Investigation Of Rate Adaptation For Wireless Local Area Networks

With the wireless network more and more popularized and its rapid development, the demands for the wireless mobile network are increasing continuously, and especially with the high-speed wireless broadband multimedia business development in recent years, higher requirements for the bandwidth of wireless local area network are also needed. In order to support for the high-speed multimedia business in wireless network, IEEE standard organization is proceeding to work out 802.11ac/ad standard which is expected to be completed in 2013, and at that time the transmission rate will reach the level of 1Gbps, to support wireless HD video, internet access, game playing and data download. The high-speed broadband multimedia wireless network has become once again the hot spot in network development.In spite of that with the continuous perfection and improvement to the protocol standard, the transmission rates in the wireless local area network are higher and higher. Many different coding modulation technologies, which can be selected according to different network environment, are stipulated for the physical layer in the IEEE 802.11 system. However the protocol does not regulate how to make switch between these different rates. That means automatic selection of the optimal rate to deal with data sending based on the channel's real-time changes is needed, which is also called rate adaptation. Therefore how to make the rate adaptation according to the different network environment to reach better network throughput has become a popular research field.In this thesis, firstly the system architectures and network characteristics of the IEEE 802.11 protocol are introduced to elaborate the background knowledge; and then the factors which affect the network throughput are analyzed. We conclude that the rate control is one of the key factors that affect network throughput. On the above basis, a comparison of some current important rate adaptation algorithms is made, and their study results are analyzed, which clear my research direction. After that, a test frame mechanism, which can improve the performance of rate adaptation, is proposed, and its performance is simulated. The results of simulation show that the mechanism can prevent system from increasing rate mistakenly when the channel dose not really ameliorate, thus it can reduce the packet loss ratio, so as to improve system performance. And then, an algorithm based on statistical information is studied and its deficiencies are pointed out. To overcome its shortages an improved rate adaptation algorithm, in which its parameter can be dynamically adjusted according to environment changes, is proposed, which can adapt to different channel environments better. At last, on the basis of the algorithm analysis, its performance and versatility are simulated. The simulation results show that the improved algorithm can better adapt to different channel environments and it does not need to do many changes to apply this algorithm into protocol compared with some other algorithms based on getting physical channel information. Additionally, the dynamic parameter conception can also be used for other protocol improvement, so it has a good versatility.