Joint Deployment of LAU and HAU for Hierarchical Space-Air-Ground Communications

Unmanned aerial vehicles (UAVs) are becoming increasingly crucial in facilitating flexible and on-demand wireless connections in 5G and beyond (B5G) communication systems. This paper examines the joint deployment of Low Altitude UAVs (LAUs) and High Altitude UAVs (HAUs) within a four-tier Space-Air-Ground (SAG) communication system, which comprises ground IoT nodes, LAUs, HAUs, and satellites organized in a hierarchical structure, with the objective of achieving efficient and reliable transmission. The communication between an IoT node and the satellite in the SAG system occurs through a cascading wireless channel, involving sequential connections from the IoT node to the LAU, HAU, and satellite. The minimal data capacity among the links of a cascading channel becomes a bottleneck for communication. Therefore, it is essential to avoid significant rate differences among the cascading channel links and ensure a similar data rate across all links to maximize resource utilization efficiency. In this context, we propose a joint optimization of the deployment of LAUs and HAUs to maximize the minimum data capacity of links on a cascading channel. Specifically, we present a Particle Swarm Optimization (PSO) algorithm to achieve this goal. Simulation results demonstrate that the proposed PSO algorithm, which jointly optimizes the deployment of LAUs and HAUs, outperforms scenarios where LAUs and HAUs are deployed in fixed positions.