Two-level precoding based interference reduction in uplink for MIMO femtocell networks

The femtocell technology is a promising concept for deploying the next generation of wireless networks. One of the most critical issues concerning femtocell deployment is the interference between femtocells and macrocells. Interference alignment (IA) is a technique that tackles the interference management problem in a macrocell/femtocell heterogeneous network (HetNet). Using IA, macrocell users (MUs) design precoders to align their signals in such a way that they do not cause interference at the femtocell base stations (FBSs). Nevertheless the availability of MIMO dimensions limit the extent of alignment and hence the residual interference degrades the performance of femtocell tier. In this paper, we design a novel two-level precoder at the MU to reduce the overall leaked interference at the FBS in uplink transmissions. IA precoding done in the first level aligns the leakage signals from MUs into the interference subspace of FBSs. In the second level, leakage based precoding further reduces the strength of the aligned interference signals. This helps to reduce error in the femtocell tier and hence provides better quality of service (QoS) guarantees. The performance advantages of the proposed precoding technique is validated through simulation studies.