Relative Calibration of Galileo receivers within the Time Validation Facility (TVF)

Abstract

GMV is the prime contractor for the Time and Geodetic Validation Facility (TGVF) in the Galileo FOC phase (Full Operational Capability), a contract of the European Space Agency (ESA). Within the TGVF, the Time Validation Facility (TVF) is the subsystem in charge of steering Galileo System Time (GST) to UTC, among other duties. The TVF is operated at GMV headquarters near Madrid, Spain. Calibrated Galileo receivers are needed in the frame of TVF activities to, among other tasks, assess the UTC-GST offset broadcast in the Galileo navigation message.Absolute receiver calibration is a complex activity involving the availability of a signal simulator and of a calibrated reference antenna. An alternative data-based method to evaluate the Galileo receiver delay in E5 signals relative to GPS is also possible. The key feature of such method is the cancellation of the GPS and Galileo ionospheric delays when combining pseudoranges from two satellites with a close position in the sky.A software tool called gecal has been developed by GMV within the Galileo TVF, implementing such method and processing RINEX 3 observation files. Satellite positions are read from a SP3 orbit file. The tool allows the rapid E5 calibration of a new or existing Galileo receiver. This paper describes the tool and the calibration of three Galileo receivers used in the TVF. Galileo Signal-In-Space validation results obtained using such receivers are also presented.

On the possibility of getting traceable time and frequency measurements via GNSS receivers

“…It is assumed that the Galileo E1 and GPS L1 signals share the same delay, and the Galileo Broadcast Group Delay (BGD) values need to be known. With the support of GMV, Tres Cantos, Spain, the internal E5a delays for several receivers operated in PTB were determined (Píriz et al 2015b), and this process was repeated when new BGD values were released. The uncertainty for the delay values was stated as 3.7 ns for the E5a delay and 4.2 ns for the ionosphere-free linear combination (Defraigne et al 2014).…”

The Time Validation Facility (TVF): An all-new key element of the Galileo operational phase

“…The satellite average at each epoch provides the station clock offset versus GST. Since the station has been calibrated [5], the station clock being UTC(PTB), we obtain UTC(PTB)-GST. We then apply the UTC-GST offset from the GESS navigation messages in order to obtain UTC(GALSIS)-UTC(PTB).…”

“…Satellite positions are read from a SP3 orbit file. Details on the GPTB calibration process can be found in [5].…”