A Systematic Investigation of Uplink Massive MIMO and Interference Management in Heterogeneous Networks

A two-tier network consisting of a Massive Multiple Input Multiple Output (MIMO) system overlaid with a hotspot tier of sub base stations (SBS) is considered. First, the achievable uplink(UL) spectral efficiency(SE) is analyzed, based on the channel estimation carried out at the base stations (BS) using UL pilot transmission. Performance of various precoding schemes are evaluated after the application of spatial channel correlation and pilot decontamination. The achievable SE expressions for the UL is derived for different UL channel estimation schemes. The SE tends to increase with the number of BS antennas. Spatial correlation enables the BS to eliminate the coherent interference. The SE for schemes such as Regularized Zero Forcing (RZF) and Maximum Ratio Transmission (MRT) is unlikely to increase beyond a limit as it is determined by the coherent interference from pilot contamination, since only the impact of noise and non-coherent interference vanish. In MMSE channel estimation, the SE increases since the impact of noise and all the types of interference vanishes.