Downlink and uplink synchronization concepts for spread spectrum communications via satellite

A synchronous spread-spectrum communications system utilizing the resources of a nonprocessing satellite transponder is considered. The systemwide time and frequency standard (which is assumed to be maintained by the system master terminal) is transferred to the satellite, and from there it is disseminated and used by all slave terminals in synchronizing their downlink and uplink operations. The downlink and uplink time and frequency tracking processes that must be performed by each system terminal in order to achieve and maintain synchronization are described, analyzed, and evaluated. The mechanism that establishes system time and frequency reference at the satellite is also described. The authors present computer simulation results illustrating the transient as well as the steady-state performance capabilities of the synchronization mechanisms in the presence of satellite and platform motion