Study about Combination Types of M-sequences in Alternate Transmission of Different Codes for Pulse Compression

The ultrasonic pulse echo method is a famous technique to measure the distance of objects by time of flight of the reflected echo signal. The distance resolution is obtained from the pulse width, that is the M-sequence, due to improvement of the echo’s SNR[1]. Ordinarily, the n-th order of M-sequence can be used to generate the 2n-1 binary words[2]. Therefore, the alternate transmission of two different codes can improve the resolution of distance measurement. There is a trade-off between the time resolution and the measurable deapth. In the M-sequence pulse compression, the length of an M-sequence code corresponds to the pulserepetition time. Moreover, the noise characteristics of combination types are different depending on the pattern pairs. In the high order of M-sequence have a lot of noise characteristics to analyze. In this research, a relationship among combination types of M-sequence in alternate transmission of different codes for pulse compression is described.