On the Achievable Degrees of Freedom of a Relay Aided X-Channel

In this paper, we investigate the effect of a relay on the Degrees of Freedom (DoF) of a single input single output (SISO) X-channel with no channel state information at transmitters (CSIT). In contrast to previous work, which focused on two antennas at the relay to achieve the optimal 4/3 DoF, we focus on the case of a single antenna half duplex relay. We show that with a single antenna relay and delayed output feedback, the upper bound of 4/3 DoF for the X-channel is achievable and we propose the achievability scheme. Moreover, we study the alternating CSIT availability distribution for the SISO X-channel and provide few remarks on the achievability of the optimal DoF.