A New Cooperative MAC Protocol In WLAN

Cooperative communication is a kind of system where each node has one or more cooperative partners. Because of the wireless broadcast characteristic, neighbors can overhear information from transmitter and relay it to destination after processing. In order to resist multi-path fading and improve the throughput of the network, receiver can combine the two copies of information from source and relay node according to some rules. Cooperative communication in wireless network is a very new subject to investigate, which will have a vast application in the new generation wireless communication networks such as wireless ad hoc networks, wireless sensor networks and wireless local area networks.Generally, cooperative communication technology involves physical layer,MAC layer and routing layer, traditional research is focused on the physical layer and routing layer while the work on MAC layer is not sufficient, MAC layer is responsible for the important work of wireless channel access and assignment, which is worth to be investigated deeply.802.11 protocol stack is now widely used in WLAN. Compared with the two basic rate 1M/2M bps of 802.11,802.11b extends the transmitting speed to four rate 1M/2M/5.5M/11M bps, devices can drift from one rate to another according to the channel state. So it will greatly improve the overall performance of the network if higher-speed devices can assist the lower ones when transmitting information.Based on the 802.11b MAC protocol, this paper will incorporate cooperative communication mechanism into WLAN.First, this paper gives a description of what cooperative communication is and what challenge it faces, then an introduction is made about the current cooperative MAC protocols designed for WLAN.Then, a new WLAN cooperative MAC layer protocol is devised to overcome the deficiency of previous protocols. Instead of keeping a relay table, transmitters will find their best relay node when having data to send out. The source node will decide whether to start the relay finding procedure according to the feedback from destination, that is to say, relay will never be used when the quality of direct link is good enough. A competition window is introduced here to select a best relay node and direct-link transmission will start if there is no proper relay node when that window runs out.Third, this paper simulates this new MAC protocol in Matlab and compares it with the existing MAC protocols, results show that this protocol can significantly improve the network's performance in throughput and average service delay.Last, a summarization about the overall work in this paper is given and some suggestion is made for future work.