Rapid Capture Of High Dynamic Gps Signal Tracking Method

GPS (global positioning system)the next generation of navigation and orientation system, can provide precise timing and location-based services for its users. However, highly dynamic GPS signal usually results in higher Doppler shift and dynamic delay to pseudo-random codes. Thus the carrier tracking and code tracking will lose lock and can not keep synchronous anymore. It will be very difficult to adjust the receiver adaptively. In order to realize the quick blind catch for the highly dynamic GPS signal and prevent the pseudo-code delay and PLL stolen lock, most current research about fast track and capture technology for the highly dynamic receiver mainly focus on how to improve the dynamic response capability of the tracking loop.In this work, several methods about rapid capture and tracking on high dynamic GPS signal were studied. According to the characteristics of the highly dynamic C/A code, a matched filter algorithm based on the characteristic value was applied into the highly dynamic GPS signal capture. The corresponding theoretical criteria (model and process steps) for calculating and selecting the characteristic value were developed. Then the matched filter algorithm was compared in highly dynamic conditions with another two capture methods such as the time-domain-related sliding capture algorithm and the FFT-based parallel capture algorithm. According to the capture time and the calculating complexity, the simulation indicated that this method have a similar capture performance with the FFT algorithm and could be applied for the rapid capture of highly dynamic GPS signal.Furthermore, to improve the capture accuracy and speed up the lock of the follow-up tracking loop, the performance of the carrier and code tracking were discussed. The frequency-locking loop tracks the frequency of the input signal by measuring the frequency difference between the local carrier and the input carrier while the phase-locking loop tracks the phase of the input signal by measuring the phase difference between the local carrier and the input carrier. The Pseudo-code tracking is mainly a delay locking ring (DDLL) with a leading-lagging structure and the carrier tracking mainly takes a Costas (Costa) ring. Finally, the Matlab simulation results verify the correctness of the algorithm.