Time Division Multiplexing (TDM)
Time Division Multiplexing: The process called multiplexing is used in order to utilize common transmission channel or medium to transmit more than one signals simultaneously. TDM is a digital multiplexing process.
In TDM all the signals to be transmitted are not transmitted simultaneously. Instead, they are transmitted one-by-one. Thus each signal will be transmitted for a very short time. One cycle or frame is said to be complete when all the signals are transmitted once on the transmission channel. The TDM principle is illustrated
Principl of TDM
One transmission of each channe completes one cycle of operation called as a "Frame". The TDM owever system can be used to multiplex analog or digital signals, h it is more suitable for the digital signal multiplexing. The hannel of TDM will be more clear
The data flow of each source (A, B or C) is divided into units (say A, A2 or B1, C, etc.) Then one unit from each source is taken and combined to form one frame. The size of each unit such as A B, etc. can be 1 bit or several bits.
TDM system
The frames of TDM signal. For 3 inputs being multiplexed, frame of TDM will consist of 3 units i.e. one unit from each source. Similarly for n number of inputs, each TDM fram will consist of n units.
TDM frames
The TDM signal in the form of frames is transmitted on the common communication medium.
Data rate: For a TDM, the data rate of the multiplexed signal is always May 06 16 n times the data rate of individual sources, where n is the number of sources.
TDM MODULATOR
To maintain proper positions of Sample Pulse in the Multiplexer, it is necessary to synchronise the Sampling Process. Because the sampling operations are usually elec-tronics, it is typically a clock Pulse Train. That serves as a reference for all samples. At the Receiving Station, there is similar Clock synchronization can be derived from the re-ceived waveforms by observing the Pulse Sequence over many pulses and averaging the pulses. Clock Synchronization does not guarantee the proper sequence of samples is syn-chronized. Proper alignment of the Time slot sequence requires Frame Synchronisation. Hence one or more Time Slots per Frame may be used to send Synchronisation Information
Waveform for TDM modulator
Benefits of TDM
TDM is all about cost:
fewer wires and simpler receivers are used to transmit data from multiple sources to multiple destinations. TDM als less bandwidth than Frequency-Division Multiplexing (FDM) signals, unless the bitrate is increased, which will subsequently increase the necessary bandwidth of the transmission
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