Relay assignment in multiple source-destination cooperative networks with limited feedback

We consider in this paper relay assignment for cooperative systems with multiple source-destination pairs. The objective here is to assign the relays to the source-destination pairs in a such way that all pairs would achieve the maximum diversity. Normally, for a network with multiple source-destination pairs, none of the destinations can acquire the channel state information (CSI) of the entire network without feedback. To this end, we design a practical limited feedback strategy in conjunction with two relay assignment schemes, i.e., fullset selection and subset selection, which are based on maximizing the minimum end to end (E2E) signal to noise ratio (SNR) among all pairs. In this strategy, each destination acquires its signal-to-noise ratios (SNRs), quantizes them, and feeds them back to the relays. The relays construct the end-to-end (E2E) SNR matrix and select the relay assignment choice from all possible relay assignment permutations or only a subset of these permutations. We analyze the performance of these schemes over independent Rayleigh fading channels in terms of the worst E2E SNR. We investigate the asymptotic performance of the proposed schemes at high SNR. We show that relay assignment with quantized CSI can achieves the same first-order diversity as that of full CSI, but there is a second-order diversity loss. We also demonstrate that increasing the quantization levels yields performance that is close to that of having full knowledge of the CSI.