Performance Study Of IEEE802.11 Protocol Under Fading Channel

Recent years have seen the growing popularity of Wireless LAN for its convenience,flexibility,low cost and easiness to be extended,and more enterprises start to use it because of its facility and mobility.IEEE802.11 protocols as the de facto standard for the wireless local network,are attracting more and more researchers to study how to improve its network performance.Therefore,more scholars are devoting to researching and further improve the performance of it.In this thesis we briefly introduced the background,concepts,advantages and application future of the IEEE802.11 protocol in the first part.Then introduced in detail the IEEE802.11 DCF with capture effect in Rician fading channel and propose a new scheme for Rate adaptive wireless LANs.Most of the previous analytical model were based on the perfect wireless channel assumption,and assumed that a station located within the transmission range of the transmitter can correctly receive the message when no collision occurs.In recent years, the performance analysis for IEEE802.11 DCF under the wireless fading channel model has attracted a lot of attention.With a finite number of terminals,the impact of capture effect in Rician fading channel on the performance of IEEE802.11 DCF is presented for the first time.By means of taking the collision probability as an intermediate variable in the Markov chain model,the capture effect is added into the stationary transmission probability.Then the saturate throughput with capture effect in Rician fading channel is presented.With the consideration of capture effect,the throughput of the network especially with the basic access scheme is significant improved.The current IEEE802.11 PHYs only define data type on some particular transmission rates,but in MAC layer,the rate adaptation algorithm is not specified. IEEE802.11 multi-rate mechanism OAR can better utilize wireless channel conditions, based on which we proposed a MDCWS scheme to improve the overall throughput of the networks.The center node set a Multiuser Diversity Contention Window.After receiving the beacon signal from center,every node will check if the current channel condition satisfactory the required SNR,whether it is necessary to compete the channel and which slot to select.For the beacon carried the limited reply SNR,the probability to select a better channel is increased and high rate transmission in the coherence time promised the high throughput.