Improving Physical Layer Security of Uplink NOMA via Energy Harvesting Jammers

We investigate the secrecy transmission of uplink non-orthogonal multiple access (NOMA) with the aid of energy harvesting (EH) jammers. During each time frame, communication is divided into two phases. At the first phase, the base station (BS) transfers wireless power to EH receivers (EHRs). At the second phase, users perform uplink NOMA transmission to BS, while one of EHRs is selected as a friendly jammer that uses the energy harvested from the previous phase to emit the artificial noise for confusing the eavesdropper. In terms of the requirement of channel state information (CSI), we propose three friendly EH jammer selection schemes, namely random EH jammer selection (REJS) scheme without the requirement of any CSI, maximal EH jammer selection (MEJS) scheme with the CSI between BS and each EHR, and optimal EH jammer selection (OEJS) scheme where both the CSIs from BS to EHRs and from EHRs to the eavesdropper need to be known. Analytical closed-form expressions for the connection outage probability (COP), secrecy outage probability (SOP) and effective secrecy throughput (EST) are derived to evaluate the system performance achieved by the proposed schemes, respectively. Also, the asymptotic analysis is provided to gain further insights. The analytical and numerical results indicate that the proposed schemes can realize better secrecy performance than conventional scheme without an EH jammer. Both the secrecy diversity orders of the REJS and MEJS schemes are one while the OEJS scheme can achieve a full secrecy diversity order. Furthermore, owing to the impact of connection outage, the three schemes converge to the same EST floor with the increase of signal-to-noise ratio (SNR).

I. Introduction

Recently, non-orthogonal multiple access (NOMA) has emerged as a pivotal technique to satisfy the diverse requirements for the next generation of wireless communication networks, such as massive connectivity, high reliability and efficient spectrum utilization [1]–[6]. Unlike conventional orthogonal multiple access (OMA) techniques, NOMA can serve multiple users simultaneously in the same resource block (e.g.,time/frequency/code). Upon investigating the multiplexing gain gleaned from different domains, the NOMA technique can be further classified as code-domain NOMA and power-domain NOMA [2]. In this paper, we focus on the power-domain NOMA, which utilizes the super-position coding at the transmitter side and the successive interference cancellation (SIC) at the receiver side to enable multiple users to be served in the same resource block but with different power levels.¹

In the following, we will use “NOMA” to refer to “power-domain NOMA” for brevity.