Interoperability of the GNSS’s for Positioning and Timing

Abstract

Since 2014.0 we monitor 31 European multiGNSS sites with 5 different receivers (Javad, Leica, Septentrio, Topcon, Trimble), and various combinations of antennas and firmware. We work both in Single Point Positioning (SPP) mode (ionofree combination of pseudoranges, broadcast ephemeris), as a real time user would, and in Precise Point Positioning (PPP) mode (ionofree combination of carrier phases, SP3 precise ephemeris), as a post processing user would, using our MATLAB based, multiGNSS software. We simultaneously process pseudorange and/or phase data from GPS, Glonass, Galileo, Beidou, QZSS, NAVIC (formerly IRNSS) and SBAS/GAGAN in different combinations, depending on availability and receiver tracking capability. We estimate at each epoch by least squares three coordinates, one Tropospheric Zenith Delay and n_GNSS sums of the receiver time offset and the offset of the time scale of each GNSS relative to a common, interGNSS time scale, where n_GNSS is the number of tracked GNSS constellations. Differentiation of such offsets relative to the GPS data yields epochwise for each receiver estimates of the time offset GNSS to GPS. Comparing across different receivers we find that such offsets can be biased relative to each other by as much as several tens of nanoseconds. We arbitrarily select the average of six Septentrio receivers as reference, and estimate the receiver biases relative to the average Septentrio. We find that for a given receiver brand, the bias relative to Septentrio for the various GNSS is very repeatable, with a few exceptions. We show that updating the firmware version does affect the GNSS dependent receiver bias. We finalize our work with a table of ‘mean’ calibrations, for each GNSS, of comparable receivers, whenever their bias to Septentrio is within one standard deviation, and a subtable of ‘individual’ calibrations for those receivers which fall out of the mean by more than one standard deviation.