This paper details techniques for the absolute calibration of receiver chains as used in timing reference stations. The delays experienced by the GNSS signals in all elements of the receiving chain (antenna, receiver and cable) are each measured individually and with careful consideration regarding the uncertainty level assigned to them. Two different receiving chains based on different equipment units, were absolutely calibrated for GPS and Galileo signals.The calibration process and the uncertainty evaluation were then validated through the relative comparison in common clock setup in different real environments. The validation results show that some additional uncertainty has to be considered when the absolute calibration results are transferred to real signals, due to the real environment and to the difference between the chip shapes of the simulated signals and of the true signals coming from the satellites. The final 1 − σ uncertainties are below 1.1 ns for all the GPS and Galileo signals, except 1.8 ns for GPS C/A. The satellite group delays are also determined from the calibrated stations. An agreement at the ns level is found between the so-determined satellite group delays and the values provided by the system operators.

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Within the GIOVE Mission (GIOVE-M), two experimental satellites called GIOVE-A and GIOVE-B have been launched by the European Space Agency. This paper analyses the different issues involved in GPS/GIOVE interoperability for positioning and timing, including GGTO (the GPS to Galileo time offset) and timing biases, and presents practical experience and results related to EGGTO, the GIOVE-M experimental version of GGTO broadcast within the GIOVE navigation messages.

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