Relay selection methods for wireless cooperative communications

Abstract

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.