Research On Cooperative Relay Mechanism In Wireless Networks

Cooperative is the widely used virtual MIMO technology in wireless network.Cooperative diversity can provide reliable packet transmission service and enhance theoverall communication. The typical cooperative communication model contains threenodes, source node, relay node and destination node. Relay will forward the receivedpacket from source to destination node, then destination combine the two same copypackets. By this way, the signal to noise ratio is improved. Cooperative communicationis not only used to forward packets, also as a retransmission technology. That is, whenthe direct transmission between source node and destination node is fail, the cooperativecommunication will be adopted. The problem lies in that the retransmission of packet israndom, the channel reservation become a key. So, whether reserve channel forretransmission in advance or not? After years of development, cooperativecommunication also from the original three-node model, extended to multi-node model.Cooperative relay is not just a single-hop relay, and gradually step into a multi-hop relayperiod. Therefore, the research on multi-hop relay becomes necessity.Firstly, this article describes the commonly used forwarding method for relay,briefly introduction the typical channel access methods and analyze the developmentand facing problem for cooperative communication.Secondly, we comprehensive analyze the existing cooperative retransmissionscheme and potential factors, and then a retransmission strategy named E-CRS for theMAC layer is provided to solve these restrictions. The E-CRS combine CoopMAC withRTS/CTS for IEEE802.11. E-CRS reserve the channel by introducing extra controlmessage, thus avoiding the "over-reserved"(lead to channel waste) and"under-reserved"(lead to channelconflict).Then, based on the existing single-hop relay, we analyze the impact of multi-hoprelay position on the system performance. This work not only provides a reference forfuture research in the multi-hop relay and single-hop relay, also a clear direction for therelay selection. The simulation results show that as single-hop relay, the optimallocation lies in the midpoint of the source node and destination node.Finally, extended the existing single-hop relay selection that only concern two linksto the multi-hop link, we proposed a relay selection method named based on channelstate information. And then, analyze the SER performance under different select methods.