An Improved Algorithm On Cooperative Communication In MAC Layer Of Wireless Local Area Network

Cooperative Communication technology makes full use of the transmission property and spatial diversity of the wireless channel, when the signal is transmitted to the designated mobile end, the neighbour nodes which we will call cooperative nodes or candidate relay nodes can also hear the signal at the same time. Here, the cooperative node can receive the data information from the source node and then transmit it to the destination node. Of course, in order to further reduce the negative effects caused by the signal recession or channel disturbance due to the broadcast characteristic of the wireless channel, the destination node could be able to make certain integration with the information both from the source node and the cooperative node according to some specific criterion, of which can improve the high efficiency of the data communication and the wireless network performance. IEEE802.11Wireless Local Area Network has Multiple Rates and it adopts the CSMA/CA protocol as its communication protocol which will supply two kinds of delivery service, that is, distributed coordination function and point coordination function. Besides, ACK mechanism is also adopted to decide whether the data packet should be retransmitted or not in accordance with the ACK frame received or not.From802.11b MAC layer, as its point of view, we import the cooperative communication technology to further improve the WLAN performance. As it is known to us all, cooperative communication in MAC layer mainly employs the method accessing channel when it is needed. That is, when the source node has some data packet to send, it has to access the channel by competition, if it happens to collide with another node, a sort of criteria will be used until the data packet is successfully received by the destination node. Of course, PHY layer or even higher layers are also included in cooperative communication. However, MAC layer plays an important role of accessing to the channel by competition and successively allocating the channel resource, which has made it become the advanced direction, hot issue and key research in this paper as well. Firstly, we briefly introduce the background and the classification of the cooperative relay technology in wireless network, and then, we particularly describe the key point of the relay technology. Furthermore, we mainly analyze several popular MAC layer communication in WLAN based on the current problems existed at present.Secondly, to the current MAC layer communication weakness, we come up with an improved algorithm. Therefore, more detailed relay strategy and cooperative method are given. On the one hand, modified back-off time slot based on802.11b is proposed to avoid successive collision problems. On the other hand, two kinds of control frame are added to coordinate the relationship of the source node-relay node-destination node. Apart from the above, theoretical analysis, formula computing, graphic illustration and straightforward flow chart are offered as well.Eventually, we come up with throughput and service delay as its performance criteria and make some simulation work for the improved algorithm to test and verify the new algorithm’s performance. Compared to existed MAC layer communication and the traditional802.11b protocol, it proves to be more effective for the new algorithm to improve the network performance.