Gsm Evalation

Executive summary

GSM network is globally accepted standard for digital cellular system. The continuous

performance evaluation of the network is a must for better quality service. Using the Key

Performance Indicators (KPIs), to judge network performance and evaluate the Quality of

Service is a major task that has to be done for every GSM network. In this project, the main

target is to evaluate the performance of the GSM network of BAHIR DAR city using KPI and

drive test. The methodology used for this project starts with the study of the current

operational GSM network of Bahir-Dar city. And then collection of data from nearby telecom

station and from sites using drive test equipment. The analysis of the gathered data is the next

step to be done for this project. At last possible solutions are suggested based on the on the

result of KPI and drive test.

1

List of Tables:

Table 2.2 Bahir Dar city GSM network Sites

Table 2.1 GSM Frequency Allocation

List of figures:

Figure 2.1 Relation between areas in GSM

Figure 2.2 Frequency Reuse

Figure 2.3 Logical channel classifications

Figure 2.4 GSM network system block diagram

Figure 2.5 Mobile Station

Figure 2.6 Site Sectorization

Figure 2.7 Base Station Controllers

Figure 2.8 Network plan of Bahir Dar city GSM network

2

Chapter 1

Introduction

1.1. Background

In this day and age, many people‘s need to be accessible everywhere, whether they're at work

or play, in the office or at home. To meet this demand, the GSM standard (Global System for

Mobile Communications) for mobile telephony was introduced in the mid-1980s. The actual

development of GSM started in 1982, when the Conference of European Posts and

Telegraphs (CEPT) formed a study group called Groupe Spécial Mobile. The group was to

study and develop a pan-European public cellular system in the 900 MHz range (GSM-900),

using spectrum that had been previously allocated. In 1989, the responsibility for GSM was

transferred to the European Telecommunication Standards Institute (ETSI), and the Phase I

recommendations were published in 1990. Commercial operation of GSM network was

started in mid-1991 in European countries. By the beginning of 1995, there were 60 countries

with operational or planned GSM networks in Europe, the Middle East, the Far East,

Australia, Africa, and South America, with a total of over 5.4 million subscribers. Today,

GSM is the most popular mobile radio standard in the world. To provide additional capacity

and enable higher subscriber densities, two other systems were added later: GSM1800 and

GSM1900. In 2011 it is estimated that technologies defined in the GSM standard serves 80%

of the global mobile market, encompassing more than 6 billion people across more than 220

countries and territories.

3

1.2. Problem Statement

Ethio-Telecom is the only company that provides telecommunication services in Ethiopia

which include GSM mobile communication. Bahir-Dar city Ethio-telecom is one of the

branches of Ethio-telecom in north western region. The current GSM radio network of Bahir-

Dar city faces problems such as coverage, capacity and quality. Coverage, capacity and

quality are the major points to be evaluated in this project. In order to investigate and ensure

the achievement of acceptable efficiency of the network, this project is proposed to work on

the performance evaluation indicators such as KPI and drive test.

1.3. Objective

Main Objectives

To evaluate the current performance of the GSM network and then to propose on

optimization techniques for quality improvement

Specific Objectives

To study and understand the radio part of GSM system in BAHIR-DAR city

To evaluate the performance of this GSM network

To propose techniques (ways) that is used to maximize the quality of services of the

radio network

1.4. Literature Review

(Fatma HAMDI). In this paper after a description of network GSM/GPRS in terms of

architecture and functionalities, a presentation of the principal indicators of quality of service

GSM/GPRS as well as the various parameters which allow the management of this QoS is

stated. The originality of this work comes from, the development of a methodology of

performance evaluation and optimization of network GSM/GPRS. This methodology, also

aids to locate the anomalies in the network and propose some recommendations.

(Bilal Haider, M. Zafrullah and M. K. Islam). In this paper, a well-established real GSM

radio frequency (RF) network performance evaluation is presented on the basis of four major

KPIs i.e., Call set up success rate (CSSR), Call Drop Rate (CDR), Handover Success Rate

4

(HSR) and Radio traffic channel (TCH) congestion rate. Different issues, findings, trials and

improvements have been summarized and observations/recommendations have been listed to

correlate the practical aspects of RF optimization, which affect the performance, and QoS of

an operational cellular network.

(Rami Ertimo). The main contribution of this paper is to clarify issues related to visualization

of complex data associated to configuration and performance management of the network.

This requires many different visualization channels. Logical network structure requires a tree-

like view to be able to visualize relationships between different network elements. A view to

present geographical information and performance data related to the network elements on

map is also needed. The last visualization channel required needs to present configuration and

performance attribute related information in a table like form. The needs and functions of all

these views are derived from the user needs related to capacity analysis in different domains.

The main emphasis of different views is in the inter-working functions to support the overall

workflow of capacity optimization. The expandability of the solution should also be stressed

to allow future capacity network analysis domains like core network, WCDMA and WiMax

and even other vendors besides Nokia Siemens Networks.

5

1.5. Methodology of work

The methodology to be used for this project starts from study of the current operational GSM

network of Bahir-Dar city. To evaluate the network, data need to be collected and analyzed in

order to identify its problem. Finally possible solutions are suggested for each problem.

Figure 1 shows block diagram of the methodology used under this study.

End of study

6

Study of Bahir-Dar GSM network

Network evaluation

KPI Parameter Derive Test

Problem Description

Data collection and analysis

Solution Suggestion

Study the Overall GSM System of Bahir-Dar city

This is the first step of our project. In this step we study about GSM network system specifically the

Bahir-Dar one. Since our project mainly concerned on the radio part of the GSM network, our study

focused on this part.

Data Collection and Analysis

Data of the network, which is record on the network management system (NMS), is collected from

the main telecom office. The data collects the parameters information of the radio network part which

can used to find the causes for the failure of the network.

Network Evaluation

After data collection, the next step is analyzing this data by comparing the network parameters with

the key performance indicators (KPIs). Depending on the analysis result, the problems that occur on

the network are identified which cause its failure.

Solution Suggestion

This is the final stage of the evaluation process. In this part we suggest solutions for the problems that

are identified in the above step.

1.6. Assumptions

Peak hour NMS statics data are used in the evaluation

4 standard KPI parameters are used since they are more general and are benchmarking

parameter to achieve remarkable QoS

7 day average percentage of KPIs are used in the evaluation

Threshold values of KPI are compared with the average value that are used in the

evaluation

7

1.7. Project organization

This project is organized in to three chapters. In chapter One, it provides general background

information about GSM network. Chapter two gives general information about GSM network

in terms of geographical network structure, frequency reuse concept, Frequency bands used

and the radio channels. And it also provides overview of Bahir Dar city GSM network.

Chapter three provides an insight into network performance management and quality of

service (QoS) of GSM network. It identifies the components of QoS and the available

mechanisms to analyze and evaluate them. This part also identifies important KPIs and drive

test that need to be monitored and optimized.

8

Chapter Two

2. GSM Systems Overview and Architecture

2.1. GSM Systems Overview

2.1.1. GSM Geographical Network Structure

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. As subscribers move through the network, these

structures are used to monitor their location.

GSM Service Area: The GSM service area is the entire geographical area in which a

subscriber can gain access to a GSM network. The GSM service area increases as more

operators sign contracts agreeing to work together.

Figure 2.1 Relation between areas in GSM



9

Cell: A cell is the basic unit of a cellular system and is defined as the area of radio

coverage given by one BS antenna system. Each cell is assigned a unique number called

Cell Global Identity (CGI). In a complete network covering an entire country, the

number of cells can be quite high.

Location Area (LA): A Location Area (LA) is defined as a group of cells. Several cells

can compose a location area that can be set by the network operator. Within the network

a subscriber’s location is linked to the LA in which they are currently located. The

identity of the current LA is stored in the VLR. A location area can be associated with

one or more BSCs but belong to on MSC.

MSC Service Area: An MSC service area is made up of a number of LAs and

represents the geographical part of the network controlled by one MSC. In order to be

able to route a call to an MS, the subscriber's MSC service area is also recorded and

monitored. The subscriber's MSC service area is stored in the HLR.

PLMN Service Area: A Public Land Mobile Network (PLMN) service area is the entire

set of cells served by one network operator and is defined as the area in which an

operator offers radio coverage and access to its network. PLMN area is composed of one

or multiple MSC service areas and each country may have one or several of them.

2.1.2. Frequency Reuse

The concept of cellular systems is the use of low power transmitters in order to enable’s the

efficient reuse of the frequencies. If the transmitters of high power are used, there will be

interference between the users at the boundaries of the cells. However, the set of available

frequencies is limited and that is why there is a need for the reuse of the frequencies.

10


A frequency reuse pattern is a configuration of N cells, N being the reuse factor, in which

each cell uses a unique set of frequencies. When the pattern is repeated, the frequencies

can be reused. A group of cells called cluster. No channels are reused within a cluster. The

distance between the cells using the same frequency must be sufficient to avoid interference.

The frequency reuse increases the capacity in the number of users of a service provider.

2.1.3. GSM Frequency Bands

As GSM has grown worldwide, it has expanded to operate at four main frequency bands: 900, 1800,

1900 and 800. For best efficiency, GSM uses two multiple access methods, Time Division

Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA) systematically.

FDMA divides the allocated spectrum for each band up into individual carrier frequencies.

The carrier separation is 200 kHz. TDMA divided up the frequency into blocks of time and only

certain logical channels are transmitted at certain times. The time divisions in TDMA are known as

Time Slots. GSM allows for use of duplex operation. Each band has a frequency range for the uplink

(cell phone to tower) and a separate range for the downlink (tower to the cell phone). A channel

11

number assigned to a pair of frequencies, one uplink and one downlink, is known as an Absolute

Radio Frequency Channel Number (ARFCN). GSM Frequency Allocation is shown in table 2.1.


2.1.4. GSM Radio Channels

Physical Channels: Each timeslot on a TDMA frame is called a physical channel. Therefore,

there are eight physical channels per carrier frequency in GSM. Physical channels can be

used to transmit speech, data or signaling information. A physical channel may transmit

different messages, depending on the information that is to be sent.

Logical Channels: The different information carried on the physical channel is classified as

logical channel. Logical channels can also be divided into two types: traffic channels (TCH)

and control channels (CCH). There are a total of 12 logical channels in the system. Two are

used for traffic, nine for control signaling and one for message delivery. Figure 2.3 shows the

relationship between logical channels.

12

Figure 2.3 Logical channel classifications

Traffic Channels: The TCHs transmit voice and data service .According to the switching

mode, the TCH can be divided in to circuit switched channel and data switched channel.

There are two types of TCH: Full rate (TCH): transmits full rate speech (13kbits/s). Half rate

transmits half rate speech (6.5kbits/s).

Control Channels

Broadcast Channels (BCH)

It transfer broadcast message from BTS to MS. The BCH includes:

Frequency Correction Channel (FCCH): It is used for transmission information about

frequency correction of MS.

Synchronization Channel (SCH): It is used to transmit synchronization information on

the TDMA frame number and the Base Station Identity Code (BSIC) of the BTS.

13

Broadcast Control Channel (BCCH): It Broadcasts general information to BTSs. For

example, broadcast the local cell and neighboring cell information, and

synchronization (time and frequency) information on this channel.

Common Control Channels (CCCH).

The common control channel point to point bi-directional channel between the base station

and mobile station including:

Paging Channel (PCH): It is used on the down-link to broadcast the paging message

from the base station to the MS.

Random Access Channel (RACH): It is used on the up-link by the MS to reallocation

of an SDCCH, either as a Page request response or an access at MS calls origination

or registration.

Access Grant Channel (AGCH): It is used on the down-link to allocate an SDCCH or

a TCH to an MS.

Dedicated Control Channels (DCCH)

Dedicated channels are the traffic channels that transmit voice and data. Some dedicated

channels are used for the purpose of control. The DCCH includes:

Stand alone Dedicated Control Channel (SDCCH): It is dedicated point to point

signaling channel used for system signaling during call setup or registration. During

the establishment of call, the SDCCH support bi-directional data transmission and the

transfer of short text messages in idle mode.

Slow Associated Control Channel (SACCH): Control channel always assigned and

used with a TCH or an SDCCH. Measurement Reports from the MS to the BTS are

sent on the up-link. On the downlink the MS receives information from the BTS what

transmitting power to use and also instructions on Timing Advance (TA). Through

this channel, the base station send power control message and frame adjustment

message to the MS, and receive signal report and link quality report from the MS.

Fast Associated Control Channel (FACCH): Control through channel associated

with a TCH. Also referred to as Fast Associated Signaling (FAS), the FACCH works

14

in stealing mode. That is, 20ms of speech is replaced by a control message. It is used

during inter-cell handover signaling message between base station and MS. [5]

2.2. GSM System Architecture

A GSM network is made up of multiple components and interfaces that facilitate sending and

receiving of signaling and traffic messages. Figure 2.4 shows the general architectural

description of GSM network. It includes the following components and equipment:

Figure 2.4 GSM network system block diagram






15

2.2.1. Mobile Station (MS)

Mobile station is a station in the cellular radio service intended for use while in motion at

unspecified locations. It is made up of two parts, the handset and the subscriber identity

module (SIM). The SIM is a small smart card that is inserted into the phone and carries

information specific to the subscriber, such as, Service Provider Name (SPN), and Local Area

Identity (LAI). [5]


2.2.2. Radio Station Subsystem (RSS)

Base Transceiver Station (BTS): Base Transceiver Station is a fixed station in a mobile

radio system used for radio communication with the mobile stations. It provides the

physical connection to the mobile station through the air interface. They are located at the

center or edge of a coverage region, consists of transmitter and receiver antennas mounted

on top of towers. It handles speech encoding, encryption, multiplexing and

modulation/demodulation of the radio signals. It is also capable of frequency hopping. It

coordinates handoff and control functions. One BTS usually covers a single 120 degree

sector of an area. Usually a tower with 3 BTSs will accommodate all 360 degrees around

the tower. [5]

16


Base Station Controller (BSC): The BSC controls multiple BTSs. It handles allocation

of radio channels, frequency administration, power and signal measurements from the

MS, and handovers from one BTS to another (if both BTSs are controlled by the same

BSC). It reduces the number of connections to the Mobile Switching Center (MSC) and

allows for higher capacity connections to the MSC. [5]


2.2.3. Network Switching Subsystem

17

Mobile services Switching Center (MSC): The MSC performs the telephony switching

functions, that is, accomplishes the communication between the PLMN subscribers and

subscribers in the other networks. It implement the function such as the paging access of PLMN

subscribers, call connection, traffic control, billing and base station management.

Home Location Register (HLR): The HLR is a large database that permanently stores data

about subscribers. The HLR maintains subscriber-specific information such as the MSISDN,

IMSI, current location of the MS, roaming restrictions, and subscriber supplemental features.

Visitor Location Register (VLR): The VLR is a database that contains a subset of the

information located on the HLR. It contains similar information as the HLR, but only for

subscribers currently in its Location Area. There is a VLR for every Location Area.

Authentication Center (AUC): The AUC database is connected to the HLR. The AUC

provides the HLR with authentication parameters; it is used to protect network operators against

fraud.

2.2.4. Operation and Support System (OSS)

Operation and Maintenance Subsystem (OMS): The Operations and Maintenance Center

(OMC) are the centralized maintenance and diagnostic heart of the Radio Station

Subsystem (RSS). It allows the network provider to operate, administer, and

monitor the functioning of the RSS. An OMS consists of one or more Operation and

Maintenance Center (OMC). The operations and maintenance center (OMC) is

connected to all equipment in the switching system and to the BSC. The

implementation of OMC is called the Operation and Support System (OSS). The OSS

also called Network Management Center (NMC) is the functional entity from which network

operators monitors and controls the system.

GSM network of Bahir Dar city

GSM network of Bahir Dar city is currently operating with 23 BTSs. In some sites GSM 900

and GSM 1800 are being used in the same place to increase the capacity of the system.

18

Typically two antennas are used per sector, at spacing of ten or more wavelengths apart. This

allows the operator to overcome the effects of fading due to physical phenomena such as

multipath reception. The location each BTS and the detailed map of the system are shown in

Figure 2.8. Each BTS station has a unique name, a unique identity numbers called LAC

(location Area Code) so as to be identified by the central office.

The BSC and MSC are located at the central office. The BSC is in charge of controlling and

providing the resources used by both the BTS and MS. It does Handover control, channel

assignments, collection of cell configuration data. NMS (Network Management System) is

used to control traffic and locate various faults during the live performance of the GSM radio

network. NMS is used basically for network maintenance.


The dots with the identity numbers signify the base transceiver station. The interconnection

of the distributed BTSs is either by optical fiber or by microwave link. The microwave link

19

interconnect will use small microwave antenna installed on each of BTS. The main aim of

interconnection with the base station controller is to monitor the status of each base

transceiver stations from the controller office. The tabulation below shows the sites with their

antenna frequency range that means 900 MHz and 1800 MHz. As we know that the higher

the frequency, the smaller will be the Wavelength ( λ = C/ f ,where c is speed of light i.e.

3*108 & f is the operating frequency ).Therefore the propagation distance traveled by the

Signal in GSM 1800 will always be less as compared to that in GSM 900. Hence, for similar

propagation conditions and clutter scenario the losses (Propagation losses & Building

penetration losses) experienced in GSM 1800 will be more than in GSM 900.Due to this

reason the number of sites planned to cover similar Area will be more in GSM 1800 as

compared to the number of sites in GSM 900. The lists of Bahir Dar city GSM network sites

are shown in table 2.2.

Site number Site name Frequency Band (in MHz)

1 Yibab 900 -

2 B.Academy 900 1800

3 B. Airport 900 -

4 B. Finance and Economy 900 1800

5 B. Azwa Hotel 900 1800

6 B.Kebele 900 1800

7 B.Kidanemihret 900 1800

8 B. Kobel 900 1800

9 B. Medhanialem School 900 1800

10 B.Kidane 900 1800

11 B.oss 900 1800

20

12 B.Peda 900 1800

13 B.SelamQIW Church 900 1800

14 B.tele 900 1800

15 B.Univeristy 900 1800

16 Bahnrabdl 900 1800

17 Bahgrdmgb 900 1800

18 B.Gion school 900 1800

19 Bahwassch 900 1800

20 B.Textile 900 1800

21 Bahdbnter 900 1800

22 Bahir dar new4 900 -

23 Bahir dar new 5 900 -


Chapter Three

Performance Evaluation of GSM Radio Network of Bahir Dar City

With the rapid growth of the GSM networks, providing high quality of service is a competitive advantage for a service provider. Quality of service is a measure of the reliability and usability of the telecommunications network. Quality of service can be characterized by such factors as contiguity of coverage, accessibility to the network, speech quality. To provide QoS Network operators must evaluate the performance of the existing network regularly against the threshold standard and take appropriate measure for improvement if they want to keep customers. In these project two Quality of Service (QoS) determinant tools mainly the Key Performance Indicators (KPI) and drive test are used for parameters related to voice and data to evaluate the existing GSM radio network performance of Bahir Dar city.

21

The performance of the radio network is measured in terms of KPIs and drive test related to voice quality, based on the statistics generated from the radio network.

Key Performance Indicators

Key Performance Indicators (KPI) describes the key system performance of the network. The operator provides the threshold KPIs through Network Management System (NMS). For radio network optimization, it is necessary to have decided on key performance indicators. These KPIs are parameters that are to be observed closely when the network monitoring process is going on. The following KPIs are more important parameters for GSM radio network evaluation & benchmarking to achieve remarkable QoS:

1. CSSR (Call Set up Success Rate).

2. CDR (Call Drop Rate).

3. HSR (Handover Success Rate).

4. TCH (Traffic Channel) Congestion Rate.

5. SDCCH (Standalone Dedicated Control Channel) congestion rate.

Call Set up Success Rate (CSSR)

The Call Setup success rate measures successful TCH assignments of total number of TCH assignment attempts. This indicator measures the ease in which calls are established or set up. The higher the value of CSSR, the easier it is to set up a call. For instance a CSSR of 71% means that out of every 100 call attempts, only 71 are successful while the remaining 29 are unsuccessful. CSSR can be calculated as:

CSSR= Number of unblocked call attempts

Total number of call attempts

Call Drop Rate (CD R)

A dropped call can be defined as one that gets terminated on its own after being established. A value of 7% of CDR means that, out of every 100 calls established or set up, 7 will drop before any of the calling parties voluntarily terminate the set up call. CDR is calculated using the expression:

CDR= Number of dropped call

22

Total number of call attempt

Handover Success Rate (HSR)

The handover success rate shows the percentage of successful handovers of all handover attempts. HSR can be calculated as:

HSR=[(CT07+CT08)/(CT09+CT10)]*100% [ ]

Where CT07 counts no. of incoming successful handovers

CT08 counts no. of outgoing successful handovers.

CT09 counts no. of outgoing HO requests

CT10 counts no. of incoming HO requests.

TCH Congestion Rate (TCHCR)

Rate of calls blocked due to resource unavailability. The higher this value, the relative difficulty it is in making a call. TCH congestion rate can be calculated as:

TCHCR = Number of TCH blocks *100%

No. of TCH attempt [ ]

SDCCH Congestion Rate

SDCCH congestion rate provides the ratio of failed SDCCH seizures due to busy SDCCH to the total requests for the SDCCH. SDCCH congestion rate indicates the failed requests for the SDCCH for various reasons. SDCCH congestion rate also indicates the status of the SDCCH resource utilization.

SDCCH congestion rate = Failed SDCCH seizures due to busy SDCCH x 100%

Total requests for the SDCCH

23

All cells report different measurement statistics about all relevant information, but the most significant key performance indicators threshold values that this project used in evaluating the network are tabulated in table.

KPI parameter Threshold

Call drops rate 2%

TCH congestion rate 2%

SDCCH congestion rate 0.5%

Handoff success rate 95 %

Call Set up Success Rate 90%

3.3 Derive Test (DT)

Drive test allow the mobile network to be tested and take the quality of service measures to judge the quality of service of the network. The testing process starts with selection of the ‘live’ region of the network where the testing needs to be performed, and drive testing path.

A test mobile system (TEMS) is a testing tool used to read and control the information sent over the air interface between the BTS and the MS. It can be used to measure radio coverage, RXQUAL, RXLEV and other parameters.

Drive test equipment used:

MS: a mobile supporting GSM with special software which is called trace mobile.

GPS (Global Positioning System): satellite system which provides users with location of the measurement point.

PC (portable personal computer): It is a computer equipped with interface carte RS 232 in order to make the link between the serial output of the MS and the serial port of the PC.

Equipment used for this project are:

Test terminal: Sony Ericsson

Analysis software: TEMS 11.0.4

24

Drive test measurement

Drive test tool offers the measurement of many indicators. Some of them are:

Time: It is system time of computer.

Cell name: It displays the name of the sector which is serving according to the cell file that is loaded in TEMS.

CGI: It stands for the Cell Global Identity which is unique for every sector of the site. It consists of MCC, MNC, LAC, and CI. MCC: Mobile Country Code 0 – 999 MNC: Mobile Network Code 0 – 99 LAC : Location Area Code 0 -65535 CI: Cell Identity 0 – 65535

Band: It tells in which Freq. Band mobile is operating e.g. GSM 900/ 1800.

BSIC (Base Station Identity Code): It is combination of Network Color Code (NCC) (0-7) & Base Station Color Code (BCC) (0 – 7).

Mode: It is shows in which state is mobile operating, Idle, Dedicated & Packet.

25

Hopping Channel: It shows that current sector is having hopping feature or not. Values are ‘Yes’ or ‘No’.

Hopping Frequencies: It displays number of frequencies on which mobile is allowed to hop.

RxLev: Receiving level in terms of dBm that mobile is receiving from the site. Range of -30 dBm to -110dBm.

RxQual: Quality of voice which is measured on basis of BER. Range of RxQual 0 -7.

FER: Frame Erasure Rate it represents the percentage of frames being dropped due to high number of non-corrected bit errors in the frame. It is indication of voice quality in network.

BER Actual: Ratio of the number of bit errors to the total number of bits transmitted in a given time interval. BER is a measure for the voice quality in network. Depending on BER RxQual is measured. E,g, BER 0 to 0.2 % corresponds to RxQual 0. Max. BER countable and useful is up to 12.8 % which corresponds to RxQual of max. 7.

SQI: SQI is a more sophisticated measure which is dedicated to reflecting the quality of the speech (as opposed to radio environment conditions). SQI is updated at 0.5 s intervals. It is computed on basis of BER and FER.

C/I: The carrier-over-interference ratio is the ratio between the signal strength of the current serving cell and the signal strength of undesired (interfering) signal components. It should be at least > 9.

TA: Value that the base station calculates from access bursts and sends to the mobile station (MS) enabling the MS to advance the timing of its transmissions to the BS so as to compensate for propagation delay. Value of 0 means MS in radius of 550m from BS.

Result and Analysis

Since it is correspondence to the time of heavy operation of network resources, the peak hour traffic is useful. So the first step in the analysis is that selecting the peak hour of the day. From the basic traffic measurement of Bahir-Dar TEL.NWR statistics the peak hour of the day is selected as shown in figurexxx.

26

From the figure xxx1 there is one peak that corresponds to 21:00 pm. All performance evaluation of this project is done based on this average peak hour network statistic data , since it is used to examine the performance of the radio network.by taking this consideration the 7 day average percentage of the KPIs are plotted and analyzed.

TCH Congestion represents the percentage of time that a TCH has not been used due to the lack of resources and restricts initiation of a call. TCH congestion increases as traffic request increases, which results in making the available number of TCH channel insufficient for meeting the required demand and prevents a new user to establish a call and increases blocked calls. Figure xxx2 shows the 7 day average percentage of cells with TCH congestion rate greater than the threshold value. From this 8 cells have TCH congestion rate greater than the threshold value.

27

Figure sites with TCH congestion rate greater than 2%

The percentage of sites whose TCH congestion rate values deviated from the recommended value is tabulated in Table xxx.

Site name TCH congestion rate

LAC20005 CI 14606 7.84%

LAC20005 CI 14618 12.89%

LAC20005 CI 14619 5.95%

LAC20005 CI 24607 8.43%

LAC20070 CI 24626 5.36%

LAC20005 CI 24627 2.16%

LAC20005 CI 34048 2.73%

LAC20005 CI 34465 2.32%

LAC20005 CI 14606 7.84%

Table cells TCH congestion rate

28

Handover success rate indicates the success of hand over when the mobile station moves from one

cell to another cell while a conversation is in progress. There are a total of 14 cells whose 7 day

average percentage Handover success rate deviates from the threshold. The plot is shown in figure

Figure Handover success rate of cells less than 95%

The percentage of sites whose hand off success rate values deviated from the recommended value is

tabulated in Table

Site name Handover success rateLAC20005 CI 34624 71.42%LAC20005 CI 34605 90.82%LAC20005 CI 34056 93.32%LAC20005 CI 34054 91.18%LAC20005 CI 34048 90.86%LAC20005 CI 24624 65.13%LAC20005 CI 24056 94.37%LAC20005 CI 24054 93.53%

Table cells handover success rate

In the network under study there are no cell sectors whose call drop rate, SDCCH congestion rate and Call Set up Success Rate values which deviated from the recommended value.

29

Abbreviations

AGCH Access Grant Channel

ARFCN Absolute Radio Frequency Channel Number

AuC Authentication Center

BCCH Broadcast Control Channel

BSS Base Station Sub-System

BTS Base Transceiver Station

BSC Base Station Controller

BSS Base Station Subsystem

BCCH Broadcast Control Channel

BSIC Base Station Identification Code

Conference of European Posts and Telegraphs (CEPT)

European Telecommunication Standards Institute (ETSI)

Fast Associated Control Channel (FACCH)

Frequency Correction Channel (FCCH)

FDMA Frequency Division Multiple Access

GSM Global System for Mobile Communication

HLR Home Location Register

ISDN Integrated Service Digital Network

KPI Key Performance Indicators

MS Mobile Station

30

MSC Mobile-service Switching Center

NSS Network Sub System

OMC Operation and Maintenance Center

OSS Operating Sub-System

PLMN Public Land Mobile Network

QoS Quality of Service

RACH Random Access Channel

PCH Paging Channel

SDCCH Stand alone Dedicated Control Channel

SACCH Slow Associated Control Channel

SCH Synchronization Channel

SMS Short Message Service

TDMA Time Division Multiple Access

Traffic Channels (TCH)

TBF Temporary Block Flow

VLR Visitor Location Register

31

Appendix A

M0MSCS23.ZTE..BDTEL.NWR-Basic Traffic Measurement(2011-12-30 00-00-00_2011-12-30 23-59-59)

Time Measurement Object Description

Times of Attempted Call

Times of Call Occupancy

2011-12-30 00:00:00

All types of calls 79672 79672

2011-12-30 01:00:00


2011-12-30 02:00:00


2011-12-30 03:00:00


2011-12-30 04:00:00


2011-12-30 05:00:00


2011-12-30 06:00:00


2011-12-30 07:00:00


2011-12-30 08:00:00


2011-12-30 09:00:00


2011-12-30 10:00:00


32

2011-12-30 11:00:00


2011-12-30 12:00:00


2011-12-30 13:00:00


2011-12-30 14:00:00


2011-12-30 15:00:00


2011-12-30 16:00:00


2011-12-30 17:00:00


2011-12-30 18:00:00


2011-12-30 19:00:00


2011-12-30 20:00:00


2011-12-30 21:00:00


2011-12-30 22:00:00


2011-12-30 23:00:00


33

References

[1] R. Mishra John Ajay. “Fundamentals of Cellular Network Planning and Optimizations

2G/2.5G/3G... Evolution to 4G”

[2] Kechagias, S.Papaoulakis, N.Nikitopoulos, D. Karambalis: “A Comprehensive Study on

Performance Evaluation of Operational GSM and GPRS Systems under Varying Traffic

Conditions”. IST Mobile and Wireless telecommunications Summit, 2002, Greece

[3] Jyri, H. (2007).Cellular Network Planning and Optimization. Helsinki University.

Retrieved November 7 2011 from

http://www.comlab.hut.fi/.../ Cellular _ network _ planning_and_optimization ..

[4] GSM .Retrieved Nov 18, 2011 .from http://en.wikipedia.org/wiki/GSM

[5] GSM Network Architecture .Retrieved November 14 from

http://www.gsmfordummies.com/architecture/arch.shtml

[6] Region 4 Network Topology

[7] From Mr. Samson who is network assistance officer and Mr.Ephinos who is a BSC

engineer in Ethio Telecom, Bahir Dar(NWR)

34

http://www.gsmfordummies.com/architecture/arch.shtml

http://en.wikipedia.org/wiki/GSM

http://www.comlab.hut.fi/.../Cellular_network_planning_and_optimization

Documents

Gsm Evalation