A feasibility study on opportunistic interference alignment: Limited feedback and sum-rate enhancement

In this paper, we illuminate opportunistic interference alignment (OIA) for multi-input multi-output (MIMO) interfering multiple-access channels (IMACs) by tackling the following two practical challenges: i) feedback overhead due to scheduling metrics sent by users and ii) sub-optimality in terms of sum-rate derived from the conventional OIA. To reduce the feedback overhead, we first propose an opportunistic feedback strategy based on interference leakage, which guarantees the total generating interference to other-cell base stations to be smaller than a predefined threshold. In addition, we also consider the channel gain of the desired link for improving the achievable sum-rate for uplink, while the conventional OIA only uses the generating interference to other cells as a scheduling metric. Simulation results show that the effective sum-rate of the proposed technique is significantly higher than that of conventional scheduling methods, including the conventional OIA, for all signal-to-noise ratio (SNR) regimes. The effective sum-rate is obtained by considering the effect of feedback overhead on the total throughput of the MIMO IMAC model.