Correlation property analysis for the pulse position modulation sequence used for non-crosstalk sonar systems

The correlation property of pulse position modulation (PPM) sequences for non-crosstalk sonar systems is analyzed. To eliminate ultrasonic crosstalk, normally each ultrasonic transducer is assigned a coded excitation signature in the transmission and then the code is identified using a correlation match in the receiver. Therefore, the correlation property is very important for the excitation sequence of a non-crosstalk sonar system. Two ratios are used to characterize the correlation property, one is the ratio between the maximal side lobe and main lobe in the autocorrelation function, and the other is the ratio between the maximal peak of cross-correlation function and the main lobe of the autocorrelation function. The smaller the two ratios are, the better the correlation property is. A sufficient condition is derived and obtained to achieve the suboptimal correlation property for PPM excitation sequences. Experiments using SensComp 600 series electrostatic transducers validate the derived sufficient condition.