Research On Key Technologies Of VDES Integration Of Space And Earth

VHF Data Exchange System(VDES)is a future maritime communication system developed on the basis of the traditional maritime Automatic Identification System(AIS).It is the core of the e-Navigation and Global Maritime Distress and Safety System led by International Maritime Organization.VDES integrates the AIS,Application Specific Message(ASM)and VDE channels and includes two communication scenarios,i.e.,terrestrial and satellite,named as VDE-TER and VDE-SAT,forming a space-ground system.This dissertation focuses on the frame synchronization algorithms for VDE-TER and VDE-SAT scenarios and the compatibility issues between VDE-SAT and Land Mobile System(LMS)in the shared bands.First of all,this dissertation deeply investigates the core technology of VDES physical layer,including its architecture and frequency utilization plan,physical frame structure,modem technique and simulation of error rate and suggests on the modem technology of AIS,ASM and VDE.The above content provides the basis for the design and simulation of the subsequent frame synchronization algorithms.Secondly,this dissertation studies synchronization algorithms for VDE-TER and VDE-SAT,respectively.(1)Firstly,the double barker synchronization algorithm with low complexity and small computation for VDE-TER is studied,and the focus is on the derivation of frequency offset estimation algorithm.(2)Then,considering the low SNR,large delay and frequency offset of satellite links,time-frequency joint algorithm and differential detection are implemented,then the computation complexity of the former is simplified via performing correlation in frequency domain and step-by-step search of local sequences.(3)In terms of the potential miss detection of the right timing under low SNR and large frequency offset,the performance of differential detection is improved via hypothesis in advance.(4)Finally,this dissertation designs the VDES frame synchronization system and simulates the performance of all above algorithms in MATLAB to verify the feasibility and compares the two synchronization algorithms for VDE-SAT from perspectives of performance and complexity.Finally,this dissertation studies the compatibility issues between VDE-SAT and LMS in the same bands.Based on in-depth study of ITU recommendations,the LMS reference model and VDE-SAT interference model are established.And then based on limit of harmful interference imposed on LMS,this dissertation gives explanations in detail of problems faced by VDE-SAT from perspectives of link budget,spectrum efficiency,coverage,etc.,which can be reference for further decision of VDE-SAT frequency utilization plans.