3.9 Time-Division Multiplexing Definition Time-division multiplexing (Tdm) is the time interleaving of samples from several sources so that the information from these sources can be transmitted serially over a single communication channel
1 3.9 Time-Division Multiplexing • Definition. Time-division multiplexing (TDM) is the time interleaving of samples from several sources so that the information from these sources can be transmitted serially over a single communication channel
3.9 Time-Division Multiplexing Analog input signal Channel I ansmitter (from source 1) i i sampler Channel2 PAM TDM (from source 2) PCM Quantizer encoder Channel 3 (from source 3) --------. Synchronization Channel Receiver TDM PCM Channel 1 plus noise Decoder PAM Channel 2 Channel 3 Output analog signals Figure 3-35 Three-channel TDM PCM system
2 3.9 Time-Division Multiplexing
3.9 Time-Division Multiplexing in the transmitter the pulse width of the TDM PAM: the pulse width of the TDM PCM:
3 3.9 Time-Division Multiplexing • in the transmitter the pulse width of the TDM PAM: the pulse width of the TDM PCM: 3 Ts Ts
3.9 Time-Division Multiplexing At the receiver the decommutator has to be synchronized with the incoming waveform so that the PAM Samples corresponding to source l will appear on the channel l output. This is called frame synchronization, which is very important for TDM system Low-pass filters are used to reconstruct the analog signals from the Pam samples Because of isi resulting from poor channel filtering, PCM samples from one channel may appear on another channel. often called crosstalk, even though perfect bit and frame synchronization were maintained
4 3.9 Time-Division Multiplexing • At the receiver the decommutator has to be synchronized with the incoming waveform so that the PAM samples corresponding to source 1 will appear on the channel 1 output. This is called frame synchronization, which is very important for TDM system. • Low-pass filters are used to reconstruct the analog signals from the PAM samples. • Because of ISI resulting from poor channel filtering, PCM samples from one channel may appear on another channel, often called crosstalk, even though perfect bit and frame synchronization were maintained
3.9 Time-Division Multiplexing Frame synchronization -grouping data yncnronous Word synchronization (start up signaling) system e Digital bit synchronization -regenerating data system Asynchronous system Synchronous system: all devices have same clock, by data signal with clock, by separate clocking line) Asynchronous system: receiver clock is started aperiodically and no synchronization with a master clock
5 3.9 Time-Division Multiplexing • Synchronous system: all devices have same clock, by data signal with clock, by separate clocking line) • Asynchronous system: receiver clock is started aperiodically and no synchronization with a master clock. Digital system Synchronous system Asynchronous system Frame synchronization -- grouping data Word synchronization (start up signaling) bit synchronization -- regenerating data