Lattice-coded cooperation protocol for the half-duplex Gaussian two-way relay channel

Shahab Ghasemi-Goojani,Hamid Behroozi

doi:10.1186/s13638-015-0483-2

Shahab Ghasemi-Goojani, Hamid Behroozi

Open Access

https://doi.org/10.1186/s13638-015-0483-2

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Abstract

This paper studies the Gaussian two-way relay channel (GTWRC), where two nodes exchange their messages with the help of a half-duplex relay. We investigate a cooperative transmission protocol, consisting of four phases: multiple access (MA) phase, broadcast (BC) phase, and two cooperative phases. For this setup, we propose a new transmission scheme based on superposition coding for nested lattice codes, random coding, and jointly typical decoding. This scheme divides the message of each node into two parts, referred to as satellite codeword and cloud center. Depending on the phase type, the encoder sends a linear combination of satellite codewords or cloud centers. For comparison, a rate region outer bound using a cut-set bound is provided. We show that the proposed scheme can achieve the capacity region in the high signal-to-noise ratio (SNR) regime. In addition, the achievable rate region is within 0.5 bit of the outer bound, regardless of all channel parameters. Using numerical examples, we show that our proposed scheme achieves a larger rate region than the best known 4-phase transmission strategy so far, called the Hybrid Broadcast (HBC) protocol by Kim et al. Our proposed scheme not only improves upon previous 2- and 3- and 4-phase protocols but also can perform superior at some cases to the introduced 6-phase protocol by Gong, Yue, and Wang (which has more complexity relative to our 4-phase protocol).

Highlights

In the last couple of years, cooperative communication and relaying has attracted great interest in wireless networks and some scenarios have been studied from information theory perspective
Since we have studied a 4-phase protocol, and the Multiple Access and Broadcast (MABC) and Time Division Broadcast (TDBC) protocols have two and three phases, respectively, we compare the achievable rate region of our protocol with the outer bound of MABC and TDBC protocols
6 Conclusions In this paper, the Gaussian two-way relay channel in the half-duplex mode, which operates in four phases, is studied

Summary

Introduction

In the last couple of years, cooperative communication and relaying has attracted great interest in wireless networks and some scenarios have been studied from information theory perspective. Using doubly nested lattice codes, an achievable rate region for this scheme is obtained and it is shown numerically that the CoMABC outperforms the MABC and TDBC protocols in terms of sum rate in asymmetric channel conditions. In contrast to [27], instead of increasing the number of phases in order to achieve a larger rate region than the HBC protocol, we propose a new 4-phase cooperative MABC protocol for the half-duplex GTWRC, including phases 1, 2, 3, and 4 of Fig. 1. It is well known that lattice codes can achieve the capacity region of the MABC protocol within 0.5 bit [6, 12] It seems that we do not need to consider GTWRC with more transmission phases (i.e., three or four or six phases).

Channel model

The rate region outer bound and capacity results

Conclusions