Opportunistic Interference Alignment for MIMO Interfering Broadcast Channels

In this paper, we propose an opportunistic interference alignment (OIA) technique for cellular downlink networks, which efficiently reduces the effect of inter-cell interference from base stations (BSs) in other cells and eliminates intra-cell interference among spatial streams in the same cell. We show that the user scaling per cell required to achieve a target degrees-of-freedom can be fundamentally lowered, compared with the previous results. In addition, we relate the derived user scaling law to the interference decaying rate with respect to the number of users for given signal-to-noise ratio. Simulation results show that the proposed OIA significantly outperforms the previous schemes in terms of both sum-interference and achievable sum-rate even in practical environments.