Relay Selection Issues for Amplify-and-Forward Cooperative Systems with Interference

In this paper, an Amplify-and-Forward (AF) cooperative strategy in interference limited networks is considered. In contrast to previously reported work, where the effect of interference is ignored, the effect of multi-user interference in AF schemes is analyzed. It is shown that the interference changes the statistical description of the conventional AF protocol and a statistical expression is subsequently derived. Asymptotic analysis of the expression shows that interference limits the diversity gain of the system and the related channel capacity is bounded by a stationary point. In addition, it is proven that previously proposed relay selection criteria for multi-relay scenarios become inefficient in the presence of interference. Based on a consideration of the interference term, two new selection criteria suitable for different system set-ups are proposed. A theoretical framework for selecting when to apply the proposed selection criteria is also presented.