Impletation And Algorithm Research Of Space-Based Ais

With the continuous development of the marine traffic, it is becoming increasingly important that effective real-time maritime supervision to guarantee navigation safety. Space-based AIS has attracted extensive attention worldwide due to its features, which include wide coverage, good real-time ability, not restrict by nationality and so on. Reasonable construction and proper demodulate technology of Space-based AIS are critical, because of the received signal collision problem which wide coverage caused.The detailed research and analysis of the AIS signal source and AIS signal receiver is given in this paper, which is supported by Academy of Spaceflight Technology.First, research purposes and significance of AIS and space-based AIS is elaborated in this paper. The mechanism of received signals and the core technology of space-based AIS presented in GB/T20068-2006AIS technical protocol are selectively analyzed.Second, the project design of space-based AIS is proposed in the paper, which has realized the design of AIS signal source and receiver based on the protocol. The design includes the establishment of satellite channel model, the implementation of AIS signal source and receiver, the improved algorithm of GMSK signals demodulation and so on. On the basis of system implementation requirement, a time-frequency frame synchronization algorithm is proposed. The proposed algorithm is improved respectively in allusion to the received signal with and without collisions. Finally, the system is simulated respectively using MATLAB to validate the feasibility and validity of the system when received signal is single-user or multi-user. Bit error rate and frame error rate are also simulated while conflicting signals have different power difference, delay difference and frequency offset difference. The simulation result indicates that the system with improved algorithm can demodulate the signals which software generated or hardware received. The system performance of single-user signal demodulation is very high, while the greater the diversity that signals has, the better performance of multi-user signal demodulation is.