Apparatus, systems and methods for enhanced detection, synchronization and online Doppler scale estimation for underwater acoustic communications
Advantageous online and/or real-time OFDM-based underwater acoustic (UWA) apparatus, systems and methods are provided according to the present disclosure. The apparatus, systems and methods employ a receiver with a bank of parallel branches, with each branch having a self-correlator matched to a different waveform scaling factor. A detection is declared when any of the branches leads to a correlation metric larger than a pre-defined threshold. The branch with the largest metric yields a Doppler scale estimate and a coarse synchronization point. The proposed apparatus, systems and methods use one OFDM preamble, thereby avoiding the need to buffer the whole data packet before data demodulation and enabling online and/or real-time operation. Thus, the disclosed apparatus, systems and methods are advantageously applicable to UWA communications.
1. A method for processing an underwater acoustic (UWA) signal, the method comprising the steps of:
(a) detecting a multi-carrier based UWA signal with a receiver that includes a bank of parallel branches, with each branch having a self-correlator matched to a different waveform scaling factor, the UWA signal including one or more packets;
(b) synchronizing the received UWA signal on the branch that yields the maximum correlation metric; and
(c) providing a Doppler scale estimation of the received UWA signal.
2. The method according to claim 1 , further comprising the step of determining Doppler scale spacing in the parallel self-correlator structure.
3. The method according to claim 2 , wherein the step of determining the Doppler scale spacing includes analyzing false alarm and detection probabilities of a single branch as a function of a threshold and the Doppler scale.
4. The method according to claim 1 , further comprising the step of demodulating the UWA signal, and wherein the one or more packets are not buffered before demodulation.
5. The method according to claim 1 further including the steps of:
(i) resampling in a passband with a resampling factor; and
(ii) performing fine Doppler shift compensation to obtain an estimated Doppler shift.
6. The method according to claim 1 , wherein each of the one or more packets includes a preamble followed by data transmission.
7. The method according to claim 6 , wherein each preamble includes two identical orthogonal frequency division multiplexing (OFDM) symbols preceded by a cyclic prefix (CP).
8. The method according to claim 1 , wherein detection of the UWA signal is declared when any of the branches leads to a correlation metric larger than a pre-defined threshold.
9. The method according to claim 1 , wherein the branch that leads to the largest correlation metric defines a base repetition period.
10. The method according to claim 1 , wherein the Doppler scale estimation includes a Doppler scale factor, and wherein the Doppler scale factor is determined at least in part by a base repetition period.
11. The method according to claim 1 , wherein the branch that leads to the largest correlation metric defines a coarse synchronization point.
12. The method according to claim 1 , wherein the bank of parallel branches compensates for time compression and dilation in UWA signals.
13. The method according to claim 1 , wherein the received UWA signal is converted to baseband before processing.
14. An underwater acoustic (UWA) receiver unit comprising:
(a) at least one receiving element configured to receive at least one multi-carrier based UWA signal, the at least one receiving element including a bank of parallel branches, with each branch having a self-correlator matched to a different waveform scaling factor, the at least one UWA signal including one or more packets; and
(b) a processor associated with the at least one receiving element, the processor adapted and programmed to: (i) detect the at least one UWA signal, (ii) synchronize the at least one UWA signal, and (iii) provide a Doppler scale estimation of the at least one UWA signal.
15. The unit according to claim 14 , wherein the processor is further programmed to determine Doppler scale spacing in the parallel self-correlator structure.
16. The unit according to claim 15 , wherein the processor determines the Doppler scale spacing by analyzing false alarm and detection probabilities of a single branch as a function of a threshold and the Doppler scale.
17. The unit according to claim 14 , wherein the one or more packets are not buffered before demodulating the at least one UWA signal.
18. The unit according to claim 14 , wherein the processor is further programmed to mitigate channel Doppler effect; and wherein the channel Doppler effect is mitigated by: (i) resampling a passband with a resampling factor; and (ii) performing fine Doppler shift compensation to obtain an estimated Doppler shift.
19. The unit according to claim 14 , wherein each of the one or more packets includes a preamble followed by data transmission.
20. The unit according to claim 19 , wherein each preamble includes two identical orthogonal frequency division multiplexing (OFDM) symbols preceded by a cyclic prefix (CP).
21. The unit according to claim 14 , wherein detection of the at least one UWA signal is declared when any of the branches leads to a correlation metric larger than a pre-defined threshold.
22. The unit according to claim 14 , wherein synchronization of the at least one UWA signal is performed on the branch that leads to the largest correlation metric.
23. The unit according to claim 22 , wherein the branch that leads to the largest correlation metric defines a base repetition period.
24. The unit according to claim 14 , wherein the Doppler scale estimation includes a Doppler scale factor, and wherein the Doppler scale factor is determined at least in part by a base repetition period.
25. The unit according to claim 22 , wherein the branch that leads to the largest correlation metric defines a coarse synchronization point.
26. The unit according to claim 14 , wherein the bank of parallel branches compensates for time compression and dilation in the at least one UWA signal.
27. The unit according to claim 14 , wherein the received at least one UWA signal is converted to baseband before processing by the processor.
28. An underwater acoustic (UWA) communications system comprising:
(a) a transmitter unit adapted to transmit a multi-carrier based UWA signal, the UWA signal including one or more packets;
(b) at least one receiving element adapted to receive the multi-carrier based UWA signal, the at least one receiving element including a bank of parallel branches, with each branch having a self-correlator matched to a different waveform scaling factor; and
(c) a processor associated with the at least one receiving element, the processor programmed to: (i) detect the UWA signal, (ii) synchronize the UWA signal, and (iii) provide a Doppler scale estimation of the UWA signal.
29. The system according to claim 28 , wherein the processor is further programmed to determine Doppler scale spacing in the parallel self-correlator structure.
30. The system according to claim 29 , wherein the processor determines the Doppler scale spacing by analyzing false alarm and detection probabilities of a single branch as a function of a threshold and the Doppler scale.
31. The system according to claim 28 , wherein the one or more packets are not buffered before demodulating the UWA signal.
32. The system according to claim 28 , wherein the processor is further programmed to mitigate channel Doppler effect; and wherein the channel Doppler effect is mitigated by: (i) resampling a passband with a resampling factor; and (ii) performing fine Doppler shift compensation to obtain an estimated Doppler shift.
33. The system according to claim 28 , wherein each of the one or more packets includes a preamble followed by data transmission.
34. The system according to claim 33 , wherein each preamble includes two identical orthogonal frequency division multiplexing (OFDM) symbols preceded by a cyclic prefix (CP).
35. The system according to claim 28 , wherein detection of the UWA signal is declared when any of the branches leads to a correlation metric larger than a pre-defined threshold.
36. The system according to claim 28 , wherein synchronization of the UWA signal is performed on the branch that leads to the largest correlation metric.
37. The system according to claim 36 , wherein the branch that leads to the largest correlation metric defines a base repetition period.
38. The system according to claim 28 , wherein the Doppler scale estimation includes a Doppler scale factor, and wherein the Doppler scale factor is determined at least in part by a base repetition period.
39. The system according to claim 36 , wherein the branch that leads to the largest correlation metric defines a coarse synchronization point.
40. The system according to claim 28 , wherein the bank of parallel branches compensates for time compression and dilation in the UWA signal.
41. The system according to claim 28 , wherein the received signal is converted to baseband before processing by the processor.