Research And Realization Of High Dynamic GPS Signal Tracking Algorithm

GPS (Global Positioning System) is the use of the most extensive navigation and positioning system for the military and civilian areas to provide services in many areas. With the continuous development of GPS technology, the application of GPS positioning system in high dynamic environment is more and more important. Due to the high dynamic environment,GPS carrier will produce a large Doppler frequency, likely to cause GPS signal tracking loss of lock, can not be stable tracking. In order to overcome the influence of Doppler frequency, this paper studies the GPS signal tracking loop algorithm under high dynamic, mainly from the following aspects:Firstly, the tracking result of the traditional carrier tracking loop is affected by the signal to noise ratio. The carrier tracking loop is composed of a phase-locked loop and a frequency-locked loop. By adjusting the size of the signal to noise ratio, find the best phase of the phase-locked loop and frequency-locked loop. The higher the signal-to-noise ratio, the better the performance of the phase-locked loop, due to the noise bandwidth is too high, the noise power will increase. When the carrying capacity of the carrier tracking ring is exceeded, it will cause the loop to lose its lock.Secondly, applying the extended Kalman filter to the carrier tracking loop, replacing the filter and discriminator of the traditional carrer tracking loop with the extended Kalman filter.By introducing the Taylor function of the nonlinear function in the high dynamic, and the first-order linearization is cut off, then the other high-order terms are removed, which transforms the nonlinear problem into a linear problem and implements carrier tracking.Finally, applying the unscented Kalman filter to the carrier tracking loop, replacing the filter and discriminator of the traditional carrier tracking loop with the unscented Kalman filter.Based on UT transformation, the probability density distribution of high dynamic nonlinear function is approximated, and a series of sampling points are used to approximate the posterior probability density of the state, and finally the carrier tracking is realized.Through the simulation results can be drawn, when the signal to noise ratio is relatively low,the traditional carrier tracking loop on the Doppler frequency estimation error is relatively large,resulting in tracking loss of lock. When improving the signal-to-noise ratio, the traditional carrier tracking loop has improved the estimation error of Doppler frequency, but the error of the first derivative and second derivative of Doppler frequency is relatively large. In the case of low signal-to-noise ratio, the extended Kalman tracking loop and the unscented Kalman tracking loop have better performance than the traditional tracking loop in tracking accuracy and dynamic stress, and the estimation error of Doppler frequency and its first derivative and second derivative is smaller. When improving the signal-to-noise ratio, the tracking accuracy of the extended Kalman tracking loop and the unscented Kalman tracking loop is improved, and the UKF carrier tracking algorithm is better than the EKF carrier tracking algorithm in terms of tracking accuracy and convergence speed.