De-collision algorithm for AIS for multi-user on single satellite antenna

Abstract

The Automatic Identification System (AIS), acquired popularity and preferences to be deployed in navigational systems for collision avoidance due to wider coverage. The recently developed satellite AIS provides better precision than the earlier employed Terrestrial AIS. Satellite AIS technology utilizes Gaussian Mean Shift Keying (GMSK) to modulate the message. The modulated AIS message is then transmitted and received between ships and satellite AIS over SOTDMA channel. The conventional single axis satellite AIS transceiver failed to decode the message accurately due to message overlap. In earlier work 3-AIS trans-receiver was developed to reduce the chance of message collision; however, system became bulky and complex. In this paper, collision mitigation algorithm is developed and the single axis transceiver is retained. Thus the complexity is reduced greatly and collision is eliminated as well. Hard Viterbi Algorithm developed in this work corrects the overlapped AIS message for proper decoding of the received messages. The transmitter, receiver and Viterbi algorithm are designed in VHDL Language and simulation of all blocks is performed in Eldo Simulator.