Research On Tightly-Coupled RTK/INS Algorithm Based On Partial Ambiguity Resolution Strategy

The Global Navigation Satellite System(GNSS)can provide high-precision three-dimensional position and speed information,and has the characteristics of long-term accuracy.However,the sampling frequency of GNSS observations is generally low and the GNSS signals are susceptible to external environment,such as high-rise buildings and lakes,Trees,active ionosphere,etc.,which in turn affect the accuracy and reliability of positioning.The inertial navigation system(INS)has the characteristics of high sampling frequency,autonomous operation,complete navigation parameters,and high short-term accuracy.It has strong ability to be interfered by the outside world,but the error of INS quickly diverges as the derivation time increases.The two technologies of GNSS and INS are highly complementary,and the combination of the two can provide more reliable,continuous,stable and high-precision navigation and positioning parameters.At the same time,GNSS and INS integrated navigation is currently widely used in mobile measurement,smart city,autonomous driving and other fields,and plays an important role in real life.Real-time kinematic(RTK)is a simple,high-precision,and high-reliability positioning method that has a far-reaching impact in the current GNSS navigation and positioning field.For the short baseline,this mode can effectively eliminate the ionospheric and tropospheric errors,and because the double difference can eliminate the hardware delay and other errors at the satellite and receiver ends,the whole-period ambiguity restores the whole-period characteristic,and the least squares can be used to reduce The correlation adjustment method LAMBDA(Least-square Ambiguity Decorrelation Adjustmenst,LAMBDA)algorithm performs ambiguity resolution and provides centimeter-level positioning.Integrating RTK and Inertial Navigation Technology(INS,Inertial Navigation System)to build an RTK / INS integrated navigation and positioning system,which can achieve high data rate,high accuracy,and high reliability navigation and positioning services.RTK/INS integrated navigation is an important component of current integrated navigation section.The combination navigation can be divided into loose combination model,tight combination model and deep combination model.At present,the loose combination has been very mature and applied to various fields,but the research of tightly-coupled integrated navigationis still the hotspot and difficulty of the current research.Based on this background,this paper carried out the theory and algorithm research of the RTK / INS tight combination algorithm.The main contents are as follows:1)Introduce the relevant background and significance of the selected topic,summarize and summarize the research status of RTK / INS integrated navigation at home and abroad;the mechanical layout of INS,INS error observation equations,one-step prediction and coordinate conversion between common INS matrix.2)The mathematical model of RTK positioning,error sources and corresponding error correction algorithms,are studied.The basic methods of ambiguity fixation and ambiguity confirmation in RTK positioning are studied.The robust kalman filter is adopted to reduce the effect of the pseudorange gross error and undetected phase cycle slip on the RTK solution.3)The method of INS-assisted ambiguity resolution algorithm is studied.The INS coordinates calculated by INS inertial navigation and the lever arm vectors measured in advance are used to obtain the position and variance of the GNSS antenna position.The position information of the GNSS antenna phase center derived as the virtual observation equation is used to reduce the search space of the ambiguity.Thereby improving the ambiguity resolution fix rate.4)The application of partial ambiguity fixed algorithm in RTK / INS tightly-coupled is studied.Two strategies are used,one is based on the success rate threshold for ambiguity screening,but when some of the ambiguities screened by this method do not meet the ambiguity confirmation threshold,then the ambiguity in the de correlation ambiguity space with the largest variance is removed until the number of ambiguities is less than the threshold or the ambiguity is fixed successfully.5)Through the measurement data of vehicle-mounted GNSS / INS,the effectiveness and correctness of robust strategy,partial ambiguity resolution and INS-assisted ambiguity resolution are verified.The results show that the tight combination algorithm has better positioning accuracy in the open environment,and also has stronger stability and reliability in the urban environment.