Method for determining the timing of the receipt of a radio message

A device for determining a time of receipt of a binary coded Automatic Identification System (AIS) message comprising:

• a radio receiver including an antenna, an analogue-to-digital (AD) converter, a memory, and a processor, wherein the antenna receives the binary coded AIS message via a first modulated radio signal, and wherein the processor controls the device to:
• generate a second analogue electrical signal from the received first modulated radio signal;
• sample, using the AD converter, the second analogue electrical signal;
• generate a third digital signal from the sampled second analogue electrical signal;
• demodulate either the second analogue electrical signal or the third digital signal;
• decode the third digital signal to generate a data content of the binary coded AIS message as a stream of data bits, the stream of data bits comprising a predetermined signal element;
• determine a time of receipt of the predetermined signal element;
• generate a digitally stored, constructed comparison signal based on said stream of data bits, wherein the constructed comparison signal is constructed to correspond to the third digital signal;
• determine an optimum value for a time variable, wherein the time variable indicates a time position of the constructed comparison signal relative to the third digital signal, and wherein, for the optimum value, a correlation between the constructed comparison signal and the third digital signal is maximal;
• correct the determination of the time of receipt of the predetermined signal element using the optimum value of the time variable;
• and
• use the corrected determination of the time of receipt of the predetermined signal element as the time of receipt of the binary coded AIS message.

A system for determining a location of a sender emitting a binary coded Automatic Identification System (AIS) message comprising:

• at least three receiving devices, wherein at least one of the three receiving devices comprises an antenna, an analogue-to-digital (AD) converter, a memory, and a processor, wherein the antenna receives the binary coded AIS message via a first modulated radio signal, and wherein the processor controls the at least one receiving device to:
• generate a second analogue electrical signal from the received first modulated radio signal;
• sample, using the AD converter, the second analogue electrical signal;
• generate a third digital signal from the sampled second analogue electrical signal;
• demodulate either the second analogue electrical signal or the third digital signal;
• decode the third digital signal to generate a data content of the binary coded AIS message as a stream of data bits, the stream of data bits comprising a predetermined signal element;
• determine a time of receipt of the predetermined signal element;
• generate a digitally stored, constructed comparison signal based on said stream of data bits, wherein the constructed comparison signal is constructed to correspond to the third digital signal;
• determine an optimum value for a time variable, wherein the time variable indicates a time position of the constructed comparison signal relative to the third digital signal, and wherein, for the optimum value, a correlation between the constructed comparison signal and the third digital signal is maximal;
• correct the determination of the time of receipt of the predetermined signal element using the optimum value of the time variable;
• and
• use the corrected determination of the time of receipt of the predetermined signal element as a time of receipt of the binary coded AIS message.