Tightly GPS/INS Integrated Navigation Algorithm Based On Carrier Phase Differential

The global positioning system(GPS)and inertial navigation system(INS)have an irreplaceable position and advantage in their respective fields,but there are also defects that can not be made up at the same time.If they are combined in a proper way,the overall navigation accuracy and navigation performance of the system will be further improved.The advantages of GPS/INS integrated navigation are obvious.Firstly INS consumes little time and has high precision which can make up the navigation without the satellite signal and ensure the continuity of navigation.Secondly the measurement value of GPS has high precision which not only can control the error of inertial navigation system which accumulates with time,but also can estimate the error of inertial components and improve the accuracy of the navigation system.Thirdly INS can assist GPS in ambiguity resolution and cycle slip detection.The combination of GPS and INS can increase the redundancy of the system and enhance the reliability of the navigation system.The combination of the two can improve the anti-interference ability of the system and improve the integrity of the system.No matter in the field of Surveying and mapping or in other fields,the application prospect of GPS/INS integrated navigation is very wide.But at present,the overall level of research and application in China is still different from that in other countries,so it is necessary to carry out this research.In addition,our country is vigorously promoting the Beidou satellite navigation system.Studying GPS/INS integrated navigation can also lay a good foundation for combination of Beidou and INS in the future.In the face of high-rise buildings and increasingly complex urban environments,GPS may be unable to navigate and locate because of insufficient visible satellites.Therefore,it is imperative to study GPS/INS integrated navigation,especially the integrated navigation can also provide the attitude information of the carrier in the movement.Integrated navigation is generally divided into three kinds:loose combination,tight combination and deep combination.Loose combination is to combine the position and velocity information obtained by GPS and INS respectively in the Kalman filter to estimate the INS navigation parameter error and inertia element error and perform feedback correction.This is the GPS-assisted INS mode.The tight combination uses the original observations of the GPS receiver,such as carrier,pseudorange,pseudorange,etc.as the observations of the Kalman filter to perform the integrated navigation solution,to estimate the errors of the INS components and the navigation parameters,and to correct the errors.The tight combination belongs to the mutual assistance mode of GPS and INS.Deep combination is a combinationmode with deeper level and hardware level.The most important feature is that INS is used to assist GPS signal tracking and capture.It belongs to INS-assisted GPS mode.The tight combination has better accuracy and robustness than the loose combination.When the visible satellite is insufficient,the tight combination can make full use of the existing observation information to measure and update the system.Therefore,the main research in this paper is the tight combination.Compared to the pseudo-range measurement with an accuracy of meter level,the GPS carrier phase measurement accuracy is two orders of magnitude higher,and the centimeter-level positioning accuracy can be obtained.In order to further improve the accuracy of the integrated navigation,carrier phase measurement technology must be adopted.Differential techniques can reduce or eliminate many errors in GPS observations and are an important means to improve the accuracy of GPS observations.Based on the above,this paper studies a GPS/INS tightly integrated navigation algorithm based on carrier phase difference.The main research work of this paper is as follows:(1)A GPS/INS tight combination algorithm based on carrier phase difference is proposed and programmed.Carrier phase observation can not avoid the difficulty of the whole-period ambiguity.This paper uses the integer ambiguity as the system state quantity,deduces the system state equation including the integer ambiguity,and uses the carrier phase double-difference observation value to establish the system observation equation.And Fix the ambiguity of high-precision floating-point solution.(2)An adaptive Kalman filtering algorithm based on normalized innovation detection is designed for the case that GPS observations are vulnerable to external interference.By introducing a method of normalized innovation,it can be detected whether a problem has occurred in the system observations.If a problem arises,the system noise covariance matrix and the observed noise covariance matrix are estimated in real time based on the value of the new information,through amplification or the corresponding covariance matrix isreduced to adjust the weight ratio between the observed value and the predicted value of the system,so as to be able to resist the occurrence of gross errors in the observation to a certain extent.(3)The GPS/INS tight combination algorithm based on carrier phase difference is verified in the open environment and urban environment respectively,and compared with the GPS/INS loose combination effect based on carrier phase difference in the same environment.The results show that the GPS/INS tight-combination algorithm based on carrier phase difference has high precision in open environment,and can fully utilize existing information in urban environment to suppress filter divergence and make the combined navigation error not too large.Tight combination has great advantages compare to the loose combination.In this paper,an experimental comparison of BDS/INS compact combination effects based on carrier phase difference is also performed.The results show that the usability and accuracy of Beidou satellites are comparable to those of GPS satellites.