A Novel Relay-Aided Successive Aligned Interference Cancellation for X Channels with Blind Transmitters

In this paper, we propose a novel relay-aided successive aligned interference cancellation (RaSAIC) method for a 2 × K X channel with L full-duplex relays. The key idea behind the RaSAIC is to apply a cooperative relays' precoding technique that aligns interference signals at unintended receivers while creating an Alamouti structure for the desired signals. With the proposed cooperative relay transmission technique, it is shown that both the optimal degrees of freedom gain of 2K/K+1 and the diversity gain of two are achievable for constant channels when the numbers of relays' antennas are enough to satisfy the derived feasibility conditions without requiring channel state information (CSI) at transmitters but with global and local CSI at relays and receivers, respectively.