URLLC in UAV-enabled multicasting systems: A dual time and energy minimization problem using UAV speed, altitude and beamwidth

Realizing ultra-high reliability for short packets in sixth-generation (6G) networks is a crucial task for network designers as classical Shannonian capacity bounds become obsolete. Moreover, for multiuser communications, due to distinct aerodynamics, the trajectory design for a fixed-wing unmanned aerial vehicle (UAV) fundamentally differs from rotary-wing UAVs, which poses a challenge for systems designers. This paper addresses these challenges and relies on a fixed-wing UAV-enabled multicasting system to deliver common short blocklength ultra-reliable and low-latency (URLLC) packets to the ground nodes (GNs) using a Snake Traversal trajectory path. To accomplish this task, we consider the fly-and-communicate protocol for the UAV, where the UAV sweeps a large rectangular area to disperse a common file to GNs with obscure positions. In this vein, we investigate the dual time and energy minimization problems by presenting a quasi-optimal design of the UAV's flying speed, altitude, and antenna beamwidth. Simulation results of numerical search reveal the optimal altitude and half-power beamwidth, which minimize the completion time and energy consumption, respectively. Moreover, for optimized beamwidth, the UAV speed monotonically increases with the altitude, whereas both the completion time and energy consumption monotonically decrease with the altitude. We also analyze the effects of the blocklength and decoding error probability on optimal UAV speed, completion time, and energy consumption. Additionally, simulation results show that for the completion time, the percentage difference between minimum UAV altitude h(max) and maximum UAV altitude h(max) is 195.252%, whereas for the energy consumption, the percentage difference at h(min) and h(max) is 196.912%. Similarly, for the completion time, the percentage difference at minimum UAV antenna beamwidth theta(max) and maximum UAV antenna beamwidth theta(max) is 181.586%, whereas for the energy consumption the percentage difference at theta(min) and theta(max) is 189.269%. This demonstrates the efficacy of the proposed technique is almost two times in reducing the completion time and the energy consumption effectively between the minimum and the maximum values of the UAV altitude and the UAV antenna beamwidth. Lastly, the results show that for both the blocklength and decoding error probability, the UAV speed monotonically increases, while completion time and energy consumption monotonically decrease.