Ergodic Rate Analysis of Massive MIMO Systems in K-Fading Environment

Massive MIMO (multiple-input multiple-output) has been identified as a key technology for next generation cellular systems. This paper considers a multi-cellular system with large antenna arrays at the base station (BS) and single antenna user terminals (UTs), operating in a time division duplex (TDD) mode, under a composite fading-shadowing environment. In the uplink transmission, the pilot contamination occurs as the UTs transmit pilots to their respective BSs, and the serving BS estimates the channel state information using a minimum mean squared error estimation. This channel information is further used to design beamforming (BF) and regularized zero-forcing (RZF) precoders for downlink (DL) transmission. We analyze the ergodic rates for DL transmission using different precoding schemes and varying shadowing intensity. It has been observed that shadowing does not average out as we increase the number of antennas as opposed to multi-path fading, and the severity of shadowing badly affects the performance of massive MIMO systems.