Performance improvements to the 802.11 wireless network medium access control sub-layer : a thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering in Computer Systems Engineering at Massey University

Abstract

This thesis presents the outcome into the research and development of improvements to the 802.11 wireless networking medium access control (MAC) sublayer. The main products of the research are three types of improvement that increase the efficiency and throughput of the 802.11 protocol. Beginning with an overview of the original 802.11 physical layer and MAC sub-layer standard, the introductory chapters then cover the many supplements to the original standard (including a brief on the future 802.11n supplement). The current state of the 802.11 MAC sub-layer is presented along with an assessment of the realistic performance available from 802.11. Lastly, the motivations for improving the MAC sub-layer are explained along with a summary of existing research into this area. The main improvement presented within the thesis is that of packet aggregation. The operation of aggregation is explained in detail, along with the reasons for the significant available throughput increase to 802.11 from aggregation. Aggregation is then developed to produce even higher throughput, and to be a more robust mechanism. Additionally, aggregation is formally described in the form of an update to the existing 802.11 standard. Following this, two more improvements are shown that can be used either with or without the aggregation mechanism. Stored frame headers are designed to reduce repetition of control data, and combined acknowledgements are an expansion of the block acknowledgement system introduced in the 802.11e supplement. This is followed by a description of the simulation environment used to test the three improvements presented, such as the settings used and metrics created. The results of the simulations of the improvements are presented along with the discussion. The developments to the basic improvements are also simulated and discussed in the same way. Finally, conclusions about the improvements detailed and the results shown in the simulations are drawn. Also at the end of the thesis, the possible future direction of research into the improvements is given, as well as the aspects and issues of implementing aggregation on a personal computer based platform.