Small Cell Range Expansion with Interference Mitigation for Downlink Massive MIMO HetNets

We propose a downlink cell-edge-aware zero forcing (CEA-ZF) and block diagonalization (BD) cooperative precoding scheme to reduce the downlink interference caused by the small cell range expansion in a heterogeneous network (HetNet). The CEA-ZF precoding algorithm adopted in the downlink transmission of macro base station (MBS) exploits the spatial degrees of freedom from large antenna array to suppress the inter-cell interference, and the BD precoding algorithm is introduced in the small access point (SAP) to eliminate the multi-user interference. Simulation results demonstrate the benefits of the proposed downlink precoding scheme over the alternative approach, and verify the proposed scheme as a more effective interference mitigation scheme for the downlink massive multiple-input multiple-output (MIMO) HetNet. Moreover, the optimal range expansion bias (REB) of small cell range expansion is obtained, and we also give a lower bound for the UE sum-rate of the proposed precoding scheme.