Pilot Contamination Effect in Massive MIMO and Analysis of Mitigation Techniques

Neha Mehrotra, Ashutosh Kr. Chaubey

Pilot contamination is the major factor to limit the performance of massive MIMO systemsdue to degraded channel estimation. In this paper, we have tried to provide an extensive survey on pilot contamination, and identify all possible sources causing it. We mostly cover the theoretical aspect and review the established theories that have analyzed the effect of pilot contamination on the performance of massive MIMO systems. We studied about a pilot pattern design where zero pilot symbols are inserted into the pilot sequence to reduce the pilot contamination impact on uplink channel estimate and bit error rate performance. We evaluate the achievable rate in forward link with maximum-ratio and zero-forcing precoding at the BS. We analyze spectral efficiency when employing maximum ratio transmission or zero forcing precoding at the base station. We investigate the performance of simple least-squares channel estimator with the higher-complexity minimum mean square error estimator. A brief analysis of mitigation techniques based on existing long term evolution (LTE) measurements - open loop power control (OLPC) and pilot sequence reuse schemes, that avoid PC within a group of cells has been done. Finally, some open problems are highlighted and concluded with broader perspective and a look at future trends in pilot contamination inmassive MIMO systems.