Reconfigurable Antenna Based Blind Interference Alignment over Heterogenous Block Fading Channels

This paper studies the blind interference alignment (BIA) of a heterogeneous 3-user 2x1 broadcast channel (BC). In the BC considered, the transmitter equipped with two antennas broadcasts information symbols to three receivers with each possessing a unique reconfigurable antenna. By heterogeneous it means that the three 2x1 links connecting the transmitter and the three receivers experience independent block fading and different coherence times. To meet the requirement of BIA on the 3-user 2x1 BC, the heterogeneous channel structure could be simply transformed into a homogeneous 3-user broadcast channel by applying reconfigurable antennas to perform mode switching. However, the DoF gain achieved by BIA should compensate the expense on frequent mode switching. To this end, an utility measure is established, and an optimization problem maximizing the achievable utility value is modeled. The solution of the optimization problem is derived, and the impact of the three coherence times on the optimal solution is investigated.