Wideband sonar receiver and sonar signal processing algorithms
A wideband sonar receiver is provided that includes: a selectable bandpass filter adapted to filter a received sonar signal to produce a filtered signal and a correlator adapted to correlate the baseband samples with baseband replica samples to provide a correlated signal. In addition, the wideband sonar receiver may include a shaping filter to shape unshaped received pulses. Finally, a variety of sonar processing algorithms are described with regard to reducing clutter and interference, target detection, and bottom detection.
1. A wideband signal receiver, comprising:
a digital stage adapted to digitize samples of a received wideband signal to produce filtered samples of the received wideband signal; and
a correlator adapted to correlate the filtered samples with replica samples to provide a correlated signal, wherein the correlator comprises a digital signal processor (DSP) configured to divide a frequency domain representation of the replica samples (FRS) by a frequency domain representation of the received wideband signal (FS) to provide a first filter response, to multiply a shaping filter response by a conjugate of the FRS to provide a second filter response, and to multiply the second filter response by the FS to provide a third filter response.
2. The wideband signal receiver of claim 1 , wherein the digital stage is adapted to baseband and decimate the received wideband signal.
3. The wideband signal receiver of claim 1 , further comprising an analog stage adapted to modify the received wideband signal.
4. The wideband signal receiver of claim 3 , wherein the analog stage comprises a selectable bandpass filter adapted to filter the received wideband signal to produce a filtered signal.
5. The wideband signal receiver of claim 4 , wherein the selectable bandpass filter comprises a plurality of selectable bandpass filter bands.
6. The wideband signal receiver of claim 4 , wherein the analog stage further comprises a variable gain amplifier adapted to apply a time-varying gain to the filtered signal from the selectable bandpass filter to produce an amplified filtered signal.
7. The wideband signal receiver of claim 6 , wherein the variable gain amplifier applies an increasing gain to the filtered signal as a function of time.
8. The wideband signal receiver of claim 6 , wherein the analog stage further comprises an anti-alias filter adapted to filter the amplified filtered signal from the variable gain amplifier.
9. The wideband signal receiver of claim 3 , further comprising an analog-to-digital converter for converting an analog output of the analog stage into a digital input for the digital stage.
10. The wideband signal receiver of claim 1 , wherein the received wideband signal is a sonar signal.
11. A method of processing a wideband signal, the method comprising:
converting a received wideband signal into a frequency domain representation of the received wideband signal (FS);
converting a replica sample of the received wideband signal into a frequency domain representation of the replica sample (FRS);
in the frequency domain, dividing the FRS by the FS to obtain a first filter response;
in the frequency domain, multiplying the first filter response by a conjugate of the FRS to obtain a second filter response; and
in the frequency domain, multiplying the second filter response by the FS to obtain a third filter response.
12. The method of claim 11 , further comprising transforming the third filter response into a time domain representation.
13. The method of claim 12 , wherein transforming the third filter response into the time domain representation comprises using an inverse fast Fourier transform algorithm.
14. The method of claim 11 , further comprising extracting a power of the third filter response and taking the log of the power to product a detected echo signal.
15. The method of claim 11 , wherein the received wideband signal comprises a chirp pulse.
16. The method of claim 11 , wherein the received wideband signal comprises a frequency-modulated sonar signal.
17. The method of claim 11 , further comprising digitizing the received wideband signal to produce digitized samples.
18. A method of processing a wideband signal, the method comprising:
filtering a received analog signal into a filtered analog signal;
converting the filtered analog signal into a digital signal; and
applying a shaping filter to the digital signal in the digital domain to produce a shaped signal, comprising:
converting the digital signal into a frequency domain representation of the digital signal (FS);
converting a replica sample of the digital signal into a frequency domain representation of the replica sample (FRS);
in the frequency domain, dividing the FRS by the FS to obtain a shaping filter response;
in the frequency domain, multiplying the shaping filter response by a conjugate of the FRS to obtain an intermediate shaping filter response; and
in the frequency domain, multiplying the intermediate shaping filter response by the FS to obtain the shaped signal.
19. The method of claim 18 , wherein filtering the received analog signal comprises:
filtering the received analog signal using a selectable bandpass filter to produce a filtered signal; and
applying a time-varying gain to the filtered signal.
20. The method of claim 19 , wherein the received analog signal comprises a sonar signal.