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.