Coherent demodulation of AIS-GMSK signals in co-channel interference

Gaussian Minimum Shift Keying (GMSK) modulation is used by GSM phone networks, the maritime Automatic Identification System (AIS) and other communication systems. These systems are designed to handle large numbers of users by time and frequency management. However, when the system is heavily loaded, the signals may interfere with each other, resulting in co-channel interference. We demonstrate accurate and effective methods to blindly estimate and track GMSK signal parameters needed for signal demodulation, including carrier frequency, carrier phase, baud rate, baud center and modulation index. We further demonstrate the use of these parameters in the demodulation of the signal even in severe noise and co-channel interference.