Relay selection methods for wireless cooperative communications

We study the problem of relay selection in a wireless cooperative network. Assuming a single source, a single destination, and N uniformly distributed candidate relays, we seek to select a set of cooperating relays to minimize the total transmission time of a fixed amount of data. We propose two selection methods: Best expectation, which adaptively selects the relays, and Best-m, which selects an optimally pre-determined number of relays. Each method is implemented with a simple and optimal algorithm. We further provide closed-form, analytical approximations of these algorithms´ performance, which help simplify the process of finding the optimal number of cooperating relays. Simulations illustrate the performance of the proposed relay selection methods and show a close match between the analytical approximations and the numerical values. Through some initial studies, we also observe a simple and intriguing connection between the Best-m selection method and the network geometry. Provided that the relays are uniformly distributed, the source can simply cooperate with all the relays within a radius of a fixed proportion of the source-destination distance.