Adaptive pulselength correction (APLECORR): a strategy for waveformoptimization in ultrawideband active sonar

This paper describes adaptive pulselength correction (APLECORR), an environmentally adaptive technique for optimizing the detection performance in wide-band active sonars in so-called doubly spread channels. It works by allocating available transmit energy to frequency bands according to the in situ measured reverberation and ambient noise spectra. It optimizes the waveform and the detection processor at the same time. It is appealing in its simplicity and achieves significant gains whenever the reverberation-to-noise ratio is not constant across frequency, thus its applicability to wide-band systems. The method extends easily to PRN and other non-FM waveforms. The paper includes a proof that time spreading and frequency-spreading distortion have an approximately equivalent effect if the waveform is linear or hyperbolic frequency modulation     

On detecting linear frequency-modulated waveforms in frequency- andtime-dispersive channels: alternatives to segmented replica correlation

In modern active sonars, so-called “high-gain” waveforms are used to obtain processing gain for improved detection performance in reverberation. In time and frequency spread channels, the full processing gain of these waveforms is not achievable and robust detectors are needed. It is common practice to use a segmented replica correlator (SRC) detector for robust detection in such environments. In this paper, we show that an alternative processor formed by integrating the full replica correlator output magnitude squared, denoted RCI for replica correlator integrator, has advantages over the SRC when the waveform is linear frequency modulated (LFM). The RCI is better suited to the case of unknown time spreading through the use of a bank of integrators tuned for a wide range of spreading widths. The SRC, on the other hand, may be designed only for a fixed amount of distortion. Computer simulations are used to show how a multihypothesis RCI processor improves upon the fixed SRC by up to 4 dB over a realistic range of time spreading widths