Optimizing limited channel state information in wireless cooperative networks

Over the last decade, the development of resource allocation algorithms for cooperative communication networks has focused on optimal, or acceptable suboptimal, solutions assuming full knowledge of channel state information (CSI) in the network. This assumption is, unfortunately, unlikely to be satisfied in practice. Here we turn our attention to the effects of limited CSI on the performance of a cooperative network. We show that the performance gap between the fully centralized approaches and fully distributed algorithms falls exponentially with the number of CSI bits per link available at the central node. We use this to show that, for a large class of objective functions, a close-to-optimal solution is achievable with limited CSI. We also show that proper allocation of the CSI bits to different links in the network is a crucial issue. We propose a simple upper bound on the performance gap and a bit allocation algorithm that minimizes the upper bound. Our numerical results confirm that through optimal bit allocation considerable savings in CSI bits is achieved.