AIS Signal Non-coherent Demodulation Of Co-channel Interference

Automatic Identification System (AIS) is a kind of new system helping navigation and applying to sea aboard ship exchanging information. It can be used to identify and communicate each other of ships at sea, including between ships and between ships and shore units. The use of AIS can effectively improve the safety of maritime navigation, and help management of the maritime administration. But with the increasing of the number of ships at sea, sailing environment has become increasingly complicated. The existing AIS system cannot satisfy modern marine management needs, so the aviation and aerospace technology reference to the maritime management has become a new research area. When the AIS system is in high-altitude state from ship, due to ship and AIS systems relative motion, space AIS system covers more than one cell in the cellular communications and other reasons, at the same time slot, the receiver receives two or more AIS signal, thus, demodulation of co-channel interference signal of AIS research has important significance.This paper discussed the signal non-coherent demodulation to be used on the co-channel AIS signal demodulation process, which focused on the differential demodulation and the non-coherent demodulation based on Viterbi algorithm. Differential demodulation includes 1-bit difference demodulation,2-bit difference demodulation and multi-bit combined differential demodulation. The differential demodulation performance with co-channel interference is not good enough, so we put forward the non-coherent demodulation based on Viterbi algorithm. It has a better demodulation performance with co-channel interference, so we choose it for the co-channel AIS signal separation process. In this paper, multi-channel processing, signal reconstruction and signal subtraction techniques are used to achieve the co-channel AIS signal separation. In the AIS baseband signal processing, we also need frame head detection, frequency shift estimation and symbol timing algorithm to assist our demodulation process. In this paper, we also conducted all the algorithms researched in detail.