Signal Design And GDOP Calculation Of Very Low Frequency Navigation

Navigation system is a key infrastructure of a country.Many important industries rely on accurate location and time information.People can obtain relevant information through radio navigation.Radio navigation mainly includes satellite-based radio navigation and land-based radio navigation.Satellite-based radio navigation has high positioning and timing accuracy,and can achieve global surface and near-Earth space coverage;land-based radio navigation has the characteristics of strong signal power and resistance to interference,and can be used as supplement and backup for satellite-based radio navigation.In particular,VLF radio navigation can provide a wide range of navigation for various users on the surface,under water,in the air,and on land.And timing services.VLF radio navigation involves many technical points.The article focuses on the two key technical points of signal design and GDOP calculation.The main research contents include:(1)Aiming at the characteristics of limited bandwidth of VLF navigation band and complex signal propagation path,combining the advantages of MSK modulation power spectrum with main lobe concentration,fast side lobe drops,and good anti-interference performance of spread spectrum,a direct spread MSK modulation method is proposed.The article proposes to use the AICML model to generate chaotic spread spectrum sequences,and analyze the phase space,balance,correlation,and complexity of the generated sequences.The sequences generated by this model have good performance.(2)Designing and realizing the parallel DS-MSK signal based on chaotic spread spectrum sequence,studying and simulating serial DS-MSK signal using Chebyshev ?filter to approximate and optimize.In order to realize the verification of the designed signal,the FFT method is used to complete the signal acquisition,and the code tracking and carrier tracking are performed.The acquisition and tracking results of the DS-MSK signal are given.(3)Aiming at the problem that the existing GDOP calculation method does not consider the positioning point area,the longitude transformation method of GDOP calculation is proposed,and the Alpha radio navigation system station information is used for simulation verification.The results show that the proposed method can effectively identify the area where the positioning point belongs,and the calculated GDOP value is more reasonable and reliable.