Detection of quadratic phase coupling in shallow underwater channel

This paper addresses the problem of detection of quadratic phase coupling (QPC) at the receiver when the source signal has traversed through an underwater channel. The channel has been numerically modeled using normal mode theory In a bounded underwater channel, the phase associated with each frequency varies with range as well as due to the characteristics of the channel. We have performed extensive simulations of the received signal of moving and stationary targets in shallow underwater channel, to arrive at a robust algorithm for detection of QPC. The algorithm takes advantage of the slow variation of the bispectrum phase of the received signal which is due to the channel characteristics. Specifically, the detector is based on the zero crossings of the bispectrum phase of the received signal across observation intervals. The proposed detector is observed to be robust in several typical shallow underwater channels. We will present detailed results of the detection performance of the algorithm in different SNR conditions.