Volker Frevert's research while affiliated with Technische Universität Dresden and other places

Publications (7)

Article
Full-text available
In 2020, Garmin released one of the first consumer devices with a dual-frequency GNSS chip and a quadrifilar helix antenna: GPSMAP 66sr. The device is intended to serve as a positioning and navigation device for outdoor recreation purposes with positioning accuracies on the few meter level. However, due to its highly accurate GNSS dual-frequency ca...
Article
Full-text available
For a few years now, GNSS multi-frequency quadrifilar helix antennas (QHA) are available to be used for precise GNSS applications. We performed test measurements with two types of multi-frequency QHA and compared them with a geodetic patch antenna. Although code and carrier phase noise and high-frequent multipath was determined to be larger as comp...
Article
Precise GNSS positioning requires the calibration of the receiving antennas. Antenna field calibrations, in contrast to lab calibrations, use the signals transmitted by GNSS satellites. With the present transition to additional GNSS and new frequencies we encounter the problem that field calibrations have to be performed with incomplete satellite c...
Article
Antenna changes at GNSS reference stations frequently produce discontinuities in their coordinate time series, especially in the height component. These coordinate shifts are mainly caused by changes of carrier-phase multipath effects and also, but usually to a smaller extend, by errors in the antenna phase center corrections. A monitoring method w...
Article
Summary GPS signal diffraction occurs whenever the direct GPS signal is obstructed but nevertheless a diffracted signal is received and processed. The longer propagation time of a diffracted signal causes carrier phase errors of up to several cm or even a few tens of cm. Diffraction effects are a common and often dominant error source in rapid stat...
Article
GPS signal diffraction occurs whenever the direct GPS signal is obstructed but nevertheless a diffracted signal is received and processed. The longer propagation time of a diffracted signal causes carrier phase errors of up to several cm or even a few tens of cm. Diffraction effects are a common and often dominant error source in rapid static or ki...

Citations

... The post-processing considers the GPS and Galileo L1 and L5 signal in PPP mode. For more details, please see Wanninger et al. (2022), who supported us in doing and evaluating the measurements. For the processing, the commercial WaPPP software was used. ...
... A great advantage of the GPSMAP 66sr in comparison with other consumer devices with dual-frequency GNSS chips, e.g., smartphones such as Xiaomi Mi8 or Huawei P30 [5], consists of its quadrifilar helix antenna (QHA). QHA produces a circularly polarized hemispherical radiation pattern and, thus, is able to mitigate multipath signals [6]. It proved to be a major advantage of the equipment that GNSS observations can be stored internally in RINEX 3.04 format [7] and that these files can be easily transferred to a computer for postprocessing. ...
... To obtain the position solution, three different observation weighting approaches were processed and compared to a reference solution: identical weighting (IDEN), elevation dependent weighting (COS2) and C/N0 based weighting (CN0), [18]. The reference solution is obtained by a carrier phase based ionosphere free (L3) double difference approach, whereby the reference station is located at our rooftop GNSS laboratory in Hannover. ...