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UBC Theses and Dissertations

Performance evaluation and enhancement of RAP protocol for OFDM-based wireless lan Fong, Victor K.


Because of the scarce transmission capacity of radio channels, an efficient Medium Access Control (MAC) protocol is needed to coordinate the activities of the Mobile Nodes (MNs) that coexist in a wireless Local Area Network (LAN). The design of efficient MAC protocols has become an important research activity. In this thesis, one specific class of MAC protocol, named as Randomly Addressed Polling (RAP), is investigated. Our purpose is to analyze the performance of RAP protocol at the MAC layer, and to propose and evaluate some protocol enhancements. Considering the limitations to the collision resolution capability of the protocol, we propose a new signaling mechanism based on the signal constellation scheme to increase the number of random addresses. In addition, we propose a simple service differentiation mechanism based on the restriction on accessible random addresses for different priority classes to implement Quality of Service (QoS) guarantees for the protocol. Finally, we propose a new two-dimensional Markovian model to analyze the protocol performance. Comparisons of our analytical results with those from OPNET software simulations demonstrate that our model is accurate in predicting system throughput, packet delay, and the expected number of active users. Using our model, we evaluate the system performance of the protocol, showing that the new signaling mechanism significantly improves the collision resolution capability of the protocol for both perfect and imperfect channel conditions. Our results also indicate that our service differentiation mechanism can offer effective service differentiation for different priority classes, and can also improve the collision resolution capability of the protocol.

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