Time transfer using a multi-channel code-based GPS receiver

We report on time-transfer experiments using a GPS receiver that we have constructed using a commercial GPS "engine" and a standard PC. The receiver measures the time difference between the local clock and a 1 pps signal that is synchronized to GPS time using data from up to eight satellites. The receiver also reports the difference between GPS time as estimated using each of the satellites being tracked and the composite output pulses that have a rate of 1 Hz (1 pps signal). These data can be used to construct the standard 13-minute tracks as defined in the BIPM standard; the same data can also be averaged in other ways that make better use of the multi-channel capabilities of the hardware. The 13-minute averages can be directly compared with standard time-transfer receivers using common-view analysis. The results of our tests suggest that we should re-examine the methods currently used for national and international time and frequency coordination, and we suggest an alternative approach based on multi-channel receivers that should be more flexible, simpler and easier to operate than the current system.