3.9 Time-Division Multiplexing (Frame Synchronization Methods for frame sync (1) Sending a frame sync signal from the transmitter over a separate channel (2) Deriving the frame sync from the TDM signal itself. TDM frame sync format … Channel s1s2…sk| Channel Channel… Channel s1s2|… n data 1 data2 data n dat Information sync words Information sync words words words Frame Fig 3-36 TDM sync format
6 3.9 Time-Division Multiplexing (Frame Synchronization) • Methods for frame sync: • (1) Sending a frame sync signal from the transmitter over a separate channel • (2) Deriving the frame sync from the TDM signal itself. • TDM frame sync format Channel N data … s1 s2 … sk Channel 1 data Channel 2 data … Channel N data s1 s2 … Information words sync words Information words sync words Frame Fig.3-36 TDM sync format
3.9 Time-Division Multiplexing Frame synchronization word: A segmented bits data stream which obeys same rules. Usually, it should be unique in the data stream, or at least, the appear probability is very small in information words Sw----the sync word, usually it appears in the TDm data stream periodly. So if we locate the sw, then we could separate Ai from data stream, at same time, it can be located at other a: anda
7 3.9 Time-Division Multiplexing • Frame synchronization word: A segmented bits data stream which obeys same rules. Usually, it should be unique in the data stream, or at least, the appear probability is very small in information words • SW ----the sync word, usually it appears in the TDM data stream periodly. So if we locate the sw, then we could separate Ai from data stream, at same time, it can be located at other Ai and Aj
3.9 Time-Division Multiplexing (principle of frame synchronizer circuit TDM input Amplifer Sampler and Regenerated tdM data e z(t)and decision filter circuit Frame synchronizer hift register Bit Stage Stage Stage synchronizer 12 Coincident detector is a Coincident detector Frame sync K-input p T AND gate. Figure 3. 37 Frame synchronizer with TDM receiver format end 8
8 3.9 Time-Division Multiplexing (principle of frame synchronizer circuit ) • Coincident detector is a K-input AND gate. Amplifer and filter Sampler and decision circuit TDM input Bit synchronizer Stage 1 Tb Ts Stage 2 Stage 3 Stage i … Frame synchronizer shift register 2 s 3 s i s Coincident detector Figure 3.37 Frame synchronizer with TDM receiver format end Z(t) Regenerated TDM data Frame sync 1 s