Secondary Network Throughput Optimization of NOMA Cognitive Radio Networks Under Power and Secure Constraints

Abstract

Recently, the combination of cognitive radio networks with the nonorthogonal multiple access (NOMA) approach has emerged as a viable option for not only improving spectrum usage but also supporting large numbers of wireless communication connections. However, cognitive NOMA networks are unstable and vulnerable because multiple devices operate on the same frequency band. To overcome this drawback, many techniques have been proposed, such as optimal power allocation and interference cancellation. In this paper, we consider an approach by which the secondary transmitter (STx) is able to find the best licensed channel to send its confidential message to the secondary receivers (SRxs) by using the NOMA technique. To combat eavesdroppers and achieve reasonable performance, a power allocation policy that satisfies both the outage probability (OP) constraint of primary users and the security constraint of secondary users is optimized. The closed-form formulas for the OP at the primary base station and the leakage probability for the eavesdropper are obtained with imperfect channel state information. Furthermore, the throughput of the secondary network is analyzed to evaluate the system performance. Based on that, two algorithms (i.e., the continuous genetic algorithm (CGA) for CR NOMA (CGA-CRN) and particle swarm optimization (PSO) for CR NOMA (PSO-CRN)), are applied to optimize the throughput of the secondary network. These optimization algorithms guarantee not only the performance of the primary users but also the security constraints of the secondary users. Finally, simulations are presented to validate our research results and provide insights into how various factors affect system performance. INDEX TERMSCognitive radio network, NOMA, Imperfect CSI, Throughput optimization, Performance constraints I. INTRODUCTION Recently, non-orthogonal multiple access (NOMA) has been regarded as a viable technology to increase not only spectrum usage but also support for many connections [1]-[7]. The key idea is that multiple NOMA users are able to access the same frequency at the same time [1]. Here, the transmitter may employ the superposition coding technique to combine multiple signals, while the receiver implements successive interference cancellation (SIC) to decode its signal [2]. The work reported in [7] showed that the capacity of