Benefits of Using Carrier Phase Tracking Errors for Ultratight GNSS/INS Integration: Precise Velocity Estimation and Fine IMU Calibration

We explore the benefits of using carrier phase tracking errors (CPTEs) as measurements for an ultratightly coupled (UTC) global navigation satellite system (GNSS)/inertial navigation system (INS) integration system. It is demonstrated that CPTEs and time-differenced carrier phases (TDCPs) are equivalent under the condition of zero initial phase error. Hence, for the UTC integration, precise velocity estimations at the millimeter/second level can be expected by using CPTEs as measurements. Furthermore, low-noise CPTE measurements benefit the fine online calibration of an inertial measurement unit (IMU). A high-accuracy IMU error model is included in the integration Kalman filter (IKF). The corresponding measurement model is derived in detail. A static field test and a dynamic road test are used to assess the performance. For the static test, standard deviations of velocity errors range from 2.29 to 3.17 mm/s. Standard deviations of velocity errors in the road test are found to be at the 6.01 & x2013;6.07 mm/s level for horizontal components and 8.05 mm/s for vertical components. Again, for the dynamic test, the effect of IMU calibration is evaluated via inertial coast errors. The results show that the combination of CPTEs and the high-accuracy error model exhibits the smallest free-inertial coast errors, as compared with other considered methods.