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Computationally Efficient Active Sonar Detector for Pulse Train FM

The performance of an active sonar in short ranges is significantly affected by bottom reverberation. To mitigate the effect of reverberation in active sonar operation, different Doppler sensitive waveforms are introduced in literature. For example, the waveforms like pulse train linear frequency modulated signal (PT-LFM) or pulse train hyperbolic frequency modulated signal (PT-HFM) are commonly used to detect a slow moving target in the presence of reverberation. In the receiver processing, the beam time series is correlated with the replica of the transmitted waveform (replica correlation) to decide the presence of target. When we transmit Doppler sensitive waveforms to detect a moving target in the presence of reverberation, a bank of correlators should be implemented on each beam time series. The replica in each correlator caters different Doppler velocity. The implementation of a bank of correlators at the receiver side demands more computational power. The computational complexity of the receiver processing increases with pulse duration as well as Doppler resolution. Hence a computationally efficient detector is essential to realize the Doppler sensitive waveforms in sonar systems. In this paper, we introduce a computationally efficient detector for pulse train FM, where the detection processing is carried out in two stages. In the first stage, the beam time series is correlated with transmitted subpulse.The second stage requires only a few arithmetic operations, where the subpulse detector outputs are combined coherently. The processing in second stage caters Doppler search with less number of arithmetic operations.