Broadband Doppler flow measurement based on orthogonal complementary coding signal

In broadband Doppler current measurement, in order to meet the testing speed and simultaneously search and identify different types of targets, traditional transmitted signals usually adopt a continuous coding form that lasts for a long time. This results in effects from the center peak of the autocorrelation function and side lobes, which can be mitigated. Therefore, this article introduces the use of positive complementary coding. First, orthogonal coding can reduce the standard deviation of velocity measurements to some extent. Then, complementary coding is introduced into the continuous coding signal segments. The ambiguity function of the complementary coding form has the advantage of a more concentrated main lobe at the origin and almost no side lobes at high amplitudes, which enhances the signal's anti-aliasing properties. Through simulation studies, it is proven that the standard deviation of speed estimation under positive complementary coding signals shows significant improvement compared to traditional methods, demonstrating robustness to noise and achieving gains in signal-to-noise ratio, thereby extending the measurement range.