A Multi-cell MMSE Detector for Massive MIMO Systems and New Large System Analysis

TL;DR

This paper introduces a novel multi-cell MMSE detector for massive MIMO systems that leverages all estimated channel directions to suppress interference, providing a new large-system analysis and demonstrating significant spectral efficiency improvements.

Contribution

It proposes a multi-cell MMSE detector utilizing all estimated channel directions and derives a deterministic equivalent for uplink SINR in large systems.

Findings

Significant spectral efficiency gains over traditional detectors.

Deterministic SINR expression accurately predicts performance.

Performance improves with higher pilot reuse factor and number of users.

Abstract

In this paper, a new multi-cell MMSE detector is proposed for massive MIMO systems. Let $K$ and $B$ denote the number of users in each cell and the number of available pilot sequences in the network, respectively, with $B = \beta K$, where $\beta \ge 1 $ is called the pilot reuse factor. The novelty of the multi-cell MMSE detector is that it utilizes all $B$ channel directions that can be estimated locally at a base station, so that intra-cell interference, parts of the inter-cell interference and the noise can all be actively suppressed, while conventional detectors only use the $K$ intra-cell channels. Furthermore, in the large-system limit, a deterministic equivalent expression of the uplink SINR for the proposed multi-cell MMSE is derived. The expression is easy to compute and accounts for power control for the pilot and payload, imperfect channel estimation and arbitrary pilot allocation. Numerical results show that significant sum spectral efficiency gains can be obtained by the multi-cell MMSE over the conventional single-cell MMSE and the recent multi-cell ZF, and the gains become more significant as $\beta$ and/or $K$ increases. Furthermore, the deterministic equivalent is shown to be very accurate even for relatively small system dimensions.