Complementary Coding-Based Waveform Design for Broadband Acoustic Doppler Current Profilers

Acoustic Doppler Current Profilers (ADCP) are typical equipment for underwater velocity measurement using layered echo signal processing. However, the aliasing effect influences the measurement accuracy, which is related to the auto-correlation function of the echo signal. To this end, a novel complementary coding-based waveform is proposed in this article. First, we establish a current velocity measurement framework for broadband ADCP (BBADCP), consisting of a complex auto-correlation algorithm and an ambiguity-resolving algorithm. Second, we find that the waveform design criteria are proportional to or inverse proportion to the symbol length, symbols repetition times, and bit-width, resulting in mutual constraints of each other. Thus a parameter compromise scheme is proposed to solve the mutual constraints among various metrics, including depth cell thickness, velocity accuracy, and maximum measurable velocity. Third, we propose an aliasing effect count-measure method by transmitting two repeat coding pulses using a pair of complementary codes with a time delay. We also offer a concatenation method to extend the complementary codes, which improves the velocity estimation precision without affecting the range resolution. Simulation results demonstrate that the waveform embedding extended complementary codes provides advantages in both velocity estimation accuracy and maximum measurable velocity.