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

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.