Research Of Relay Selection Algorithm In Cooperative Communication Systems

Multiple antennas may be unavailable in the mobile terminals due to size, power and cost limitations. Sendonaris was inspired by relay channel, and then put forward a diversity technology called cooperative diversity which is suitable for single antenna. Cooperative diversity is a virtual multi-antenna diversity techniques, which can effectively resist channel fading and is becoming one of the hot topics in wireless communication fields. The nodes in the wireless networks share their antennas as a virtual multi-antenna systems. In this sense, cooperative diversity provides a new alternative implementation approach for multi-antenna technology. However, there may be more than one potential partners in the system, which partner will be chose for cooperation is worth researching on. Partner (relay) selection is an important factor of influence on the performance of cooperative diversity system.Cooperative diversity and relay selection sheme were studied in this paper, the main work is as follows: diversity technology which is widely used in the mobile communication systems; The basic theory as well as the current development and compare of cooperative diversity protocols; The current development and compare of relay selection shemes.Aimed at the problem of low efficiency of the Full-search relay selection algorithm, an improved symbol error probability-based relay selection is proposed. First, based on the equal power allocation and symbol error probability of the system an equivalent channel gain was brought in. Then with the descending order of the parameter, the signal-to-noise ratio can be taken as the threshold, and different relay node set was choosen to minimize the symbol error probability in case of equal power allocation. As is shown in the simulation results, the error probability performance of this relay selection scheme is similar to the optimal Full-search scheme while the complexity is reduced at least 1/20.Aimed at the problem that the spending of centralized control relay selection algorithm for obtaining the instantaneous channel state information is large, inspired by distributed relay selection algorithim, a Semi-Distributed relay selection algorithm is discussed for decode–and-forward wireless relay networks. In the proposed algorithm, each relay node can make decision on its feasibility individually, and the ultimate decision on the relay node selection among multiple feasible ones is made in centralized manner. Since there is no need on exchanging channel state information among different nodes, the proposed algorithm is simple for implementation and suitable for practical applications,and can provide the same system capacity with centralized control relay selection algorithim.