network parameters

configuration of the BSC hardware administration of the BSC equipment


34/86

Network and Switching Subsystem (NSS)

The switching system (SS) is responsible for performing call processing and subscriber-

relatedfunctions.

The different components of the NSS are described below:

Mobile services Switching Centre (MSC)

The MSC performs the telephony switching functions for the mobile network. It controls calls to

and from other telephone and data systems such as Public Switched Telephone Network (PSTN),

Integrated Services Digital Network (ISDN), public data networks, private networks and other

mobile networks.

Explanation

The Mobile Switching Center or MSC is the primary service delivery node for GSM, responsible

for handling voice calls and SMS as well as other services (such as conference calls, FAX and

circuit switched data). The MSC sets up and releases the end-to-end connection, handles

mobility and hand-over requirements during the call and takes care of charging and real time

pre-paid account monitoring.

In the GSM mobile phone system, in contrast with earlier analogue services, fax and datainformation is sent directly digitally encoded to the MSC. Only at the MSC is this re-coded into

an "analogue" signal .

There are various different names for MSCs in different contexts which reflects their complex

role in the network, all of these terms though could refer to the same MSC, but doing different

things at different times.


35/86

A Gateway MSC is the MSC that determines which visited MSC the subscriber who is being

called is currently located. It also interfaces with the Public Switched Telephone Network. All

mobile to mobile calls and PSTN to mobile calls are routed through a GMSC. The term is only

valid in the context of one call since any MSC may provide both the gateway function and the

Visited MSC function, however, some manufacturers design dedicated high capacity MSCs

which do not have any BSSes connected to them. These MSCs will then be the Gateway MSC for

many of the calls they handle.

The Visited MSC is the MSC where a customer is currently located. The VLR associated with this

MSC will have the subscriber's data in it.

The Anchor MSC is the MSC from which a handover has been initiated. The Target MSC is the

MSC toward which a Handover should take place.

Mobile Switching Centre Server (MSS)

The Mobile Switching Centre Server or MSC Server is a soft switch variant of Mobile Switching

Centre, which provides circuit-switched calling, mobility management, and GSM services to the

mobile phones roaming within the area that it serves. MSC Server functionality enables split

between control (signalling) and user plane (bearer in network element called as Media

Gateway), which guarantees more optimal placement of network elements within the network.

Other GSM Core Network Elements connected to the MSCThe MSC connects to the following elements:

1. The HLR for obtaining data about the SIM and MSISDN

2. The Base Station Subsystem which handles the radio communication with 2G and 2.5G mobile

phones.

3. The UTRAN which handles the radio communication with 3G mobile phones.

4. The VLR for determining where other mobile subscribers are located.
http://en.wikipedia.org/wiki/Base_Station_Subsystemhttp://en.wikipedia.org/wiki/Base_Station_Subsystem


36/86

Tasks of the MSC include

1. Delivering calls to subscribers as they arrive based on information from the

VLR .

2. Connecting outgoing calls to other mobile subscribers or the PSTN.

3. DeliveringSMSsfrom subscribers to the SMSCand vice versa.

4. Arranginghandoversfrom BSC to BSC.

5. Carrying out handovers from this MSC to another.

6. Supportingsupplementary servicessuch as conference calls or call hold.

7. Generating billing information.

Home Location Register (HLR)

The HLR is a centralized network database that stores and manages all mobile subscriptions

belonging to a specific operator. It acts as a permanent store for a persons subscription

information until that subscription is canceled. The information stored includes:

1. Subscriber identity.

2. Subscriber supplementary services.

3. Subscriber location information.

4. Subscriber authentication information.

The 'Home Location Register' or HLR is a central database that contains details of each mobile

phone subscriber that is authorized to use the GSM core network. There is one logical HLR per

PLMN, although there may be multiple physical platforms.

The HLR stores details of every SIM card issued by the mobile phone operator. Each SIM has a

unique identifier called an IMSI which is the primary key to each HLR record.

The next important items of data associated with the SIM are the MSISDNs, which are the

telephone numbers used by mobile phones to make and receive calls. The primary MSISDN is the

number used for making and receiving voice calls and SMS, but it is possible for a SIM to have

other secondary MSISDNs associated with it for fax and data calls. Each MSISDN is also a

primary key to the HLR record.

Examples of other data stored in the HLR against an IMSI record are:

1. GSM services that the subscriber has requested or been given

2. GPRS settings to allow the subscriber to access packet services
http://en.wikipedia.org/wiki/GSM_services#Call_set_up_process_for_incoming_callshttp://en.wikipedia.org/wiki/Short_message_servicehttp://en.wikipedia.org/wiki/SMSChttp://en.wikipedia.org/wiki/Handoverhttp://en.wikipedia.org/w/index.php?title=Supplementary_services&action=edit&redlink=1http://en.wikipedia.org/wiki/MSISDNhttp://en.wikipedia.org/wiki/MSISDNhttp://en.wikipedia.org/w/index.php?title=Supplementary_services&action=edit&redlink=1http://en.wikipedia.org/wiki/Handoverhttp://en.wikipedia.org/wiki/SMSChttp://en.wikipedia.org/wiki/Short_message_servicehttp://en.wikipedia.org/wiki/GSM_services#Call_set_up_process_for_incoming_calls


37/86

3. Current Location of subscriber (VLR and SGSN)

4. Call divertsettings applicable for each associated MSISDN.

5. The HLR data is stored for as long as a subscriber remains with the mobile phone operator.

The HLR is a system which directly receives and processes MAP transactions and messages from

elements in the GSM network, for example, the Location Update messages received as mobile

phones roam around.

The HLR connects to the following elements:

1. The Gateway MSC (G-MSC) for handling incoming calls2. The VLR for handling requests from mobile phones to attach to the network

3. The SMSC for handling incoming SMS

4. The voice mail system for delivering notifications to the mobile phone that a message is

waiting.

Procedures implemented The main function of the HLR is to manage the fact that SIMs and

phones move around a lot. The following procedures are implemented to deal with this:

Manage the mobility of subscribers by means of updating their position in administrative areas

called 'location areas', which are identified with a LAC. The action of a user of moving from one

LA to another is followed by the HLR with a Location area update while retrieving information

from BSS as BSIC (cell identifier).

Send the subscriber data to a VLR or SGSN when a subscriber first roams there.

Broker between the GMSC or SMSC and the subscriber's current VLR in order to allow

incoming calls or text messages to be delivered. Remove subscriber data from the previous VLR

when a subscriber has roamed away from it.

Visitor Location Register (VLR)

The VLR database contains information about all the mobile subscribers currently located in the

MSC service area. Thus, there is one VLR for each MSC in a network. The VLR temporarily

stores subscription information so that the MSC can service all the subscribers currently visiting

that MSC service area. The VLR can be regarded as a distributed HLR as it holds a copy of the

HLR information stored about the subscriber.
http://en.wikipedia.org/wiki/Call_forwardinghttp://en.wikipedia.org/wiki/Call_forwarding


38/86

When a subscriber roams into a new MSC service area, the VLR connected to that MSC requests

information about the subscriber from the subscribers HLR. The HLR sends a copy of the

information to the VLR and updates its own location information. When the subscriber makes a

call, the VLR will already have the information required for call set-up.

Authentication Center (AUC)

AUC provides authentication and encryption parameters that verify the user's identity and

ensure the confidentiality of each call. The AUC protects network operators from different types

of fraud found in today's cellular world. The AUC is a database connected to the HLR which

provides it with the authentication parameters and ciphering keys used to ensure network

security.

The 'Authentication Centre' or AUC is a function to authenticate each SIM card that attempts to

connect to the GSM core network (typically when the phone is powered on). Once the

authentication is successful, the HLR is allowed to manage the SIM and services described

above. An encryption key is also generated that is subsequently used to encrypt all wireless

communications (voice, SMS, etc.) between the mobile phone and the GSM core network.

If the authentication fails, then no services are possible from that particular combination of SIM

card and mobile phone operator attempted. There is an additional form of identification check

performed on the serial number of the mobile phone described in the EIR section below, but this

is not relevant to the AUC processing.Proper implementation of security in and around the AUC is a key part of an operator's strategy

to avoid SIM cloning.

The AUC does not engage directly in the authentication process, but instead generates data

known as triplets for the MSC to use during the procedure. The security of the process depends

upon a shared secret between the AUC and the SIM called the Ki. The Ki is securely burned into

the SIM during manufacture and is also securely replicated onto the AUC. This Ki is never

transmitted between the AUC and SIM, but is combined with the IMSI to produce a

challenge/response for identification purposes and an encryption key called Kc for use in over

the air communications.

Other GSM Core Network Elements connected to the AUC

The AUC connects to the following elements:


39/86

The MSC which requests a new batch of triplet data for an IMSI after the previous data have

been used. This ensures that same keys and challenge responses are not used twice for a

particular mobile.

Procedures implemented

The AUC stores the following data for each IMSI:

1. The Ki

2. Algorithm id (the standard algorithms are called A3 or A8, but an operator may choose a

proprietary one).

When the MSC asks the AUC for a new set of triplets for a particular IMSI, the AUC first

generates a random number known as RAND. This RAND is then combined with the Ki to

produce two numbers as follows:

The Ki and RAND are fed into the A3 algorithm and a number known as Signed response or

SRES is calculated.

The Ki and RAND are fed into the A8 algorithm and a session key called Kc is calculated.

The numbers (RAND, SRES, KC) form the triplet sent back to the MSC. When a particular IMSI

requests access to the GSM core network, the MSC sends the RAND part of the triplet to the

SIM. The SIM then feeds this number and the Ki (which is burned onto the SIM) into the A3

algorithm as appropriate and an SRES is calculated and sent back to the MSC. If this SRES

matches with the SRES in the triplet (which it should if it is a valid SIM), then the mobile isallowed to attach and proceed with GSM services.

After successful authentication, the MSC sends the encryption key Kc to the Base Station

Controller (BSC) so that all communications can be encrypted and decrypted. Of course, the

mobile phone can generate the Kc itself by feeding the same RAND supplied during

authentication and the Ki into the A8 algorithm.


40/86

The AUC is usually collocated with the HLR, although this is not necessary. Whilst the

procedure is secure for most everyday use, it is by no means crack proof. Therefore a new set

of security methods was designed for 3G phones.

Radio Interface

Radio interface is the interface between the MS and the RBS. It is also called as Um interface.

This interface has three layers (OSI). They are Physical Layer (Layer1), Data Link Layer (Layer2)

and Network Layer (Layer3)Network Layer (Layer3):

This layer provides the Mobile Network Signaling (MNS) service to the user application.

The basic functions of this layer are to establish, maintain and terminate circuit switched

connections across a GSM PLMN and other networks to which the PLMN is connected.

Also it supports functions for supplementary services and short message service

This layer consists of three-sub layer which are basically protocol control entities. They

are a. Connection Management (CM) b. Mobility Management (MM) c. Radio Resource

Management (RR)

In the MS, entities from all three sub layers are present however on the network sidethere is a distribution of the signaling functions between different network equipment.

The RR function resides mainly in the BSC. The MM and CM functions are located in the

MSC. In the BTS most of the RR messages are handled as transparent message. However

some of them must be interpreted by the BTS.

a. Mobility Management:The following functions are being carried out by this Mobility management MM sub layer.

All the functions regarding the location of the MS, which includes location updating type

normal, location update type periodic registration and location updating type IMSI attach.


41/86

It provides the user identity procedures. These procedures are authentication, TMSI

reallocation, IMSI detach and identification of the MS by requesting either IMSI or IMEI.

c. Radio Resource Management:

The main purpose of this sub layer is to establish, maintain and release a dedicated

connection between the MS and the network. This includes handover procedures, cell

selection at power on and cell re-selection in idle mode, recovery from lack of coverage in

idle mode. The following are the basic RR functions.

On the downlink, the RR sub layer sends system information to the busy MS.

On the uplink, the MS transmits measurement reports.

The network may use the RR ciphering mode-setting procedure for setting the ciphering

mode.

The class mark change procedure is used by the MS to provide the system with additional MS

class mark information. It is also used to indicate to the network a change in class mark. For

example, when the power capabilities of a hand held MS are changed because the MS is

connected to external power in a vehicle.

Equipment Identity Register (EIR)The EIR is also used for security purposes. It is a register containing information about the

mobile equipments. More particularly, it contains a list of all valid terminals. A terminal is

identified by its International Mobile Equipment Identity (IMEI). The EIR allows then to forbid

calls from stolen or unauthorized terminals (e.g., a terminal which does not respect the

specifications concerning the output RF power).


42/86

z

EXPLANATION

1. UmThe air interface between the MS (Mobile Station) and the BTS. This interface uses

LAPDm protocol for signaling, to conduct call control, measurement reporting, Handover,

Power control, Authentication, Authorization, Location Update and so on. Traffic and Signaling

are sent in bursts of 0.577 ms at intervals of 4.615 ms, to form data blocks each 20 ms.

The traffic channels in the Air interface are allocated onto a TDMA frame. The TDMA frame

consists of 8 time slots. Generally, all time slots are used for traffic channels. Time slot 0 and

sometimes also time slot 1 can be used for the signaling between the BTS (BSC, MSC) and the

MS.

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

TDMA Frame = 8time slots

2. Abis The interface between the Base Transceiver Station and Base Station Controller.

Generally carried by a DS-1, ES-1, or E1 TDM circuit. Uses TDM sub channels for traffic


43/86

(TCH), LAPD protocol for BTS supervision and telecom signaling, and carries synchronization

from the BSC to the BTS and MS.

It is a 2 Mbit/s interface which can carry up to 96 channels. The capacity of the Abis depends on

the type of signaling used between the BSC and the BTS. When using 64 kbit/s signaling, the 2

Mbit/s link capacity is 80 traffic channels. Using 16 kbit/s signaling, the 2 Mbit/s link capacity is

96 traffic channels.

3. A The interface between the BSC and Mobile Switching Center. It is used for carrying

Traffic channels and the BSSAP user part of the SS7 stack. Although there are usually

transcoding units between BSC and MSC, the signaling communication takes place between

these two ending points and the transcoder unit doesn't touch the SS7 information, only the voice

or CS data are transcoded or rate adapted.

4. AterThe interface between the Base Station Controller and Transcoder. It is a proprietary

interface whose name depends on the vendor (for example Ater by Nokia), it carries the A

interface information from the BSC leaving it untouched.

5.Gb Connects the BSS to the Serving GPRS Support Node (SGSN) in the GPRS Core

Network.

6. B-Interface b/w MSC-VLR

7. C-Interface b/w MSC-HLR

8. E-Interface b/w MSC-MSC

9. F-Interface b/w MSC-EIR

Channel structure

A total of 156.25 bits is transmitted in 0.577 milliseconds, giving a gross bit rate of 270.833

kbps. There are three other types of burst structure for frame and carrier synchronization and

frequency correction. The 26bit training sequence is used for equalization, as described above.

The 8.25 bit guard time allows for some propagation time delay in the arrival of bursts.


44/86

Physical channels

In the air interface, frequency channel C0 and time slots TS0 and TS1 on that channel constitute

the physical channels. Each cell has a dedicated C0 channel. Most logical control channels for

signaling across the air interface are carried by LAPDm.

In the interface between the base station and the BSC, all signaling is carried by LAPD links,

which in turn use PCM channels. Signaling that is also transported across the air interface is

carried by links having 0 as the service access point identifier (SAPI) address. Since a BSC is

responsible for the maintenance of its base stations, BSC-BTS communication is extensive. The

maintenance signals are carried by LAPD links having 62 as the SAPI address for base station

maintenance and 63 for maintenance of LAPD. The LAPD links are in turn carried by a time slot

(usually TS1) on the PCM link connecting a base station to its BSC.

In the interface between a BSC and its MSC, there are three levels of physical channels. The

topmost level is the discrimination mechanism of the BSSAP protocol, which distinguishes

between signals to be transported between a mobile and the MSC and signals that are to be

transported only between the MSC and the BSC. In both cases, BSSAP signals are carried by the

SCCP in SS7. All call-related signaling uses SCCP's connection-oriented service, while the

connectionless service is used in all other cases. SS7 normally uses one or more time slots in a

PCM system.The physical channels - together with the relay functions - are used to create logical channels

through all or part of the access network. In the air interface, these logical channels are divided

into nine types of control channel and two types of traffic channel, all of which are mapped onto

the time slots of the physical channels.

Control channels


45/86

Control channels are divided into three classes, based on how and when they are used:

broadcast channels (BCH); common control channels (CCCH); and dedicated control channels

(DCCH).

The GSM system has 11 logical channels

Broadcast channels

Class BCH channels continuously send information about cell and network parameters to the

mobiles. They are unidirectional (from base station to mobile) and used jointly by all mobiles.

There are three types of broadcast channel:

A frequency correction channel (FCCH) carries frequency correction information.

A synchronization channel (SCH) carries frame synchronization information and information for

identifying the base station.

A broadcast control channel (BCCH) carries cell-specific information.

These channels are shown in the lower part ofFigure.

Common control channels

Class CCCH channels are used for access to the network. These three channels, too, are

common to all mobiles.

A paging channel (PCH) is used by the network to call terminals.A random access channel (RACH) is used by a mobile to answer paging calls and call the

network when the mobile initiates set-up.

An access granted channel (AGCH) is used by the network to allocate a dedicated control

channel (SDCCH - see below) for continued signaling or some other channel (FACCH - see

below) for handover.
http://www.ericsson.com/support/telecom/part-d/#14101http://www.ericsson.com/support/telecom/part-d/#14101


46/86

All these logical channels are unidirectional: PCH and AGCH from network to mobile and

RACH from mobile to network. The signals sent on RACH, AGCH and PCH are relayed via the

base station and transferred to and from the BSC on LAPD links.

Dedicated control channels

Class DCCH channels are used for signaling between a mobile and the network before and

during a call. These three channels are allocated to individual connections and are always

bidirectional.

A stand-alone dedicated control channel (SDCCH) is used for signaling during the set-up phase;

that is, before traffic channel has been allocated. This channel is also used for registration,

authentication and signaling in connection with clearing.

A slow associated control channel (SACCH) is a locating channel that the mobile uses to

continuously report received signal strength in the visited cell and from surrounding cells. The

channel can also be used for controlling the output power of the mobile. Note, however, that

SACCH does not have the signaling capacity required to control handover.

A fast associated control channel (FACCH) - only available in conversation state - is used for

handover operations. FACCH is allocated 20 ms of the traffic channel when rapid signaling is

required. The listening party does not notice the loss of 20 ms conversation because the

receiving unit repeats the last 20 ms. There is one FACCH for each traffic channel.

Signals on SACCH, FACCH and SDCCH are relayed to the BSC via the base station. Signalsrelated to call handling; authentication and registration are relayed via SDCCH and then sent to

the MSC. Connection handling is performed in both the BSC and the MSC.

All control channels except SCH and FCCH use LAPDm.

The following comments complete the information given in figure:

Between the BSC and base stations, LAPD links are used for maintenance of base stations (base

control function, BCF, in GSM).

Between the BSC and the MSC, BSSAP (discrim.) signaling is used for paging (in the case of a

call to a mobile) and for handover, if the MSC is involved in this handover.

Traffic channels

A traffic channel (TCH) is used to carry speech and data traffic. Traffic channels are defined

using a 26-frame multiframe, or group of 26 TDMA frames. The length of a 26-frame multiframe

is 120 ms, which is how the length of a burst period is defined (120 ms divided by 26 frames
http://www.ericsson.com/support/telecom/part-d/#14101http://www.ericsson.com/support/telecom/part-d/#14101


47/86

divided by 8 burst periods per frame). Out of the 26 frames, 24 are used for traffic, 1 is used for

the Slow Associated Control Channel (SACCH) and 1 is currently unused (see Figure). TCHs for

the uplink and downlink are separated in time by 3 burst periods, so that the mobile station does

not have to transmit and receive simultaneously, thus simplifying the electronics.

In addition to these full-rate TCHs, there are also half-rate TCHs defined, although they are

not yet implemented. Half-rate TCHs will effectively double the capacity of a system once half-

rate speech coders are specified (i.e., speech coding at around 7 kbps, instead of 13 kbps).

Eighth-rate TCHs are also specified, and are used for signaling. In the recommendations, they

are called Stand-alone Dedicated Control Channels (SDCCH).

CALL SETUPCall set up can be classified into two major categories, they are (i) Call From MS (Mobile

Originated call) (ii) Call to MS (Mobile Terminated call)

(i) Call From MS (Mobile Originated Call)

Mobile Originated call is possible when the MS is attached with the MSC/VLR and is

listening to the system information.


48/86

1. The MS requests a SDCCH using RACH2. The MS indicates that it wants to set up a call. The identity of the MS, IMSI is

analyzed and the MS is marked as busy in the VLR

3. Authentication is performed4. Ciphering may be initiated.5. The MSC receives a setup message from the MS. This includes the kind of service the

MS wants and the B-number. MSC verify that the MS doesnt have services like

barring of outgoing calls. If the MS is not barred, the setup of call proceeds.

6. Between the MSC and the BSC a link is established and a PCM time slot is seized.The MSC sends a request to the BSC to assign a TCH. The BSC assigns a TCH to the

call (if there is an idle TCH available) and tells the BTS to activate the channel. The

BTS sends an acknowledgement when the activation is completed and the BSC orders

the MS to switch over to the TCH. The BSC informs the MSC when the assignment is

complete.

7. An alert message is sent to the MS indicating that a ringing tone has been generatedon the other side. The ringing tone generated in the exchange on the B- subscriber

side is sent t the MS via the group switch in the MSC.

8. When the B subscriber answers, the network sends a connect message to the MSindicating that the call is accepted . The MS returns a connect acknowledgement

which completes the call set-up.

Call to MS (Mobile Terminated Call)


49/86

Figure : Call to MS from PSTN.

1. The number dialed by the calling party is called the Mobile station ISDN number(MSISDN). If the call is being made from a PSTN exchange, the exchange analyses

the number and decides that the call is for a GSM subscriber

2. From PSTN, the call is routed to the GMSC in the home PLMN of the called MS.3. By analyzing the MSISDN, the GMSC finds out which HLR the subscriber is

registered in. GMSC asks the HLR for information so the call can be routed to the

MSC/VLR where the MS is temporarily registered.

4. The HLR contacts the VLR and gets the roaming number.

5. The HLR forwards the roaming number to the GMSC.

6a. With the help of the roaming number, the GMSC can route the call to the

appropriate MSC.

6b. The call is routed to the MSC

7. The MSC knows which location area the MS is located in and sends a paging

message to the BSCs handling this location area.

8. The BSC distributes the paging message to the BTSs in the LA

Transit

Exchange GMSC

MSC/VLR

BSC

HLR

(2) (3)

(6a) (5)

(4)(6b)

(1)

(7)

(8) (8)

Signaling connectionSpeech path

(9)

(9)

PSTN

BTSBTS


50/86

9. The BTSs page the MS using IMSIThe MS sends a request for a SDCCH when it detects its identity in the paging message.

The MSC performs authentication and starts ciphering. The MSC may send information

to the MS about requested services like speech, data, fax etc.,

The BSC orders the BTS to activate a TCH and release the SDCCH. The MS is ordered to

tune to the frequency of the TCH. An alerting message is sent from the MS indicate that a

ring tone has been generated in the MS. The ringing tone for the calling subscriber is

generated in the MSC. When the mobile subscriber answers, the MS sends a connect

message. The network completes the through connection path and sends a connection

acknowledgement to the MS. The duplex path for traffic is open now.


51/86

MODULATION

GSM is a digital mobile standard But radio frequencies are analogue. So the question is how do

we transmit digital information in an analogue signal ?

It looks difficult, but if we think about the values that must be transmitted (0 and 1), suppose thatthe frequency varies between two values, one representing 0 and the other representing 1. By

altering the value of a certain characteristic of frequency at every specified interval (the bit

duration), we can translate an analogue signal into a bit stream in the frequency domain. This

technique is called modulation. The characteristics that can be varied is the frequency, the

amplitude or the phase shift. The modulation technique used in GSM is the Gaussian Minimum

Shift Keying (GMSK).

Multiplexing

In telecommunications and computer networks, multiplexing (known as muxing) is a term used to

refer to a process where multiple analog message signals or digital data streams are combinedinto one signal over a shared medium. The aim is to share an expensive resource. For example,

in telecommunications, several phone calls may be transferred using one wire.

The multiplexed signal is transmitted over a communication channel, which may be a physical

transmission medium. The multiplexing divides the capacity of the low-level communication

channel into several higher-level logical channels, one for each message signal or data stream

1 Bit duration

Phase ModulationAM Amplitude ModulationFM Frequency Modulation

M

M Modulation Signal


52/86

to be transferred. A reverse process, known as demultiplexing, can extract the original channels

on the receiver side.

A device that performs the multiplexing is called a multiplexer (MUX), and a device that

performs the reverse process is called a demultiplexer(DEMUX).

Inverse multiplexing (IMUX) has the opposite aim as multiplexing, namely to break one data

stream into several streams, transfer them simultaneously over several communication channels,

and recreate the original data stream.

Categories of multiplexing

The two most basic forms of multiplexing are time-division multiplexing (TDM) and frequency-

division multiplexing (FDM), both either in analog or digital form. FDM requires modulation of

each signal.

Variable bit rate digital bit streams may be transferred efficiently over a fixed bandwidth

channel by means of statistical multiplexing, for example packet mode communication. Packet

mode communication is an asynchronous mode time-domain multiplexing, which resembles but

should not be considered as time-division multiplexing.

Digital bit streams can be transferred over an analog channel by means of code-division

multiplexing (CDM) techniques such as frequency-hopping spread spectrum (FHSS) and direct-

sequence spread spectrum (DSSS).

HANDOVER

HANDOVER:1. The GSM handover process uses a mobile assisted technique for accurate and fast

handovers, in order to:

Maintain the user connection link quality.

Manage traffic distribution

2. The overall handover process is implemented in the MS,BSS & MSC.

3. Measurement of radio subsystem downlink performance and signal strengths received

from surrounding cells, is made in the MS.

4. These measurements are sent to the BSS for assessment.
http://en.wikipedia.org/wiki/Demultiplexerhttp://en.wikipedia.org/wiki/Demultiplexer


53/86

5. The BSS measures the uplink performance for the MS being served and also assesses the

signal strength of interference on its idle traffic channels.

6. Initial assessment of the measurements in conjunction with defined thresholds and

handover strategy may be performed in the BSS. Assessment requiring measurement

results from other BSS or other information resident in the MSC, may be perform. in the

MSC.

7. The MS assists the handover decision process by performing certain measurements.

8. When the MS is engaged in a speech conversation, a portion of the TDMA frame is idle

while the rest of the frame is used for uplink (BTS receive) and downlink (BTS transmit)

timeslots.

9. During the idle time period of the frame, the MS changes radio channel frequency and

monitors and measures the signal level of the six best neighbor cells.

10.Measurements which feed the handover decision algorithm are made at both ends of

the radio link.

MS END:

1. At the MS end, measurements are continuously signaled, via the associated control

channel, to the BSS where the decision for handover is ultimately made.

2. MS measurements include:

Serving cell downlink quality (bit error rate (BER) estimate).

Serving cell downlink received signal level, and six best neighbor cells downlink

received signal level.

3. The MS also decodes the Base Station ID Code (BSIC) from the six best neighbor cells,

and reports the BSICs and the measurement information to the BSS.

BTS END:

1. The BTS measures the uplink link quality, received signal level, and MS to BTS site

distance.

2. The MS RF transmit output power budget is also considered in the handover decision.


54/86

3. If the MS can be served by a neighbor cell at a lower power, the handover is

recommended.

4. From a system perspective, handover may be considered due to loading or congestion

conditions. In this case, the MSC or BSC tries to balance channel usage among cells.

MS IDLE TIME REPORTING:

1. During the conversation, the MS only transmits and receives for one eighth of the time,

that is during one timeslot in each frame.

2. During its idle time (the remaining seven timeslots), the MS switches to the BCCH of the

surrounding cells and measures its signal strength.

3. The signal strength measurements of the surrounding cells, and the signal strength and

quality measurements of the serving cell, are reported back to the serving cell via the

SACCH once in every SACCH multiframe.

4. This information is evaluated by the BSS for use in deciding when the MS should be

handed over to another traffic channel.

5. This reporting is the basis for MS assisted handovers

The following measurements is be continuously processed in the BSS:

1. Measurements reported by MS on SACCH

Down link RXLEV

Down link RXQUAL

Down link neighbor cell RXLEV

2. Measurements performed in BSS

Uplink RXLEV

Uplink RXQUAL

MS-BS distance

Interference level in unallocated time slots


55/86

Every SACCH multiframe (480 ms) a new processed value for each of the measurements

is calculated.

HANDOVER CONDITIONS:

Handover is done on five conditions:

1. Interference

2. RXQUAL

3. RXLEV

4. Distance or Timing Advance

5. Power Budget

Interference - If signal level is high and still there is RXQUAL problem, then the RXQUAL

problem is because of interference.

RXQUAL - It is the receive quality. It ranges from 0 to 7 , 0 being the best and 7 the

worst.

RXLEV - It is the receive level. It varies from -47dBm to -110dBm.

Timing Advance - Ranges from 0 to 63.

Power budget - It is used to save the power of the MS.


56/86

INTRA-CELL HANDOVER

1. Handover takes place in the same cell from one timeslot to another timeslot of the same

carrier or different carriers (but the same cell).

2. Intra-cell handover is triggered only if the cause is interference.

3. Intra-cell handover can be enabled or disabled in a cell.

INTER-BSC HANDOVER

Handover takes place between different cells which are controlled by the different

BSC.

HANDOVER TYPESInter-BSC Handover

BSS1

BTS1 Call is handed from timeslot 3of cell1 to timeslot 1 of cell2 .

Both the cells are controlled

by the different BSC.

0 1 2 3 4 5 6 7

BSS2

MSC

0 1 2 3 4 5 6 7

BTS2

BSC

Call is handed

from timeslot 3 to timeslot 5

0 1 2 3 4 5 6 7

BTS


57/86

Handover Priority1.Up Link Interference ---- Intra cell handover

2.Down Link Interference ---- Intra cell handover

3.Up Link Quality Poor ---- Inter cell handover

4.Down Link Quality Poor ---- Inter cell handover

5.Up Link Strength Poor ---- Inter cell handover

6.Down Link Strength Poor ---- Inter cell handover

7.MS-BS Distance exceed TA ---- Inter cell handover

8.Better Cell ---- Inter cell handover

9.Macro-Micro delay handover ---- Intra cell handover

10.GOOD C/I handover ---- Intra cell handover11.Directed Retry ---- Inter cell handover

Base Station Identity CodeProblem defination

A problem could arise when the mobile station in a given position is performing a

handover, but is receiving two cells using the same BCCH frequency. This can happen

when the mobile station is moving along the national borders, where on each side of theborder the different PLMN operators have some frequencies in common.

In order to discriminate between cells transmitting the BCCH channels at the same

frequency, the mobile station uses the Base Station Identify Code (BSIC). The BSIC is

broadcast on the SCH (Synchronization Channel) of each cell.

Definition of BSICThe BSIC is a local color code that allows a mobile station to distinguish between different

neighboring base stations. However, it is not an unambiguous identification of a basestation. Many cells bear the same BSIC. The scheme of BSIC values to be used are

normally laid down in a bilateral agreement between the concerned PLMN operators to

prevent


58/86

FREQUENCY HOPPINGThe Frequency Hopping function permits the dynamic switching of radio links from one carrier

frequency to another. Frequency Hopping changes the frequency used by a radio link every new

TDMA frame in a regular pattern. Frequency Hopping is a GSM feature which can be enabledor disabled on a per cell basis.

Reasons for frequency hopping Decreasing the probability of interference

Frequency Hopping will spread the annoyance of interference over different mobile

stations in a particular cell

Suppressing the effect of Rayleigh fadingRayleigh fading (or multipath fading) is caused by different paths followed by the radio

signal. Rayleigh fading can cause coverage holes.

Rayleigh fading is location and frequency dependent. When the mobile station is stationary

or moves at a slow speed, Frequency Hopping will significantly improve the level of theair-interface performance. However, when the mobile station moves at a high speed,

Frequency Hopping does not harm, but does not help much either. The more frequencies

are used in a particular cell, the more Frequency Hopping can gain in suppressing the

effect of Rayleigh fading.

In GSM, the frequency hopping is implemented through:

Baseband hopping (BH)

Divert a call to different transceiver on a frame basis

Synthesiser hopping (SH)

Fix a call on a transceiver which re-tunes the frequency on a frame basis


59/86

Baseband Hopping (BH)

Number of transceiver units in place equals number of hopping frequencies in the

sequence

Each transceiver unit is tuned to a fixed frequency

A call is routed to different transceivers on a frame basis

Hopping spectrum is limited by the number of transceiver units

Combining loss is independent of number transceiver units in place

1. Tuned cavity combiners used 2. BH introducing high EIRP


60/86

Synthesiser Hopping (SH)

Transceivers are tuned to new frequencies on a frame basis

Number of hopping frequencies is not limited by the number of transceivers in place

A call is always routed to a given transceiver

Hybrid combining is required for SH

High carrier numbers reduces EIRP

Air combining is recommended to recover EIRP

Key Differences (BH ~ SH) Both can be used to improve quality or increase capacity

BHs effectiveness is limited by the number of transceivers equipped

SH can hop over a wide range of frequencies and is independent of number of

transceivers equipped


61/86

Key AdvantagesSH SH is more effective to provide frequency diversity and interference diversity

Extending coverage area - frequency diversity

Improving quality - frequency diversity

Enabling aggressive reuse - interference diversity

Realising the potential benefits to operators, the synthesiser frequency hopping capability

has been made available since the first generation of Motorolas BTS equipment

Frequency Hopping Parameters Cell Allocation (CA):Refer to all available frequency carriers in a cell. The allocation

should be consecutive starting from effective frequency carrier 0.

Mobile Allocation (MA): Set of frequencies to hop over. Maximum of 63 frequencies can

be defined in the MA list.

Hopping Sequence Number (HSN): Order used to hop over the frequencies. There are

64 different sequences:

Hopping Sequence Number (HSN): Order used to hop over the frequencies. There are

64 different sequences:

1. 0 is cyclic2.1 - 63 are pseudo random

Mobile Allocation Index Offset (MAIO): used to define initial frequency of hopping. The

value of MAIO ranges between 0 to (N-1) where N is the number of frequencies defined

in the MA list. MAIO of all channel of one hopping TRX must be identical but of different

hopping TRX in same cell must be different.

Frequency Hopping Indicator (FHI): Defines a hopping system, made up by an

associated set of frequencies (MA) to hop over and sequence of hopping (HSN).

Training Sequence Code (TSC): Used for delay equalization at RX end. TSC must be the

same as BTS code.

Planning for frequency hoppingThe plan depends upon the type of Frequency Hopping system used. As in case of

Documents

Kamal Kiran