Spectral- and Energy-Efficiency of Massive MIMO Two-Way Half-Duplex Hybrid Processing AF Relay

Multi-pair two-way massive multiple-input multiple-output (MIMO) relaying is being actively explored. Most of the massive MIMO relaying literature analyzes the spectral efficiency (SE) and energy efficiency (EE) of full radio-frequency (RF) chain relaying systems. We consider a multi-pair hybrid massive MIMO amplify-and-forward relay, with lesser RF chains than antennas. We consider zero-forcing processing at the relay, and analytically derive its asymptotic SE and EE expressions, with the number of relay antennas approaching infinity. We numerically demonstrate that for certain power scaling schemes, a hybrid relay has only marginally inferior SE and EE than a full-RF relay.