FM Discriminator for AIS Satellite Detection

The Automatic Identification System (AIS) is a tracking system used on ships for several decades to improve traffic monitoring and safety at sea in a short range. The modulation technique used is Gaussian Minimum Shift Keying (GMSK). Recently, the idea of receiving AIS signals from space arose. This presents mainly two challenges. The first one is that received signals present a large Doppler range due to the satellite speed. The second one is the simultaneous reception of signals from ships because of the broad satellite coverage. In this paper, a novel non-coherent GMSK demodulator is proposed to handle the large Doppler shift problem based on several FM discriminators in parallel. A frame collision detection algorithm is presented but the collision problem is not addressed. In addition, computer simulated and real signals are used to study the receiver performance on an AWGN channel.