Interference mitigation with MIMO precoding in femtocellular systems

Femtocells have the potential to provide significant benefits for cellular users. However, the introduction of femtocells also introduces new sources of interference for existing users. In this paper, three techniques for interference mitigation using MIMO precoding are considered at the femtocellular base stations to reduce the interference to the macrocellular users: Precoding Matrix Index (PMI) restriction, Least Interference (LI) and Codebook-based Beamforming with Nulling (CBN). Different sizes of codebooks are generated and applied in these three methods in a single-cell environment. We show that PMI restriction improves macrocellular performance at the expense of femtocellular throughput; LI maximizes the former while minimizing the latter; and CBN theoretically achieves a balance between the two.