On the Impact of GNSS Receiver Settings on the Estimation of Codephase Center Corrections

Abstract

The role of codephase center corrections (CPC), also known as group delay variations (GDV), becomes more important nowadays, e.g. in navigation applications or ambiguity resolution. CPC are antenna dependent delays of the received codephase. They are varying with the angle of arrival of the signal at the GNSS antenna, i.e. with azimuth and elevation. CPC can be determined with a robot in the field with a similar approach as used for phase center corrections (PCC) for carrierphase measurements. The big challenge in the estimation of reliable CPC pattern is to deal with relatively noisy codephase observations compared to the correction magnitude. A better repeatability can be reached by reducing the overall codephase noise. One possibility to do this is to understand and improve the tracking loops of the receiver, especially the loop filters, within the calibration process. Due to highly dynamic stress caused by the fast robot motion, a perfect tracking of the GNSS signals is challenging. In this paper, a detailed look on the impact of different loop filter settings, like the noise bandwidth, the filter order or the use of an aided or unaided delay lock loop, on the time differenced single differences is done. To this end, an antenna calibration experiment was carried out, where, in addition to the hardware receivers, the IFEN Sx3 software receiver was used. The software receiver allows to change the settings in post-processing. The experiment shows, that the noise of the observations can be reduced by decreasing the noise bandwidth, but pattern information can be lost by using a bandwidth, which is too small. The trade-off between a small bandwidth and consequently less overall noise and the signal dynamics, caused by the fast robot motion, must be chosen carefully. At the end, an improvement in the pattern repeatability from 99.2 mm, using a hardware receiver, to 65.6 mm, using a software receiver with carefully chosen parameters, can be achieved.