Research Of BDS/GPS Dual-systems Positioning Based On Nonlinear Filtering

Along with the constantly improving of Beidou Navigation System(BDS), BDS now can provide all-weather navigation service for Asian-Pacific region. According to information statistics, dozens of navigation systems whatever existing, being built or planning would include a huge amount of satellites throughout the world. The number will be close to or more than 140 satellites. After all systems being deployed, there will be a dozen or even dozens satellites in sight of view at the same time in any region. How to take advantage of the satellites or navigation systems from different country, age, demanding and design is a new and challenging topic.Nowadays we can receive contious and steady signal from Global Positioning System(GPS) and BDS. Put more manpower and material resources on the research of BDS and GPS dual system positioning is very important. It will make significant progress in combining Global Navigation Satellite System(GLONASS) and Galileo satellite navigation system(Galileo) in the future.There are five important aspects in this paper:Firstly, research background and status of multiple satellite navigation system fusion at home and abroad are reviewed in this paper. Details concerning the states of development, system compositions, time systems, references coordinate systems of BDS and GPS.Secondly, introduced the basic positioning principle, important concept in satellite navigation and the most widely used iterative least squares(ILS) estimation. On the basis of carefully consideration of factors that affect the GNSS positioning error, state model and measuring model for nonlinear filter have been structured. The nonlinear filter method is more reliable than least squares iterative estimation.Then, apply the traditional method ILS to BDS positioning to verify the effectiveness. Apply the nonlinear filter method to BDS for high accuracy positioning estimation. Comparing with the results of GPS, the navigation performance of BDS is almost the same with GPS in china.After that, the difference of the time systems and coordinate systems of BDS and GPS are discussed. Set up appropriate and new model for GPS and BDS dual systems positioning. Use dual-ILS which fit for dual systems positioning and nonlinear filter method respectively to estimate location. The results show that the latter performs better.Finally, bad condition positioning has been studied. In the urban canyon environments, it is more likely fail to estimate user’s position with only one single-navigation system receiver because the lackness of satellites’ signals. But if dual systems positioning method based on nonlinear filter with proper satellites selection strategy used, the problem can be solved. In this situation, as long as the sum of BDS and GPS satellites is no less than 5, high accuracy positioning results can be obtained.