The Secrecy Analysis over Physical Layer in NOMA-Enabled Cognitive Radio Networks

An underlay cognitive radio network (CRN) with non- orthogonal multiple access (NOMA) is a promising multiple access scheme to solve the problem of scarce spectrum. This novel NOMA-enabled underlay CRN can also enhance the transmission secrecy via employing the deliberately introduced interference. In this paper, we intend to investigate the secrecy capacity of a pair of primary users (PUs) and randomly deployed secondary users (SUs) in the NOMA- enabled underlay CRN. Considering an existing eavesdropper in the network, we derive a closed-form expression of the secrecy sum rate (SSR) of all SUs. Then, we further formulate an SSR optimization problem for both PUs and SUs and design a simulated annealing algorithm to find the optimal power allocation. Simulation results demonstrate that the secrecy performance of all NOMA-enabled SUs is higher than that of SUs with frequency division multiple access (FDMA). In other words, the use of the NOMA technology can improve the secrecy performance of the cognitive radio system.