The Research Of Tracking The Weak GPS Signal

Nowadays, the GPS have been widely used all over the world, but the existing GPS receiveris usually works in the ideal signal condition. With the depth of the various aspects of theapplication of the GPS, and the expanded of the sphere of activities, as well as the complex ofthe city environments, the GPS signal becomes very unsatisfactory. So people gradually increasethe requirements for GPS positioning and navigation technology in the weak signal environment.The conditions such as indoor, urban and forest generally referred to as the complex conditions.Compared with the outdoor ideal conditions, attenuation and weakening of the GPS signalenergy to be seriously. The GPS system’s reliability and positioning accuracy will be severelyaffected. The existing technology is difficult to meet the higher demand. But with the continuousdevelopment of the GPS receiver applications, and portability and miniaturization in the device,the use of GPS is in the unideal complex conditions. Therefore, research of the GPS positioningtechnology has great significance for the weak signal.This paper describes the composition of the GPS system, the work principle of GPS receiver,and analysis of the traditional receiver tracking loop. In the weak signal condition which existingthe problem of loosing lock, and lack of tracking capabilities and other issues, the traditionalmethod need to be improved. In this paper, the tracking algorithm which uses Kalman filter inplace of the phase locked loop (PLL) and delay locked loop (DLL), improving the trackingaccuracy and sensitivity in the weak signal conditions. In order to be able to continue to trackingto the lower carrier-to-noise ratio of weak signals, a further improvement of the general Kalmanfilter algorithm. In the calculation process, using the square of computing to reduce the impact ofthe navigation data bit on the accumulation process. At the same time, add the incoherentintegration to the coherent. By increasing the integration time can effectively improve thetracking capability in the weak signal condition. The simulation results show that the weak GPSsignal with carrier-to-noise as lower as20dB-Hz can be tracked.