Coherent demodulation of ais-GMSK signals in co-channel

A method of demodulating a signal, comprising the steps of:

• a) receiving said signal including a carrier;
• b) estimating a carrier frequency having a carrier residual;
• c) basebanding said signal;
• d) tracking said carrier frequency having said carrier residual;
• e) removing said carrier residual from the baseband signal;
• f) detecting a data burst signal from the results of step (e);
• g) generating a bank of poly-bit matched filters;
• h) generating a plurality of correlation signals by applying said bank of poly-bit matched filters to said signal detected in step (f);
• i) determining a magnitude and a phase of each correlation signal of said correlation signals generated in step (h);
• j) determining a maximum M(t) of said magnitudes determined in step (i);
• k) determining a location of a baud center nB+b;
• l) evaluating said bank of poly-bit matched filters at said baud center determined in step (k);
• m) estimating a carrier phase φc from the results of step (l);
• n) removing the estimated carrier phase of the correlation signals;
• o) applying a Viterbi decoding algorithm to the results of step (n);
• and
• p) estimating a transmitted data sequence from the results of step (o).