Wireless Powered Cooperative Jamming for Secrecy Multi-AF Relaying Networks

Abstract

This paper studies secrecy transmission with the aid of a group of wireless energy harvesting (WEH)-enabled amplify-and-forward (AF) relays performing cooperative jamming (CJ) and relaying. The source node in the network does simultaneous wireless information and power transfer (SWIPT) with each relay employing a power splitting (PS) receiver in the first phase; each relay further divides its harvested power for forwarding the received signal and generating artificial noise (AN) for jamming the eavesdroppers in the second transmission phase. In the centralized case with global channel state information (CSI), we provide closed-form expressions for the optimal and/or suboptimal AF-relay beamforming vectors to maximize the achievable secrecy rate subject to individual power constraints of the relays, using the technique of semidefinite relaxation (SDR), which is proved to be tight. A fully distributed algorithm utilizing only local CSI at each relay is also proposed as a performance benchmark. Simulation results validate the effectiveness of the proposed multi-AF relaying with CJ over other suboptimal designs.On the other hand, privacy and authentication have increasingly become major concerns for wireless communications and physical (PHY)-layer security has emerged as a new layer of defence to realize perfect secrecy transmission in addition to the costly upper-layer techniques such as cryptography. In this regard, relay-assisted secure transmission was proposed [5,6] and PHY-layer security enhancements by means of cooperative communications have since attracted much attention [7][8][9][10][11][12][13][14][15][16][17][18][19][20].In particular, cooperative schemes can be mainly classified into three categories: decode-and-forward (DF), amplify-and-forward (AF), and cooperative jamming (CJ) [7] with CJ being most relevant to PHY-layer security.Specifically, coordinated CJ refers to the scheme of generating a common jamming signal across all single-antenna relay helpers against eavesdropping [7,10,12,13], while uncoordinated CJ considers that each relay helper emits independent artificial noise (AN) to confound the eavesdroppers [15,16]. It is expected that in the scenarios where the direct link is broken between the transmitter (Tx) and the legitimate receiver (Rx), some of the relays have to take on their conventional role of forwarding the information while others will perform CJ [17,18]. A recent paradigm that generalizes all the above-mentioned cooperation strategies is cooperative beamforming (CB) mixed with CJ [19,20], where the available power at each relay is split into two parts: one for forwarding the confidential message and the other for CJ.However, mixed CB-CJ approaches may be prohibitive in applications with low power devices because idle relays with limited battery supplies would likely prefer saving power for their own traffic to assisting others' communication. In light of this, SWIPT provides the incentive for potential helpers to perform dedicated CB mixed with CJ at no expense of its own power,...

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