Wenfei Gong

Performing the high-precision Global Navigation Satellite System (GNSS) applications with low-cost antennas is an up-and-coming research field. However, the antenna-induced phase biases, i.e., phase center corrections (PCCs), of the low-cost antennas can be up to centimeters and need to be calibrated in advance. The relative field antenna calibration method is easy to conduct, but the classical procedure entails integer ambiguity resolution, which may face the problem of low success rate under the centimeter-level PCCs. In this contribution, we designed a relative field calibration method suitable for the low-cost GNSS antennas. The triple-differencing operations were utilized to eliminate the carrier-phase ambiguities and then construct PCC measurements; the time-differencing interval was set to a relatively long time span, such as one hour, and the reference satellite was selected according to the angular distance it passed over during a time-differencing interval. To reduce the effect of significant triple-differencing noise, a weight setting method based on the area of a spherical quadrilateral was proposed for the spherical harmonics fitting process. The duration of the data collection with respect to GPS and BDS was discussed. The performance of the proposed method was assessed with real GPS and BDS observations and a variety of simulated phase patterns, showing that calibration results could be obtained with millimeter-level accuracy. The impact of cycle slip and elevation mask angle on the calibration results was also analyzed.

After the front-end, the first step of a GNSS receiver is acquisition. Beidou B3I signal provides high chipping rate and long PRN code to improve performance. However, these new features bring challenges to the acquisition unit. For Beidou B3I signal in dynamic scene, Doppler effect on carrier and PRN code should be considered at the same time, which brings limit to acquisition time. With presence of these problems, this article proposes an algorithm based on parallel code search and a fast second search. Monte Carlo simulation shows that proposed algorithm has the similar distribution of probability of detection with parallel code search algorithm and better time performance than conventional acquisition algorithms.