Pilot Study on the Validation of the Software-Defined Receiver for TWSTFT

Abstract

The Software-Defined Radio (SDR) receiver [1-5] has been developed at the Telecommunications Laboratory (TL, Chinese Taipei) for implementation in two-way satellite time and frequency transfer (TWSTFT/TW) Earth stations, aiming at improving the stability of TW time transfer, with particular impact on the diurnal signature present in almost all the links, which is the major uncertainty source in TW time links. The BIPM and the Consultative Committee for Time and Frequency (CCTF) Working Group on TWSTFT launched in February 2016 a pilot study for validating the SDR receiver in view of its implementation for use in UTC time links. Participants to this pilot study are the laboratories contributing to UTC which operate the SDR receiver and the BIPM Time Department. Goals of the pilot study are first, to validate the efficacy of the SDR receiver for improving the TWSTFT uncertainty and significantly reduce the diurnal effects; second to implement routine TW code measurement data through SDR receiver to improve the UTC time comparisons. In the frame of the pilot study, the SDR receiver has been installed and is operational by the end of 2016 at TL, NICT, KRIS, NTSC in Asia, PTB, OP and SU in Europe and NIST in the US. The project to install the SDR receiver in all the TW laboratories is ongoing. We present the results obtained at the BIPM Time Department in the preliminary steps of the analysis and validation of the SDR measurement data by using different methods, such as the time deviation (TDev), the triangle closures, the comparison with GPSPPP [6]. We analysed the data obtained from the pilot study and observed that in some TW links there is significant improvement, while in others no noise reduction is visible. This preliminary result needs more investigation, together with other open points as the calibration, the discontinuities observed after restarting the receiver etc. If the conclusion of this pilot project is positive, a proposal could be discussed at the CCTF to include TW time links with the SDR receiver in the computation of UTC. We study also the potential strategies to further improve the TWSTFT SDR; its combination with GNSS links [7] and the computation of SDR indirect links [8, 9].