GNSS and its Impact on Position Estimates

This study evaluates the impact of multi-GNSS (Glob-al Navigation Satellite System) signals on the estima-tion of precise position with millimetre accuracy. Compared to standalone satellite systems like the Global Positioning System (GPS), multi-GNSS im-proves start-up time, performance, satellite visibility, accuracy, spatial geometry and reliability. However, on the flip side it increases the noise, signal inter-ference, hardware complexity of the receiver, inter-system interference and computation complexity which may degrade its performance. Though GNSS is similar at fundamental levels, differences exist in sig-nal structures, reference frames and timing standards. Compatibility and interoperability between the differ-ent constellations of the highest order is required to achieve the best results. At present, GPS and Glonass navigation systems are fully functional with global coverage and comparable precision. Glonass satellite constellation, signal structure is slightly different when compared to GPS, whereas major differences exist in the reference frame and epoch time. Com-bined GPS–Glonass solution significantly improves the accuracy in navigation applications with increased satellite signal observations and spatial distribution of visible satellites. For precise geodetic studies using static post-processing, combined solution may degrade the accuracy, if these differences are not handled care-fully. Currently for geodetic studies, only GPS obser-vations are majorly used worldwide. For the first time, daily precise position is estimated for continuous GNSS stations located in India using static post-processing with standalone GPS, Glonass as well as combined GPS–Glonass to study the impact of multi-GNSS signals for geodetic studies.