Study On Methods Of Precision Monitoring And Assessment Of Broadcast Ionospheric Model Of GNSS

Broadcast ionospheric model is an important means to weaken the ionospheric delay error, and an effective way for single-frequency receiver to improve the accuracy in navigation and positioning. GNSS(including GPS / BDS / Galileo) comes to correct the ionospheric delay error by sending broadcast ionospheric coefficients to users. Meanwhile, GNSS system through continuous improvement of monitoring network and treatment strategies to optimize and develop its global broadcast ionospheric model. With the increasingly widespread application of GNSS, compatibility and interoperability between the various systems have also developed. Thus, beginning the performance evaluation of satellite navigation systems under a unified system is necessary, in which the precision monitoring and assessment of the broadcast ionosphere is a key element. It is necessary to select more precise, more reliable ionospheric valuation and appropriate assessment methods, in order to mornitor and assess the precision of the broadcast ionospheric timely and accurately. Currently, the main method is using IGS(CODE) ionospheric grid(GIM) as precision assessment benchmarks of GNSS broadcast ionosphere. However, considering the lack of CODE monitoring stations in China, this paper carried out the methods study on precision mornitoring and assessment of GNSS broadcast ionospheric, which are precision mornitoring and assessment of broadcast ionospheric model of GNSS based on the improved CODE model ionospheric grid and based on real data of base station. In addition, we carry out tests on precision monitoring and assessment of GNSS broadcast ionospheric model. The main contents and results are showed in the following:(1) Elaborated the basic theory of GNSS ionospheric modeling and assessment in detail, analyzes the impact of ionospheric delay error, given the model and method of GNSS ionospheric delay correction.(2) Carried out precision monitoring and assessment of GNSS broadcast ionospheric models with reference to the CODE GIM,and analyzed the accuracy of GPS / BDS / Galileo broadcast ionospheric model.(3) Considing the condition of few IGS stations distributed in China, an improved CODE model(also known as CODE + model) ionospheric grid assessment method was proposed. It can improve the accuracy of ionospheric modeling in the surrounding area by increasing domestic monitoring station data. On the basis of it,we carried out the test of precision monitoring and assessment of GPS / BDS / Galileo broadcast.(4) Based on the global ionospheric benchmarks established by measured data, using the measured ionospheric delay of the slant of satellite and receiver on base station as a reference to achieve precision assessment of GNSS broadcast ionosphere based on the measurement on base stations.(5) Compared the advantages and disadvantages of three methods which includes the precision monitoring and assessment of GNSS broadcast ionospheric models based on CODE GIM, CODE+ GIM, as well as the measured ionospheric delay on base station. The experimental analysis showed that the three methods conclude to the same results. The accuracy of BDS broadcast ionospheric model is better than GPS and Galileo in China and the surrounding area. The average rate of correct is about 75%, the accuracy of GPS Klobuhar model is lowest. Klobuchar model shows a significant correlation with latitude, model accuracy at mid-latitude and high-latitude is higher than low-latitude.