Pilot Assignment for Joint Uplink-Downlink Spectral Efficiency Enhancement in Massive MIMO Systems with Spatial Correlation

TL;DR

This paper introduces a flexible pilot assignment method for massive MIMO systems that jointly optimizes uplink and downlink spectral efficiency, improving performance in correlated Rayleigh fading channels.

Contribution

It presents a novel joint optimization framework with a closed-form spectral efficiency expression and a two-step algorithm for pilot assignment and power control.

Findings

Algorithm converges quickly to higher minimum sum SE.

Joint uplink-downlink optimization outperforms previous methods.

Effective in correlated Rayleigh fading environments.

Abstract

This paper proposes a flexible pilot assignment method to jointly optimize the uplink and downlink data transmission in multi-cell Massive multiple input multiple output (MIMO) systems with correlated Rayleigh fading channels. By utilizing a closed-form expression of the ergodic spectral efficiency (SE) achieved with maximum ratio processing, we formulate an optimization problem for maximizing the minimum weighted sum of the uplink and downlink SEs subject to the transmit powers and pilot assignment sets. This combinatiorial optimization problem is solved by two sequential algorithms: a heuristic pilot assignment is first proposed to obtain a good pilot reuse set and the data power control is then implemented. Numerical results manifest that the proposed algorithm converges fast to a better minimum sum SE per user than the algorithms in previous works.