Massive MIMO with Multi-cell MMSE Processing: Exploiting All Pilots for Interference Suppression

TL;DR

This paper introduces a multi-cell MMSE scheme for massive MIMO networks that exploits all available pilots for interference suppression, leading to significant spectral efficiency gains and practical implementation advantages.

Contribution

It proposes a novel multi-cell MMSE processing method that utilizes all pilot signals for interference suppression, accounting for practical factors like power control and imperfect estimation.

Findings

Significant spectral efficiency improvements over existing schemes.

Effective interference suppression using all pilot directions.

Accurate large-scale SINR approximations for system optimization.

Abstract

In this paper, a new state-of-the-art multi-cell MMSE scheme is proposed for massive MIMO networks, which includes an uplink MMSE detector and a downlink MMSE precoder. The main novelty is that it exploits all available pilots for interference suppression. Specifically, let $K$ and $B$ denote the number of users per cell and the number of orthogonal pilot sequences in the network, respectively, where $\beta = B/K$ is the pilot reuse factor. Then our multi-cell MMSE scheme utilizes all $B$ channel directions, that can be estimated locally at each base station, to actively suppress both intra-cell and inter-cell interference. The proposed scheme is particularly practical and general, since power control for the pilot and payload, imperfect channel estimation and arbitrary pilot allocation are all accounted for. Simulations show that significant spectral efficiency (SE) gains are obtained over the single-cell MMSE scheme and the multi-cell ZF, particularly for large $\beta$ and/or $K$. Furthermore, large-scale approximations of the uplink and downlink SINRs are derived, which are asymptotically tight in the large-system limit. The approximations are easy to compute and very accurate even for small system dimensions. Using these SINR approximations, a low-complexity power control algorithm is also proposed to maximize the sum SE.