Message ring-based channel reallocation for cellular wireless networks

Abstract

Wireless communication suffers from many restrictions due to the inherent limitations of wireless media and existing wireless communication protocols. Limited radio frequency spectrum (or bandwidth) is one of the major issues in wireless communication. Wireless multiple access techniques were first developed to enhance channel bandwidth utilisation under limited frequency. Different channel allocation (or channel assignment) schemes have been developed to further increase the utilisation of limited frequency.

In this paper we propose a frequency reallocation scheme, message ring-based channel reallocation (MRCR) to improve channel utilisation in wireless communication systems. MRCR uses software agents (known as BS ring agents) to circulate and maintain a message ring that carries bandwidth information. The ring agent is also responsible for borrowing channels and locking the co-channels to avoid interference. MRCR uses channel re-arrangement techniques to improve performance. We present results of simulation studies to demonstrate the effectiveness of the MRCR scheme. Simulation experiments were carried out to evaluate the performance of the MRCR scheme under different mobility environments, namely: (i) high; (ii) medium; and (iii) low. Tests were also conducted under normal and heavy traffic environments to compare the MRCR scheme with other existing schemes. Results show that the MRCR scheme performs better than other schemes under varying mobility and traffic load environments.

Introduction

The way we communicate and conduct business has come a long way since the invention of the telephone. Today we are able to communicate, access the Internet and obtain electronic information while on the move. Advances in wireless telecommunication and computing technologies are the main factors for this revolution. The combination of wireless telecommunication and computing has resulted in the advent of mobile computing [1]. Mobile computing is envisaged to enhance the accessibility of information sources to computer users.

Typically, a mobile host (MH) (also known as mobile client or mobile subscriber) uses a mobile computer (MC) to communicate with the computer network via wireless media, such as radio waves or pulsing infrared rays. An MC can be a portable computer, a personal digital assistant (PDA) or a wearable computer with a built-in or external wireless communication device (known as the wireless transceiver).

The flexibility offered by mobile computing has resulted in an increase in the number of wireless communication subscribers. Affordable MCs and wireless communication devices have hastened the process. According to Ref. [2], the overall number of wireless users is growing at 40% a year, mainly in the area of voice and not data usage.

The growing demand for wireless communication systems requires better, faster and flexible services. Development, however, in wireless communication systems faces many restrictions and challenges, such as frequency limitation, a high risk of disconnection, limited resources, high error and low bandwidth communication channels [3], [4], [5]. In recent years, research work has been carried out to improve or develop new resources, management schemes, communication protocols, network infrastructure, file transfer schemes, user interfaces and hardware to provide better mobile computing services.

Wireless multiple access techniques were first developed to get more wireless bandwidth channels from the limited frequency spectrum [6], [7]. Currently, there are three general techniques used in dividing frequency spectrum into sets of disjoint channels: frequency division, time division and code division. Frequency division works by dividing the frequency spectrum into a set of fixed bandwidth channels. Channel in time division is a specific time slot within a frame of the frequency spectrum transmission time. Code division uses modulation code in transmission of data to identify channels.

Frequency management and channel assignment (also known as channel allocation) schemes were developed to further increase the utilisation of limited frequency [7], [8]. Many channel allocation schemes have been proposed to assign frequency channels to cells. Available frequency channels are efficiently used to maximise frequency reuse and consequently reduce the number of blocked calls in each cell. Channel allocation schemes can be classified into three general classes [7], [9]: fixed assignment (FA), dynamic assignment (DA), and flexible assignment (FLA). A cell is said to be hot if all its channels are occupied; a cell that is not hot is said to be cold.

Recently, research has been carried out on the use of software agents in distributed and mobile computing environments [10], [11], [12]. This paper proposes the use of software agents to facilitate resources management in mobile computing environments. The main focus of this paper is to investigate issues of improving existing channel allocation schemes. The rest of this paper is organised as follows. Section 2 looks at some existing channel allocation schemes. Section 3 describes the proposed MRCR scheme. Results of our simulation experiments are reported in Section 4. Section 6 concludes the paper.