Study Of Cooperative MAC Protocols Based On IEEE802.11

Due to the influence of multipath fading, the mobility of nodes and the transmit power, it is difficult for wireless networks to achieve satisfying date transfer rate and communication quality. Moreover, the number of users of wireless networks is increasing quickly, and the business is becoming more and more abundant. All of these demand better performance of wireless networks. Therefore, wireless communication technology is facing great challenges.Traditional point-to-point wireless communication technology is approaching shannon limit. It is unavoidable to explore new technology and scheme. Researchers put forward cooperative communication technology in the process of exploration. Cooperative communication technology originates from the research of Cover T and Gamal A E on relay channel information theory in 1970s. Its basic idea is to maximize the throughput by resource sharing of nodes in wireless communication system. Cooperative communication technology blends relay transmission technology and cooperative diversity technology. It applies to traditional wireless networks and can acquire performance gain of MIMO and multi hop transmission. It is suitable for wireless Ad hoc network, wireless local area network, cellular mobile communication system and wireless sensor network. So, cooperative communication technology has great research value and significance.Current researches of cooperative communication technology mostly focus on the physical layer. Cooperation on physical layer takes advantage of the openness and broadcast nature of wireless channel, while traditional MAC protocols regard these as difficulties to be overcame rather than useful resource.In order to fully exploit the advantage of cooperative communication, MAC protocols should be redesigned.All of existing researches of cooperative MAC protocols at home and abroad are based on IEEE 802.11. The article studies the problems of design of MAC protocols caused by cooperative communication technology. Differed by the usage scenario and implementation model, the thesis proposes two cooperative MAC protocols based on IEEE 802.11:cooperative MAC protocol based on cooptable and cooperative MAC protocol based on instantaneous channel state. The former uses cooptable to store information of relay nodes. The transmitter select relay nodes according to the records in cooptable before RTS/CTS hand shaking process, and select data transfer mode according to the channel state. An invitation frame back-off algorithm is used to reduce extra overhead caused by cooperative communication. Simulation results show that the former can effectively enhance the performance of wireless networks. It can achieve higher throughput and shorter end-to-end delay than IEEE 802.11. The later does not maintain cooptable. Potential relay nodes acquire instantaneous channel state in the process of RTS/CTS hand shaking and determine whether it meet the condition of acting as a relay node. All nodes that meet the condition compete to be the relay node. P-persist back-off algorithm is used to reduce the possibility of invitation frame collision. The later can preferable adapt to the channel variance under mobile scenario.