Network-Coded Cooperation With Outdated CSI

The impact of outdated channel state information (CSI) on the performance of multiple-source, multiple-relay network-coded cooperation (NCC) with relay selection (RS) is investigated. In RS-based NCC, K relays are selected (from M cooperative relays). Each of these will decode N > 1 sources' messages, uses a non-binary network coding based on maximum distance separable codes to form a network-coded packet, and forwards it to the destination. We derive the exact outage probability and simple and accurate outage approximations (asymptotics) at high signal-to-noise ratio. We show that the full diversity gain of d = M + 1 is only achieved when K >= N and CSI are perfect. Outdated CSI, however, degrades the system performance, and the asymptotic diversity gain is always equal to d = K + 1. We also give simulation results to validate the theoretical study.