Calibration of the delay time in the GMS/GPS time transfer receivers using portable reference receivers

The Communications Research Laboratory (CRL) of Japan and the National Measurement Laboratory (NML) of Australia have performed international time transfer using the Geostationary Meteorological Satellite (GMS) and the Global Positioning System (GPS) since 1986. The precision of the time transfer using GPS is 10 ns, while that using GMS is 20 ns. However, there has been a bias of 200 ns between the time transfer results of the two time links, which is mainly due to the estimation error of the delay time in the time transfer receivers. To improve this bias error, CRL developed a portable reference receiver (PRX) for the GMS time transfer to calibrate the delay time in the time transfer receivers. In November and December 1987, a calibration experiment was carried out by the PRX method for GMS and GPS between CRL and NML. As the result of the experiment, the bias was reduced from 200 to 75 ns and the accuracy of the time transfer between CRL and NML was significantly improved