Massive MIMO over Correlated Fading Channels: Multi-Cell MMSE Processing, Pilot Assignment and Power Control

TL;DR

This paper develops a large-scale approximation for uplink SINR in multi-cell massive MIMO systems with correlated fading, enabling efficient pilot assignment and power control to reduce interference and improve spectral efficiency.

Contribution

It introduces a novel large-scale SINR approximation and a low-complexity pilot assignment scheme that exploits channel correlation, along with power control strategies for enhanced performance.

Findings

The SINR approximation is asymptotically tight in large systems.

The proposed pilot assignment reduces pilot contamination significantly.

Power control schemes improve spectral efficiency and fairness.

Abstract

We consider a multi-cell massive multiple-input-multiple-output (MIMO) system with correlated Rayleigh fading channels, where pilot reuse is permitted within each cell (to reduce pilot overhead), and each base station (BS) utilizes multi-cell minimum mean square (M-MMSE) precoders and combining. We derive a large-scale approximation of the uplink signal-to-interference-and-noise ratio (SINR) that is asymptotically tight in the large system limit. By leveraging the derived SINR approximation, we (i) develop a low-complexity multi-cell pilot assignment (PA) scheme aimed at minimizing pilot contamination from pilot-sharing users, via effectively exploiting the channel spatial correlation matrices of all users in the network, (ii) design pilot and data power allocation schemes, using both the weighted sum and max-min spectral efficiency (SE) metrics. Simulations demonstrate the superiority of our multi-cell PA scheme, requiring significantly less pilot overhead. The proposed power allocation schemes also achieve substantial sum SE gains with good fairness among users compared to equal power allocation.