Systems and methods for decoding automatic identification system signals

1. A method of extracting, from at least one signal received by a satellite, message segments employed in the maritime communications Automatic Identification System (AIS), the method comprising:

(a) receiving at least one AIS signal from at least one satellite antenna;

(b) generating multiple versions of the at least one AIS signal;

(c) extracting message segments contained within each of the multiple versions of the at least one AIS signal using at least one AIS receiver, wherein each message segment comprises at least a Maritime Mobile Service Identity (MMSI);

(d) sorting the message segments by time; and

(e) deleting any duplicate message segments.

2. The method of claim 1 , wherein generating multiple versions of the at least one AIS signal comprises varying at least one of (i) a parameter of the at least one AIS signal; and (ii) a parameter of the at least one AIS receiver.

3. The method of claim 2 , wherein the parameters of the at least one AIS signal comprise the frequency and amplitude of the at least one AIS signal.

4. The method of claim 2 , wherein the parameters of the at least one AIS receiver comprise centre frequency, frequency response, and bandwidth of a bandpass filter internal to the at least one AIS receiver.

5. The method of claim 2 , wherein the parameters of the at least one AIS signal and the at least one AIS receiver are varied in a predetermined manner.

6. The method of claim 2 , wherein the parameters of the at least one AIS signal and the at least one AIS receiver are varied in an adaptive manner based on the number of message segments extracted.

7. The method of claim 1 , wherein generating multiple versions of the at least one AIS signal comprises:

(b.1) splitting the at least one AIS signal into a predetermined number of equivalent AIS signals; and

(b.2) filtering each of the equivalent AIS signals using a separate bandpass filter to produce the multiple versions of the at least one AIS signal.

8. The method of claim 7 , wherein the number of bandpass filters and the bandwidth of each of the bandpass filters are selected in accordance with

B c = B+ ( N− 1)*( B−B D )= 9 N*B− ( N− 1)*B D

where B D is the minimum bandwidth to extract message segments, B is the bandwidth of each bandpass filter, B c is the bandwidth of the AIS channel and N is the number of bandpass filters.

9. The method of claim 8 , wherein the bandwidth of each bandpass filter is between approximately 10 kHz and approximately 14 kHz.

10. The method of claim 9 , wherein the number of bandpass filters is 7 and the bandwidth of each bandpass filter is approximately 12 kHz.

11. The method of claim 1 , wherein first and second AIS signals are received from first and second antennas respectively, and generating multiple versions of the at least one AIS signal comprises:

(b.1) splitting the first AIS signal into a predetermined number of first equivalent AIS signals;

(b.2) splitting the second AIS signal into the predetermined number of second equivalent AIS signals;

(b.3) phase shifting each of the second equivalent AIS signals by a different amount to produce a plurality of phase shifted AIS signals; and

(b.4) combining each of the first equivalent AIS signals with one of the phase shifted AIS signals to produce the multiple versions of the at least one AIS signal.

12. The method of claim 11 , wherein the amount of each phase shift is predetermined.

13. The method of claim 12 , wherein the predetermined number is four and the amount of the phase shifts is 0°, 90°, 180° and 270°.

14. The method of claim 12 , wherein the predetermined number is eight and the amount of the phase shifts is 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°.

15. The method of claim 11 , wherein the amount of each phase shift is adaptively determined based on the number of message segments extracted from each of the multiple versions of the at least one AIS signal.

16. The method of claim 11 , wherein generating multiple versions of the at least one AIS signal further comprises adjusting the amplitude of at least one of the first equivalent AIS signals and the phase shifted AIS signals prior to combining each of the first equivalent AIS signals with one of the phase shifted AIS signals.

17. The method of claim 1 , wherein generating multiple versions of the at least one AIS signal comprises:

(b.1) generating an AIS signal representing the extracted message segments; and (b.2) subtracting the AIS signal representing the extracted message segments from the at least one AIS signal to generate a version of the at least one AIS signal.

18. The method of claim 17 , wherein generating multiple versions of the at least one AIS signal further comprises repeating steps (b.1) to (b.2) until a number of new extracted messages falls below a predetermined threshold.

19. The method of claim 1 , wherein first and second AIS signals are received from first and second antennas respectively, and generating multiple versions of the at least one AIS signal comprises:

(b.1) splitting the first AIS signal into a first predetermined number of first equivalent AIS signals;

(b.2) splitting the second AIS signal into the first predetermined number of second equivalent AIS signals;

(b.3) filtering each of the first equivalent AIS signals using a separate bandpass filter to produce a plurality of first filtered AIS signals;

(b.4) filtering each of the second equivalent AIS signals using a separate bandpass filter to produce a plurality of second filtered AIS signals;

(b.5) splitting each of the first filtered AIS signals into a second predetermined number of first equivalent filtered AIS signals;

(b.6) splitting each of the second filtered AIS signals into the second predetermined number of second equivalent filtered AIS signals;

(b.7) applying at least one of a phase shift and an amplitude shift to each of the second equivalent filtered AIS signals to produce a plurality of shifted AIS signals, wherein different phase and amplitude shifts are applied to each of the second equivalent filtered AIS signals corresponding to a particular second filtered AIS signal; and

(b.8) combining each of the first equivalent filtered AIS signals with one of the shifted AIS signals to produce the multiple versions of the at least one AIS signal.

20. The method of claim 1 , wherein first and second AIS signals are received from first and second antennas respectively, and generating multiple versions of the at least one AIS signal comprises:

(b.1) splitting the first AIS signal into a first predetermined number of first equivalent AIS signals;

(b.2) splitting the second AIS signal into the first predetermined number of second equivalent AIS signals;

(b.3) applying at least one of a phase shift and an amplitude shift to each of the second equivalent AIS signals to produce a plurality of shifted AIS signals, wherein different phase and amplitude shifts are applied to each of the second equivalent AIS signals;

(b.4) combining each of the first equivalent AIS signals with one of the shifted AIS signals to produce a plurality of combined AIS signals;

(b.5) splitting each of the combined AIS signals into a second predetermined number of equivalent combined AIS signals; and

(b.6) filtering each of the equivalent combined AIS signals using a separate bandpass filter to produce the multiple versions of the at least one AIS signal.