Optimization of coherent amplify-and-forward cooperative transmissions in spatially-multiplexed MIMO-OFDM systems

We consider a wireless cooperative network, where communication between a source-destination pair is assisted by multiple relaying nodes. To cope with the wideband nature of the wireless channel, all network nodes are equipped with multiple antennas and employ orthogonal frequency-division multiplexing (OFDM) modulation. Leveraging on an approximate yet accurate performance analysis of the network, carried out in terms of symbol error probability (SEP), a closed-form minimum-SEP optimal design of precoding and relaying matrices is proposed, which allows one to fully exploit the distributed diversity inherent to the cooperative approach, but requires accurate channel state information at the source and the relays. Monte Carlo numerical results are provided to assess the performance advantages that can be achieved by the proposed design.