Secure Wireless-Powered NOMA Communications in Multi-UAV Systems

This paper investigates the green and secure communications of multi-UAV NOMA systems. A joint energy transfer and artificial noise (ETAN) scheme is proposed to enhance the endurance and secrecy performance of the system. In particular, communication can be divided into two phases during each time frame. In the first phase, the multi-UAV system harvests energy from a power beacon. In the second phase, UAVs perform NOMA to transmit confidential messages uplink to a base station in the presence of eavesdropping UAVs. Simultaneously, to safeguard the multi-UAV system, the power beacon transmits artificial noise to degrade the eavesdropping channel. The closed-form expressions of connection outage probability (COP), secrecy outage probability (SOP) and effective secrecy throughput (EST) of the system are derived to evaluate the system performance. The asymptotic analysis of SOP and EST is also performed for further insights. Numerical results are presented to validate the correctness of theoretical derivations and the superiority of the proposed scheme. Analysis and simulation results demonstrate that the secrecy diversity order of the proposed scheme is determined by the jamming channel. When the number of UAVs increases, the time of energy harvesting should be appropriately extended. Moreover, substantial improvement to the system can be achieved by UAV pairing.