Frequency and time dissemination using spread-spectrum coded signals transmitted via direct-TV broadcasting satellites

Summary form only given. Wideband spread spectrum-coded signals are routinely used for satellite tracking and positioning purposes. These signals are transmitted using very low power levels simultaneously to the main digital or analogue direct-TV signal without any interference. The round-trip time-delay is measured, which provides the range at precisions of better than 5 cm. The line-of-sight velocity is determined at the same time with accuracies of better than 0.1 mm/sec. These ranging-signals have been received with independent time-receivers located in the footprint area of the satellite. The locally re-generated spread-spectrum symbol-rate stabilizes a low-phase-noise crystal oscillator, whose frequency is corrected for the Doppler shift induced by the satellite´s relative movement. Orbital information and measured velocity is continuously broadcast from the ranging site to the user with minimum time delay in the form of user data modulating the spread-spectrum signal. Frequency and time-transfer accuracies achieved so far are presented. The system shows a potential frequency transfer accuracy compatible with good H-maser clocks for integration times of about one day and more. Further enhancements to the system are investigated to provide a reliable, highly accurate frequency and time reference