On Achievable Rate Regions of the Asymmetric AWGN Two-Way Relay Channel

TL;DR

This paper explores the achievable data rate regions in an asymmetric Gaussian two-way relay channel, proposing improved coding schemes and identifying optimal strategies based on SNR conditions.

Contribution

It introduces three new achievable rate regions for the asymmetric AWGN two-way relay channel using modified coding schemes.

Findings

Complete-decode-forward is optimal at low SNR for both users.

Functional-decode-forward with nested lattice codes excels at high SNR.

Rate splitting and time-division multiplexing improve performance at mixed SNR levels.

Abstract

This paper investigates the additive white Gaussian noise two-way relay channel, where two users exchange messages through a relay. Asymmetrical channels are considered where the users can transmit data at different rates and at different power levels. We modify and improve existing coding schemes to obtain three new achievable rate regions. Comparing four downlink-optimal coding schemes, we show that the scheme that gives the best sum-rate performance is (i) complete-decode-forward, when both users transmit at low signal-to-noise ratio (SNR); (ii) functional-decode-forward with nested lattice codes, when both users transmit at high SNR; (iii) functional-decode-forward with rate splitting and time-division multiplexing, when one user transmits at low SNR and another user at medium--high SNR.