Researches Of Relay Selection Schemes In Cooperative Communication Networks

Cooperative communication is classified into cooperative transmission andcooperative relaying. In cooperative transmission, using several users’ antennas innetworks to form a distributed system, MIMO technology is applied intomulti-antennas-limited mobile terminals, which can obtain space diversity gain. Usingrelay transmission of users in network, cooperative relaying could extend cover regional,eliminate blind area or weak area, decrease networking costs, increase system capacityand improve spectrum efficiency the edge of the cell. There are several potential relaynodes in cooperative communication networks, so how to choose one or several relaynodes to assist source node appropriately and effectively and make cooperative schemeshave an important effect on increasing channel capacity, decreasing end-to-endtransmission delay, reducing data transmission energy consumption and loweringreceiving bit error rate. In this dissertation, we focus on researches of relay selectionschemes in cooperative communication networks. Adaptive relay selection schemes insingle source multiple relays networks and relay selection schemes combined withpower allocation in multiple sources multiple relays networks are explored. The mainresearch contents are as follows:1）The key technology of cooperative communication, cooperative protocols,cooperative performance and relay selection basic criterion are analyzed andsummarized.2）Single-source-multi-relay adaptive relay selection schemes were researched.According to the decode-and-forward cooperative communication network model, anadaptive relay selection scheme (ARS) based on SNR threshold was proposed. Whenthe direct transmission between source and destination is fail, according to the channelquality, the destination orders relay nodes in the decode set, and the ordered relays areincluded in cooperation in turn until the instantaneous received SNR at destination isnot smaller than the preset SNR threshold. The proposed algorithm ARS can get optimaloutage performance, decrease the average numbers of cooperative relays efficiently, tohigher bandwidth efficiency and lower system overhead.3） Multi-source-multi-relay relay selection schemes combined with powerallocation were researched. According to the amplify-and-forward cooperativecommunication network model, in order to minimize system total transmit power while guaranteeing the expected outage probability at the same time, a relay selection schemecombined with power allocation was proposed. In the proposed scheme, according tothe priority factor of each source, the destination decides in turn whether directtransmission or select relay to cooperate and corresponding optimal transmit power ofsource and relay. The proposed statistic channel information-based scheme withoutreal-time updating has low system costs and computational complexity. Comparing withthe direct transmission and AF scheme, the proposed scheme has lower system totaltransmit power than the greedy scheme and has a similar performance to the optimalexhaustive search scheme.