Heterogeneous Massive MIMO with Small Cells

A heterogeneous system of a Massive multiple- input-multiple-output (MIMO) macro cell with low power ancillary small cells can achieve higher spectral and energy efficiency than a Massive MIMO macro cell alone. The performance of such heterogeneous system is examined in this paper. A few small cells are used to enhance the spectral and energy efficiency of the overall system. 

Macro Massive MIMO base station uses a large number of antennas, which enables accurate nulling of small cell users to suppress the interference between macro cell and small cells. We derive analytical expressions for the capacity and signal-to- interference-plus-noise-ratio (SINR) lower bounds for both the downlink (DL) and uplink (UL) of the heterogeneous Massive MIMO system. Our simulation results show that nulling from macro cell Massive MIMO is essential for small cells' good and stable performance.