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UBC Theses and Dissertations

Downlink packet scheduling for IEEE 802.16 point-to-multipoint fixed broadband wireless access systems Zhang, Yonghong


The release of the IEEE 802.16 standard has stimulated commercial interest in deploying fixed broadband wireless access networks. Although the fixed wireless environment is generally less harsh than the mobile environment, the expectations for reliability and performance are also higher. In suburban neighbourhoods, wind-blown foliage is one of the main factors that contribute to fading on fixed wireless channels. It seems likely that fading events associated with the onset of wind will occur simultaneously on multiple links within a given cell. This has important implications for both system performance and radio resource management. In this thesis, we consider the impact of such fading on a single-cell point-to-multipoint system based on the IEEE 802.16 standard. Using an improved Ricean K-factor model that combines elements of previously disclosed models, we show that the performance of the system is degraded when the fading events on multiple links are correlated. Further, we propose two channel-state-dependent downlink schedulers that exploit multi-user diversity for use with TDMA mode IEEE 802.16 point-to-multipoint systems. The first is intended for use with real-time traffic while the second is intended for use with a mixture of real-time, minimum-rate ensured, and best effort traffic. We propose the use of fair degradation for real-time traffic and fair resource allocation for delay-tolerant traffic in order to maintain quality of service (QoS) and mitigate wind-induced fading during heavy wind conditions. Using the new concepts of flexible time and urgent time, our proposed schedulers are able to maximize system throughput while meeting users’ different levels of QoS requirements. Simulation results show that the proposed schedulers outperform existing scheduling schemes, especially during fading events associated with wind blowing through foliage.

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