On Forward Channel Estimation for MIMO Precoding in Cooperative Relay Wireless Transmission Systems

Linear precoding for wireless multi-input multi-output (MIMO) transceivers has demonstrated substantial strength in cooperative relay networks for achieving high system throughput and performance. However, traditional precoder optimization critically assumes knowledge of channel state information (CSI) at source nodes. For linear MIMO source precoding design, we propose a novel method to estimate the quadratic product of forward-link channel information between source and relay nodes. To conserve bandwidth, our source estimates the forward-link MIMO CSI by utilizing inherent signals transmitted by amplify-and-forward (AF) relays without requiring the cumbersome default method of coordinated relay channel estimation and relay feedback of its estimated CSI. From the overheard AF relay signal, the source node simply extracts the quadratic channel information of its forward-link for designing its precoder. In addition to presenting a low overhead method for forward channel estimation, we also analyze the channel estimation performance by investigating its bias and its Cramer-Rao lower bound. Finally, we present analytical results in comparison with simulations.