A PERFORMANCE COMPARISON OF FRAME STRUCTURES IN WIMAX MULTI-HOP RELAY NETWORKS
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Wireless multi-hop relay systems are the newest amendment to the IEEE 802.16 standard for local and metropolitan area networks, else known as WiMAX. Relay systems come in different flavours, based on their capabilities and have the potential to offer many advantages over the single-hop technology. Upcoming broadband wireless technologies, that utilize multi-hop relays, need good network planning and design in order to achieve their full potential. There are two main types of multi-hop relay stations: transparent, which are not able to transmit control information and non-transparent, which have the capability to transmit such information. This study focuses mainly on non-transparent relay stations due to their complexity and ability to operate in a more than two hop environment. Currently, the latest IEEE amendment provides two different frame structures − single and multi-frame − for utilization in multi-hop relay networks, to allocate bandwidth. The purpose of this thesis is to evaluate the two proposed frame structures, in various network scenarios in terms of delay, throughput, rate, and user capacity. In addition, we will discuss some of the issues that need to be considered to cost effectively plan and design a multi-hop relay network. The evaluation methodology that we utilize is in accordance with the Multi-hop Relay System Evaluation Methodology developed by the IEEE 802.16 Broadband Wireless Access Working Group. To evaluate the above frame structures we developed an evaluation model for use in the network simulator 2 (ns2) from University of California Berkeley, by modifying the light WiMAX (LWX) add-on from Taiwan University. Unlike the original LWX module, which supports only transparent relay configurations, our module supports both multi-frame and single frame structures, as well as non-transparent multi-hop relay environments. To our knowledge there is no previous work, which analyzes the performance of the single frame and multi-frame system in multi-hope relay environments using the guidelines from the latest amendment to the standard (IEEE 802.16j-2009). Moreover, there is no publicly available software that will enable the study of such performance. The resulting source code of our work has been made publicly available and can be obtained from our website.