Spectral efficient protocols for half-duplex fading relay channels

TLDR

We study two‑hop communication protocols with half‑duplex relays, where each source‑to‑destination transmission occupies two channel uses, causing a spectral‑efficiency loss reflected by a pre‑log factor of one‑half in capacity expressions. We propose two new half‑duplex relaying protocols that eliminate this pre‑log factor. The first protocol implements two‑way relaying via an amplify‑or‑decode‑and‑forward relay, extended to a multi‑user setting with orthogonalize‑and‑forward relays employing distributed zero‑forcing, while the second protocol uses two alternating relays to perform two‑path relaying. Both protocols recover a significant portion of the half‑duplex loss.

Abstract

We study two-hop communication protocols where one or several relay terminals assist in the communication between two or more terminals. All terminals operate in half-duplex mode, hence the transmission of one information symbol from the source terminal to the destination terminal occupies two channel uses. This leads to a loss in spectral efficiency due to the pre-log factor one-half in corresponding capacity expressions. We propose two new half-duplex relaying protocols that avoid the pre-log factor one-half. Firstly, we consider a relaying protocol where a bidirectional connection between two terminals is established via one amplify-and-forward (AF) or decode-and-forward (DF) relay (two-way relaying). We also extend this protocol to a multi-user scenario, where multiple terminals communicate with multiple partner terminals via several orthogonalize-and-forward (OF) relay terminals, i.e., the relays orthogonalize the different two-way transmissions by a distributed zero-forcing algorithm. Secondly, we propose a relaying protocol where two relays, either AF or DF, alternately forward messages from a source terminal to a destination terminal (two-path relaying). It is shown that both protocols recover a significant portion of the half-duplex loss