Asynchronous Respond-Based Autonomous Time Synchronization for Low-SNR High-Dynamic Frequency Hopping System

High-speed unmanned aerial vehicle (UAV) cluster under frequency hopping system boasts advantages of efficiency, flexibility, reliability, and anti-interference, making it widely applicable in military, scientific research, and civilian applications. Accurate execution of tasks among communication nodes within the high-speed UAV cluster requires that the time references between nodes are consistent, and in the absence of external time reference requires the use of autonomous time synchronization to achieve time synchronization between nodes. In high-dynamic application scene of high-speed UAV clusters, time synchronization accuracy is affected by low signal-to-noise ratio (SNR) and high-dynamic Doppler frequency. Therefore, this paper proposes an asynchronous multi-hop difference-fitting algorithm. Firstly, the dynamic Doppler is estimated through the phase information in the multi-hop signal. Then the time of arrival (TOA) estimation accuracy is improved by using multi-hop joint approach. Finally, the nodes interact with each other through asynchronous respond and correct the timestamps, thus achieving high-precision time synchronization among nodes.