Unmanned aerial vehicles (UAVs) have found extensive applications across diverse domains owing to their cost-effectiveness, uncomplicated structure, and adaptable takeoff and landing functionalities. Multi-UAV network systems can be coordinated to improve system performance significantly. Network time synchronization is a crucial prerequisite for establishing and operating multi-UAV networks, whereas the high-speed movement of UAVs presents challenges for time synchronization within multi-UAV networks. In this paper, we develop a practical information exchange model with high relative radial velocity and Gaussian distribution random transfer delay. By introducing Doppler information and a novel clock skew and clock offset consensus model, a Doppler and timestamp joint (DATJ) network time synchronization algorithm has been developed. Assessing the performance of the algorithms, we provide rigorous theoretical proof of network time synchronization convergence. Simulation results further validate the theoretical analysis and demonstrate that the proposed algorithm outperforms similar approaches in terms of synchronization performance.

Due to the considerable fading arising from the long-distance transmission between satellites and terrestrial terminals as well as the complex geographic environments on the earth, aerial relays have been designed to facilitate the information delivery between the satellites and terrestrial terminals when reliable direct data transmissions cannot be achieved. In this paper, a cooperative satellite-aerial-terrestrial network (CSATN) system including a satellite (S), an aerial relay (R), and a terrestrial receiver (D) is considered, while decode-and-forward relay scheme is adopted. Specifically, inspired by the beam shape of the transmission signal from S, we model the operation space of R as a circular truncated cone to accurately reflect the practical large-scale transmission scenarios, the height of which is decided by the upper and lower limitations of the operation height of R. Thus, considering the randomness of R and D and employing geometric probability theory, the exact and asymptotic outage probability (OP) of S-R, S-D, and R-D links is studied, and then the end-to-end outage performance of CSATN is investigated accordingly by using approximation method. Finally, numerical results are presented to validate our proposed analysis.