Joint Precoder Design for SWIPT-Enabled MIMO Relay Networks With Finite-Alphabet Inputs

Baojun Chen,Xiaodong Tu,Xiaodong Zhu

doi:10.1109/access.2020.3027548

Abstract

In this paper, the problem of mutual information maximization in a two-hop multiple-input multiple-output (MIMO) relay network with simultaneous wireless information and power transfer (SWIPT) is investigated, where the relay node, without constant power supply, harvests the energy for information forwarding. The goal is to maximize the mutual information by using the joint design of source and relay precoders, which is formulated as an optimization problem under the constraints of transmit power and harvested energy. Two scenarios with practical energy harvesting schemes employed at the relay, i.e., power splitting (PS) and time switching (TS) schemes, are considered. Although the formulated optimization problems in the two scenarios are both nondeterministic polynomial-time (NP)-hard, by exploiting the structure of the optimization problems and analyzing the characteristics of precoders, we develop near optimal joint source and relay precoding algorithms for them. Additionally, we analyze the feasible regions of PS and TS ratios, respectively, and propose a backtracking line search based method to find near optimal PS and TS ratios. The main contributions of this paper are as follows: 1) Unlike existing works based on the assumption of ideal Gaussian signals, this paper supposes the inputs to the network are finite-alphabet signals, which is a more practical scenario. 2) The high complexity of mutual information with finite-alphabet signals leads to an intractable optimization problem; however, an efficient solving framework based on semidefinite relaxation (SDR) and Karush-Kuhn-Tucker (KKT) theorem is proposed. Finally, simulation results verify the efficacy of the proposed joint precoding designs.

Highlights

Relay communication technology has attracted much research interest because it can further improve the channel capacity and system coverage in wireless networks [1]
2) The high complexity of mutual information with finite-alphabet signals leads to an intractable optimization problem; an efficient solving framework based on semidefinite relaxation (SDR) and Karush-Kuhn-Tucker (KKT) theorem is proposed
The main contributions of this paper are as follows: first, we investigate the problem of maximizing mutual information in simultaneous wireless information and power transfer (SWIPT)-enabled multiple-input multiple-output (MIMO) relay networks with finitealphabet inputs, which, as far as we know, has not been reported in literature

Summary

Introduction

Relay communication technology has attracted much research interest because it can further improve the channel capacity and system coverage in wireless networks [1]. In order to improve the end-to-end performance of MIMO relay system, precoding operation, whose goal is usually to maximize the source-destination information rate, is generally performed at the source, relay, or both source and relay nodes. MIMO relay networks usually adopt two protocols, namely amplify-and-forward (AF) and. For the AF based networks, [3] designed a relay precoding algorithm that is used to maximize the information rate without source node processing, while [4] and [5] showed that joint precoder design at the source and relay nodes can further enhance the network performance. For the DF based networks, a precoding technique at the source node was proposed in [6] to maximize the information rate; in [7], a rate-maximizing linear precoder design considering time, power, and spatial stream allocation was developed

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Results

Conclusion