| Summary: | 碩士 === 國立臺灣科技大學 === 電機工程系 === 95 === IEEE 802.11 wireless local area networks have gained a lot of popularity in recent years due to its low cost and mobility. With applications over IEEE 802.11 increasing, users expect more functions from WLANs. Quality of Service (QoS) demands increase rapidly due to the popularity of multimedia. To guarantee QoS of real-time information, IEEE 802.11e is proposed. The MAC layer of IEEE 802.11e has adopted many methods to achieve QoS differentiation, including EDCA (Enhanced Distributed Channel Access). EDCA introduces four access categories (AC), and each AC uses different system parameters to realize QoS differentiation. EDCA adopts uniform backoff state assignment scheme to avoid collisions. When the number of stations increases, uniform backoff state assignment scheme may result in serious degradation of system performance. In this work, we adopt a new nonuniform backoff state assignment scheme to improve system performance of an IEEE 802.11e WLAN when the number of stations increases. We use a three dimensional Markov chain to model the system considered, and an analytical method is derived to calculate the performance measures of interest, e.g., throughput. It is demonstrated that when the number of stations is large, nonuniform backoff state assignment scheme can achieve significant performance improvement for either basic or RTC/CTS access mechanism. Last but not least, computer simulation programs are written in C language to verify the accuracy of analytical results and perform more complicated performance analysis.
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