Sub-pulse processing of m-sequences phase-coded Continuous waveforms in shallow water

Abstract

The performance of active sonar operating in shallow water is often limited by the reverberation level. If a target is moving relative to the reverberating scatters, the resulting Doppler effect from movement can be utilized to improve the detection of moving targets against stationary reverberation. In practice, the choice for Doppler processing is to use the Continuous waveform (CW) signal or one of its modifications. However, this narrow-band signal provides poor range resolution. This paper presents a novel Continuous waveform whose phase is coded by m-sequences, called BPSK signal. The BPSK signal is characterized by a comparable Doppler resolution as the CW signal, but with better range resolution. In this paper, the waveforms are composed of diverse pulses with a high duty ratio of up to 80%. These pulses are nearly orthogonal to each other. Sub-pulse processing is a method of breaking up the long-duration to achieve a faster update rate of the target scene. Increasing the number of sub-pulses increases the update rate, but the corresponding result will lead to a decrease in the Time Bandwidth Product, and be expected to reduce signal-to-reverberation ratio. The paper provides Doppler processing gain estimates and the theoretical prediction concerning BPSK signal are supported by simulation results.