Objective Discrete waypoint-based navigation of unmanned surface vehicles (USVs) often results in discontinuous reference trajectories and abrupt heading variations. Conventional guidance systems may exhibit significant overshoot and slow convergence when large initial position errors occur. Moreover, existing approaches rarely account for both USV maneuverability constraints and fixed-time error boundary regulation, which limits their effectiveness in practical marine navigation performance.
Method An integrated trajectory tracking framework combining waypoint smoothing, optimal virtual vectoring (OVV) and fixed-time prescribed-performance line-of-sight (FTPP-LOS) guidance is proposed. A circular arc transition strategy is introduced to smooth discrete waypoints while ensuring continuous differentiability of the reference trajectory. A quadratic programming-based OVV model is developed to minimize the position error norm, with surge and yaw maneuverability constraints incorporated to enable rapid and smooth trajectory convergence. Furthermore, an FTPP-LOS guidance law is designed in conjunction with a fixed-time sideslip observer to compensate for cross-flow-induced drift disturbances and constrain both transient and steady-state tracking errors within predefined bounds. Comparative simulations and multi-condition sea trials are conducted using a 4.9-meter USV prototype.
Results Simulation results demonstrate that the convergence time of position errors in the X and Y directions are 65.4 s and 48.3 s, respectively, both outperforming the 70 s benchmark achieved by the comparison methods. The maximum waypoint overshoot is less than 0.8 m, and the steady-state tracking errors remain within the prescribed 0.5 m boundary. Sea trials further verify smooth trajectory transitions under various initial position offsets, with all tracking errors satisfying the predefined performance constraints throughout navigation process.
Conclusion The proposed integrated guidance framework fully accommodates USV maneuverability constraints while achieving fixed-time stability. It effectively constrains tracking error amplitudes and suppresses oscillations and overshoots near waypoints, demonstrating reliable performance and promising potential for practical marine engineering applications.
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