Research On Time-differenced Carrier Phase/SINS Integrated Navigation Approach

Beidou-â… satellite navigation system is the only Chinese satellite navigation system with full independent intellectual property.However,Beidou-â… is inferior to GPS in system structure,positioning mechanism and range of application.To fulfill the requirements of national defense and economic development,there are urgent needs to develop applied technologies based on Beidou system.To overcome the shortcomings of Beidou-â… ,e.g.,large time delay,weak secrecy and limited capacity in active positioning,this thesis proposes a Beidou/SINS integrated navigation technology using time differenced carrier phase,and researches on major theoretic problems and related key technologies.The main works of this thesis are:(1) The mathematic model of time differenced carrier phase is established based on the model of carrier phase and the analyses of temporal/spatial correlation characters of main error sources in carrier phase measurements.The basic principle of time differenced carrier phase/INS integration is presented.It is argued that time differenced carrier phase is an accurate measurement of delta range without ambiguity,because the ambiguity,which is constant unless cycle slips take place,and the common mode errors that are strongly correlated in space and time both are canceled out by time difference. The time differenced carrier phase,which is a function of user's position changes,can be used to damp the accumulation of navigation errors of INS,obtaining satisfactory navigation accuracy in a relatively long time span.(2) A newly proposed nonlinear global observability analysis approach starting directly from basic concept of observability is introduced to analyze the observability of nonlinear satellite navigation system/INS integrated navigation system.Sufficient conditions for global observability of satellite navigation system/INS integrated navigation system considering the uncertainty of lever arm are presented.The analysis results are supported and validated by simulations and vehicular tests.The global observability analysis approach is straightforward and intuitive,avoiding cumbersome rank evaluation in traditional methods.Because there is no need to approximate the original nonlinear system by a linear models(linear time-varying models or piecewise linear constant models),the analysis reveals more comprehensively and profoundly the relationship between the system's observability and the carrier's movements.The global observability analysis provides the theoretic foundation and a mathematic tool to aid the design of the filter for integrated navigation and online lever arm calibration.(3) By utilizing the approach of global observability analysis and the sufficient conditions,the observability of time differenced carrier phase/SINS system is investigated.It is indicated that for a general navigation satellite system all the states of satellite navigation system/INS integration system except position are observable in normal conditions,if more than 4 satellites are observed.For Beidou I system all the states except position are observable in normal conditions,if the carrier is a land vehicle or a ship,of which the motion is limited in the up direction.Under the guidance of global observability analysis,the filtering models and integrated navigation algorithms are designed.Several key problems of the integrated navigation system,e.g.,reduced order filter,the effect and detection of cycle slips and the application of nonholonomic constrains are studied.The models and algorithms are validated by experiments, including static tests,land vehicle tests and ship tests.The resultes show that the time differenced carrier phase/SINS integration can estimate the errors of SINS precisely, and helps attenuate the accumulation of navigation errors effectively.The Beidou time differenced carrier phase/SINS integrated navigation system can be applied to land vehicles and ships,and has the ability to keep adequate accuracy for a relatively long time without sending out signals and limitations on capacity of users.(4) The problem of velocity determination using time differenced carrier phase is investigated.The research is mainly concentrated on:algorithms of velocity determination,analyses about the precision of velocity estimation and main factors affecting the accuracy,algorithms for deriving carrier phase rate using nonlinear tracking-differentiator and method of time delay compensation.Simulations and vehicular tests are performed to support and validate the theoretic analyses and the algorithms.Simulations and tests show that the user's velocity can be determined precisely by using time differenced carrier phase.The use of nonlinear tracking-differentiator can weaken the noise amplification and minimize the time delay in differentiation.Under normal observation conditions(6 satellites with velocity geometric dilution of precision at 3-4),and using single GPS receiver,the velocity accuracy reaches 10^-3 m/s level in static cases,and is comparable to that of DGPS in dynamic cases.But for Beidou system,the accuracy is limited by the number and the geometry of satellites.Under the aid of up-direction constraint,the velocity accuracy reaches 10^-1 m/s in north and 10^-2m/s in east.By analyzing the accuracy of velocity estimation the inner relationship between position accuracy of Beidou time differenced carrier phase/SINS integrated navigation system and the geometry of satellites is explained.Through the analyses of velocity geometric dilution of precision and the comparision of GPS and Beidou system,it is shown that the velocity accuracy could be upgraded if the geometry of Beidou satellites was improved.With the evolution of Beidou system there are great potentials in improving the performance of time differenced carrier phase/SINS integrated navigation system and velocity determination using carrier phase of Beidou system.