Interference alignment aided by relays for the quasi-static X channel

In this paper, two relay-aided interference alignment (IA) schemes are proposed for the quasi-static M×2 X channel. The first scheme utilizes one full-duplex relay and the second scheme utilizes two half-duplex relays. In the proposed schemes, transmitters transmit in every time slot and relays operate in amplify-and-forward (AF) mode. By confirming the linear independence between the desired signals and interference and also among the desired signals, it is shown that the proposed schemes can achieve 2M/(M + 1) degrees of freedom (DoF) which is the maximum DoF of M × 2 X channel.