Interference cancellation in HetNet uplink with and without MU‐CSIR: a subspace‐based approach

One of the prime concerns regarding multi-tier architecture in heterogeneous networks (HetNets) is the interference between users in macrocells and femtocells. Interference mitigation (IM) in femtocells is of critical importance due to high power interfering signals from macrocells. However, such IM techniques generally demand intensive signalling overhead that adversely affect the benefits of multi-tier network architecture. A novel interference cancellation technique with very low signalling overhead that does not require global channel state information at the transmitter is proposed in this study for the uplink of HetNets. The proposed subspace nulling (SN)-based method projects the composite received signal onto the intersection space of the left null space of the interfering space and the row space of desired space to cancel the cross-tier interference. This is achieved both in the presence and absence of macrocell user channel state information at receiver (MU-CSIR). The authors also propose a low complexity subspace method that works with the knowledge of MU-CSIR. Exhaustive simulation studies show that the proposed schemes fully cancel the cross-tier interference in femtocell tier resulting in better bit error rate performance for the FU receiver.