Hybrid Block Diagonalization for Massive MIMO Two-Way Half-Duplex AF Hybrid Relay

TL;DR

This paper proposes a hybrid relay architecture for massive MIMO two-way systems that reduces RF chain costs while maintaining near-optimal spectral efficiency through advanced baseband and RF processing techniques.

Contribution

It introduces a block-diagonalization-based baseband processing and an algebraic norm maximizing relay strategy for hybrid relays in massive MIMO systems, balancing cost and performance.

Findings

Hybrid relay achieves near full RF-chain relay spectral efficiency.

Block-diagonalization effectively cancels inter-user interference.

Hybrid relay reduces RF chain costs with marginal spectral efficiency loss.

Abstract

We consider a multi-pair two-way amplify-and-forward massive multi-input multi-output (MIMO) hybrid relay with MIMO user-pairs. A hybrid relay has lesser number of radio frequency (RF) chains than the antennas, which significantly reduces the implementation cost. We employ block-diagonalization-based baseband processing at the hybrid relay to cancel the inter user-pair interference and equal-gain-combining-based RF processing to maximize the beamforming gain. We also use an algebraic norm maximizing relay transmit strategy to maximize the spectral efficiency (SE) of each user-pair. We numerically show that the proposed hybrid relay has only marginally inferior SE than a full RF-chain relay.