Research On Decoding Algorithms Of Satellite-based AIS Signals

Automatic Identification System is a new navigation system used for between the shipsand the base station which plays an important role in ships at sea to identify, safety monitoring,Communication navigation and so on. With the rapid development of economic globalization,the shipping industry is increasingly busy, the establishment of ship safety monitoring systemwithin the scope of global sea is particularly important. Thus the research of Satellite-BasedAIS attracts much attention. The satellite-based AIS system has the characteristics of LargerDoppler shift, faster channel change, severe multi-user interferences and etc so that thecomplexity of coherent detection is increased and it offers a serious challenge to the existingalgorithms. At the same time, the traditional AIS system sets two receivers for two channelsand each receiver lets the received signals to the antenna go through all levels to enlarge,down-conversion, A/D conversion and Subsequent decoding processing generally. While forthe receiver of satellite-based AIS system, the performance requirements such as the stability,the accuracy and etc of the analog device are higher. Based on this, this thesis researches thedecoding algorithm in the satellite-based AIS system and proposes improved programs on thebasis of analyzing the disadvantages of the current algorithm:(1) A new simplified non-coherent sequence detection algorithm based on the Viterbialgorithm has been done in this thesis. The algorithm is based on maximum likelihoodcriterion and the received signals are processed by filters and matched with the primarycomponent in the Laurent decomposition without whitening filter. The simulation resultsshow that the improved algorithm not only greatly reduces the computational complexity, andimprove the detection performance.(2) A phase adaptive noncoherent detection algorithm which is based on maximumlikelihood criterion is proposed in the thesis. This algorithm combines the process phasecompensation with path selection avoiding the tedious PLL design. The phase adaptivenoncoherent detection method can greatly reduce the system complexity, and gains the idealdetection performance under the low SNR.(3) Aiming at the high performance requirements of satellite receiver for Analog Devices,a new method proposed directly samples the RF signal. A digital demodulation method ofsatellite-based AIS signal and the information detection recovery technology is proposed.Finally, the experiments of AIS signal of AIS signal transmitted by the practical berth throughthe oscilloscope are done, and the results verify the correctness of the whole processing of thereceiver.