A Network-Free Time Synchronization Algorithm for Ship-Borne Repeater Station Based on AIS Message Information

The effectiveness of AIS data depends critically on the validity of its time information. A key bottleneck restricting forwarded data validity is the cumulative error in AIS repeater stations? local clocks, caused by crystal oscillator frequency drift without network connection. This paper proposes and implements a high-precision, network-free time synchronization algorithm based on AIS message fusion. It uses the high-precision UTC time embedded in vessels? AIS broadcast messages as an external true value reference, periodically calibrating the repeater?s local clock UTC time and seconds-counter value. This eliminates absolute time deviation from crystal oscillator drift, prevents clock error accumulation, and enables the repeater to indirectly synchronize with GNSS time without network-ensuring long-term stability and accuracy of its time information. MATLAB simulation analysis of the algorithm shows that even in fully offline, harsh environments, it consistently controls AIS data timestamp error within one second. This has significant theoretical and practical value for enhancing vessel dynamic monitoring and regulation across all sea areas.