Pilot Contamination Mitigation in Massive Multi-Input Multi-Output (MIMO) System

Abstract

Massive MIMO is one of the key components in the technologies of the next generation wireless communication network; the fifth generation (5G). Although massive MIMO is considered a promising technology in 5G, its efficiency is limited by the challenge of the pilot contamination problem. Pilot contamination problem occurs when user terminals in different cells concurrently share the same control signal set (called pilot sets), which results in causing interference in the estimated channel. In this paper, a model to reduce the pilot contamination problem and to increase the system sum-rate is proposed. The proposed model is a combination of three schemes: 1) A time-shifting protocol where the pilots are transmitted by users without overlapping in time; 2) A directional pilot scheme where the users directionally transmit the pilot; 3) A pilot allocation scheme for channel estimation based on the greedy algorithm to optimize the system sum-rate and the signal to interference and noise ratio with low complexity, and to mitigate the pilot contamination. Simulation results show that significant improvements are achieved compared to existing directional, time shifting and pilot allocation schemes.