On the Achievable Rates of Multihop Virtual Full-Duplex Relay Channels

TL;DR

This paper investigates multihop virtual full-duplex relay channels, proposing a mixed decode-and-forward and quantize-map-and-forward scheme that improves achievable rates, especially as the number of relay stages increases.

Contribution

It introduces a hybrid relay scheme combining DF and QMF with rate-splitting, outperforming previous QMF-only schemes in multihop relay networks.

Findings

The mixed scheme achieves higher rates than QMF alone.

Performance gains grow with the number of relay stages K.

The scheme approaches capacity more closely as K increases.

Abstract

We study a multihop "virtual" full-duplex relay channel as a special case of a general multiple multicast relay network. For such channel, quantize-map-and-forward (QMF) (or noisy network coding (NNC)) achieves the cut-set upper bound within a constant gap where the gap grows {\em linearly} with the number of relay stages $K$. However, this gap may not be negligible for the systems with multihop transmissions (i.e., a wireless backhaul operating at higher frequencies). We have recently attained an improved result to the capacity scaling where the gap grows {\em logarithmically} as $\log{K}$, by using an optimal quantization at relays and by exploiting relays' messages (decoded in the previous time slot) as side-information. In this paper, we further improve the performance of this network by presenting a mixed scheme where each relay can perform either decode-and-forward (DF) or QMF with possibly rate-splitting. We derive the achievable rate and show that the proposed scheme outperforms the QMF-optimized scheme. Furthermore, we demonstrate that this performance improvement increases with $K$.