Modeling and optimization of wireless local area networks MAC protocols

As wireless local area network (WLAN) technology is gaining popularity, performance analysis and optimization of it becomes more important. However, as compared to wired LAN, wireless channels are error-prone. Most of the existing work on the performance analysis of IEEE 802.11 distributed coordination function (DCF) assumes saturated traffic and ideal channel condition. In this dissertation, DCF is analyzed under a general traffic load and variable channel condition. A more realistic and comprehensive model is proposed to optimize the performance of DCF in both ideal and error-prone channels. Many factors, such as the number of contending nodes, the traffic load, contention window, packet overhead and channel condition, which affect the performance of a wireless network have been incorporated.; It is shown that under error-prone environment, a trade-off exists between the desire to reduce the ratio of overhead in the data packet by adopting a larger packet size, and the need to reduce the packet error rate by using a smaller packet length. Based on our analytical model, both the optimal packet size and the optimal minimum contention window are determined under various traffic loads and channel conditions. It is also observed that, in error-prone environments, optimal packet size has more significant improvement on the performance than optimal contention window. Our analytical model is validated via simulations using ns-2.; We provide a novel approach to model the different channel conditions incurred by different nodes. This work has applications in performance optimization by establishing tradeoffs between transmission error rate and transmission power, modulation, coding scheme, packet size.; A better approach of modeling the wireless channel is considered. A Markov chain with alternating good and bad states is adopted to model the bursty characteristics of wireless channel errors. Furthermore, we introduce an analytical model to investigate the energy efficiency of 802.11 DCF.; Our future work will extend existing work to further performance enhancement for 802.11 DCF. Also we plan to apply our work in 802.11 to UWB (Ultra-wideband) since CSMA/CA is defined for UMB MAC protocol. To solve the new research challenge of UWB, we will consider a new channel model and channel estimation approach.