Reseach On Dual Mode Satellite Navigation And Positioning

As a surge in demand for location-based services, researches on global navigation and postioning system and other positioning technology utilizing electromagnetic waves are in the ascendant. Although there are many advantages in using global navigation and postioning system, such as it can work with all-weather and its position precision is high, the traditional global navigation and postioning system could be easily interferenced and public cannot use the confidential spread-spectrum sequences to acquire higher positioning precision. In order to enhance the independence and security of satellite navigation services in the field of some key areas, this artice examines the practicability and performance of a dual-mode satellite navigation system which combinating low Earth orbit satellites and global navigation and positioning system. This new dual-mode satellite navigation system using the large dynamic characteristics of LEO satellite itself to generate high Doppler frequency offset, and use Doppler frequency offse as a target measurement to solve a user’s position.First of all, this article explains principle of Doppler position and make a detailed derivation of how to use Doppler frequency observations via least square method and Kalman Filtering method to solve a user’s location. Then, we give a brief analysis of error sources in the process of Doppler measurement and effects of satellite geometric distribution on positioning accuracy. We also classify danger of common interference and how to measure it, and compare two types of smoothing method to smooth nosiy Doppler measurement. According to the results of Doppler position both using simulated data of low Earth orbit and real GPS data, dual-mode satellite navigation system can give user a positioning accuracy of ten to hundreds of meters.This article focus on design method of tracking loop in Doppler reveicer for dual-mode satellite navigation system. Using this tracking loop, the receiver can not only work under high dynamic circrmustance of low Earth orbit satllites but also can effectively reduce the amount of calculation of initial acqusiton unit. First, we describe a new type frequency discriminator.Then, we give the equtions of calculating variance of both estimated frequency and phase of traditional third-oeder Phase-locked loop based on Kalman Filter, and also analysis its performance.Finally, with the combination of the new frequency disceiminator and modified adaptive two stage Kalman Filter loops, we proposed a new frequency-locked loop aided Kalaman Filter tracking loop.This new tracking loop is tested by using both the collected real GPS data and simulated low orbit satellite’s data. Experimetal results show that our new tracking loop can work well in a highly dynamic environment, meanwhile it can tolerate greater initial frequency bias and significantly reduce the calculating load of acquction.