Research On IEEE 802.11 Rate Adaptation And Fragmentation

WLAN is widely used nowadays as the fast development of the technologies of computer networks and wireless communication, and its mainstream standard IEEE 802.11 has become a hotspot of current research. But most of the research are based on the assumption that wireless channel is ideal, which can't realistically reflect the real channel condition. Aiming at improving throughput performance of the network, in-depth research and analysis on IEEE 802.11 standard in real-time varying channel is maken in this thesis, which includes rate-adaptive protocol and Fragmentation.Firstly, this thesis proposes a rate-adaptive protocol EARF, in which the statistic information of ACK frames are used to estimate wireless channel condition so that the sending station selects a proper rate. EARF can be implemented in practice by software driver program, without any modification to IEEE 802.11 standard. The simulation indicates that throughput of EARF outperforms similar protocols such as ARF and ARF3-10.Fragmentation is another way to improve network performance in IEEE 802.11 when wireless channel condition is awful. In order to validate the performance of Fragmentation, the author first implements it by GloMoSim simulation software, and then takes several sets of simulation. The simulation result indicates that Fragmentation is very effective in awful channel condition, while at the same time, several problems of Fragmentation need improving are found out, e.g., backoff of Fragmentation doesn't work well in uncontested network, which will be the further research of the author.At last, a practical WLAN testbed is established. We have taken much measurement for IEEE 802.11b and IEEE 802.11g Fragmentation scheme in various practical environments. By comparing the measurement data with the theoretical come out, the author concludes that there is a far way between theoretical and practical research because of interfere around measurement environment; implementing theoretical protocol in practice is also a challenging process. As further work, a full-functional testbed of WLAN will be gradually set up to validate and analyze the theoretical results of our related study.