Performance Improvement And Evaluation Of DCF In IEEE 802.11 Wireless Networks

In recent years, IEEE 802.11 based wireless networks are becoming increasingly prevalent. Compared to the traditional wired networks, performance is expected to be worse in wireless networks in general. Yet, performance degradation is not only caused by inherent wireless characteristics, but also due to the inefficiencies within the Medium Access Control (MAC) protocol. As a result, to further improve the efficiency of IEEE 802.11 based networks, it remains necessary to study and improve the performance of IEEE 802.11 MAC protocol.In fact, since all WLAN data frames are routed through a centralized AP, and the AP shares the same priority as the other wireless stations in accessing the channel, the wireless AP is indeed a bottleneck in WLANs. This bottleneck effectively causes serious performance degradation within the network. In this thesis, we analyze the AP bottleneck problem in WLANs, and we proposed two approaches to alleviate this problem: cut-through forwarding method and a priority AP method. We performed various theoretical analysis and related simulations. The results shows that our proposed methods can indeed improve DCF performance in WLAN (compare to the original standard).IEEE 802.11 based wireless network can support multiple transmission rates. Stations in such network can adaptively adjust their transmission rate according to the environment. We also analyze the performance of WLANs under multiple transmission rates and propose an algorithm to guarantee fairness and to improve the aggregate throughput in WLANs. More specifically, we use the Channel Occupancy Time (COT) instead of the channel access probability in analyzing the fairness of WLANs. With our algorithm, all the wireless stations in the WLAN can achieve COT-based fairness by adjusting their packet length, sending the multiple back-to-back packets at one time, or giving up an opportunity to access the channel altogether. Our algorithm also leads to significant improvements to the aggregate throughput in multi-rate WLANs.Moreover, based on our previous work, we analyze the delay performance of IEEE 802.11 MAC layer protocol. Based on our analysis, we analyze impact of the RTS threshold and initial contention window size on the WLANs'performance. We further propose two algorithms that adaptively adjust these two parameter values to improve WLAN performance.Lastly, we recognize that transmitting very small packets worsens the performance of...