Detection Probability Analysis of Space-Based AIS Signal by Using Geometrical Model

To analyze the detection probability of shipborne AIS (automatic identification system) signal from space, a mathematical model dependent upon three factors of message collision avoidance, power of signal received by satellite and interference ratio of signal received is presented in the paper. The altitude and footprint area of the AIS satellite are discussed to overcome the collision of messages transmitted in the different time slots from different SOTDMA (self organizing time division multiple access) cell areas, but arrive at the same time slot due to the different signal path lengths. The simulated result shows that compared to the normal LEO (low earth orbit) satellite system, on average the maximum signal coverage area and the maximum FOV (field of view) of the AIS satellite system are reduced by 74% and 38%. The majority of power of signal transmitted from shipborne 12W-power AIS transmitters located within the maximum signal coverage area may be received with the sufficient margin of power of signal by the LEO satellite, but the space-based AIS system generally suffers from the insufficient CIR (carrier to co-channel interference ratio) of signal received since around 95% pairs of message simultaneously received by satellites may not be correctly decoded. The insufficient CIR of signal received is the bottleneck for the high message detection probability. Therefore, the measure of separating the collision messages should be further taken by the space-based AIS system to increase the detection probability.