ABSTRACT
Wireless Communication is one of the most active areas of technological development of our time. It covers a very wide array of applications that lead to an ever growing demand on the limited radio resources. Consequently, the need for efficient management of the limited radio resources has become imperatively a global issue. The complexity of the cellular system and the propagation channel resulted in the interference issues that degrade the system performance. Transmit power otherwise known as Power Control is an efficient radio resource management technique that mitigates both adjacent and co-channel interference under fading condition. It also suppresses the Near – Far problems, enhances the battery life and the system capacity. In the light of this, different power control algorithms have been proposed by different authors but the choice of an appropriate power control algorithm is of great importance, as it should aim at improving the quality of service (QoS) to all the users and increasing the efficiency of the system. In this work, therefore, comparative analyses have been carried out on three popular distributed power control algorithms using performance metrics such as speed of convergence and total power consumption of the network. However, results have shown that Fully Distributed Power Control Algorithm (FDPCA) has a better efficiency in handling transmit power of the system more than New Distributed Power Control Algorithm (NDPCA) and Improved Distributed Power Control Algorithm (IDPCA) algorithms by 0.44% and 0.01% respectively, while IDPCA is more efficient in conserving power on the network than FDPCA and NDPCA by 0.04% and 2.38% respectively. Furthermore, analysis of variance (ANOVA) test carried out on the simulated data using means and standard deviation at 95% confidence level showed that the degree of variance of the algorithms is negligible.
CHAPTER ONE
INTRODUCTION
1.1 Background of Study
Wireless communication systems have experienced tremendous growth over the last decade, and this growth continues at a full strength worldwide [1]. Such development is mainly driven by strong market demand for personal communication systems and services, which provide ever- present and Seamless connectivity with other devices and fixed networks [2, 3].
The need to provide for user mobility in wireless system was designed to amend the errors of traditional wired and wireless communication networks which provide communication between the moving unit (User Equipment) and the stationary unit (Base Station) and vice versa [4]. These errors range from the inability of the traditional wireless communication networks to cope with travelling speed of fast mobile units, its low data rate and low capacity [5].
The concept of cellular communication came into place by dividing the coverage area into small regions called cells [6]. The cell size changes with time and is dependent on the traffic in the area to be covered. However, it is controlled by the transmitter power and the frequency of the cell operation, which also, could apply some cell techniques like; Frequency reuse, cell splitting etc to improve on the capacity of the system [7].
This rapid demand in the number of wireless communication users has led to tremendous technological advancement and evolution of the cellular systems. Hence, the need to develop a standard that will improve the performance of the system moved the evolution from the first generation (1G) which offered only voice service, and this led to the deployment of the 2nd generation (2G) systems which provided for both voice and data communications [4, 8]. But with the growing demand in the data service, there became a need to accommodate more services while enhancing the speed of the system [1, 9]. The limited capacity of 2G systems and the never-ending need for higher data rates are the main reasons for developing next generation mobile
communication systems [10]. This is to provide multi-purpose functionality with higher data rates. Some improvements like General Packet Radio Services (GPRS) [11] and Enhanced Data Rates for Global Evolution (EDGE) were developed to repair the bottlenecks of the existing 2G systems [12]. These are often called as 2.5G techniques. GPRS enables the connectivity to the packet networks and the EDGE provides higher data rates for the GPRS. However, the current solutions to the problem are Universal Mobile Telecommunication Systems (UMTS) and Code Division Multiple Access 2000 (CDMA2000) [13], techniques for the 3G (third generation) mobile communication systems. Data transmission rates up to 384 kbps are provided at regular urban outdoor environments for the UMTS. The CDMA is used as a radio transmission technique to improve the network spectral efficiency.
The development of the third generation (3G) of mobile communication could support some multimedia services like voice, paging, messaging, Internet and broadband data [14]. The
3G technology ran two separate networks concurrently with help of the UMTS Terrestial Radio Access Network (UTRAN) as could be seen in the system architecture. UMTS represents the move into 3G of mobile networks. It is an umbrella term for the third generation radio technologies developed within the Third Generation Partnership Project (3GPP). It addresses the growing demand of mobile and Internet applications for new capacity in today’s overcrowded mobile communications [15].
However, radio resource management is very important when the number of users and the demand for bandwidth increase. Effective allocation and utilization of resources will improve the performance and increase the capacity of the wireless network. In such case, Power control as one of the Radio Resource Management (RRM ) techniques is the most important and critical function technique.
In Wideband Code Division Multiple Access (WCDMA), the capacity of the system [16] is limited by the total interference, called Multiple-Access Interference (MAI), from all connected mobiles using the same frequency band on the uplink (mobile to base station link). Therefore,
MAI is a dominant factor in system capacity and quality of communications, and must be suppressed or reduced if a high capacity cellular mobile system with a satisfactory performance is to be implemented [17]. Hence; efficient channel reuse is of paramount importance in the design of high capacity cellular radio systems. And it is especially important for uplink transmission.
In other words, WCDMA systems are self-interference systems. This is because every User Equipment (UE) transmitting on the system serves as a source of interference to other UEs on the system [18]. Also in uplink transmission, if user equipment is transmitting high power signals at a close location to node B, it can easily over shout the other user equipments which are farther than it or at cell edge. It can even block the whole cell. On the other hand, if a UE is transmitting at very low power, thenNode B will never hear that UE. This phenomenon is known as near-far problem [19]. In the downlink transmission, the radio system capacity is determined by the required power for each User Equipment. That is why this is essential to transmit the signal at minimum level with required signal quality at receiving end. This work is therefore, aimed at carrying out a comparative study on different distributed power control algorithms with a view to ascertaining the algorithm with efficient network performance and reduced interference.
1.2 Aims and objectives
The aim of this research is to carry out a comparative study on different distributed power control algorithms with a view to ascertaining the algorithm with efficient network performance and reduced interference.
The specific objectives of this thesis include the following:
To carry out a critical review of the advances made in the area of power control schemes.
To analyse some of the promising distributed power control algorithms proposed by some authors.
To write a pseudo-code for the three selected distributed power control algorithms.
To finally carry out a performance analysis on the three selected distributed power control algorithms on the basis of their speed of convergence and total power consumption of the network using Microsoft Excel.
1.3 Problem Statement
In WCDMA, many users transmit over the same radio channel using the same frequency band and time slots so that the signal of an individual user becomes interference for the other users. But the power control problem can be termed, “Near-Far effect”. In a way, power control ensures that the mobiles in a network system transmit with equal power levels.
However, to accommodate greater number of these users, the available radio spectrum is divided among the users with some multiple access techniques and the same spectrum can be reused with different criteria. But, if the power levels of a user are not controlled, it may result in some interference to both co-channel and adjacent channel users.
To ensure an efficient cellular network, many researchers have looked into this area and came up with different power control algorithms which could be used to ensure that users transmit at the same power level, thereby mitigating the effect of all kind of interference. But not much
significant works have been done on performance evaluation of some of the power control algorithms.
1.4 Scope of the Work
The scope of this work covers the Distributed Power Control (DPC) algorithms especially on the uplink aspect of cellular network. A comparative analysis of the three selected algorithms was carried on the bases of the selected performance metrics. No physical implementation of the algorithms was required for the analysis. Hence, only analytical and logical models were used for the comparative study of the algorithms using Microsoft Excel as a tool for the work.
1.5 Methodology
The following methodology was adopted to realizing the set objectives:
1. Review of the different power control algorithms in UMTS.
2. Review of distributed power control algorithms that could be employed in the uplink part of UMTS and choice of three popular algorithms.
3. Development of power control system model.
4. Model simulation result analysis based on standard performance metrics and algorithms comparisons.
1.6 Thesis Structure
This thesis is structured in the following way: Chapter one introduced the concept and the topic at hand. Chapter two handled the evolution and general background knowledge of 3G of Global System for Mobile Communications (GSM). It also reviewed the related works carried out under Power Control aspect of UMTS and cellular systems at large. Chapter three presented the physical model, the general system design employed, the flow chart of operation and the analytical analyses of the three algorithms in view. Chapter four discussed the programming of the three
distributed power control algorithms and their result analysis. Finally, Chapter five deals with the conclusion and recommendation.
This material content is developed to serve as a GUIDE for students to conduct academic research
COMPARATIVE ANALYSIS OF DISTRIBUTED POWER CONTROL ALGORITHMS IN CELLULAR NETWORK
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