In this paper, the data wipe-off technique is incorporated into the vector tracking loop of the Global Positioning System (GPS) receiver for performance improvement. It is a challenge to continuously track the satellite’s signal in weak signal environment. The data wipe-off algorithm on the basis of pre-detection method is adopted to detect data bit sign reversal every 20 ms. The method presented in this paper has an advantage to continuously estimate the navigation data bit and achieve improved tracking performance. Conventional GPS receivers use scalar tracking loop and satellite signals from all the channels are processed independently. On the vector tracking loop, signals in the channels are shared with each other, therefore, the receiver can track signals successfully even the signal strength from individual satellite is weak. The navigation data, which contains information that is necessary to perform navigation computations, are binary phase-shift keying (BPSK) modulated onto the GPS carrier phase with the bit duration of 20 ms (i.e., 50 bits per second). Tracking accuracy of a weak GPS signal is decreased by possible data bit sign reversal every 20 ms to the integration interval. To achieve better tracking performance in weak signal environment, the coherent integration interval can be extended. However, increase of the integration time lead to decrease of the tracking accuracy by possible data bit sign reversal every 20 ms to the integration interval. When the integration interval of the correlator is extended over 20 ms in low C/No levels, the navigation data wipe-off algorithm can be employed to avoid energy loss due to bit transitions. The tracking loop based on the discriminator as well as the pre-filter will be compared. The pre-filter provides more flexible adjustment to specific environments to reduce noise interference. Evaluation of the tracking performance based on the various algorithms for the vector tracking loop of a GPS receiver will be presented.

Keywords：global positioning system (GPS), vector tracking loop, Pre-filter, data wipe-off, weak signal