Two-way time transfer via communication satellites

The history of two-way satellite time transfer is provided and developments in satellite communications technology conducive to this time transfer technique are briefly reviewed. The difference between one-way and two-way satellite time transfer is explained, and the advantages and disadvantages of the two-way method are pointed out. The theory of the two-way technique using geostationary communication satellites is presented showing the high accuracy potential of the method. The advantages of the use of spread spectrum techniques are outlined. The implementation of the two-way method using communication satellites and small Earth stations using pseudonoise (PN) modems is described. Methods for signal delay calibration are dealt with. Existing links are listed and their performances are given. The future use of the two-way technique using communication satellites is discussed