Research On The Errors Of Propagation Path And Correction Technology In The AIS Autonomous Positioning System

In order to ensure the safety of coastal navigation,IMO has explicitly recommended that ships should be equipped with a space-based and land-based dual backup positioning and navigation system.The AIS is a mandatory ship-equipped navigation system of SOLAS and its location information comes from the embedded GNSS chip.Once the GNSS signal is unavailable,the AIS will crash,which will seriously threaten the navigation safety of the ship.Therefore,IALA’s World Wide Radio Navigation Plan has called on member states to study land-based positioning systems based on the AIS actively,the so-called AIS autonomous positioning systems.The positioning accuracy of the land-based positioning system mainly has three aspects,including the transmitting system of the reference station,the signal propagation path and the receiving system.This article mainly studies the influence of the positioning error caused by the propagation path on the positioning accuracy.The positioning information of the positioning system generates in the channel,and the influence of channel propagation medium on the phase velocity of the signal is the main factor that determines the positioning accuracy of the system.The propagation path of the land-based positioning system is quite complex,so the research on propagation path errors is extremely challenging.The geometric references of measurement parameters of positioning information are mainly TOA and TDOA.Since the AIS is essentially a communication system,for the research of these positioning geometric parameters measurement based on the AIS signal,there are no references available yet,and no results have been found on measurement errors of these positioning geometric parameters.Therefore,in order to make the land-based positioning system based on AIS shore stations a world-recognized land-based radio positioning and navigation system,it is necessary to first break through the influence of the propagation medium on the phase velocity of the AIS signal,thus affecting the technical difficulty of the positioning measurement accuracy.Therefore,based on the in-depth study of the propagation characteristics of the AIS signal,two solutions for the ASF correction of the AIS signal are presented in this article.One of the solutions is the model correction,which is to study the ASF prediction algorithm,derive the ASF prediction model and verify it by actual measurements.The other solution is the ASF real-time correction technology,that is,designing and developing an ASF real-time correction system and applying the system in an autonomous positioning verification system based on AIS shore stations.The main contributions of this thesis are summarized as follows:Firstly,in response to the problem that the propagation medium affects the phase velocity of the AIS signal transmitted over the sea surface,the influence factors of each path signal are analyzed according to compositions of multipath signals received at the receiving end.Multipath AIS signal losses and phases caused by the propagation distance,the seawater temperature,the seawater salinity,the wind speed and the wave height are analyzed and evaluated.On this basis,quantitative algorithms for the propagation characteristics of AIS multipath signals transmitted over the sea surface under different multipath conditions are given.It provides a theoretical basis for the multipath signal suppression design of AIS positioning receivers and the subsequent ASF prediction algorithm of the AIS signal.Secondly,in response to the problem that the propagation medium influences the phase velocity of the AIS signal to generate the measurement error of TOA,an ASF prediction algorithm for the AIS signal under the smooth sea surface condition is proposed.Based on the propagation characteristics of the AIS signal transmitted over the sea surface,the received phase composition of each path signal is analyzed and the ASF prediction algorithm is obtained by decomposing and reconstructing the phase of the received signal,which can be used for the model correction of positioning errors.Thirdly,in response to the problem that the extreme weather seriously affects the positioning accuracy of the AIS signal,an ASF prediction algorithm for the AIS signal under the rough sea surface condition is proposed.The ASF theoretical model and experimental analysis results of the AIS signal transmitted over the rough sea surface are given based on the theoretical derivation and numerical calculation for the received phase of each path signal.The obtained model quantitativeficationally studies the error characteristics of ASFs caused by environmental factors and the correction parameters are provided for the high-precision positioning of the AIS under the severe sea condition.Finally,based on the in-depth study of the ASF real-time correction technology,the design proposal of the real-time correction system is given and the ASF real-time correction system for the AIS signal is designed and developed.The transmission delay monitored by the real-time correction system can be used to verify the ASF prediction model derived in this paper.At the same time,the ASF real-time correction platform was actually built in the AIS autonomous positioning system based on AIS shore stations.By monitoring the propagation delay errors between the transceivers in different environments and broadcasting ASF corrections,the original measurements of the positioning receivers are corrected in real time.The correction system improves the autonomous positioning accuracy of the AIS signal in the coverage sea area.Therefore,the research on the errors of propagation path and correction technology in the AIS autonomous positioning system has great theoretical and practical significance on improving the positioning accuracy of the AIS autonomous positioning system.It makes certain contributions to develop the AIS autonomous positioning system in the world.