Patent ID: 7876865

Claim:
A method for detecting and decoding Automatic Identification System (AIS) signals, the method comprising: receiving a plurality of AIS signals at a satellite in space and pre-processing the plurality of AIS signals to produce digital input data; processing the digital input data by correlating the digital input data with a plurality of predefined signals having different Doppler offsets to compute a plurality of corresponding correlation signals and identifying one or more candidate AIS message signals based on the correlation signals, wherein processing the digital input data comprises generating the plurality of predefined signals by applying the different Doppler offsets to a predetermined AIS code sequence, and scanning the plurality of correlation signals for amplitude peaks exceeding neighbouring amplitude peaks by a predetermined amount in order to identify the one or more candidate AIS message signals; determining Doppler offset estimates and time estimates for the one or more candidate AIS message signals; decoding the one or more candidate AIS message signals to obtain corresponding message segments; validating decoded message segments for proper AIS formatting; de-correlating the validated decoded message segments to obtain modified digital input data, and performing the processing, determining and decoding steps on the modified digital input data.