Soft Pilot Reuse and Multi-Cell Block Diagonalization Precoding for Massive MIMO Systems

TL;DR

This paper proposes a combined approach of soft pilot reuse and multi-cell block diagonalization precoding to mitigate pilot contamination and improve the quality of service for edge users in massive MIMO systems, with significant uplink and downlink rate enhancements.

Contribution

The paper introduces a novel scheme integrating SPR and MBD precoding tailored for massive MIMO, effectively reducing inter-cell interference for edge users.

Findings

Significant uplink and downlink rate improvements for edge users.

Reduced inter-cell interference through MBD precoding.

Slight decrease in center users' rates.

Abstract

The users at cell edge of a massive multiple-input multiple-output (MIMO) system suffer from severe pilot contamination, which leads to poor quality of service (QoS). In order to enhance the QoS for these edge users, soft pilot reuse (SPR) combined with multi-cell block diagonalization (MBD) precoding are proposed. Specifically, the users are divided into two groups according to their large-scale fading coefficients, referred to as the center users, who only suffer from modest pilot contamination and the edge users, who suffer from severe pilot contamination. Based on this distinction, the SPR scheme is proposed for improving the QoS for the edge users, whereby a cell-center pilot group is reused for all cell-center users in all cells, while a cell-edge pilot group is applied for the edge users in the adjacent cells. By extending the classical block diagonalization precoding to a multi-cell scenario, the MBD precoding scheme projects the downlink transmit signal onto the null space of the subspace spanned by the inter-cell channels of the edge users in adjacent cells. Thus, the inter-cell interference contaminating the edge users' signals in the adjacent cells can be efficiently mitigated and hence the QoS of these edge users can be further enhanced. Our theoretical analysis and simulation results demonstrate that both the uplink and downlink rates of the edge users are significantly improved, albeit at the cost of the slightly decreased rate of center users.