QoS guarantees in relay networks with multiple source-destination pairs and imperfect CSI

A scenario is considered in which one relay with multiple antennas facilitates the communication of multiple single-antenna source-destination pairs. The communication occurs in two slots; in the first slot, the sources transmit simultaneously to their distinct destinations, and in the second slot, the relay forwards the received signal in an amplify-and-forward (AF), zeroforcing beamforming (ZFBF) fashion. The ZFBF matrix is designed to minimize the relay transmit power, while meeting the signal-to-interference-ratio (SINR) requirements at the destinations. Errors in the channel state information (CSI) result in inter-destination interference, and thus in SINR reduction. Based on knowledge of the CSI errors statistics, a robust ZFBF design is proposed that iteratively adjusts the magnitudes of the relay beamforming weights, based on the channel conditions of all S-D pairs, so that the worst case SINRs at the destinations are higher than the required thresholds.