ANALYSIS OF GSM CALL FLOW WITH SS7

MESSAGES & OPTIMIZATION IN GSM

NETWORK

PROJECT REPORT

Submitted by

GAYATHRI S

Register No: 14MAE004

in partial fulfillment for the requirement of award of the

degree

of

MASTER OF ENGINEERING

in

APPLIED ELECTRONICS

Department of Electronics and Communication Engineering

KUMARAGURU COLLEGEOF TECHNOLOGY

(An autonomous institution affiliated to Anna University, Chennai)

COIMBATORE-641049

ANNA UNIVERSITY: CHENNAI 600 025

APRIL 2016

2

BONAFIDE CERTIFICATE

Certified that this project report titled “ANALYSIS OF CALL FLOW WITH

SS7 MESSAGES AND OPTIMIZATION IN GSM NETWORK” is the

bonafide work of GAYATHRI S [Reg. No. 14MAE004] who carried out the

research under my supervision. Certified further, that to the best of my

knowledge the work reported herein does not form part of any other project or

dissertation on the basis of which a degree or award was conferred on an earlier

occasion on this or any other candidate.

HHHH

The Candidate with university Register No. 14MAE004 was examined by us

in the project viva –voice examination held on............................

SIGNATURE

Dr.M.Alagumeenaakshi, Ph.d.,

PROJECT SUPERVISOR

Department of ECE

Kumaraguru College of Technology

Coimbatore-641 049

SIGNATURE

Dr. A.VASUKI, Ph.d.,

HEAD OF THE DEPARTMENT

Department of ECE

Kumaraguru College of Technology

Coimbatore-641 049

3

ACKNOWLEDGEMENT

First, I would like to express my praise and gratitude to the Lord, who has

showered his grace and blessings enabling me to complete this project in an excellent

manner.

I express my sincere thanks to the management of Kumaraguru College of

Technology and Joint Correspondent Shri. Shankar Vanavarayar for the kind

support and for providing necessary facilities to carry out the work.

I would like to express my sincere thanks to our beloved Principal

Dr.R.S.Kumar, Kumaraguru College of Technology, who encouraged me with his

valuable thoughts.

I would like to thank Dr.A.Vasuki,Ph.d., Head of the Department, Electronics

and Communication Engineering, for her kind support in completion of the project.

In particular, I wish to thank with everlasting gratitude to the project

coordinator Mrs.S.Umamaheswai,M.E.,(Ph.D)., Associate Professor, Department of

ECE and I wish to convey my deep sense of gratitude to all teaching and non-teaching

staff of ECE Department for their help and cooperation.

I am greatly privileged to express my heartfelt thanks to my project guide

Dr.M.Alagumeenaakshi,Ph.D.,Assisstant Professor(SRG), Department of ECE, for

her expert counseling and guidance to make this project to a great deal of success.

make this project to a great deal of success.

I would like to thank Mr.K.Ramesh (Sub-Divisional Engineer) from

RGMTTC (Rajiv Gandhi Memorial Telecom Training Centre) of BSNL (Bharat

Sanchar Nigam Limited) at Chennai, for his support in completion of this project

successful.

Finally, I thank my parents and my family members for giving me the moral

support and abundant blessings in all of my activities and my dear friends who helped

me to endure my difficult times with their unfailing support and warm wishes.

Iii

4

ABSTRACT

As cellular communication has become one of the fast growing communication

medium with dynamically increasing usage and users. It requires a constant

evaluation towards its parameters to ensure the quality and performance. RF

optimization is a way to optimize the GSM network and to evaluate the quality of

service. This project is proposed with an intention of reducing the call drops, which

seems to be a very high issue among the subscribers as well as among the service

providers. It is found that call drops in conventional networks is less than 0.01% and

in mobile network it is greater than 0.1%. As per TRAI (Telecom Regularity

Authority of India), call drops have doubled in last one year. Call drops jumped

two-fold on 2G and 65% on 3G networks. Since continuation of an active call is a

prime importance in cellular system, a new approach has been designed to minimize

the rate of call drops as well as increase the quality of the network related to

customer satisfaction and performance of cellular operator to enhance the revenue of

the company. This approach deals with the design of increasing the number of

carriers in each sector of the BTS (Base Transceiver Station). This leads to the

reduction call drops to a greater extent even during peak hours. The improvement in

number of carriers from 3|3|3 to 5|5|5 is done by radio frequency planning in BCCH

(Broadcast Channel) and optimisation in TCH (Traffic Channel). The optimisation

process is done using a commercial tool “RF AGILENT TEST DRIVE TOOL”,

which pinpoints the spot where capacity issues exist in radio access network.

This project also provides a way to increase the signal strength at various areas

with in a cell thereby increasing the coverage area of the cell and reduce the amount

of call dropping and call blocking for both long call and short call and ensure a

successful call handoff. This helps the operator to successfully utilize the limited

number of available carrier to produce greater quality. Also effective utilization of

the carrier makes the system more economical.

5

TABLE OF CONTENTS

CHAPTER NO. TITLE PAGE NO.

ABSTRACT iv

LIST OF FIGURES vii

LIST OF ABBREVIATIONS viii

1 INTRODUCTION 1

1.1 INTRODUCTION TO MOBILE

COMMUNICATION

1

1.2 DUPLEXING

METHODOLOGY

2

1.2.1 Frequency Division Duplex 2

1.2.2 Time Division Duplex 2

1.3 MULTIPLE ACCESS

TECHNOLOGIES

2

1.3.1 Frequency Division Multiple

Access

3

1.3.2 Time Division Multiple Access 3

1.3.3 Code Division Multiple Access 4

1.4 GEOGRAPHICAL AREAS OF

THE GSM NETWORK

4

1.5 GSM ARCHITECTURE 5

6

1.5.1 Network and Switching

subsystem

6

1.5.1.1 Mobile Switching Centre 6

1.5.1.2 Home Location Register 6

1.5.1.3 Visitor Location Register 6

1.5.1.4 Equipment Identity

Register

7

1.5.1.5 Authentication Centre 7

1.5.2 Operation and Maintenance

Centre

7

1.5.3 Base Station Subsystem 8

1.5.3.1 Base Transceiver Station 8

1.5.3.2 Base Station Controller 8

1.5.4 Mobile Station 8

1.5.4.1 The Terminal 8

1.5.4.2 The SIM 9

1.6 CONTROL CHANNELS 9

1.6.1 Traffic channels 10

1.6.1.1 Traffic Channel Full rate 10

1.6.1.2 Traffic Channel Full rate 10

1.6.1.3 Enhanced Full Rate 10

7

1.6.2 Broadcast channels 10

1.6.3 Common control channels 11

1.6.4 Dedicated control channels 12

1.7 TELECOM SIGNALING

MECHANISM

13

1.8 PROJECT OUTLINE 17

2 LITERATURE SURVEY 18

3 RF OPTIMIZATION 22

3.1 INTRODUCTION TO RF

OPTIMIZATION

22

3.2 THE OPTIMIZATION

PROCESS

22

3.3 DRIVE TESTING 23

3.4 WORKING EQUIPMENT 25

3.5 PARAMETERS MEASURED 25

3.6 FREQUENTLY OBSERVED

ISSUES

26

3.6.1 Cell Dragging 26

3.6.2. Dropped Calls 26

3.6.3. Ping-Ponging 26

3.6.4. System Busy 27

3.6.5. Handover boundary 27

8

3.6.6. Blocked Calls 27

3.7 SOLUTIONS PROPOSED 28

3.8 SUMMARY 28

4 AGILENT DRIVE TEST TOOL

CONFIGURATION

29

4.1 INTRODUCTION 29

4.2 PARAMETERS TO MEASURE 30

4.3 HARDWARE

REQUIREMENTS

33

4.4 PROCESS OF

CONFIGURATION

34

4.5 MS MODE OF THE DRIVE

TEST

36

4.5.1 IDLE mode 36

4.5.2 Long Call mode 37

4.5.3 Short Call mode 38

4.6 Receiver Quality Plot 40

4.7 Receiver Level Plot 41

5 RESULTS AND DISCUSSIONS 42

6 CONCLUSION AND FUTURE

ENHANCEMENT

50

REFERENCES 52

9

LIST OF FIGURES

FIGURE NO. CAPTION PAGE NO.

1.1 Access Network 1

1.2 FDMA Frame 2

1.3 TDMA Frame 4

1.4 GSM Network Areas 4

1.5

1.6

1.7

1.8

GSM Architecture

Channels of GSM Network

CCS7 Signaling Network

Architecture

Structure of CCS7 protocol

5

12

14

17

3.1 Optimization Process 22

3.2

4.1

4.2

4.3

4.4

4.5

Drive Test in Practice

Cyclic Optimization Process

Signal level received from

the BTS

Neighbor BSIC

Radio Parameters

C/I Ratio

25

29

30

32

33

33

10

4.6

4.7

4.8

4.9

4.10

4.11

5.1

5.2

5.3

5.4

5.5

5.6

5.7

5.8

Physical setup of AGILENT

TOOL

Snap shot of MS in IDLE

mode

Snap shot of MS in long call

Snapshot of MS in short call

Plot of receiver quality

Plot of received signal level

GPS Location with BTS

Connection

GPS Location with BTS

Connection after Handover

Before Optimization

After Optimization

Analysis of dropped call

before and after

optimization

Analysis of blocked call

before and after

optimization

Analysis of good call before

and after optimization

Analysis of received signal

quality before and after

34

37

38

39

40

41

42

43

44

45

45

46

46

46

11

5.9

5.10

5.11

optimization

Analysis of received power

before and after

optimization

OMCR report before

Optimization

OMCR report after

Optimization

48

47

48

12

13

LIST OF TABLES

TABLE.NO CAPTION PAGE NO.

4.1 Received signal quality range 30

4.2 Speech quality range 31

4.3 Properties of long call and short call 36

14

LIST OF ABBREVIATIONS

GSM Global System for Mobile

FDMA Frequency Division Multiple Access

TDMA Time Division Multiple Access

CDMA Code Division Multiple Access

NSS Network Switching and Subsystem

MSC Mobile Switching Centre

HLR Home Location Register

VLR Visitor Location Register

EIR Equipment Identity Register

AUC Authentication Centre

OMC Operation and Maintenance Center

BSS Base Station Subsystem

BTS Base Transceiver Station

BSC Base Station Controller

MS Mobile Station

ND Network Dimensioning

QOS Quality Of Service

PSTN Public Switched Telephone Network

PLMN Public Land Mobile Network

15

LU Location Updation

LAI Location Area Identity

TCH Traffic Channel

BCCH Broadcast Control Channel

RACH Random Access Channel

AGCH Access Grant Channel

SIM Subscriber Identity Module

TMSI Temporary Mobile Subscriber Identity

ISDN International Service Digital Network

MSISDN Mobile Station International Service Digital Network

MSRN Mobile Station Roaming Number

ARFCN Absolute Radio Frequency Channel Number

ATOOL

OMCR

SDCCH

CBCH

Acceptance, Test Or Launch Language

Operation Maintenance and Center-Radio

Standalone Dedicated Control Channel

Cell Broadcast Channel

16

CHAPTER-1

INTRODUCTION

1.1 Introduction to Mobile Communication:

In Telecom network conventionally each user is connected to the Telephone

exchange individually. This dedicated pair starts from MDF(Main Distribution

Frame), where it is connected to the appropriate Equipment point and ends at the

customer premises Telephone.

Fig 1.1. Access network

The connectivity from exchange to customer premises is called “Access

Network or Local Loop”, and mostly comprises of underground cable from

exchange up to DP(Distribution Point) and insulated copper wires (Drop Wires).

Later on this type of Access Network does not require separate authentication of

customer before extending services. Whenever the cable capacity has reached the

maximum, additional cable is laid to augment the capacity. Even though there are

advantages in introducing wireless connectivity in Subscriber’s loop, there are

certain issues to tackle viz,

1. Duplexing methodology.

2. Multiple Access methods.

3. Cellular principle or reuse concept.

4. Techniques to cope with “mobile” environment

17

1.2 Duplexing Methodology:

Duplexing is the technique by which the send and receive paths are separated

over the medium, since transmission entities (modulator, amplifiers, demodulators)

are involved.

There are two types of duplexing:

• Frequency Division Duplexing (FDD)

•Time Division Duplexing (TDD)

1.2.1 Frequency Division Duplexing (FDD):

Different Frequencies are used to send and receive paths and hence there will

be a forward band and reverse band. Duplexer is needed if simultaneous

transmission (send) and reception (receive) methodology is adopted .Frequency

separation between forward band and reverse band is constant.

1.2.2 Time Division Duplexing (TDD):

TDD uses different time slots for transmission and reception paths. Single

radio frequency can be used in both the directions instead of two as in FDD. No

duplexer is required. Only a fast switching synthesizer, RF filter path and fast

antenna switch are needed. It increases the battery life of mobile phones.

GSM and CDMA systems use Frequency Division Duplexing and corDECT

uses Time Division Duplexing.

1.3 Multiple Access methodologies:

The technique of dynamically sharing the finite limited radio spectrum by

multiple users is called Multiple Access Technique. By adopting multiple access

techniques, all users cannot get the services simultaneously and some amount of

blocking is introduced by the system. This is known as GOS (Grade of Service).

Generally there are three different types of multiple access technologies. They are

• Frequency Division Multiple Access (FDMA)

• Time Division Multiple Access (TDMA)

• Code Division multiple Access (CDMA)

18

1.3.1 Frequency Division Multiple Access (FDMA):

FDMA is a familiar method of allocating bandwidth, where a base station is

allowed to transmit one or more number of preassigned carrier frequencies and a

mobile unit transmits corresponding reverse channels. No other base station within

range of the mobile will be transmitting on the same forward channel, and no other

mobile within range of the base station should be transmitting on the same reverse

channel. Both the base station and the mobile usually transmit continuously during a

conversation, and fully occupy their assigned forward and reverse channels. No

other conversation can take place on these channels until the conversation is

completed.

Fig 1.2. Frequency division multiple access

1.3.2 Time Division Multiple Access (TDMA):

TDMA is a more efficient but more complicated way of using FDMA

channels. In a TDMA system, each channel is split up into time segments and a

transmitter is given exclusive use of one or more channels only during a particular

time period. A conversation, then, takes place during the time slots to which each

transmitter (base station and mobile) is assigned. TDMA requires a master time

reference to synchronize all transmitters and receivers.

19

Fig 1.3. Time division multiple access

1.3.3 Code Division Multiple Access (CDMA):

CDMA is fundamentally different than TDMA and FDMA whereas FDMA

and TDMA transmit a strong signal in a narrow frequency band but CDMA

transmits a relatively weak signal across a wide frequency band. Using a technique

called direct sequence spread spectrum, the data to be transmitted are combined with

a pseudo-noise code (a pre-determined binary sequence that appears random) and

transmitted broadband. CDMA under Interim Standard 95(IS-95) uses a bandwidth

of 1.25MHz. The pseudo-noise code (PN code) is a series of binary "chips" that are

much shorter in duration than the data bits. Since the chips appear to be in a random

pattern and there are many chips per data bit (in IS-95 there are 128 chips for each

data bit), the modulated result appears to normal (FDMA) receivers as background

noise.

1.4 Geographical areas of the GSM network:

The Fig 1.4 presents the different areas that form a GSM network.

Fig 1.4. GSM network areas

20

A cell identified by its Cell Global Identity number (CGI) corresponds to the

radio coverage of a base transceiver station. A Location Area (LA) is identified by

its Location Area Identity (LAI) number which is a group of cells served by a single

Mobile Switching Centre/ Visitor Location Register (MSC/VLR). A group of

location areas under the control of the same MSC/VLR defines the MSC/VLR area.

A Public Land Mobile Network (PLMN) is the area served by one network operator.

1.5 GSM Architecture:

Fig 1.5. GSM Architecture

The GSM network is divided into four major systems

Network and switching subsystem(NSS)

Operation and maintenance centre(OMC)

Base station Subsystem(BSS)

Mobile station(MS)

21

1.5.1 Network and switching subsystem (NSS):

The NSS is responsible for performing call processing and subscriber-related

functions. The switching system includes the following functional units:

Mobile Switching centre

Home location register

Visitor location register

Equipment identity register

Authentication centre

1.5.1.1 Mobile switching centre (MSC):

MSC performs all switching functions for all mobile stations located in the

geographic area controlled by its assigned BSS’s. Also it interfaces with

PSTN(Public Switched Telephone Network) with other MSC’s and other system

entities.

1.5.1.2 Home location registers (HLR):

The HLR is the main database of permanent subscriber information for a

mobile network. The HLR is an integral component of CDMA (code division

multiple access), TDMA (time division multiple access) and GSM (Global System

for Mobile communications) networks.

It contains

The identity of mobile subscriber called IMSI

ISDN(Integrated Services Digital Network) directory number of mobile

station

Subscription information on services

Service restrictions.

1.5.1.3Visitor location registers (VLR):

The VLR always integrated with the MSC. When a mobile station roams into a

new MSC area, the VLR gets connected to that MSC, which would request data

about the mobile station from the HLR. Later, if the mobile station makes a call, the

VLR will have the information needed for call setup without having to interrogate

the HLR.

22

1.5.1.4 Equipment identity registers (EIR):

Equipment identity register consists of identity of mobile station equipment

called IMEI( International Mobile Station Equipment Identity), which may be valid,

suspect and prohibited. The information is available in the form of three lists.

White list - the terminal which is allowed to connect to the network.

Black list - the terminal reported as stolen are not kept approved. They are not

allowed to connect to the network.

Grey list - The grey list consists of the IMEI numbers of the devices which are

outside of the white and black lists and of which electronic communication

connections are open.

1.5.1.5 Authentication Centre (AUC):

It is associated with the HLR. It stores an identity key called Ki for each

mobile subscriber. This key is used to generate the authentication triplets.

It is authenticated using a RAND(random number)

It consists of SRES(signed response)-to authenticate IMSI

Also, it has another key called Kc(Cipher key)- to cipher

communication over the radio path between the MS and the network.

1.5.2 Operation and Maintenance Centre (OMC):

The OMC function allows the operator to monitor and control the system as

well as to modify the conFiguration of the elements of the system. Not only the OSS

acts as a part of the OMC but also the BSS and NSS participate in its functions as it

is shown in the following examples:

• The components of the BSS and NSS provide the operator with all the

information it needs. This information is then passed to the OSS which is in charge

of analyzing it and control the network.

• The self-test tasks usually incorporated in the components of the BSS and

NSS, also contribute to the OAM functions.

• The BSC, which is in charge of controlling several BTS's is another

example of an OAM function performed outside the OSS.

23

1.5.3 Base Station Subsystem (BSS):

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

transmission and reception. The BSS comprises of BTS (Base Transceiver Station)

and BSC (Base Station Controller).

The characteristics of the Base Station System (BSS) are:

• The BSS is responsible for communicating with mobile stations in cell

areas.

• One BSC controls one or more BTSs and can perform inter-BTS and intra-

BTS handovers

• The BTS serves one or more cells in the cellular network and contains one

or more TRXs (Transceivers or radio units).

• The TRX serves full duplex communications to the MS.

The BSS can be divided into two parts:

1.5.3.1 The Base Transceiver Station (BTS):

The BTS corresponds to the transceivers and antennas used in 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 up to sixteen transceivers depending on the

density of users in the cell.

1.5.3.2 The Base Station Controller (BSC):

The BSC controls a group of BTS and manages their radio resources. A BSC

is principally in charge of handovers, frequency hopping, exchange functions and

control of the radio frequency power levels of the BTSs.

The BSS takes the authentication of OMCR (Operation Maintenance Control for

Radio Network). It maintains the entire network elements. OMCR is a centralised

monitor system for BSC, BTS and TCU(Transceiver Coding Unit).

1.5.4 Mobile Station (MS):

A Mobile Station consists of two main elements:

1.5.4.1 The Terminal:

There are different types of terminals distinguished principally by their power

and application:

24

• The 'fixed' terminals are the ones installed in cars. Their maximum allowed

output power is 20 W.

• The GSM portable terminals can also be installed in vehicles. Their

maximum allowed output power is 8W.

• The handheld terminals have experienced the biggest success in 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 0.8

W.

1.5.4.2 The SUBSCRIBER IDENTITY MODULE (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 not operational. 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.

1.6 Control channels:

One or more logical channels can be transmitted on a physical channel. There

are different types of logical channels. The type of logical channel is determined by

the function of the information transmitted over it.

The following types of logical channels exist:

Traffic channels

Broadcast channels

Common control channels

Dedicated control channels

Note that the first channel type carries speech and data, and the other types control

information (signalling).

25

1.6.1 TRAFFIC CHANNELS (TCH):

The traffic channels are used to send speech or data services. There are two

types of traffic channels. They are distinguished by their transmission rates. The

following traffic channels are provided:

1.6.1.1 TCH/F (Traffic Channel Full rate):

The TCH/F carries information at a gross bit rate of 22.8 Kbit/s (after channel

coding). The net (or effective) bit rate at the TCH/F is for speech 13 Kbit/s and for

data 12, 6 or 3.6 Kbit/s (before channel coding). The transmission rates of the data

services allow services which are compatible to the existing, respectively, 9.6, 4.8

and 2.4 Kbit/s PSTN and ISDN services.

1.6.1.2 TCH/H (Traffic Channel Half rate):

The TCH/H carries information at a gross bit rate of 11.4 Kbit/s. The net bit

rate at the TCH/H is for speech 5.6 Kbit/s and for data 6 or 3.6 Kbit/s.

1.6.1.3 TCH/EFR (Enhanced Full rate):

The EFR provides a voice coding algorithm offering improved speech quality.

The algorithm is fully compatible with a BSM(Base Station Manager) speech

quality. The algorithm is fully compatible with a GSM 13 Kbit/s speech channel.

The main benefit will be improved voice quality which offers prospects to compete

with PSTN networks. A TCH/F or a TCH/H may also be used to send signalling

information (for example call forwarding and short messages).

1.6.2 BROADCAST CHANNELS

The information distributed over the broadcast channels helps the mobile

stations to orient themselves in the mobile radio network.

The broadcast channels are point-to-multipoint channels which are only defined for

the downlink direction (BTS to the mobile station). They are four types:

26

1.6.2.1 BCCH (Broadcast Control Channel):

The BCCH gives information about the system configuration parameters (for

example Local Area Identification, Cell Identity and Neighbour Cells) the mobile

station. Using this information the mobile stations can choose the best cell to attach

to. The BCCH is also known as beacon.

1.6.2.2 FCCH (Frequency Correction Channel):

To communicate with the BTS, the mobile station must tune to the BTS. The

FCCH transmits a constant frequency shift of the radio frequency carrier that can be

used by the mobile station for frequency correction.

1.6.2.3 SCH (Synchronization Channel):

The SCH is used to time synchronize the mobile stations. The data on this

channel carries the TDMA frame number and the BSIC (Base Station Identity

Code).

1.6.2.4 CBCH (Cell Broadcast Channel):

The CBCH is used for the transmission of generally accessible information

(Short Message Service messages) in a cell, which can be polled by the mobile

station.

1.6.3 COMMON CONTROL CHANNELS

Common control channels are specified as point-to-multipoint channels which

only operate in one direction of transmission, either in the uplink or downlink

direction. There are three types:-

1.6.3.1 PCH (Paging Channel):

The PCH is used in the downlink direction for paging the mobile stations.

27

1.6.3.2 AGCH (Access Grant Channel):

The AGCH is also used in the downlink direction. A logical channel for a

connection is allocated via the AGCH if the mobile station has requested such a

channel via the RACH.

1.6.3.3 RACH (Random Access Channel):

The RACH is used in the uplink direction by the mobile stations for

requesting a channel for a connection. It is an access channel that uses the slotted

Aloha access scheme.

The Following Fig 1.6 gives an overview of the different types of logical

channels.

Fig 1.6. Channels of GSM network

1.6.4 DEDICATED CONTROL CHANNELS

Dedicated control channels are full-duplex, point-to-point channels. They are

used for signalling between the BTS and a certain mobile station.

They are three types:

28

1.6.4.1 SACCH (Slow Associated Control Channel):

The SACCH is a duplex channel which is always allocated to a TCH or

SDCCH. The SACCH is used for transmission of signalling data, radio link

supervision measurements, transmit power control and timing advance data. Note

that the SACCH is only used for non-urgent procedures.

1.6.4.2 FACCH (Fast Associated Control Channel):

The FACCH is used as a main signalling link for the transmission of

signalling data (for example handover commands). It is also required for every call

set-up and release. During the call, the FACCH data is transmitted over the allocated

TCH instead of traffic data; this is marked by a flag called a stealing flag. The

process of stealing a TCH for FACCH data is called pre-emption.

1.6.4.3 SDCCH (Stand-alone Dedicated Control Channel):

The SDCCH is a duplex, point-to-point channel which is used for signalling

in higher layers. It carries all signalling between the BTS and the mobile station

when no TCH is allocated. The SDCCHs are used for service requests (for example

Short Message Service), location updates, subscriber authentication, ciphering

initiation, equipment validation and assignment to a TCH. The net SDCCH bit rate is

about 0.8 Kbit/s.

1.7 Telecom Signalling Mechanism:

Before initiation of a call, signalling is the first process in telecom network. In

wired network, signalling is the mechanism for end to end process. Signalling

System7 (SS7) is architecture for performing out-of-band signalling in support of the

call-establishment, billing, routing, and information-exchange functions of the public

switched telephone network (PSTN). It identifies functions to be performed by a

signalling-system network and a protocol to enable their performance. There are two

types of signalling mechanism such as Common Channel Signalling(CCS) and

Common Associate Signalling(CAS).

29

At present, CCS7 signalling is the leading signalling mechanism because traffic

handling capacity is high since separate bandwidth is given for each process hence

timeslot is not wasted.

As users of the PSTN, signalling is exchanged with network elements all the

time. Examples of signalling between a telephone user and the telephone network

include: dialling digits, providing dial tone, accessing a voice mailbox, sending a

call-waiting tone, dialling *66 (to retry a busy number), etc. SS7 is a means by

which elements of the telephone network exchange information. Information is

conveyed in the form of messages.

Fig 1.7 CCS7 signalling network architecture

The architecture of CCS7 protocol is based on the OSI layer whereas Level-1.

Any node with the capability of handling CCS7 is termed a Signalling Point. The

direct interconnection of two signalling points with CCS7 uses one or more

signalling links. Level 1 of the 4-level structure defines the physical, electrical and

functional characteristics of the signalling link. Defining such characteristics within

level 1 means that the rest of the signalling system (level 2 to 4) can be independent

of the adopted transmission medium. Any changes within level1 do not affect the

higher levels and also the interface between levels 1 and 2 is kept constant. In a

30

digital environment, usually the physical link is a 64 Kbps channel. This is typically

within a digital transmission system using pulse-code modulation (PCM). Other

types of link (including analogue) can be used without affecting levels 2 to 4.

Level 2 defines the functions that are relevant to an individual signalling link,

including error control and link monitoring. Thus, level 2 is responsible for the

reliable transfer of signalling information between two directly connected signalling

points. If errors occur during transmission of the signalling information, it is

responsibility of level 2 to invoke procedures to correct the errors. Such

characteristics can be optimised without affecting the rest of the signalling system,

provided that the interfaces to levels 1 and 3 remain constant.

The functions those are common to more than one signalling link, i.e.

signalling network functions and „signalling network management‟ functions.

When a message is transferred between two exchanges, there are usually

several route that the message is transferred between two exchanges, there are

usually several routes that the message can take including via a signal-transfer point.

The message-handling functions are responsible for routing of the messages Through

the signalling network to correct exchange. Signalling network management

functions control the configuration of the signalling network. These functions

include network reconfigurations in response to status change in the network. For

example, if an exchange within the signalling network fails, the level 3 of CCS7 can

re-route messages and avoid the exchange that has failed.

Message Transfer Point (MTP) Levels 1 to 3 constitute a transfer that is

responsible for transferring information in messages from one signalling point to

another. The combination of level 1 to 3 is known as the message transfer point

(MTP). The MTP controls a number of signalling message links and network

management functions to ensure correct delivery to appropriate exchange in an

uncorrupted form and in the sequence that they were sent, even under failure

conditions in the network.

31

Level 4 comprises the „user parts‟. The meaning of the messages transferred

by the MTP and the sequence of actions for a particular application is defined by the

„user parts‟. A key feature is that many different user parts may use the standardised

MTP. Hence, if new requirements arise, that had not been foreseen previously, the

relevant user part can be enhanced without modifying the transfer mechanism or

affecting other user parts. Three user parts have been defined, the Telephone User

Part (TUP), the ISDN User Part (ISUP) and the Data User Part (DUP). Along with

SCCP, this provides the Network Layer functionalities of the OSI model. The user

parts of NSP are Operations and Maintenance Application Part (OMAP) and Mobile

Application Part (MAP). Signalling connection control Part (SCCP) The Signalling

Connection Control Part (SCCP) has the functions of the network as well as the

transport layers of the CCS7 protocol stack. Together with the MTP, it provides true

OSI transport layer capabilities. Unlike MTP which provides only datagram service,

SCCP provides connection –oriented and connection-less service as well. Thus,

while MTP is sufficient for circuit switched applications like TUP and ISUP, for

non-circuit related applications, such as database querying, the enhanced addressing

capability of SCCP is required. SCCP has a unique scheme of addressing and

routing based on Global Titles. SCCP utilizes the service OF MTP to route its

payload from one node to other. In addition to routing transaction related messages

submitted by the Transaction Capabilities Application Part (TCAP), SCCP also

segments and sequences large TCAP messages to fit into the MTP packet size. At

the distant node it is the responsibility of the peer SCCP to re-assemble the

segmented message.

Transaction Capabilities Application Part (TCAP) TCAP is an application part in the

CCS7 stack and is responsible for establishing dialogue with remote databases. It

carries the data of higher layers like INAP and MAP and invokes remote operations.

An operation at remote end requires a series of queries and responses as part of

a TCAP dialogue. TCAP layer is a compound layer in the sense that it is composed

of two sub-layers, namely, Transaction Sub layer (TSL) and Component Sub layer

(CSL). Transaction Sub layer is responsible for establishing, managing and

32

maintaining the integrity of the dialogue whereas Component Sub layer is

responsible for packing the upper layer message into a component and assigning an

invoke ID to the component. When CCS7 is specified as a signalling system, level 4

specifies a number of call-control functions. Indeed, the circuit-related mode of

CCS7 is so closely associated with controlling the set-up and release of physical

circuits that it is essential that some aspects of call control are defined within the

user part specification in order to optimise the procedures that are adopted.

Fig 1.8. structure of ccs7 protocol

1.8 Project outline:

Chapter 2 briefs about the literature survey on the topic under study.

Chapter 3 gives the idea to the activity of achieving and maintaining the

required quality (best possible) as designed. It also involves in identifying potential

faults in the network and resolving them before they affect the network.

Chapter 4 deals about the physical set up of the hardware components with the

optimization software tool. It also demonstrates mobile station in various modes

under various BTS connection.

Chapter 5 talks about the conclusion which was arrived after implementing all

the steps and discuss about the scope for the future work.

33

CHAPTER-2

LITERATURE SURVEY

The literature survey is done based on reduction of call drops, performance of

existing handovers, concept of MIMO antennas and call block theory, optimization

issues, network quality and coverage of the GSM network. Based on the survey, this

project proposes the method of RF planning and optimization.

1. Effective frequency planning to achieve improved KPI's, TCH and

SDCCH drops for a real GSM cellular network.

The objective of this paper is to provide a quality

communication to maximum the number of users. To establish

the quality communication, they have been investigated KPI (key performance

indicators), TCH (traffic channel) and SDCCH (stand alone dedicated control

channel) drop on 93 GSM sites for a cellular operator in a city of India. This paper

found a significant improvement in KPI's, TCH drop and SDCCH drop which

performs the previous frequency plan. TCH drop in NBH period is improved by 15

%, SDCCH drop in NBH (national busy hour) period is improved by 6 %. In this

paper, during BBH (bouncing busy hour) period as per TRAI (telecom regulatory

authority of India) guideline TCH drop ≤ 2 % is improved by 47 % and SDCCH

drop ≤ 2 % is improved by 43 % with respect to previous frequency plan has been

observed. It is relevant with customer satisfaction and enhances revenue for the

cellular operator.

2. Improving Call Setup Success Rate in GSM service area using RF

optimisation.

All GSM operators use Key Performance Indicators (KPIs) to judge

their network performance and evaluate the Quality of Service (QoS) regarding end

user perceived quality. KPIs are becoming increasingly important in the context

of network rollouts as well as within mature network optimization cycles. The

performance of the mobile network is measured based on several counters describing

34

the most important events over a measurement period. The KPIs are derived with the

help of these counters using different formulations. Call Setup Success Rate (CSSR)

is one of the most important KPIs used by all mobile operators.

3. A design approach to maximize handover performance success rate and

enhancement of voice quality samples for a GSM cellular network.

In this paper, a new approach has been designed to maximize handover

success rate (HOSR) and voice quality for a GSM cellular network.

To improve handover, neighbour list verification is done and unnecessary

neighbours are deleted. The results are found as overall HOSR (handover success

rate) in NBH (national busy hour) is improved by 11 % and during BBH (bouncing

busy hour) HOSR ≥ 95 %improved by 12 % in comparison of previous frequency

plan. Additionally, voice quality samples in DL (downlink) and UL (uplink) are

also improved. In NBH period DL RX (receiver) quality samples(0-

5) improved by 8% and UL RX quality samples (0-5) improved by 2% over previous

quality samples.

4. Reducing Call Drop in Mobile Cellular Communication by using MIMO

Antenna.

In this manuscript, call drops are reduced in mobile cellular communication

by using MIMO (multiple input and multiple output) antennas. The multiple reasons

behind the call drop is handover failure call drops, LAPD (Link Access Protocol on

D-channel) call drops and the radio frequency call drops. A novel approach to

solving these problems of call drops has been discussed by using MIMO antenna.

5. Impact of mobility on call block, call drops and optimal cell size in small

cell networks.

Assuming Poisson call arrivals at random positions with random velocities,

they have discussed about the characterization of handovers at the boundaries. In this

paper, the explicit expressions for call block and call drop probabilities using tools

from spatial queuing theory have been derived. These expressions are used to derive

35

optimal cell sizes for various profiles of velocities in small cell networks via some

numerical examples.

6. RF optimization issues in GSM networks.

The paper describes simple procedure for cellular network performance

estimation. In this paper, it has been analytically proved that optimization of an

existing cellular network using different methodologies and fine parameter tuning to

offer remarkable QoS to the end users can be performed. Optimization teams use

QoS reports in order to detect bad service quality areas. GSM network RF

performance evaluation is based on some major KPIs such as Call set up success

rate (CSSR), Handover Success Rate (HSR), Call Drop Rate (CDR) ASCOM tool.

7. Radio Frequency Optimization & QoS Evaluation in Operational GSM

Network.

This paper describes simple procedure for cellular network performance

estimation. Also, it has been analytically proved that we can optimize an existing

cellular network using different methodologies and fine parameter tuning to offer

remarkable QoS to the end users. The QoS reports based on different key parameters

such as Call set up success rate (CSSR), Call Drop Rate(CDR), Handover Success

Rate (HSR) and Traffic channel(TCH) congestion rate are duly beneficial for

Management team to compare network performance with the competitor’s one

called as benchmarking and to plan network evolution and strategy.

8. Cost Effective Coverage and Capacity Optimization in Wireless Cellular

Networks.

This paper presented a cost effective coverage and capacity optimization

method for connection oriented wireless cellular networks. The method allows

traffic overflows into neighbour networks when coverage and capacity limitations

arise within the home network. Extra RF spectrum licensure and deployment of new

network nodes are avoided by utilizing available resources at neighbour networks,

hence reducing both capital expenditure (CAPEX) and operational expenses

36

(OPEX). Performance evaluation of the model using MATLAB simulations reveals

significant improvement to the QoS offered to subscribers. Most techniques used for

coverage and capacity optimization results in the increase of network complexity,

radio frequency interferences.

9. A quantitative study of authentication and QoS in wireless IP networks.

In this paper, the impact of authentication on security and quality of service

(QOS) in combination of mobility and traffic patterns, which are critical to deliver

secure and efficient services in wireless IP networks are investigated. The system

performance with respect to authentication delay and call dropping probability at

different security levels based on a system model and challenging response

authentication mechanism are analyzed. Therefore, this work provides an in-depth

understanding of the authentication impact and reveals a framework for future

design of efficient authentication schemes. By taking traffic and mobility patterns

into account, a direct and quantitative relationship between the security and QoS

through the authentication can be established.

37

CHAPTER 3

RF OPTIMIZATION

3.1Introduction:

As voice and data networks continue to grow and expand worldwide, the

need for network deployment and test tools grows accordingly. Wireless service

providers need to attract new customers and retain existing customers while

maintaining the highest quality of service throughout their networks. Network

equipment manufacturers need to gain rapid acceptance of their infrastructure, which

requires fast and accurate optimization of the network. Optimization of the

network, expanding service coverage, and introducing new technologies and data

services are critical to the retention and acquisition of customers.

Fig 3.1. Process of Optimization

3.2 The optimization process:

Normally in the field, after planning the network and implementing it, based

on the feedback about the performance, field staff will go on optimization.

38

The optimization is needed due to the following reasons:

1. Inaccuracy of radio planning

Statistical variations in the path loss characteristics

Finite terrain database resolution

2. Implementation

Antenna radiation pattern and effective radiated power of antenna

Antenna pattern distortion

3. Environment

Seasonal environmental changes, e.g., trees, leaves

Environmental changes such as new highways, new buildings

The optimization is being carried out for meeting parameters such as

1. Coverage - Good signal level across the whole cell in maintained and

coverage holes within a cells service area must be minimized.

2. Interference - A reasonable level of interference must be contained at cell's

service area in order to provide a quality air-interface.

3. Handover Behaviour - The quality of the air-interface in a cell with respect

to handover behaviour is good, no unnecessary handovers, Rx quality at acceptable

level, BTS & MS use minimum transmit power.

4. Traffic Distribution - The quality of the air-interface in a cell with respect

to traffic distribution is good, maximum amount of traffic can be handled.

3.3 DRIVE TESTING:

As the optimization of the network is being carried out by traveling/ moving

on the route, the testing equipments and tools are taken by a vehicle and so got the

name as Drive Test.

39

For Optimization purpose, the drive tests are carried out on different

occasions.

Initial network coverage verification and benchmarking

Verification before and after changes

Locating and measuring interference

Locating areas where traffic problems exist

Locate coverage holes

Preventive maintenance

Simultaneous measurements of the other networks

Before taking drive test the entire geographical coverage area is divided into three

groups as Primary, Secondary and Miscellaneous routes as follows.

Primary route(Major Road level)

Includes all major roads, highways and wide thoroughfares

Secondary route(street level)

Includes all streets, subdivisions and compounds when accessible

Miscellaneous routes (in-building and special locations)

Includes golf courses, beach resorts, shopping malls, department stores, convention

centres, hotels and resorts.

And depending upon the different environment (areas), there may be

complaint on poor quality, call disconnection etc. for which we have to go for the

analysis of data. And the following Data Collection is possible in the drive tests

which are essential for network development

40

Fig 3.2. Optimization Process in real time GSM network

3.4 Working Equipment:

The following list is the typical example of drive test equipment components:

• Test Mobile phone

• Transceiver system

• GPS

• Visual display unit

• Laptop computer

3.5 Parameters measured:

CELL ID including BSIC, LAC, and time slot

RXLEVEL for the serving and the neighbour cells

RXQUALITY for the serving cell

BCCH, BSIC for the serving and the neighbour cells

TIMING ADVANCE

TRANSMIT POWER

GPS POSITION DATA

41

3.6 Frequently observed issues:

The frequently encountered performance problems during drive tests are:

1. Cell Dragging

2. Dropped Calls

3. Ping-Ponging

4. System Busy

5. Handover boundary

6. Blocked Calls

3.6.1 Cell Dragging:

Calls may drag a cell beyond the desired handover boundary. This might result

dropped calls or bad Rx quality.

Suggestions:

• Create an appropriate neighbour cell list

• Change HO parameters such as thresholds, margin, cell baring, etc

• Check serving cell’s cell identifier in the neighbour cell’s neighbour list

• Check neighbour cell’s BCCH, BSIC, LAC, Cell ID, etc

3.6.2 Dropped Calls

Dropped calls are caused by either RF environments or incorrect system

parameters

Suggestions:

• Check if an appropriate neighbour cell list is defined

• Check HO parameters

• Existing or new coverage holes

• Interference, Co-channels, Adjacent channels or External interference

• Serving cells might go down, coverage smaller as before

• Abnormalities such as call setup failure

3.6.3 Ping Ponging

The Server keeps changing and occurs as a result of bad audio quality

Suggestions:

• Interference, Co-channels, Adjacent channels or External interference

42

• Lack of dominant server

• Poor coverage

• Not optimal antenna configuration

3.6.4 System Busy:

The subscriber gets System busy on several call attempts and site appears

consistently on the traffic.

Suggestions:

Short Term:

• Reduce the traffic on the congested cell/site. However, the proposed

changes must not create any unacceptable problems such as coverage holes, dropped

calls, etc short term solutions are re-design the antenna configuration, add additional

RTs, change BTS configuration

Long Term:

• Build a new cell site to off-load traffic

3.6.5 Handover Boundary:

Handovers do not occur at the desired HO boundary, the result is an

imbalance in traffic distribution across the system

Suggestions:

• Check if an appropriate neighbour cell list is defined

• Check HO parameters

• Inappropriate antenna configurations of the serving and neighbour cells

• Interference, Co-channels, Adjacent channels or External interference

• No TCH available (neighbour cells congestion)

3.6.6 Blocked Calls:

The call gets disconnected without the availability of the channels for call

process.

Suggestions:

Solve internal interference through checking frequency planning

43

After internal interference is excluded, the external interference with spectrum

analyzer should be located.

3.7 Solutions proposed:

AGILENT TEST DRIVE TOOL provides you the full suite of key

performance indicators spanning radio and handset environment

With these KPI’s and smart reporting, you can quickly identify anomalies and

then drill down to pinpoint the root cause.

It will reduce the time required to solve issues leading to greater productivity.

3.8 Summary

This chapter explained about the significance of the drive test and challenges in

the drive test. This test analyses the potential problems existing in the system and

provides solutions to them before they affect the network performance.

44

CHAPTER-4

AGILENT DRIVE TEST TOOL CONFIGURATION

4.1 Introduction:

Agilent technologies have introduced the industry’s first integrated test

solution that in a single protocol analysis tool, seamlessly combines mobile device

data captured from a RF interface and from a mobile terrestrial network. Rapid

growth in the number of subscribers and in-data network usage has challenged the

radio access network in both RF capacity and data throughput performance

measurements and without visibility to the air interface, network operators must

manually correlate data from independent drive test and protocol analysis tools.

Agilent’s E6474A drive test tool has revolutionized and simplified end to end

troubleshooting. The software allows users to correlate signalling procedures from

the air interface and radio access network interfaces in a single view to detect and

troubleshoot problems from the mobile phone to the network.

With the help of RF AGILENT test drive tool (ATDT) the intelligent data is

plotted in visual maps. With this we can easily see where the capacity parameters

exist in your radio access network by ATDT. This helps to plan the capital

expenditures to address areas that will give a best return on the investment done.

Features:

Cost effective

Extensive phone support

Comprehensive technology support

Easy, flexible alarms

Network performance improves as the maintenance cost go down

Fig 4.1. Overall processes

45

4.2 PARAMETERS TO MEASURE:

Rx level [Received signal level]

Rx Qual[Received signal quality]

SQI [Speech Quality Index]

Other factors

Rx level:

The power obtained from Base station to Mobile Station. The power level at

MS is measured in dBm or Steps. If it is in steps, convert to dBm by subtracting the

value of 110 from the Steps value to get in the form of dBm.

Fig 4.2. Signal level received from the BTS

RX Qual:

Received signal quality level is measured based on BER (bit error rate). The

value is between 0-7 and it is clear that the lower value better is the quality.

BETTER Table no.4.1 Received signal quality range

46

SQI:

The parameter used by TEMS to measure Speech Quality. SQI has been

designed to cover all factors that Rx Qual lack to measure.

SQI computation considers the factors:

the bit error rate (BER)

the frame erasure rate (FER)

data on handover events

statistics on the distribution of these parameters

Table no.4.2 Speech quality range

Other parameters:

FER

BCCH

BSIC

Hopping Sequence

C/I

TA

C1 (Path loss criterion parameter )

C2 (Cell reselection criterion parameter in hierarchical cell structure)

47

The Fig.4.3 shows that the call is on process. Also, it indicates the serving

neighbouring BTS, which are around the current serving BTS. The

ARFCN(Absolute Radio Frequency Channel Number) shows which carriers can

serve for the MS with maximum RxLev (Receiver level). The green colour depicts

the best power received from BTS to MS and yellow colour depicts the optimum

power received from BTS to MS.

Fig 4.3. Neighbours BSIC

The Radio parameters includes the Receiver Level, Receiver Quality,

FER(Frame Error Rate), SQI(Speech Quality Index), Transmitter power,

DTX(Discontinuous Transmission), TA(Timing Advance), C1 and C2, where C1

and C2 are the Cell Channel parameters, which is shown in Fig 4.4.

By standard, the RxLev should be between -60dBm to -104dBm, RxQual

should be within 0 and 7, FER must be always 0, SQI is between 0 and 30, Tx Power

should be 4 and 14, DTX must be always 0, TA should be 0 for good signal quality

and C1 and C2 should be always 0 to get high quality of the network. But in real

time GSM network, during drive test the results obtained are shown using different

colours, where green colour depicts the value for best quality, yellow depicts the

optimum and red colour depicts the poor quality of the network.

48

Fig 4.4. Radio Parameters

Fig 4.5 C/I Ratio

The C/I(Channel to Interference) ratio is the occurrence of interference

between the carriers and also between the sectors. Due to interference, the speech

quality will be decreased which tends to the poor quality of the network. The Fig 4.5

shows that the interference value for particular channel in real time GSM network,

which is depicted using green, yellow and red colours indicating best, optimum and

worst signals.

4.3 Hardware Requirements:

Hardware connection only after installing software

49

High speed direct connect Hub expands the serial communication

capabilities of computer

The computer and hub communicate via USB (Universal Serial Bus)

and the hub converts USB to serial ports (maxi. 6) for connecting

phones(2), digital Receivers(2) , GPS Receiver and also for providing

power to all devices, phone battery charging, phone audio monitoring.

The Fig 4.6 shows the physical setup of AGILENT tool with which the hotspot test

and drive test are performed. The equipments used are explained in the working

equipment section 3.2.

Fig 4.6 Physical setup

4.4 Process of configuration:

Step 1: Open the installed AGILENT E6474A software tool from the start menu

Step 2: Add the required hardware that are used in the working. The hardware is

Long mobile (Nokia 6121 WCDMA phone)

Short mobile (Nokia 6121 WCDMA phone)

GPS receiver

Step 3: Check the properties and allot the port numbers for the hardware added

Step 4: Probe all the hardware.

50

Probing refers to the establishment of the logical connection to the established

physical connection in the step 2

Step 5: Add the map

For our project we considered the TN map which is already provided by

the software as per the requirements of area to be considered. The Parameters-

RXLevel(Sub) and RXQuality(sub) are to be dragged into the map

Step 6: Add cell site

For the map we added in the Step 5 we need to consider some area for

the study of parameters. So we considered area of Chennai as the region for the cell

site. These cell sites are to be embedded in the map

Step 7: Call control

With this step we establish a test bench platform for the functioning and

controlling of the long and short calls

Step 8: Add data items

In this we open the dialogue boxes of our study and observe the

variations of the parameters during the call process. The various data items added are

Call Status

GSM 3GPP

GSM servers and neighbours

Step 9: The following properties are checked and corrected(if needed) before going

for the execution

Property Long call Short call

Name Call control Call control

Active Yes Yes

51

Number of times 999 999

Wait time 5sec 5sec

Auto-dial Yes Yes

Call status Yes Yes

Immediate dial Yes Yes

Continuous call Yes No

Call duration - 25sec

Call setup 20 25

Call number 334455 334455

Auto answer No No

Com-port assigned Any port Any port

Table no.4.3 Properties

Step 10: Execute in the log mode to record the values and to start the process of call

processing.

4.5 MS mode of the drive test:

4.5.1 In IDLE mode:

The IDLE mode represents that along the drive test activity, the MS is

“ON” but no call occurs without any channel allocation.

52

Fig 4.7 snap shot of MS in IDLE mode

The Fig 4.7 represents the MS on ideal mode. Here, no channel is assigned for

call process. The receiver Level from BTS for the initiation of call can be measured

during this mode. The ARFCN and BSIC numbers can also be measured as an

additional parameter in this mode.

4.5.2 Dedicated/continuous/long call mode:

The characteristics of long call includes:

Before starting the route, call the drive test number.

And only stop the call when the route (drive test) is finish.

Also used to see the quality and coverage of the network( Reliable for

Call drop).

53

Fig 4.8 Snap shot of MS in long call

The Fig 4.8. shows the Long Call process of the MS. Here, the duration of the call is

not specified. The Red colour in the map indicates the route of the drive test.

4.5.3 Sequential/QoS/Short calls Mode:

Before starting, the route creates call sequence, for example: create call for 70s and

idle for 10s. Along the drive test, play this sequence until the route is finished.

54

Fig.4.9 Snapshot of MS in short call mode

The Fig 4.9. shows the Short Call process of the MS. Here, the duration of the call is

specified. The MS automatically redials to the server after the stipulated time period.

The Red colour in the map indicates the route of the drive test.

55

4.6 Receiver Quality Plot:

Fig.4.10 Plot of receiver quality

56

The Fig 4.10 shows the receiver quality of the network. The receiver quality of the

network lies between 0 and 7. The green, yellow and red colour indicates the best,

optimum and poor receiver quality respectively.

4.7. Receiver Level Plot:

Fig 4.11 Plot of received signal level

57

The Fig 4.11 shows the receiver level of the network. The receiver level of the

network lies between -60 to -104 in practice. The green, yellow and red colour

indicates the best, optimum and poor receiver quality respectively.

58

CHAPTER-5

RESULTS AND DISCUSSION

LONG CALL AND SHORT CALL ANALYSIS USING AGILENT TOOL

Two mobile phones and a GPS receiver are interfaced with the laptop and

the quality of calls and the network performance are measured using AGILENT

E6474A tool. Drive test is carried out in a moving vehicle for call of various

duration classified as long call and short call using the setup connected to the server.

The communication link of the mobile phones in the test setup (i.e. between the

current location and the corresponding BTS) and its linkage with the neighbourhood

BTS during call establishment are visualized through the map displayed in the tool

using GPS. During the call, important parameters like the received signal strength,

quality of received signal and channel assignment are monitored using the setup. In

Fig 5.1 the red line represents the route undergone for drive test with BTS

connection.

Fig 5.1 GPS Location with BTS Connection

59

The GPS Location with BTS connection in Fig 5.1 shows the caller or

subscriber location and its link with the BTS based on various QoS parameters. Here

the subscriber is located near Meenambakkam and connected with Meenambakkam

BTS which is highlighted in red colour indicating the GPS location with BTS

connection. The caller or subscriber is connected to that particular BTS because the

signal strength of that BTS is high compared to the neighbouring BTS.

GPS location with BTS connection after handover in Fig 5.2 shows that the

caller or subscriber is connected to St.Mount BTS due to signal strength variation

during mobility of the subscriber from one BTS to another BTS. As the subscriber

penetrates deeper into the neighbouring cell, the signal strength of the

communication link between the subscriber and St.Mount BTS has been increased

compared to that with Meenambakkam BTS. So the call is handedover to St.Mount

BTS from the current BTS (i.e. from Meenambakkam BTS to St.Mount BTS).

Fig 5.2 GPS Location with BTS Connection after Handover

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Fig 5.3 Before Optimization

Using Agilent E6474A tool, the details of the connected BTS and the quality

of call established are recorded in the form of snap shot. The quality parameters are

evaluated in terms of total number of calls attempted, number of Blocked calls,

number of dropped calls and number of good calls. Fig 5.3 shows the screenshot of

long call connectivity between mobile devices before optimization process. It is

found that the number of dropped calls is high out of the total calls and is due to

insufficient carriers allocated for the subscribers in the current location. This

situation can be modified after optimization with increased carriers in that particular

BTS

45

Fig 5.4 After Optimization

A similar drive test is executed in the same route after implementing the

solution as mentioned above. It is clearly shown in Fig 5.4 that after optimization

process, the lesser number of dropped calls has been drastically reduced because of

the increased availability of carriers for the subscribers in the corresponding BTS.

With the observations carried out using AGILENT TOOL, proper optimization has

been implemented in the BTS under test.

ANALYSIS AND INFERENCE:

DROPPED CALLS:

Before Optimization

After Optimization

Fig 5.5. Analysis of dropped call before and after optimization

46

BLOCKED CALLS:

Before Optimization

After Optimization

Fig 5.6. Analysis of blocked call before and after optimization

GOOD CALLS:

Before Optimization

After Optimization

Fig 5.7. Analysis of good call before and after optimization

RECEIVED SIGNAL QUALITY:

Before Optimization

After Optimization

Fig 5.8. Analysis of received signal quality before and after optimization

46

RECEIVED POWER LEVEL:

Before Optimization

After Optimization

Fig 5.9. Analysis of received power before and after optimization

From the observations tabulatedfor long call and short call during drive test

using AGILENT TOOL setup, the parameters such as dropped calls, blocked calls and

good calls before and after optimization are geographically represented in Fig 5.5, Fig

5.6 and Fig 5.7. It is obvious that the dropped calls and blocked calls has been

drastically reduced with a significant increase in good calls has been reported by

increasing the carriers from 3/3/3 to 5/5/5, the call rate has been improved to a greater

extent. As call rate increases, the quality of the network also gets improved. As

expalined in section 3.6, with the parameters such as dropped calls, blocked calls and

good calls, the performance measures like HOSR(Handover Success Rate),

TCH(Traffic Channel), CDR(Call Drop Rate) and CSSR(Call Setup Success Rate) are

obtained from OMCR report generated at base station. As explained in section 4.6 and

4.7. the receiver quality and receiver level meets its optimum range by increasing the

carriers and is shown in Fig 5.8 and Fig 5.9.

Fig 5.10 OMCR report before Optimization

46

Fig 5.11 OMCR report after Optimization

From the OMCR report generated, which is shown in Fig 5.10 and Fig 5.11 for the

network parameters under test are compared before and after optimization. The results

shows a promising improvement in HOSR, TCH, CDR and CSSR values. On analysis

made, the results are promising that HOSR rate gets improved from 96.93% to

98.19%, TCH is reduced from 0.88% to 0.2%, CDR decreased from 0.252% to 0.24%

whereas CSSR showed its improvement from 99.37% to 99.69%.

47

CHAPTER-6

CONCLUSION AND FUTURE ENHANCEMENT

This project work describes an empirical study focusing on the performance of

real time GSM network in Chennai zone. Specifically, the combination of KPIs such as

HSR, CSR is employed. The analysis on call establishment and call quality is made by

the use of drive test done by AGILENT tool setup. By increasing the number of

carriers from 3\3\3 to 5\5\5 in each sector, 38 more subscribers are benefitted by the

GSM network under test during peak hours with a great improvement in dropped calls,

blocked calls, good calls, receiver quality and receiver level. The analysis results varies

time to time as the network utilizes an unreliable media. In spite of this unreliability,

practically an optimum range of call drop rate for both long and short calls has been

assured after optimum number of carriers has been used.

In this work, a new approach has been designed to maximize handover success

rate (HOSR) and voice quality for a GSM cellular network. To improve handover,

neighbour list verification is done and unnecessary neighbours are deleted. The results

are found as overall HOSR (Handover Success Rate) is increased to 98.19%,

TCH(Traffic Channel) reduced to 0.2%, CDR(Call Drop Rate) has been reduced to

0.24% and CSSR(Call Setup Success Rate) has improved to 99.69% in comparison of

previous frequency plan. Additionally, the improvement in voice quality samples in

DL (downlink) and UL (uplink) has also been visualized during test performance.

In addition, it describes simple procedure for cellular network performance

estimation. Also, it has been analytically proved that the existing cellular network can

be optimized using different methodologies and can be tuned to offer remarkable QoS

to the end users. These reports also helps us to enhance coverage, improve quality and

increase capacity in the days to come. A mobile service providers can also set his own

QoS as targets based on the KPIs in order to ensure end user satisfaction. QoS reports

48

based on different KPIs are duly beneficial for management team to compare network

performance with the competitor’s one and to plan proper network strategy.

Future Enhancement

In future, there is an opportunity to improve the network performance by focusing on

the various other factors such as the missing neighbour relations, proposing new sites or

sector additions with before & after coverage plots, proposing antenna tilt changes,

proposing antenna type changes, BTS equipment/filter change, re–tuning of interfered

frequencies, base station identity code/BSIC changes, adjusting handover margins (Power

Budget, Level, Quality, and Umbrella HOs), adjusting accessibility parameters (RX Lev

Acc Min, etc.,), changing power parameters, Tower Mounted Amplifier/TMA adds.

Moreover, it is hereby strongly recommended that all mobile operators must ensure a

better QoS up to certain threshold and baselines in order to satisfy official regulatory bodies

who penalize operators in case of customer complaints regarding service quality.

Hence, during radio network planning, it is suggested to all mobile service providers

that they must divert attention towards better network dimensioning and topology, allocated

band scanning, traffic prediction and modelling, network operational expense (OPEX), and

network parameter settings to avoid subsequent issues during optimization phase. Secondly,

end users require stringent QoS, which compels cellular service providers to optimize

network performance to meet revenue and commercial targets as well.

49

REFERENCES

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Wiley & Sons Ltd,.

[2] ITU-T recommendation G. 1000 (2001), Communication quality of service: A

framework and definition.

[3]Bilal Haider, M Zafrullah Khan, M.K.Islam, "Radio Frequency Optimization and QOS in

operational GSM network".

[4]S.Kyriazakos,G.Karetsos,E. Gkroustiotis, C. Kechagias, P. Fournogerakis (2001),

"Congestion Study and Resource Management in Cellular Networks of present and Future

Generation", IST Mobile summit, Barcelona, Spain.

[5]Jens Zander (2001), "Radio Resource Management for Wireless Networks". Artech

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[6] Wireless Communications, Principles and Practice, 2nd edition, Theodore S. Rappaport,

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optimisation", Electronics, Computer and Computation (ICECCO), 11th International

Conference.

[8]Singh,P.; Kumar,M.; Das,A., (2014), "Effective frequency

planning to achieve improved KPI's, TCH and SDCCH drops for a

real GSM cellular network", Signal Propagation and Computer Technology (ICSPCT), .

[9] Singh, P.; Kumar, M.; Das, A., (2014), "A design approach to maximize handover

performance success rate and enhancement of voice quality samples for

a GSM cellular network", Signal Propagation and Computer Technology (ICSPCT).

50

[10] Rohit Das1 , Vikas2 , Hrishikesh Narayan Tripathi, (2014), "Reducing Call Drop in

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[14] Bilal Haider, M. Zafrullah and M. K. Islam. (2009), "Radio Frequency Optimization &

QoS Evaluation in Operational GSM Network", in the Proceedings of the World Congress

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[16] Liang, W. ; Dept. of Electr. & Comput. Eng., North Carolina State Univ., Raleigh, NC,

USA ; Wenye Wang, (2005), "A quantitative study of authentication and QoS in wireless IP

networks" in the proceedings of INFOCOM, 24th Annual Joint Conference of the IEEE

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[17] Osahenvemwen, O.A. and Ikheba, O.S (2015), "Evaluation of QoS in Mobile

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Telecommunications , Vol- 6, Issue 11.

51

ACKNOWLEDGEMENT

I would like to express my special thanks of gratitude to my guide Mr.K.RAMESH (SUB-

DIVISIONAL ENGINEER) from RGMTTC (Rajiv Gandhi Memorial Telecom Training

Centre) of BSNL (Bharat Sanchar Nigam Limited) at Chennai, who gave the valuable

guidance for the project which was like golden opportunity to do the wonderful work on this

project, which also helped me in doing lot of work in finalizing this project within the

limited time frame.

52

LIST OF PUBLICATIONS

Presented a paper titled " ANALYSIS OF GSM CALL FLOW WITH SS7

MESSAGES & OPTIMIZATION IN GSM NETWORK " in the IEEE Sponsored

International Conference On Innovations In Information, Embedded And

Communication Systems (ICIIECS '16) during 17 & 18 March 2016 at Karpagam

College of Engineering, Coimbatore.