Underwater LPI Waveforms Design Based on LAS Code and Chaos

In view of the requirement for low probability of intercept (LPI) waveform characteristics in underwater detection, we serialize the chaotic sequences and use it to modulate the signal phase such that the basic waveform is obtained. Then the large area synchronized (LAS) codes are introduced for both interpulse and intrapulse modulations to design two new waveforms. Relying on the zero-delayed section and zero-Doppler section of an ambiguity function, we compare the discrimination property of the two new waveforms intuitively with four kinds of typical underwater detection waveforms, i.e. continuous waveform (CW), linear frequency modulation (LFM) waveform, binary phase shift keying (BPSK) waveform and Costas waveform. Quantification analysis is made by their time resolution constants and frequency resolution constants. In addition, nonzero-Doppler section of an ambiguity function is used to compare their Doppler sensitivity characteristics under the ideal background, followed by a further comparison of reverberation suppression capability via the Q function. The results show that two new waveforms have outstanding distance resolution, Doppler tolerance and reverberation suppression capability over whole velocity ranges required by practical use.