Access and synchronization schemes in the ESA OBP system

An outline of the main characteristics of a satellite communication system based on a regenerative payload with onboard processing (OBP) capabilities, is given. This system is presently being developed by the European Space Agency (ESA) in a laboratory version and plans are being made for an implementation of a preoperational version. The access and synchronization schemes proposed for the system are presented. The synchronization of the network users is checked onboard by the estimation of the arrival times of the different synchronization bursts with respect to the nominal onboard system frame. The adopted onboard clock lock technique, in conjunction with the possibility of ensuring an extended free wheeling window, provides a synchronization hot redundancy with a consequent improvement in the overall satellite availability. In particular, the initial acquisition and synchronization of the master control terminal and the access and synchronization procedures utilized by the user traffic terminals are described