Secrecy Performance for Full-Duplex Jamming-Aided Uplink NOMA System

Full duplex (FD) is one of the most attractive technologies in enhancing spectral efficiency for potentially doubling the system throughput. In this work, we employ FD jamming to improve the secrecy performance of an uplink non-orthogonal multiple access (NOMA) system at the presence of one eavesdropper. We first evaluate the individual secrecy performance in terms of effective secrecy throughput (EST), by deriving its closed-form expression. Valuable insights are provided into the impacts of transmit power, jamming power as well as the number of antennas. Asymptotic analyses concerning these three arguments show the secrecy performance is location-dependent only in the high regime of transmit power and approaches to the main capacity in the high regime of the other two arguments. A special case, beamforming FD jamming, is next studied such that $N$-fold power gain on jamming is available, in turn, improving the secrecy performance. Limited gains from high transmit and jamming power prompt us to further investigate two optimal power allocation problems: (1) optimal power allocation to minimize total power, subject to an overall secrecy performance requirement; (2) optimal power allocation to maximize overall secrecy performance, with constraint of total power. The solutions to these two optimization problems are given and demonstrated numerically with appropriate cases.

I. Introduction

Security and spectral efficiency are two key issues that restrict the development of future wireless communications, and they have become research hotspots for some time [1]–[5]. Traditionally, security issues have been addressed in the upper layers of the network protocol stack, like the data encryption standard (DES) and the advanced encryption standard (AES), which are based on the mathematical computational hardness. With the substantial increase in computing power and the development of quantum computing in the near future, conventional encryption techniques will become increasingly unreliable, let alone the difficulties and the security vulnerabilities in secret key distribution and management [6]. As an alternative or a complement to the conventional security technologies, the physical-layer security has been received tremendous attentions since the notion of secrecy capacity [7] was put forward, by exploiting characteristics of the channels (e.g., fading, noise, and interference). More importantly, the physical-layer security has been proven to be reliable from an information-theoretic perspective [8].