Performance Analysis of the Ultra-Tight GPS/INS Integration Based on an Improved Kalman Filter Design for Tracking Loops

Compared with loose and tight integration, ultra-tight GPS/INS integration offers improved performance under exposure to high dynamics, jamming and interference by employing the advanced Kalman filter design methods. The ultra-tight configuration delivers unique advantages by aiding the GPS tracking loops with velocity estimates derived from the Kalman Filter. In this manner, only the errors in the aiding velocity need to be tracked by the receiver as opposed to the absolute motion. Hence, the code & carrier tracking loop measurements, i.e. the pseudorange & pseudorange-rate measurements are correlated with the inaccuracy of the estimated velocity derived from Kalman filter. Due to these correlations, between the tracking loop measurements and estimated velocity errors, it is necessary to consider the correlations of not only the code tracking loop but also the carrier tracking loops in the design of the Kalman filter. In this way, accurate pseudorange-rate measurements and finally the optimal velocity estimation may be achieved. In this paper, the performance of the ultra-tight system which takes into account the correlations of both the code and carrier tracking loops is analyzed. Various simulation testing scenarios are examined to comprehensively evaluate the proposed Kalman filter configuration. Experimental testing results indicate that the mitigation of the correlations of tracking loops and therefore minimizing the tracking loop errors does, in fact, lead to more accurate pseudorange-rate and pseudorange measurements and therefore velocity estimations, which in turn enhance the tracking performance and the stability of the ultra-tight Kalman filter.