Effect of pilot contamination on channel estimation in massive MIMO systems

In this paper, we consider the uplink transmission in Massive MIMO systems with OFDM over frequency selective channels. Channel state information (CSI) is essential for exploiting the potential benefits of such systems. So far, few researches have addressed the effect of pilot contamination (PC) on channel estimation. In this paper, analytical expressions on the mean square error (MSE) of two classical channel estimation algorithms in the presence of PC are presented. It is shown that minimum mean square error (MMSE) is more resistant to PC compared to least square (LS). Increasing the number of pilot subcarriers, for both algorithms, does not contribute to better suppression to PC. However, from the results given herein, a clue for mitigating PC can be obtained. The performance of LS and MMSE algorithms in the presence of PC could be improved as the increase in the length of channel impulse response (CIR) and OFDM subcarriers, respectively.