Monitoring And Assessment Of Broadcast Ephemeris Error And Ionospheric Correction Accuracy

Satellite navigation systems have important economic and military significance,and all countries in the world are vigorously promoting the process of independent research and cooperative development of satellite navigation systems.So far,in addition to the two existing global satellite navigation systems(US GPS and Russia's GLONASS),China's Beidou-3 will also cover the Belt and Road area at the end of 2018,and Global satellite navigation service capabilities will be available by the end of 2020.In addition,the European Union's Galileo satellite navigation system is also actively moving towards globalization.As an important part of satellite navigation messages,broadcast ephemeris plays an important role in real-time positioning.It can be received by the navigation user in real time,which is very convenient for the user's real-time positioning,but the accuracy of the broadcast ephemeris is not high enough to meet the needs of precise positioning.The precise ephemeris is an after-the-fact ephemeris,which can be considered as the actual orbit of the satellite,but the precise ephemeris cannot meet the real-time positioning needs of the user.Therefore,this paper calculates the error of broadcast ephemeris to evaluate the accuracy of broadcast ephemeris through comparing the satellite orbit caloulated by broadcast ephemeris with the satellite orbit given by precise ephemeris after their fitting.Among them,the broadcast satellite ephemeris error of GPS satellite is the smallest;the error of R direction in the broadcast ephemeris of the four navigation systems is the smallest;the error of GEO satellite broadcast ephemeris in the Beidou system is the largest,especially in T direation.When the navigation signal passes through the ionosphere,it will produce a delay error,which we call the ionospheric error.It is one of the key issues in navigation and positioning technology.The reason of ionospherise error is that when satellite signal passes through the ionosphere,all kinds of free electrons in the ionosphere will affect the propagation path of the navigation signal,and then affect the propagation time of the signal,which results in the error of the system.It is necessary for us to study the influence of ionosphere on navigation signals in depth to eliminate the influence of ionosphere on navigation and positioning.Therefore,the ionospheric grid data is used as a benchmark to evaluate the accuracy of broadcast ionospheric correction in this thesis.Among them,the Galileo system has the best radio ionospheric correction accuracy,followed by GPS.BDSK8 is only suitable for mid-latitude regions,so it is the worst for the global ionospheric correction accuracy.