Combining Relay and Direct Links for Joint Symbol and Channel Estimation in MIMO Amplify-and-Forward (AF) Systems

The non-regenerative Amplify-and-Forward (AF) relaying is a powerful yet simple way to extend signal coverage in wireless communications. Without any decoding procedure, relay stations operating under this protocol offers a very small cost of deployment and operation in comparison with regenerative protocols. However, the AF protocol has its disadvantages, particularly the challenge of estimating the channel matrices that compose the relay link. Besides, few works were dedicated to estimate those channels without using bandwidth-consuming pilot symbols. We resort to a recent nested PARAFAC tensor modeling of the considered relay MIMO system, and then we propose a semi-blind receiver that combines the signals from the relay link with an eventual direct link, providing an improved symbol estimation along with the identification of the channels that compose the relaying network. Compared with an inspiring previous receiver that exploits the PARATUCK2 tensor model, our new receiver have presented consistent coding gains.