Research Of Power Allocation And Relay Selection Algorithm In Cooperative Communication Systems

1. IntroductionWith respect to the wired communication network, multipath fading and nodesmoving result in poor communication environment, which seriously affectthe communication quality and the transmission rate in wireless communicationnetwork. In addition, there are a great many (we take our country as the example, thecurrent wireless network has four times as many users as wired network)users (entities/nodes) in wireless network. But its broadband is very limited, andservices are variety, all these require a higher transmission rate and bettercommunication quality. Therefore, wireless communication technology isfacing unprecedented challenges.Since the traditional point-to-point wireless communication technology has beenclose to the Shannon limit, new technologies and solutions beyond the traditionalpoint-to-point communication technology are required to be further explored.Cooperative communication technology has emerged as a promising solution to solvethe problems by using the openness (Spatial domain) and the broadcast feature(information transmission) of wireless communication channels. Cooperativecommunication technology shares antenna resources through partners and forms avirtual antenna array to obtain spatial diversity. It can effectively resist the channelfading, thus become a research hot spot in the field of wireless communication. Thispaper is supported by the research of Studies on dynamic resource allocations incognitive radio systems based on control theories and matrix perturbation theory, oneof National Natural Science Foundation of China with Grant (61171079), focusing onthe great application potential of cooperative communication technology in wirelesscommunication network.Concerning the development tendency of cooperative communication technologyand the problems existing in relay selection algorithm of multi-relay cooperativecommunication network, an algorithm of the relay selection and power allocationbased on outage probability is proposed in this paper. This algorithm has completedthe relay selection and power optimization under a joint sum power constraint,moreover the proposed algorithm has optimized system outage performance andimproved power efficiency. Although relay selection schemes for multi-relaycooperative communication network have been extensively studied, these schemes areall proposed under the condition of equal power allocation in Amplify-and-Forward(AF) cooperative network, these schemes ignore the impact on system performance asequal power allocation. Based on the above considerations, this paper further studies power optimized before relay selection technology inAF cooperative network,proposes a novel and low-complexity fast relay selection and power allocationalgorithm.2. Outage probability based power allocation and relay selection algorithmAlow-complexity fast algorithm of relay selection and power allocation based onoutage probability with a joint sum power constraint in Amplify-and-Forward (AF)network is proposed. The first step is global power optimization, optimal powerallocation among source and potential relay nodes is conducted so that the relay nodeswith good channel conditions can be selected faster and made full use of. The secondstep is relay selection, according to the SNR (signal to noise ratio), an optimal relaynode set is selected. The third step is power distribution, which is to solve a convexoptimization problem under constraint conditions. Apower allocation factor leading toa lower system outage probability is obtained by steepest descent method andLagrange multiplier method. Thus, minimize system outage probability, meanwhile,improve power efficiency.3. Simulation results and performance analysisThe simulation results show that the proposed scheme breaks the limitation ofthe condition of equality power allocation in relay selection, excludes its impact onsystem performance, significantly optimizes system outage performance and improvespower efficiency. It provides a new innovative thinking in relay selection ofmulti-relay cooperative communication system.