Akester, Richard John; (2003) Realtime multimedia performance on wireless LANs. Doctoral thesis (Ph.D.), University College London (United Kingdom).

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Abstract

This project aims to improve the performance of realtime multimedia applications over wireless LANs (Local Area Networks). This is achieved by modifying the multiple access, data-link and application protocols. The realtime multimedia applications studied are interactive (eg telephony) or non-interactive (eg video-on-demand). Performance is said to have improved if delay and loss are reduced according to the needs of the realtime application. In pursuance to the above stated aim, this dissertation starts by examining multiple access protocols revealing the problems faced by realtime applications. There follows the simulation of the IEEE802.11 MAC protocol and the validation of the results thus obtained. Point Coordination Function (PCF) is an optional part of the IEEE802.11 MAC protocol and a deterministic multiple access protocol which offers a guaranteed service to real time applications. It requires the use of a wireless access point to coordinate the transmissions of the hosts and thus is only valid in an infrastructure wireless network and not in an ad-hoc wireless network. Therefore, PCF was not included within the scope of this dissertation. Application level redundancy has also been used to reduce loss over all types of network. This technique is analysed and simulated in the dissertation. The hypothesis is that the performance of realtime applications on an ad-hoc wireless network can be improved by a cross-stack approach to reducing packet loss and delay. The cross-stack approach focuses on improvements at the data-link and application layers. Delay, delay variance and loss are used to measure realtime application performance. The originality of this dissertation stems from the proposal of a new distributed multiple access protocol. The protocol is proposed, specified and simulated and it demonstrates improved performance characteristics for realtime applications. A further original feature of this work consists of a new multicast acknowledgement extension, which is proposed, specified and simulated. A comparison with redundancy as an alternative approach to reliability is simulated and compared to the new multilple access protocol and the new multicast acknowledgement extension. It is concluded that the cross-stack approach improves both delay and loss metrics and hence improves the performance of realtime applications over wireless IEEE802.11 LANs therefore proving the hypothesis.

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