Time Division Multiplexing

Time-division multiplexing is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fraction of time in an alternating pattern.

1. TDM Time Division Multiplexing Md. Hasan Imam Bijoy Student of C.S.E Email: [email protected] Daffodil International University, Dhaka, Bangladesh

2. Let’s present… Time Division Multiplexing

3. What is TDM? Time-division multiplexing ( TDM ) is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fraction of time in an alternating pattern. TDM is a digital multiplexing technique for combining several low-rate channels into one high-rate one.

4. Is TDM analog or digital? There are two common techniques for multiplexing the signals: Time Division Multiplexing ( TDM ) and Frequency Division Multiplexing (FDM). As I understand it, FDM is commonly used to multiples  analog  signals, while  TDM  is commonly used to multiplex  digital  signals.

5. Figure : TDM

6. Schemes of TDM TDM Scheme Synchronous Statistical . We Can divided TDM into two difference Schemes:

7. Synchronous Time-division multiplexing (TDM) is a digital process that allows several connections to share the high bandwidth of a line Instead of sharing a portion of the bandwidth as in FDM, time is shared In Synchronous TDM, each input connection has an allotment in the output even if it is not sending data In synchronous TDM, the data flow of each input connection is divided into units, where each input occupies one input time slot. A unit can be 1 bit, one character, or one block of data. Each input unit becomes one output unit and occupies one output time slot. Synchronous TDM Time Slots Frames

8. Figure: Synchronous time-division multiplexing

9. More on Synchronous In synchronous TDM, a round of data units from each input connection is collected into a frame (we will see the reason for this shortly). If we have n connections, a frame is divided into n time slots and one slot is allocated for each unit, one for each input line. Time slots are grouped into frames. A frame consists of one complete cycle of time slots, with one slot dedicated to each sending device. In a system with n input lines, each frame has n slots, with each slot allocated to carrying data from a specific input line. Finally we say that: In synchronous TDM, the data rate of the link is n times faster, and the unit duration is n times shorter .

10. Interleaving Interleaving Synchronous TDM can be compared to a very fast rotating switch. As the switch opens in front of a device, that device has the opportunity to send a specified amount (x bits) of data onto the path. This process is called interleaving. Interleaving can be done by bit, by byte, or by any other data unit. TDM can be visualized as two fast-rotating switches, one on the multiplexing side and the other on the demultiplexing side. The switches are synchronized and rotate at the same speed, but in opposite directions. On the multiplexing side, as the switch opens in front of a connection, that connection has the opportunity to send a unit onto the path. This process is called interleaving.

11. Figure : Interleaving

12. Why TDM used in Digital Signal? Because it makes sense, your Rx will (usually ) be simpler that way. If you are going  TDM , you are slicing up Time and giving separate slots of time to different source  signals . So each source info must need to be digitized and multiplexed into its assigned Time Slot. Hence  digital .

13. What are the applications of TDM? It used in ISDN (Integrated Services Digital Network) telephone lines. It is used in PSTN (public switched telephone network). It is used for some telephone system. It is used in wire line telephone lines. There are some applications of time division multiplexing which are given below:

14. Advantage of TDM? Time division multiplexing systems are more flexible than frequency division multiplexing. Time division multiplexing circuitry is not complex. Problem of cross talk is not severe. Full available channel bandwidth can be utilized for each channel

15. Disadvantage of TDM? Synchronization is required in time division multiplexing. Complex to implement. Due to slow narrowband fading, all the TDM channels may get wiped out.