Design Of NAVTEX Digital Down Conversion System Based On FPGA

With the rapid development of the international ocean shipping industry,the ocean shipping industry has put forward higher requirements for ocean communications equipment.To meet the equipment requirements,the need a new technology to achieve it.The development and application of software radio technology which is the future development direction of communication technology has provided a more efficient way to realize the development of ocean communication equipment.The rapid development of programmable logic devices represented by FPGA provides a better platform for software radio technology.The emergence of FPGA programmable devices makes the flexibility and openness of software radio technology extended to the system hardware design level.This paper gives a detailed introduction on the development of NAVTEX system and analyzes the technical realization of NAVTEX system at home and abroad.On this basis,the design of NAVTEX system digital down conversion system based on FPGA is proposed,which is based on software radio technology,to replace the general conversion system based on dedicated hardware design.In this paper,the overall scheme of the digital down conversion system is designed and the theoretical analysis and introduction of the numerical control oscillator,integral comb filter,finite unit impulse response filter and quadrature demodulation module are given.According to the system function requirements of the digital down conversion system,we give a detailed theoretical analysis and the specific design process.Simulink simulation software is used to model the whole system model and the simplify system model to verify the correctness of the algorithm.According to the system theory design in the FPGA platform for each component hardware implementation.The function simulation of each component module is carried out by modelsim software,and some simulation results are analyzed by MATLAB.Finally,the digital down-conversion system is implemented on the FPGA platform,and the performance of the digital down-conversion system is tested by hardware test platform in the laboratory.Through the hardware test of the digital down conversion system,it is shown that the system can realize the correct demodulation of the IF modulation signal of 518 KHz and the demodulation output error rate of the system is less than 4% under the performance test condition,and conforms to the international standard performance requirements for NAVTEX system.At At the same time,the system can be online upgrades and functional expansion,greatly increasing the flexibility of the system design and scalability.