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

摘要

The European Space Agency (ESA) is actively working in anregenerative payload with on board processing (OBP). The system must benaccessible by low cost, low data rate, user traffic terminals (UTT). Innorder to achieve good throughput efficiency and low cost groundnstations, MF-TDMA without preambles or guard times is the preferredntransmission scheme. To keep the OBP T-stage memory within reasonablenbounds burst lengths must be kept short (for example 32 symbols); guardntimes and preambles must be eliminated and system synchronisationnbecomes one of the most critical issues, since an error in thensynchronism of one of the UTT can affect the whole system. The networknclock synchronization is achieved by means of a closed loop technique,nand all the UTT are frequency synchronized using a frequency extractionnand retransmission scheme (FERT). The paper outlines some problematicnaspects of the new system, in particular concerning clock errornmodelling, associated degradations and the stability and performance ofndifferent loop transfer functions