Contemporary Approaches to Mitigate Pilot Contamination in Massive Mimo Systems

Abstract

Massive Multiple Input Multiple Output (MIMO) is a promising technology for meeting the demand of high data capacity for mobile networks in the future. Obtaining channel state information (CSI) in MIMO systems provides energy and spectrum efficiency. Hence, the accuracy of the CSI is very important. Time Division Duplexing (TDD) is a good alternative method to obtain CSI in Massive MIMO systems. Pilot sequences are used to obtain CSI. In practice, it is not possible to assign a different pilot sequence to each user terminal. In particular, the use of the same pilot sequences in different cells in Massive MIMO systems causes the problem of pilot contamination. Many studies have been conducted in an attempt to mitigate this problem. In this study, the reasons for pilot contamination are discussed and the methods proposed in the literature for eliminating or mitigating pilot contamination are presented. In addition, the case of pilot contamination-related security in Massive MIMO and other related issues that may be important in future systems are highlighted.