Hybrid Combining Based on Constant Phase Shifters and Active/Inactive Switches

TL;DR

This paper introduces a hybrid analog-digital combining architecture for mmWave MU-MIMO systems that enhances spectral and energy efficiency by selective antenna subset activation using constant phase shifters and switches.

Contribution

It proposes a novel antenna subset selection scheme with active/inactive switches and CPS, along with three low-complexity algorithms, improving efficiency over existing methods.

Findings

Higher spectral efficiency demonstrated in simulations

Improved energy efficiency compared to conventional schemes

Effective antenna subset selection algorithms developed

Abstract

In this paper, we propose a new hybrid analog and digital combining architecture for millimeter wave (mmWave) multi-user multiple-input multiple-output (MU-MIMO) systems. The proposed structure employs antenna subset selection per radio frequency (RF) chain based on active/inactive switches and uses constant phase shifters (CPS) to control the phases of signals in the RF circuit. In this scheme, for each RF chain, a subset of receive antennas that contribute more to the desired signal power than the interference power is chosen for signal combining in the analog domain, whereas other receive antennas are excluded from signal combining, thereby enhancing sum-rates. Simultaneously, the proposed structure reduces power consumption in the RF circuit by exclusively activating switches that correspond to the antennas selected for each RF chain. We also develop three low-complexity algorithms for per-RF chain antenna subset selection. Finally, through numerical simulation, we show that the proposed structure provides higher spectral efficiency and higher energy efficiency than conventional hybrid analog and digital combining schemes for mmWave MU-MIMO systems.