Impletation And Research On Modulation And Access Algorithm Based On VDES

AIS is a maritime broadcasting system operating at very high frequency in the sea. It can provide ship speed, position, direction,identity authentication and other important information, and has gradually become a new important tool to enhance the safety of ship navigation and improve the efficiency of ship traffic management after its application.With the continuous increase of AIS users and the diversification of demands, the requirements for data exchange between ships, ships to shore and ships to satellites are increasing. The extensive application of these technologies imposes a huge burden on the AIS system, causing the link load of the AIS system to rise sharply, which has a great impact on the normal operation of the AIS system. At the same time, the demand for radio channels is increasing due to the growing number of digital communication services, such as mobile phones and data communications.In this case, IALA proposed the concept of VDES. the system will provide a global range of sea VHF band stronger data exchange capabilities for the future e navigation and GMDSS modernization to provide technical suppor, and also protects the normal functions of current AIS functions at the same time.Firstly, this paper introduces the current situation of AIS system and the background of VDES concept, expatiates the research significance of VDES system and the current research situation at home and abroad, and makes a detailed investigation and study on the link load problem of AIS system, and also summarizes the technical structure of the VDES system and its surrounding technology.Then, based on the recommendations and specifications, this paper focuses on the access, modulation and demodulation algorithm of VDES system. The key technologies of the VDES system are simulated and analyzed based on the MATLAB platform.Finally, based on the research of access mode and modulation mode,a preliminary ASM system is designed, which includes ASM signal analog source and ASM receiver. According to the satellite coverage modeling and ASM self-organizing community characteristics, the ship analog source is realized. According to the characteristics of the received signal, a dual-antenna blind separation algorithm and a time-frequency joint synchronization algorithm are adopted. At the same time, the system simulation of the ASM is carried out to verify the rationality and feasibility of the system design, and the detection performance of the system in each case is given. Simulation results show that the system can detect collision-free and double-collision signals successfully, and can provide good detection performance in practical applications.