Secure Transmission and Self-Energy Recycling for Wireless-Powered Relay Systems with Partial Eavesdropper Channel State Information

TL;DR

This paper introduces a secure, energy-efficient wireless relay protocol with self-energy recycling, improving secrecy rates by optimizing beamforming and power allocation under imperfect eavesdropper channel knowledge.

Contribution

It proposes a novel two-phase full-duplex relay protocol with self-energy recycling and joint beamformer and power allocation optimization for enhanced secrecy.

Findings

Outperforms traditional schemes with up to 80% higher secrecy rate.

Reusing idle antennas significantly improves secrecy performance.

The proposed optimization approach effectively solves the non-convex problem.

Abstract

This paper focuses on the secure transmission of wireless-powered relay systems with imperfect eavesdropper channel state information (ECSI). For efficient energy transfer and information relaying, a novel two-phase protocol is proposed, in which the relay operates in full-duplex (FD) mode to achieve simultaneous wireless power and information transmission. Compared with those existing protocols, the proposed design possesses two main advantages: 1) it fully exploits the available hardware resource (antenna element) of relay and can offer higher secrecy rate; 2) it enables self-energy recycling (S-ER) at relay, in which the loopback interference (LI) generated by FD operation is harvested and reused for information relaying. To maximize the worst-case secrecy rate (WCSR) through jointly designing the source and relay beamformers coupled with the power allocation ratio, an optimization problem is formulated. This formulated problem is proved to be non-convex and the challenge to solve it is how to concurrently solve out the beamformers and the power allocation ratio. To cope with this difficulty, an alternative approach is proposed by converting the original problem into three subproblems. By solving these subproblems iteratively, the closed form solutions of robust beamformers and power allocation ratio for the original problem are achieved. Simulations are done and results reveal that the proposed S-ER based secure transmission scheme outperforms the traditional time-switching based relaying (TSR) scheme at a maximum WCSR gain of 80%.Results also demonstrate that the WCSR performance of the scheme reusing idle antennas for information reception is much better than that of schemes exploiting only one receive antenna.