2-WAY TIME TRANSFER VIA COMMUNICATION SATELLITES

Some information on the history of two-way satellite time transfer is provided and developments in satellite communications technology conducive to this time transfer technique are mentioned. The difference between one-way and two-way satellite time transfer is explained, the advantages and disadvantages of the two-way method are pointed out, and the theory of the two-way technique using geostationary communication satellites is presented in detail showing the high accuracy potential of the method. The advantages of the use of spread spectrum techniques are outlined and the implementation of the two-way method using communication satellites and small earth stations employing pseudonoise (PN)-modems is described, and methods for signal delay calibration are dealt with. Existing links are listed and their performances are given. The precisions achieved are in the subnanosecond range and one expects accuracies of at least one nanosecond using small transportable stations for delay calibration. Finally, facts are summarized and the future use of the two-way technique employing communication satellites is discussed.