UBC Theses and Dissertations

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UBC Theses and Dissertations

Improved channel state dependent scheduling for WLANs Zhang, Limei


This thesis focuses on the study of Channel State Dependent Scheduling (CSDS) based scheduling schemes for Wireless Local Area Networks (WLAN). CSDS based scheduling schemes can improve the usage efficiency of scarce radio resource since packets transmitted on wireless channels are often subject to burst errors which cause back-to-back packet losses. By taking into account the channel state in scheduling decisions, CSDS based schemes can achieve a large improvement in total throughput compared to FIFO scheme, which is currently used in WLAN systems. However, if not properly designed, a CSDS scheme can cause unfair resource allocation among users. Various mechanisms have been proposed for addressing the fairness problem in the literature, but unfortunately most of them are too complicated to be employed in WLAN . The main contribution of this thesis is to propose a simple compensation mechanism which is easy to implement. Based on the compensation mechanism, three CSDS based scheduling schemes are designed for WLAN. Among them, Max S* selects the best channel state S*, which is calculated according to the compensation mechanism; IWRR (Improved Weighted Round Robin) adopts dynamically changing weights for users. The weight is derived based on the compensation mechanism. A hybrid scheme, IWRR+Max S*, is proposed which possesses the advantages of both of IWRR and Max S*. A WLAN system simulation is used to show that the proposed schemes can yield substantial improvements in short-term fairness compared to CSDS+RR (Round Robin) in most test scenarios, while still maintaining high channel efficiency.

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