Ranging Enhancement for Underwater Collision Avoidance Sonar via ISAC Waveform and Adaptive Sensing Acceleration

Traditional collision avoidance sonars perform a round-trip ranging measurement per operational cycle, where longer detection distances lead to longer cycle durations. The low propagation speed of acoustic signals increases their susceptibility to Doppler effects, which can ultimately degrade ranging accuracy or success rates and, in severe cases, lead to economic losses or even loss of life. To address this issue, we propose a ranging enhancement method for collision avoidance sonar inspired by integrated sensing and communication (ISAC) principles. At the signal level, we introduce a tail-flipping linear frequency modulated (TF-LFM) waveform along with a Doppler channel estimation method to maintain stability under severe channel conditions. Simulation results demonstrate that the proposed waveform achieves robust measurement under strong Doppler distortions. With a remarkably low average peak-to-average power ratio (PAPR) of approximately 3.01 dB, the signal is easy to transmit and resilient to nonlinear distortion. At the processing level, we propose an adaptive sensing acceleration (ASA) mechanism that allows the sonar to emit new pulses before previous echoes return, thereby reducing ranging latency. In a field pool experiment, the upgraded sonar system achieved a 65.9% reduction in latency per ranging cycle using the proposed method, demonstrating a substantial enhancement in measurement efficiency.