High Dynamic GPS Tracking Algorithm Research Baesed Kalman Filtering

GPS signal has a large doppler frequence and various order derivative of dopplerfrequence under high dynamic condition, which make the carrier tracking algorithm produceslarge dynamic stress error. The carrier tracking algorithm easily lose lock and receiver can’twork normally. The carrier tracking algorithm based on FLL or PLL usually need toconstantly adjust the bandwidth in above given situation. Because bandwidth switchingthreshold is difficult to determine and the loop switchs frequently. It leads to unstable state offiltering. Carrier tracking algorithm based on kalman filtering(KF) could change adaptivelybandwidth, which have better balance between high dynamic performance and high trackingprecision performance. However, KF is easy to filter divergence under the condition ofdynamic change sharply or insufficient prior information. Hence, the KF theory is introducedinto the GPS carrier tracking algorithm design in this paper, and two kinds of high dynamiccarrier tracking algorithm is proposed. The research work is mainly as follows:Firstly, the classical carrier tracking algorithm based on FLL or PLL is difficult tobalance the performance of high dynamic and high tracking precision. For solving this issue,the carrier tracking algorithm based on extended kalman filtering(EKF) and unscented kalmanfiltering(UKF) are implemented. The experimental results show that the carrier trackingalgorithm based on kalman filtering theory is better than the classical carrier trackingalgorithm in the aspects of tracking precision, convergence speed and dynamic adaptability.Compared to the traditional and complex carrier tracking loop(FLL/PLL), whenthe acceleration value of receiver is always50g, the tracking precision of the carrier trackingalgorithm based on UKF and EKF increased by82.87%and12.71%respectively.Then, carrier tracking algorithm is easy to lose lock under high dynamic situation, whenGPS signal has large Doppler frequency or dynamic change dramatically. To solve theproblem, a non-data-aided high dynamic carrier tracking algorithm based on adaptiveextended kalman filtering (AEKF) was presented. On the basic of substituting AEKF fordiscriminator and filter, the algorithm eliminate the influence of data bit jump by doublephase transformation processing, and adopts the signal-to-noise ratio estimator to estimatingand calibrating measurement noise covariance and the monitoring method of signal dynamicwith jerk to estimating and calibrating system process noise covariance, which is helpful tooptimize the filtering accuracy. In addition, the high dynamic tracking loop strategy withcarrier assisted code loop technology is further implemented on the basis of the algorithm. Itcould settle the issue, which the amplitude of navigation message is weakened and code loopdoes not provide precise code phase under the high dynamic condition. The experimentalresults show that GPS software receiver with the AEKF algorithm could work normally with the dynamic indexes of acceleration on up to200g and instantaneous jerk up to10000g/s.Finally, as the carrier tracking loop based on UKF is sensitive to initial value and scalingfactor, a high dynamic carrier tracking algorithm based on UKF with adaptive fadingfactor(FUKF) was proposed. The algorithm utilize fading factor based on the change ininnovations to correct covariance components of a series of points, which are obtained afterthe nonlinear transformation processing. It aims on utilizing fading factor to adjust therelationship between the theoretical error and the actual error. It restrain filtering divergencein the case of the wrong value of initialization or scaling factor. Because the state equationis linear. A carrier tracking algorithm based on FUKF are further simplified and a carriertracking algorithm based on simpled FUKF is further implemented. Simulation experimentsshow that GPS software receiver with the proposed algorithm could work normally with thedynamic indexes of acceleration on up to200g, and overcome the shortcoming that carriertracking algorithm based on UKF is sensitive to initial value and scaling factor. Comparedwith the algorithm with FUKF,tracking precision of the algorithm with simpled FUKF doesnot change, and a single run time of the algorithm with simpled FUKF also reduced by15.15%.