Synchronization aspects in a regenerative MF-TDMA system. Algorithms, stability and degradations

The European Space Agency (ESA) is actively working in a regenerative payload with on board processing (OBP). The system must be accessible by low cost, low data rate, user traffic terminals (UTT). In order to achieve good throughput efficiency and low cost ground stations, MF-TDMA without preambles or guard times is the preferred transmission scheme. To keep the OBP T-stage memory within reasonable bounds burst lengths must be kept short (for example 32 symbols); guard times and preambles must be eliminated and system synchronisation becomes one of the most critical issues, since an error in the synchronism of one of the UTT can affect the whole system. The network clock synchronization is achieved by means of a closed loop technique, and all the UTT are frequency synchronized using a frequency extraction and retransmission scheme (FERT). The paper outlines some problematic aspects of the new system, in particular concerning clock error modelling, associated degradations and the stability and performance of different loop transfer functions