Downlink Relay Selection Algorithm for Amplify-and-Forward Cooperative Communication Systems

In wireless networks, the cooperative relaying that provides a spatial diversity and improves the performance of system is a tendency in the future communications. There are three strategies in the cooperative communications. One is Amplify-and-Forward (AF) mode. Another is Decode-and-Forward (DF) mode and the other is Compress and Forward (CF) mode. Comparing with these three kind modes, AF mode is with the low complexity to implement. Consider the Raleigh fading environment where there are one information source, M relay stations and N destinations. The downlink signal includes two parts. One is from the source and the other comes from the relay stations. In order to achieve the maximum throughput in the system, it should obtain the maximum mutual information between the source and the destination. Hence, how to select an optimal relay station is important in the cooperative communications. This project proposes a relay selection algorithm with Amplify-and-Forward mode employed. The optimal selection scheme is based on the exhaustive search method. It is easy to be realized with a high computational complexity. In order to reduce the computational complexity, the relay station selection scheme with a maximum mutual information finding is proposed. With different relay station selection schemes, the performances are given for comparison.