Performance Analysis of UAV–RIS-Assisted Short-Packet Secure Communications

In this paper, we investigate the secrecy performance of the UAV short-packet communication system assisted reconfigurable intelligent surface (RIS). In this system, based on the phase shift differences of the RIS, the Gamma and exponential distributions are used to match the received signal-to-noise ratio (SNR) at the link terminals. Closed-form expressions for both the probability density function (PDF) and the cumulative distribution function (CDF) are derived. Based on the above PDF and CDF, we derive closed-form expressions for the average achievable rate (ASR) and the average secure block-error rate (SBLER) to evaluate the system’s security and reliability performance. In addition, a novel analytical model is proposed, which can simplify the calculation of the secrecy outage probability (SOP). Furthermore, to explore the performance boundaries, we also derive closed-form expressions for the asymptotic SOP and the asymptotic probability of positive secrecy capacity (PPSC) in high-SNR regions. The accuracy of the derived expressions is validated through simulations and numerical results, which also demonstrate the effectiveness of the proposed SOP analysis framework. In the simulation, we investigate the impact of key system parameters, such as the number of RIS elements, finite block-length channels, UAV altitude, Rician factor, as well as reliability and confidentiality constraints, on the overall system performance. The simulation results show that the proposed system provides significant performance advantages in ensuring secure and reliable transmission under various operating conditions.