Short-packet communication (SPC) and unmanned aerial vehicles (UAVs) are anticipated to play crucial roles in the development of 5G-and-beyond wireless networks and the Internet of Things (IoT). In this paper, we propose a secure SPC system, where a UAV serves as a mobile decode-and-forward (DF) relay, periodically receiving and relaying small data packets from a remote IoT device to its receiver in two hops with strict latency requirements, in the presence of an eavesdropper. This system requires careful optimization of important design parameters, such as the coding blocklengths of both hops, transmit powers, and the UAV's trajectory. While the overall optimization problem is nonconvex, we tackle it by applying a block successive convex approximation (BSCA) approach to divide the original problem into three subproblems and solve them separately. Then, an overall iterative algorithm is proposed to obtain the final design with guaranteed convergence. Our proposed low-complexity algorithm incorporates robust trajectory design and resource management to optimize the effective average secrecy throughput of the communication system over the course of the UAV-relay's mission. Simulation results demonstrate significant performance improvements compared to various benchmark schemes and provide useful design insights on the coding blocklengths and transmit powers along the trajectory of the UAV.

翻译：短包通信（SPC）和无人机（UAV）预计将在5G及未来无线网络和物联网（IoT）的发展中发挥关键作用。本文提出了一种安全的SPC系统，其中无人机充当移动解码转发（DF）中继，在有窃听者存在的情况下，周期性地从远程物联网设备接收小数据包，并通过两跳将其转发至接收端，同时满足严格的时延要求。该系统需要优化重要设计参数，如两跳的编码块长度、发射功率以及无人机的轨迹。尽管整体优化问题是非凸的，我们采用块连续凸近似（BSCA）方法将原问题分解为三个子问题并分别求解。随后提出了一种整体迭代算法，以确保收敛性并获得最终设计。所提出的低复杂度算法结合了鲁棒轨迹设计和资源管理，旨在优化无人机中继任务期间通信系统的有效平均保密吞吐量。仿真结果表明，与多种基准方案相比，所提方案性能显著提升，并为无人机轨迹上的编码块长度和发射功率提供了有价值的设计见解。