A new coding method

The principle of "waveform invariance" is used for velocity measurement of the correlation sonar, which has a bottom tracking capability for providing earth reference velocity. For earlier two-pulse sonar systems, trade-offs were made between maximum range and velocity variance due to the reason that pulse width is equal to or less than pulse repetition period. A new pulse coding technique for a single transmitted pulse is utilized in the paper with respect to the conflicting problem mentioned above. The method involves truncated Gold sequence which contains the same number of 0's and 1's. The nature of the coded pulse is such that the autocorrelation function of the pulse possesses a temporal autocorrelation peak at a predetermined time lag besides at O. The method used will increase achievable range while velocity accuracy not be deteriorated because correlation delay is less than pulse width.