Frame Synchronizer Concept for TDMA Burst Modems

A time-division multiple access (TDMA) frame-synchronizer concept for use at satellite network ground stations is presented, and results of a laboratory demonstration are reported. Synchronizer design is compatible with area coverage, fixed spot beam Satellite-Switched/TDMA, and scanning spot beam satellite systems. The frame synchronizer exploits the periodic nature of frame-marker transmissions from a master ground station to enable extremely reliable recovery of the frame-marker reference at each ground station without generation of any additional false references. Although the experimental synchronizer was designed for operation at a channel rate of 10 megabaud, digital components are readily available to enable implementation at rates as high as 300 megabaud. Detailed descriptions are provided, and operation is shown to be analogous to a phase-locked loop. As such, the frame synchronizer exhibits a slight jitter in the position of the regenerated framemarker reference caused by corruption of the arriving frame markers by channel errors. With high probability, the jitter was found to be within ±3 bits at error rates as high as 1 x 10-2. Time-to-lock of the loop from a cold start was also measured and found to have a mean value of 976 frames at the same channel error rate.