When Alamouti codes meet interference alignment: Transmission schemes for two-user X channel

Interference alignment increases transmission rate in terms of multiplexing gain for X channel. In this paper, we propose a fixed-rate transmission scheme over a two-user X channel where each of the two double-antenna transmitters has independent messages for each of the two double-antenna receivers. Each transmitter encodes symbols using Alamouti codes followed by beamformers that align interference at unintended receivers. The receiver removes the aligned interference and decouples symbols using interference cancellation followed by symbol-by-symbol decoding. Our analysis shows that the proposed scheme achieves a diversity gain of 2 at the maximum node-to-node symbol-rate of 2 over 3.