Spectral Efficiency Analysis and Achievable Rates in Massive MIMO Systems with LS Channel Estimation

Due to the re-use of limited pilot resources from one cell to another in massive MIMO systems, pilot contamination results which affects the quality of the Channel State Information (CSI). This paper considers the challenge of pilot contamination in Time Division Duplex (TDD) multi-cell massive MIMO systems. We derive closed-form lower bounds on the achievable rates for the cases of maximum-ratio combining (MRC) and zero-forcing (ZF) detectors with Least Square (LS) channel estimation. We consider mean interference case where the users are uniformly distributed in all cells, analyze the performance of three different pilot allocation scenarios. The results show the superiority of MRC to ZF for a low signalto-interference-plus-noise ratio in terms of spectral efficiency and vice versa. Our simulation results show the accuracy of the derived bounds.