Frequency Tracking for High Dynamic GPS Signals Based on Vector Frequency Lock Loop

A method of estimating high dynamic GPS signal parameters based on Vector Frequency Lock Loop(VFLL) is put forward. Instead of using the discriminator, the VFLL focus on the nonlinear estimation. The navigation filter is realized utilize Unscented Kalman Filter(UKF). The VFLL method is based on the fact that comparing with the rate of change of the Doppler frequency caused by the motions of the satellite and the receiver, the acceleration of the receiver is the dominant factor. Instead of tracking the Doppler frequency of individual channel using the traditional loop, the VFLL tracking the velocity, acceleration.etc states of the GPS receiver from the measurement value of all channels. In vector mode, the navigation processor controls the carrier numerically controls oscillators (NCOs) based on the most recent velocity solution of the receiver. A major advantage of this method is that the velocity estimation from all the channels can be more accurate than Doppler frequency estimation from individual channel.