Semi-blind interference alignment based on OFDM over frequency selective X channels

In this paper, we focus on a X channel; a system with two transmitters and two receivers each equipped with a single antenna, where independent messages need to be conveyed over channels from each transmitter to each receiver. A key concept of that arises in the context of the X channel is interference alignment (IA) that refers to an overlap of signal spaces occupied by undesired interference at each receiver while keeping desired signal spaces distinct. However, all the channel responses and the precise time synchronization are required at every transmitter and receiver to realize the IA, which are seriously demanding in practice. In this paper, we propose semi-blind IA (S-BIA) scheme exploiting frequency selectivity of wireless channels using orthogonal frequency division multiplexing (OFDM), which only requires channel responses corresponding to each transmitter. Numerical results confirm that proposed S-BIA can achieve the same degrees of freedom as conventional IA even in the presence of time synchronization errors.