Leveraging Space-Time Synchronization for Ultra-Spot Detection in mmWave/THz UAV-to-UAV Communications

In UAV-to-UAV communication, airborne UAVs need to detect the location and direction of ultra-high-speed millimeter-wave (mmWave) and Terahertz (THz) coverage areas, referred to as ultra-spots. This predictive capability allows UAVs to optimally adjust their flight paths, altitude, and velocity, thereby maximizing the utilization of ultra-spot services. A space-time synchronization technique employing multiple Wireless Two-way Interferometry devices (multi-Wi-Wi) is proposed in this paper to detect mmWave/THz ultra-spot locations during UAV operations. This paper proposes an algorithm that estimates the likelihood of nearby ultra-spots by considering the UAV flight route and ultra-spot direction, and by sharing location and pose information among UAVs in the network via a 920 MHz wireless communication link. For the first time, this work addresses the problem of optimizing UAV flight routes to maximize ultra-spot utilization. To address the inherent challenges of Wi-Wi, such as phase data unreliability, RSSI attenuation, or packet loss caused by obstructions from the UAV's own body, this study proposes the use of multiple Wi-Wi devices equipped with antennas positioned at different positions around the arms of the UAV to leverage spatial diversity effects. The proposed method's effectiveness is confirmed through experimental data derived from real-world UAV-to-UAV communication tests. An error of 37.16 cm was observed experimentally in ultra-spot location estimation, corresponding to 186 ms error in temporal prediction of ultra-spot entry from an in-flight UAV, demonstrating its effectiveness in addressing ultra-spot detection challenges in mmWave communication.