Analysis and Optimization of Inter-cell Handover Dynamics in a GSM Network (a Case Study of Airtel Kano, Nigeria)
Chapter One
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.
CHAPTER TWO
LITERATURE REVIEW
Introduction
This chapter provides an overview of a GSM system, some fundamental concepts of handover processes, handover schemes, key quality of service performance indicators and a rigorous review of similar works.
Review of Fundamental Concepts
In this subsection theoretical background of the work is set and relevant fundamental concepts are reviewed. Beginning with a discussion on generic GSM system followed by several other related concepts.
Generic GSM system
The basic building block of a typical GSM network is the cell-site also called Base Transceiver Station (BTS) or called just Base Station. Next in the hierarchy is the Base Station Controller (BSC). This controls a number of base transceiver stations. Depending on the density of users and the topology, each BSC can control anywhere between 5-20 BTSs (Madhusmita et al, 2008). Finally the upper most crucial element is the Mobile Switching Center (MSC). Each MSC covers about 5-15 BSCs (Ghaderi, 2006). Each service provider has at least one MSC. The MSC normally houses the Home Location Register (HLR), Visitor Location Register (VLR), the Authentication center (AuC) and
the Equipment Identity Register (EIR). The HLR has all the relevant details of a particular subscriber like the service plan, the supplementary services, and the details about the mobile station, the latest coverage areas visited and billing details. The VLR primarily deals with roaming and exchange details of users gotten from foreign networks and also holds latest details of its own users roaming in other networks. The VLR also assists in handovers. In order to ensure that network operators have several sources of cellular infrastructure equipment, GSM decided to specify not only the air interface, but also the main interface that identify different GSM parts. Figure 2.1 describes a typical
GSM network architecture.
There are three dominant interfaces, A interface between MSC and BSC, A-bis Interface between BSC and BTS and an Um interface between the BTS and MS.
Basic cell structure
When designing hand over algorithms, the characteristics of the communication system must be taken into account. Several cellular structures are categorized as; Macrocells, Microcells, overlay system and picocell (Nishith, 1998).
SIM
Um Abis A
Mobile Base Station Subsystem Network Subsystem Station
Different cellular structures or layouts put different constraints on handover algorithms. Disconnected microcells and macrocells are expected to coexist in the cellular systems (Polini, 1996). In this case, microcells cover hot spots, while macrocells cover low traffic areas. Different radii cells require different handover algorithm parameters (RSS, SIR threshold, etc.) to obtain good performance as in (Tripathi, 1998). Some service areas may contain microcell-macrocell overlay in which microcells serve high traffic areas and macrocells serve high speed users and overflow traffic. As the cell size decreases, the number of handovers per call increases, the variables such as RSS, SIR, and BER change faster, and the time available for processing the handover requests decreases (MunozRodriguez et al,1992). Moreover, the number of MSs to be handled by the infrastructure also increases
Frequency re-use distance and cluster size
Frequency reuse is the use of radio channels on the same carrier frequency to cover different areas which are separated from one another by sufficient distance so that cochannel interference is not a problem. The reuse of frequencies enables a cellular system to handle huge number of calls with limited numbers of channels but causes mutual interference that is Co-channel interference and adjacent channel interference (trade off link quality versus subscriber capacity) (Michael, 2004)
A GSM cellular network is made up of a number of radio cell or cells served by fixed base stations. These cells are used to cover different areas to provide radio coverage over wider area. These radio cells are combined into clusters and each frequency is used once per cluster. Cells need to be represented by regular polygon. The Hexagon was found to e an ideal choice. Each cell is assigned a-group of radio channels which is completely different from the neighboring cells. The cells will form sets called clusters where cluster size N can take any value that satisfies the equation 2.1 where i and j are shift parameters.
CHAPTER THREE
MODELING AND SIMULATION
Introduction
This chapter presents the qualities of a good handover, challenges that may be encountered when developing a good handover process. The Data collection method was described. Included also are tables displaying both NCC and Airtel benchmarks, model description, Algorithms, flow chart and simulation codes.
Data Collection Methods
The main data used in this work was obtained from Airtel network in Kano See Appendix I (HKNBSx9 call data records). The data obtained covered the period from June 2011 to August 2011. Also used was the Nigerian Communication Commissions’ technical standard data which was downloaded from their website (www.ncc.gov).
Table of NCC Benchmarks
The Nigerian Communication Commission (NCC) is the statutory regulating body for all Operators in the Telecommunication industry, in order to ensure uniform standards and quality service delivery to subscribers they have specified benchmarks for compliance by each industry operator.
Table 3.1 is an extract of NCC benchmarks extracted from their April 2012 QoS standards.
CHAPTER FOUR
RESULTS AND DISCUSSIONS
Introduction
This chapter presents the results of data analysis, significance of the results were discussed and presented. Simulated solution to handover failure problems were carried out, discussed and presented.
Data Analysis
From the data obtained for a Base Station Controller HKNBSx9 (as in Appendix I) HKNBSx9 call record data. The statistical mean of relevant parameters was computed and tabulated as shown in Table 4.1 This qualitatively presents the general picture of the individual cells performances. The aim is to compare our values with NCC recommended standards refer to Tables3.1 which is a tabulation of the various parameters and NCC recommended targets. In Table 4.1 the results for fourteen different cells are presented. The system under study performs handover when the signal strength is at 102dB or else the call is dropped.
CHAPTER FIVE
CONCLUSION AND SUGGESTIONS FOR FURTHER WORKS
Introduction
This chapter contains succinct effort made in realizing the aims and objectives of this work. Also included are the summary of results obtained after analyzing the inter cell handover dynamics based on the data obtained from an OMC of Airtel in Kano, Nigeria.
A simulated solution aimed at improving the performance of the handover dynamics, the limitations encountered and the suggestions for further research work.
Summary
The research analysed the intercell handover dynamics by profiling the performance of cells. Data was obtained in Microsoft Excel format from Airtel Kano, Quality of service (QoS) key performance indicators parameters like (HSR, CSSR, SDCCH Drop rate, TCH call Drop, SDCCH Blocking, TCH congestion) were extracted, computed and analysed
Using MATLAB as our main tool. Evaluation by way of benchmarking with NCC
recommended standards was carried out.
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 ton achieve Handover Success Rate (HSR) , Sixty four percent (64%) failed to achieve Standalone Dedicated Control Channel blocking rates targets, twenty one percent (21%) failed to achieve congestion targets. Using mathematic methods Average call drop rate per cell was predicted to be six (6%). This without doubts negatively impacted on the QoS.
To improve the inter cell handover performance, a dynamic cutoff priority handover management scheme algorithm was developed. The algorithm gives priority to handover by reserving some channels exclusively for handover initially and dynamically alters it with a view of getting minimum handover failures.
The algorithm was simulated using Netbeans 6.1 which is a JAVA variant. From the simulation an average of Ninety percent (90%) performance improvement was realized after comparing the real Handover failure rates per cell and those obtained from simulation. This is a far better result taking into consideration that from obtained data seventy two (72%) percent of the cells did not achieve the NCC recommended standard for handover success rate (>=98%), while by simulation only an average of twenty percent (20%). These clearly are an indication for optimum utilization of channel resources and maximized intercell handover performance.
Simulation System validation was achieved by comparing properties and values of simulated load and load obtained from data. MATLAB was used to graphically presents the two values.
Limitation of the Study
The research objectives were met in spite of some Limitation encountered. Limitations encountered in the cause of this work includes lack of a physical GSM Simulator that could have been used for test and trials of the program, this could have given room for real experimental experience. Deployment issues were not undertaken and the Operator only allowed use of data without access to OMC.
The research focused on GSM network but our methodology can be applied to 3G and 4G
Conclusion
The research largely achieved the set objectives. It improved on the performance of GSM intercell handover dynamics especially in area of its impact on key performance indicators and signaling resources.
Significant contributions are made in the following areas:
1. Assessment of quality of Airtel Network in Kano due to Handover traffic
2. Performance evaluation of individual cell in the network
3. Using dynamic cut-off priority an optimal solution of channel allocation was proposed based on this proposed solution an average of 90% handover failure rate was reduced.
Recommendation on Areas for Further Work
Further work may focus on the deployment of the simulated program in an existing network. This will entail construction of architecture to execute this and similar program. The dynamics of intracell handover maybe analyzed with the view of analyzing its impacts on QoS.
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