Spectral Efficiency Optimization For Millimeter Wave Multi-User MIMO Systems

TL;DR

This paper introduces a novel penalty dual decomposition method for optimizing hybrid precoding in millimeter wave multi-user MIMO systems, achieving near fully-digital performance with fewer RF chains.

Contribution

It presents the first direct solution to the nonconvex hybrid precoding problem in mmWave multi-user MIMO using PDD, with guaranteed convergence to KKT solutions.

Findings

Hybrid precoding approaches fully digital performance with minimal RF chains.

Proposed PDD method guarantees convergence to optimal solutions.

Effective in both infinite and finite resolution phase shifter scenarios.

Abstract

As a key enabling technology for 5G wireless, millimeter wave (mmWave) communication motivates the utilization of large-scale antenna arrays for achieving highly directional beamforming. However, the high cost and power consumption of RF chains stands in the way of adoption of the optimal fullydigital precoding in large-array systems. To reduce the number of RF chains while still maintaining the spatial multiplexing gain of large-array, hybrid precoding architecture has been proposed for mmWave systems and received considerable interest in both industry and academia. However, the optimal hybrid precoding design has not been fully understood, especially for the multi-user MIMO case. This paper is the first work that directly addresses the nonconvex hybrid precoding problem of mmWave multi-user MIMO systems (without any approximation) by using penalty dual decomposition (PDD) method. The proposed PDD method have a guaranteed convergence to KKT solutions of the hybrid precoding problem under a mild assumption. Simulation results show that, even when both the transmitter and the receivers are equipped with the fewest RF chains that are required to support multi-stream transmission, hybrid precoding can still approach the performance of fully-digital precoding in both the infinite resolution phase shifter case and the finite resolution phase shifter case with several bits quantization.