Performance Analysis of Linear Precoders in TDD Massive MIMO Systems

Abstract

The channel estimation of the reverse link and forward link in the massive multiple-input-multiple-output (M-MIMO) systems is projected using reverse link pilot training and channel reciprocity of time-division duplex (TDD) protocol, respectively. Nevertheless, the utilization of non-orthogonal reverse link pilot sequences in the neighboring cells, owing to limited coherence time causes pilot contamination that results in inter-cell interference in forward link data transmission. To design a TDD M-MIMO system properly under a practical multi-cell environment, it is necessary to evaluate the achievable rate of such systems. The performance assessment of multi-cell TDD M-MIMO forward-link system with linear precoders is proposed. The reverse-link and forward-link channels are first estimated by the BSs using least square channel estimator. Later, the closed-form approximate achievable forward-link sum-rate expressions of M-MIMO system with matched-filter (MF) and zero-forcing (ZF) precoders are derived. Finally, the performances of the achievable forward-link sum-rate for MF and ZF precoders are compared with respect to cell size, number of BS antennas, pilot length, and transmission SNR. Numerical simulation outcomes support the precision of closed-form rate expressions.