宽带多普勒测速技术中的发射信号

The transmit signal in broadband Doppler velocimetry technology

声波信号作为系统测速的载体,直接影响测速性能,是多普勒测速技术的关键。研究了不同发射信号的频谱特性及基于复协方差法的多普勒频移测量误差。一般假设二相编码信号频谱关于载频对称,但实际上其频谱为不关于载频对称的双边谱,不对称程度由不对称系数量化。不对称系数越小,测频偏差、标准差均越小,即测频性能更佳。仿真实验表明,在不考虑波束开角的点回波模型下,差分重复伪随机Blackman码元幅度调制编码信号与常用的非差分重复伪随机二相编码信号相比:不对称系数低3个数量级;信号频带同带宽内信噪比在0^-10 dB范围内测频标准差约下降2%~20%;信噪比高于10 dB时相对测频偏差约小5‰~6‰。

As the carrier of system velocimetry,acoustic signal directly affects the velocimetry performance,which is the key to Doppler velocimetry technology.The spectral characteristics of different transmitted signals and the Doppler shift measurement error based on complex covariance method are studied.It is generally assumed that the spectrum of the two-phase coded signal is symmetric about the carrier frequency,but in fact its spectrum is a bilateral spectrum that is not symmetric about the carrier frequency,and the degree of asymmetry is quantified by the asymmetry coefficient.The smaller the asymmetry coefficient is,the smaller the Doppler shift measurement bias and standard deviation are,that is,the Doppler shift measurement performance is better.Simulation experiments show that the differential repeated pseudo-random Blackman symbol amplitude modulation coded signal is compared with the commonly used non-differential repeated pseudo-random two-phase coded signal under the point echo model without considering the beam angle:the asymmetry coefficient is three orders of magnitude lower;when the SNR within the same frequency band of the signal is within the range of 0^-10 dB,the Doppler shift measurement standard deviation is reduced by about 2%~20%;when the SNR is higher than 10 dB,the relative Doppler shift measurement bias is about 5‰~6‰smaller.