The Research Of Ultra-Tight GPS/MIMU In Vehicle Navigation System

The booming domestic intelligent transportation systems, vehicle positioning technology hasreceived widespread attention. This thesis study the vehicle location by utral tight couplingtechnique of global positioning system(GPS) and inertial measurement unit(IMU).Major problemsare included as follows: First, there is high cost in a complete set of IMU,which does not apply tovehicle loaction; Secondly,we study VDCaP vector tracking algorithm of utral tight coupledtechnique,the carrier tracking loop which a cascaded phase lock loop (CaPLL) can not provide areliable doppler measurements,the large doppler error degraded system performance.when the loopis unlock;Finally, in the ultra tight coupled system,the vector tracking performance is controlled bythe navigation solution of the system,if the navigation solution is not accurate enough to maintainthe signal lock, the vector tracking loop system will fail when GPS signal outage. Respecting theanalysis of the above issues, the main task of this thesis are as follows:(1) This thesis adpot the low cost and high reliable micro inertial measurement unit(MIMU)instead of a complete IMU, and the forgetting factor-based recursive least square algorithm for theperformance improvement of the gyro signal noise reduction is proposed. The simulation resultsshow that this algorithm is effective to improve the used precision of the gyro.(2) Research on the ultra-tightly GPS/MIMU with VDCaP algorithm, CPFLL is a compositeloop which consists of a CaPLL and an vector frequency lock loop discrminator, is developed in thehope of eliminate large doppler measurement errors caused by large phase errors in unlocked case.Through the experiment results in weak signal and strong signal condition show that CPFLL caneliminate the extra doppler values, and improve navigation performance.(3) To overcome the drawback of the vector tracking scheme will fail when GPS outage，weproposed a switch algorithm, which through the vector tracking algorithm VDCPF switched to thecorresponding scalar tracking algorithm DPLL when GPS outage. The experiments results showthat the scalar tracking algorithm is able to maintain loop track in the GPS transient outage harshenvironment by the assisted by transient precision MIMU, and rapid recover the high precisionpositioning after the signal is restored; in contrast, the vector tracking algorithm can enhance thecapture of the weak signal when GPS is not interrupted, and provide a higher estimation accuracy.