On Secrecy Analysis of Underlay Cognitive UAV-Aided NOMA Systems With TAS/MRC

This article investigates the secrecy performance for an unmanned aerial vehicle (UAV)-aided nonorthogonal multiple access (NOMA) network in the context of an underlay cognitive radio. Specifically, a multiantenna secondary source (<inline-formula> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula>) transmits a mixed signal incorporated with NOMA to two multiantenna secondary destinations (<inline-formula> <tex-math notation="LaTeX">$D_{i}$ </tex-math></inline-formula>) via a UAV-enabled decode-and-forward relay in the presence of an eavesdropper (<inline-formula> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula>). In addition, both a transmit antenna selection scheme at <inline-formula> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> and a maximal ratio combining protocol at <inline-formula> <tex-math notation="LaTeX">${D_{i}}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula> are taken into account. Considering all the links undergo Nakagami-<inline-formula> <tex-math notation="LaTeX">$m$ </tex-math></inline-formula> fading with path loss, we analyze the secrecy performance in terms of secrecy outage probability for both users. Moreover, we also use Monte-Carlo simulations to verify the accuracy of those derived expressions.