Analysis And Optimisation Of Inter-Cell Handover Dynamics In A GSM Network (A Case Study Of Airtel Kano, Nigeria)
ABSTRACT
Efficient Handover mechanism in a GSM network is one of the parameters critical to GSM
network service quality (QoS) and customer satisfaction. Handover is the process that transfers
an ongoing call from one cell to another as the users move through the coverage areas of the
cellular systems. This research focuses on analyzing and optimizing intercell handover dynamics
in Airtel Network in Kano. A three months call record sample data was used. Several cells in the
Airtel Network in Kano were investigated by profiling and analysing their performance using
standard mathematical relationships of Handover success rate, Call setup success rate, Blocking
probability, Call drop rate which are relevant Key Performance Indicators. Data was obtained in
Microsoft Excel format. Performance evaluation was carried out using Nigerian Communication
Commission (NCC) QoS standard for Macrocell as benchmark. The evaluation revealed that
seventy two percent (72%) of cells considered performed below NCC targets for Call Setup
Success Rate (CSSR), sixty four (64%) failed to achieve NCC targets for Handover Success
Rate (HSR) and sixty four percent (64%) failed to achieve Standalone Dedicated Control
Channel blocking rates targets, twenty one percent (21%) failed to achieve congestion targets.
Average call drop rate per cell was predicted to be six percent (6%). An optimal solution was
provided using dynamic cutoff priority channel allocation scheme, this improves performance of
handover dynamics when simulated. An object oriented simulation technique was employed
using a JAVA variant NETBEANS 6.1 because of its moderate system resource requirement,
fast and responsive user interface. The result showed that handover failure rate was reduced by
an average of Ninety percent (90%) for varying loads. System validation was achieved by
comparing the real and simulated load characteristics which have similarities. A correlation
coefficient was calculated using MATLAB to be 0.9122.
TABLE OF CONTENTS
Title Page … … … … … … … … i
Declaration … … … … … … … … ii
Certification … … … … … … … … iii
Acknowledgement … … … … … … … iv
Abstract … … … … … … … … v
Table of Contents … … … … … … … vi
List of Tables … … … … … … … … vii
List of Figures … … … … … … … … viii
List of Appendixes … … … … … … … ix
List of Abbreviations and Acronyms … … … … … x
List of Symbols … … … … … … … xi
1.0 INTRODUCTION … … … … … … 1
1.1 GSM System … … … … … … … 1
1.2 Handover Process … … … … … … 1
1.3 Motivation ………. …. …. … … … 2
1.4 Statement of Research Problems … … … … 3
1.5 Research Methodology … … … … … 4
1.6 Aims and Objectives of the Research … … … 5
1.7 Research Outline … … … … … … 5
2.0 THEORETICAL BACKGROUND AND LITERATURE
REVIEW … … … … … … … 7
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2.1 Introduction … … … … … … 7
2.2 Review of fundamental concepts … … … 7
2.2.1 Generic GSM System … … … … … 7
2.2.1.1 Basic cell structure … … … … … 8
2.2.1.2 Frequency Re-use Distance and Cluster Size … … 9
2.2.1.3 Co-channel Interference … … … … 11
2.2.1.4 Adjacent Channel Interference … … … 11
2.2.2 Handover Criteria … … … … … 12
2.2.3 Other Criteria of Handover Process … … … 13
2.2.3.1 Traffic … … … … … … … 13
2.2.3.2 Call and Handover Statistic … … … … 14
2.2.3.3 Velocity … … … … … … 13
2.2.4 Qualities of handover … … … … … 14
2.2.5 Handover challenges … … … … … 15
2.2.6 Types of Handover … … … … … 17
2.2.7 The Mobile Radio Channel Environment … … 20
2.2.8 Handover Methods … … … … … 22
2.2.8.1 Threshold Methods … … … … … 22
2.2.8.2 Hysteresis Methods … … … … … 22
2.2.8.3 Threshold with Hysteresis … … … … 23
2.2.8.4 Fuzzy Handover Algorithm … … … … 23
2.2.9 Ping Pong Handover … … … … … 23
2.2.10 Source Key QoS Performance Indicators … … 24
2.2.10.1 Call Setup Failure Rate … … … … 25
2.2.10.2 Call Drop Rate… … … … … … 25
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2.2.10.3 SDCCH Congestion Radio … … … … 25
2.2.10.4 TCH Availability … … … … … 26
2.2.10.5 Handover Success Rate … … … … 26
2.2.11 Handover Arrival Rates … … … … 27
2.2.12 Receiving Signal Strength Indicator … … … 28
2.2.13 Overview of Handover Schemes … … … 29
2.2.13.1 The Non-Prioritized Scheme … … … … 29
2.2.13.2 Prioritization Schemes … … … … 30
2.2.14 Channel Allocation … … … … … 31
2.2.15 Channel Allocation Schemes … … … … 34
2.2.15.1 Fixed Channel Allocation Scheme … … … 34
2.2.15.2 Dynamic Channel Allocation Scheme … … 35
2.2.15.3 Hybrid Channel Allocation Scheme … … … 36
2.2.16 Handover Management Scheme … … … 36
2.2.16.1 Channel Reservation Schemes … … … 37
2.2.16.2 Handover Queuing Scheme … … … … 39
2.2.16.3 Channel Transferred Handover Scheme … … 41
2.2.16.4 Sub-rating Schemes … … … … … 42
2.2.16.5 Generic Handover Scheme … … … … 42
2.2.16.6 Hybrid Handover Scheme … … … … 43
2.2.17 Evaluation of Handover Scheme … … … 43
2.2.18 Handover Decision Phase … … … … 45
2.2.18.1 Measurement Phase … … … … … 46
2.2.18.2 Initiation and Resource Allocation Phase … … 46
2.2.18.3 Execution Phase … … … … … 46
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2.2.19 Handover Protocols … … … … … 47
2.2.19.1 Network Controlled Handover … … … 47
2.2.19.2 Mobile Assisted Handover … … … … 48
2.2.17.3 Soft Handover … … … … … … 49
2.2.19.4 Mobile Controlled Handover … … … … 49
2.2.20 Analysis of Handover Algorithm … … … 46
2.3 Review of Similar Works … … … … 51
3.0 MODELING AND SIMULATION … … … 54
3.1 Introduction … … … … … … 58
3.2 Data Collection Methods … … … … 58
3.3 Table of NCC Bench Marks … … … … 58
3.4 Airtel Key Performance Indicators and their Target
Value … … … … … … … 59
3.5 Predicting Expected Call Dropping Probability from
a Cell … … … … … … … 60
3.6 Cutoff Priority Model Description … … … 61
3.7 Dynamic Cutoff Priority Channel Allocation Scheme 64
3.8 Integrated Algorithm: Dynamic Cutoff Priority
Channel Allocation Scheme (DCCAS) … … 64
3.9 Simulation Flow Chart … … … … 68
3.10 Simulation … … … … … … … 69
4.0 RESULTS AND DISCUSSIONS … … … 70
4.1 Introduction … … … … … … 70
4.2 Data Analysis … … … … … … 70
4.2.1 Call Setup Success Rate … … … … 72
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4.2.2 Handover Success Rate … … … … 73
4.2.3 Mean TCH Congestion and Mean SDCCH Blocking 74
4.3 Weekly Analysis of Calls KN002A or KN003A … 75
4.3.1 Behavioral Trend Effect of Traffic Load and SDCCH
Call drop on Intercell Handover in cells KN002A and
KN003A … … … … … … 78
4.3.2 Influence of Traffic Load and SDCCH call Drop on
Intercell Handover in Cells KN002A … … … 78
4.3.3 Influence of Traffic Load and SDCCH call drop on
Intercell Handover in Cell KN003A … … … 79
4.4 Comparing the influence of TCH Cell drop and
Congestion on Intercell Handover in KN002A and
KN003A … … … … … .. 81
4.4.1 Effect of TCH Cell drop and congestion and Intercell
Handover in Cell KN002A … … … .. 81
4.4.2 Effect of TCH Call Drop and Congestion on Intercell
Handover in Cell KN0003A … … … .. 82
4.5 Impact of Intercell Handover on Call drops … 84
4.6 Simulation … … … … … .. 87
5.0 Conclusion and Suggestion for Further Works … 91
5.1 Introduction … … … … … .. 91
5.2 Summary … … … … … .. 91
5.3 Limitation of the Study … … … … 93
5.4 Conclusion … … …. … … … 92
5.5 Recommendation on Areas of further Work … 93
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CHAPTER ONE
INTRODUCTION
1.1 GSM System
Global System for Mobile Communications (GSM) is a digital wireless network standard
designed by standardization committees from major European telecommunications
operators and manufacturers. The GSM consists of cells as building blocks. A cell is a
geographical area served by a base transceiver station (BTS). GSM is characterized by
mobility and limited resource. The cells enable mobile users to be served. User mobility
during call can result in a change of cell (Base transceiver station). The effect of mobility
is handover. Handover is the process that ensures retention of the ongoing call into
another cell (Busra et al, 2010). GSM supports automatic hard handovers.
1.2 Handover Process
The process of handover within any cellular system is of great importance. It is a critical
process and if performed incorrectly can result in the loss of calls. Dropped calls are
particularly annoying to users and if the number of incidences of dropped calls rises,
dissatisfaction increases that can lead a subscriber to change of network. Accordingly
GSM handover is an area to which particular attention was paid when developing the
GSM ETS standards (Ghaderi, 2006).
One of the key elements of a mobile cellular telecommunications system is that the
system is split into many smaller cells to provide good spectrum utilisation and coverage.
However as the mobile moves out of one cell area into another, it is expected to retain the
connection.
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Handover process in cellular network automatically transfers a call from one radio
channel to another radio channel while maintaining good quality of services (QoS) of a
call (Adegoke, 2008). The number of cell boundaries increases because smaller cells are
deployed in order to meet the demand of increased capacity. Each handover requires
network resources to route the call to next base station (Jahangir, 2010).
Efficient handover algorithms cost-effectively preserve and enhance the capacity and
Quality of Service (QoS) of communication systems (Pollini, 1996). The overall
handover procedure can be thought of as having two distinct phases (Corazza et al,
1994): the initiation phase (in which the decision about handover is made) and the
execution phase (in which either a new channel is assigned to the mobile station or the
call is forced to terminate). Handover algorithms normally carry out the first phase.
Handover is generally designed to
i. Maximize quality of service QoS and capacity by ensuring maximum
reliability and communication quality,
ii. Maintain cell borders and proper traffic balancing
iii. Minimize number of handovers and global interference
These are the desirable qualities of a good handover algorithm. But the complexities of
handover may arise due to the cell dynamics i.e (cell, topography, propagation, traffic,
mobility, delay, and system constrain(s).
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1.3 Motivation
The motivation for this thesis is the need to improve on mobility management and GSM
channel resource utilization. The increasing mobile network subscriber base in Nigeria
has placed on GSM service providers the need to increase capacity. This is mostly
achieved by increasing coverage areas and channel resources to meet up. Inherently, this
creates mobility management problems because of intercell handovers which if not
properly and efficiently implemented leads to degradation in quality of service and
consequently call dropping. Call dropping affects subscribers directly and is a key quality
of service indicator that regulatory bodies look at when evaluating service quality.
Another problem associated with poor handling of handover is overloading of the system
processor which can bring about incessant system breakdown this also leads to revenue
loss and degrades quality of service.
A careful cell performance evaluation when carried out will reveal the impart of intercell
handover dynamics on quality of service. Also, a cutoff priority scheme that employs
dynamic algorithm which increases or decreases cutoff priority channels based on the
handover failure rates will be implemented to perform optimal channel resource and
mobility management.
1.4 Statement of Research Problem
In wireless cellular systems handover is key to mobility management and affects resource
allocation. The handover process is expected to be successful, imperceptible and less
frequent. Unsuccessful handover can be very annoying to subscribers. It terminates
established connections forcefully leading to dropped calls and quality of service get
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degraded in the process. In densely populated cities like Kano, High intercell handover
requests significantly increase traffic loading and could degrade QoS, increase call set up
time, call drop and call blocking probabilities. Channel allocation schemes if not properly
chosen and efficiently performed can lead to high intercell handovers as well.
The research profiles performance of cells with specific attention on the impact of
blocking probabilities, expected call dropping probability, handover failure rates and
traffic channel call drop. Performance evaluation will employ Nigerian Communication
Commission’s recommended quality of service standards for these parameters as the
benchmark. Real GSM cell call data statistics from an OMC of Airtel in Kano is sought
and processed. Attempt to optimize handover calls is made using a simulated cutoff
priority based performance model.
1.5 Research Methodology
The methodology adopted in carrying out this work includes the following
a. Data obtained from the Network Operation Maintenance Centre (OMC) section of
Airtel Network in Kano for this study are: Traffic, Call success set rate, Handover
success rate, SDCCH call drop, TCH call drop, Congestion, SDCCH blocking, TCH
call blocking, TCH Availability, Cell ID, Time and Cell Availability.
b. Analysis and extraction of relevant parameters from raw data in (a) ,
c. Compute overall arithmetic averages of extracted parameters and graphically display
it using MATLAB plot the extracted parameters are: call setup success rate, handover
Success rate, traffic channel call drop rates, Blocking probability, Standalone
dedicated control channel drop rates.
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d. Compute weekly arithmetic averages and analyse using MATLAB plot weekly trends
of call blocking probability, traffic, traffic channel call dropping, handover failure
rates, and standalone dedicated control channel from data.
e. Compute using established standard mathematical equations expected call dropping
probability for each cell. Process from obtained handover statistics average handover
failure rates values and subsequently, compute handover dropping probability from
the results and qualitatively display it applying MATLAB plot.
f. Simulate a Cut- priority model using an object oriented technique (Netbeans 6.1)
g. Validation through comparing the actual load derivable from processed data and
simulated result.
1.6 Aims and Objectives of the Research
The aim of the research is the analysis of intercell handover dynamics with a view of
optimizing the process using Airtel, Kano as a case study.
The objectives of the research work are as follows:
1) Profile performance of cells with specific attention on the impact of blocking
probabilities, call dropping probabilities, handover rates, and congestion.
2) Quality of service (QoS) impact assessment due to handover dynamics using NCC
standards as the Benchmarks.
3) Simulated system validation Using Data obtained from Airtel Kano for a period of
three months
4) To provide optimal solution using dynamic cut-off priority channel allocation
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1.7 Research Outline
Chapter One contains general introduction to the various aspect of the work. It begins
with a brief on GSM network and then handover process. These are followed by the
statement of the research problem, methodology, aims and objective of the work.
In chapter Two a detail theoretical background beginning with an overview of a GSM
system, then followed by handover processes, methods, algorithms, protocol, schemes
and some key quality of service indicators were represented. The chapter was concluded
with a rigorous literature review.
System modeling and simulation, data collection methods, bench marks, simulation
algorithm and simulation parameters were presented in Chapter Three.
Chapter Four present our results, analysis and discussions of the results.
In Chapter Five summary of the work was presented, conclusions were drawn including
limitation encountered in the course of the work and a suggestion for further work was
presented.
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