Research On The Key Techniques Of Satellite-based AIS Receiver

Automatic Identification System(referred to as AIS) is a new type of navaids which is forcibly used by International Maritime Organization and AIS has been widely used in the field of ship communications and satellite communications. Currently the shipborne AIS has become common, however, its range is limited. Satellite-based AIS developes on the basis of the shipborne AIS and it can receive AIS signals within a larger scale. Satellite-based AIS is used for analysis and processing of signal received, which is significant in both military and civilian fields.In developed countries, the research on Satellite-based AIS has gradually matured, some of which have been successfully applied to actual satellites. In China, the research in this area is still in its infancy. Many researchers in China have focused on just one aspect of it and do not study the complete AIS system. Based on the domestic and international research and the concrete requirements of project, this paper constructs a complete Satellite-based AIS system and studies multiple algorithms of modules of the system.Satellite-based AIS receiver consists of four modules, signal detection, blind source separation, modulation recognition and signal recovery. Signal detection, which detects whether signal exists. This paper proposes is a method called mean analysis on the basis of the spectrum of signal, and when the SNR is greater than 10, the probability of detection of is up to 98%. As the signal received may be mixed by multiple AIS signals, namely slot conflict, this paper solves it by the module of blind source separation in order to improve efficiency. Blind source separation algorithm is divided into two categories, multi-channel separation and single channel separation. This paper completes two algorithms of multi-channel separation, JADE and Fast ICA, whose system matrix is close to unit array. For the single-channel separation, an algorithm based on quadrature sampling is implemented, whose error rate after separation is low. Modulation recognition is used to isolate AIS signal from other signals. This paper proposes a joint algorithm based on high-order cumulants and spectrum to identificate AIS signal from the combinations of AM, FM, BPSK, 2FSK, QPSK and 16 QAM signals, and when the SNR is greater than 10, the probability of recognition of is up to 90%. AIS signal recovery includes two parts of signal demodulation and signal deframing. For the AIS signal demodulation, This paper implements methods of coherent demodulation, differential demodulation and discriminator demodulation, and analyses performances. AIS signal deframing is used to restore the original meaning of the signal according to the HDLC protocol, and this paper takes a type of signal as an example, analyses, and ultimately completes the Satellite-based AIS receiver.In this paper, algorithms of modules of Satellite-based AIS are simulated by MATLAB and analyses the performance of each algorithm, and ultimately completes the research on the algorithm of basic modules of the entire system.