Absolute Calibration of Time Receivers with GPS/Galileo HW Simulator

Abstract

Time transfer between atomic clocks operated at different locations usually is performed with the well known GNSS Common View technique. This technique is based on time receivers measuring the time differences between the connected atomic clock and the GNSS satellite clocks. The obtained results are used for time scale generation such as UTC or TAI. In order to produce a reliable and accurate time scale from all provided time difference measurements with various GNSS time receivers the accurate calibration of them is absolute essential. In the last years two main methods for time receiver calibration were proposed. One is to compare the obtained time differences of the “test receiver” relative to a calibrated receiver, the “golden receiver”. This method is actually used by the International Bureau of Weights and Measures (BIPM) for the periodically calibration of the time receivers at the different UTC laboratories. Following the second method one performs an absolute calibration of time receivers using a GPS HW simulator. In this paper the absolute calibration of time receivers with a GPS/Galileo HW simulator is performed. An analysis and description in detail is provided. The primary step is to check and adjust the calibration of the simulator itself. Therefore the GNSS signals and the 1PPS signal of DLR’s GNSS hardware simulator “Multi-output Advanced Signal Test Environment for Receivers (MASTER)” are recorded in parallel with a fast acquisition oscilloscope. The time offset between the GNSS spread code and the 1PPS signal is calculated which represents a measure for the calibration of the signal simulator itself. After the calibration of the simulator the time receiver used for UTC measurements is fed with the satellite signals generated by the simulator to determine the absolute offset of the receiver (internal delay) compared to the simulator output. Additionally data is recorded by a combined GPS/Galileo receiver connected to the simulator. The precision of the Galileo and GPS frequency transfer is determined and further investigated.