Pilot contamination mitigation for high and low interference users in multi-cell massive MIMO systems

Time division duplex massive multiple-input multiple-output (massive MIMO) technology has widely been considered as a splendid technology for enhancing the overall system performance and spectral efficiency of fifth generation wireless cellular network (5G). However, Pilot contamination (PC) due to the reuse of pilot sequences in massive MIMO is the main stumbling block to achieve the required goals. In this paper, an effective PC mitigation scheme is proposed to suppress the efficacy of PC in multi-cell massive MIMO systems. In proposed idea, all the active users are first categorized into high interference (U_H) and low interference (U_L) users based on their large scale-fading. After splitting, orthogonal pilots are allotted to U_H to mitigate the severe PC, and non-orthogonal or identical set of pilots are allotted to the low interference users. After pilot assignment, high interference users get free from serious PC but there is still slight issue of PC among low interference users, which degrades the system performance. Thus, an efficient pilot assignment strategy based on edge weighted interference graph is proposed to decontaminate U_L. The outcome of simulation demonstrates that the proposed scheme improves both achievable data rate and signal-to-interference-plus-noise-ratio. Moreover, the proposed strategy is highly capable to mitigate PC and maximize the system performance.