The advantages of on-board regeneration have been widely discussed in the literature. In the SS-TDMA systems,however,the on-board regeneration imposes new synchronisation requirements.These requirements and their possible solutions are discussed.The regenerative SS-TDMA systems can be classified into two major categories.In the first,the core of the on-board processor is estabtished by a digital switching matrix that allows any uplink to interconnect with any downlink on a time-division basis.To make this system comparable,in terms of frame efficiency,with the transparent (IF switching matrix) solution,it is necessary to locate the bit synchroniser function within the sateltite payload.In the second category of SS-TDMA system,the on-board processor is a true switching centre that includes on-board buffers for time switching.This requires that all the incoming bursts are synchronised,at the elementary channel level,with the on-board timing.This function is performed by the burst synchronlser.
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