Outline:- TDM and FDM Basics of TDM and FDM. Block Diagram of TDM and FDM. Working of TDM and FDM. Advantages and Disadvantages Applications

1. Time Division & Frequency Division
Multiplexing
Presented by:
Miss. S. S. Amale
M.Tech (Electronics)

2. 1.TDM and FDM
2.Basics of TDM and FDM.
3.Block Diagram of TDM and FDM.
4.Working of TDM and FDM.
5.Advantages and Disadvantages
6.Applications
Outline:-

3.  Time-division multiplexing (TDM) is a method of
putting multiple data streams in a single signal by
separating the signal into many segments, each having a
very short duration.
 Each individual data stream is reassembled at the
receiving end based on the timing..

4. 1. TDM is the digital multiplexing technique.
2. In TDM, the channel/link is not divided on the basis of frequency
but on the basis of time.
3. Total time available in the channel is divided between several
users.
4. Each user is allotted a particular a time interval called time slot
or time slice during which the data is transmitted by that user.

5. 5. Thus each sending device takes control of entire bandwidth of the
channel for fixed amount of time.
6. In TDM the data rate capacity of the transmission medium should
be greater than the data rate required by sending or receiving
devices.
7. In TDM all the signals to be transmitted are not transmitted
simultaneously. Instead, they are transmitted one-by-one.
8. 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.

6. 9. The TDM system can be used to multiplex analog or
digital signals, however it is more suitable for the
digital signal multiplexing.
10. The TDM signal in the form of frames is
transmitted on the common communication medium.

7. Types of TDM
1. Synchronous TDM
2. Asynchronous TDM

8. • Time slots are assigned in such a way that each
transmitting device gets its required share of the
available bandwidth. 'Because of this time-
bandwidth multiplexing technique, TDMs are
protocol insensitive and are capable of
combining various protocols onto a single high-
speed transmission link.
• In other words, we can say that multiplexer
allocates exactly-the same time slot to each
device at all times whether the device is active or
idle.

9. Figure explains more clearly the concept of TDM in a data
communication environment where three PCs are sharing
the common circuit. The packets generated by each PC are
multiplexed on the common line as A1, B1, and C1 and so
on.

10. Advantages:
•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.

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

12. Applications:
•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.

13. Difference between TDM and FDM
TDM FDM
TDM stands for time division
multiplexing.
FDM stands for frequency division
multiplexing.
TDM is preferred for the digital signals. FDM is preferred for digital signals.
The signals to be multiplexed can occupy
the entire bandwidth but they are isolated
in the time domain.
The signals to be multiplexed are added
in time domain. But they occupy different
slots in the frequency domain.
Synchronization is required. Synchronization is not required.
Cross talk like problem not occurs in
TDM.
It suffers from cross-talk like problems
due to imperfect band pass filter.
Only a few TDM channels will be affected
due to fading.
Due to wideband fading in the
transmission medium, all the FDM
channels are affected.

15. Frequency-Division Multiplexing (FDM) is a scheme in which
numerous signals are combined for transmission on a single
communications line or channel.
It is analog multiplexing technique. Each signal is assigned a different
frequency (sub channel) within the main channel.
its requires channel synchronization.

16. FDM requires that the bandwidth of a link should be greater than the
combined bandwidths of the various signals to be transmitted.
Thus each signal having different frequency forms a particular
logical channel on the link and follows this channel only.
These channels are then separated by the strips of unused bandwidth
called guard bands. These guard bands prevent the signals from
overlapping as shown in Fig.

17. In FDM, signals to be transmitted must be analog signals. Thus
digital signals need to be converted to analog form, if they are to
use FDM.

18. A typical analog Internet connection via a twisted pair telephone line
requires approximately three kilohertz (3 kHz) of bandwidth for
accurate and reliable data transfer.
Twisted-pair lines are common in households and small businesses.
But major telephone cables, operating between large businesses,
government agencies, and municipalities, are capable of much larger
bandwidths.

19. Advantages of FDM:
1. A large number of signals (channels) can be transmitted
simultaneously.
2. FDM does not need synchronization between its transmitter
and receiver for proper operation.
3. Demodulation of FDM is easy.
4. Due to slow narrow band fading only a single channel gets
affected.

20. Disadvantages of FDM:
1. The communication channel must have a very large bandwidth.
2. Intermodulation distortion takes place.
3. Large number of modulators and filters are required.
4. FDM suffers from the problem of crosstalk.
5. All the FDM channels get affected due to wideband fading.

21. Applications of FDM
1. FDM is used for FM & AM radio broadcasting. Each AM and FM radio
station uses a different carrier frequency. In AM broadcasting, these
frequencies use a special band from 530 to 1700 KHz.
2. All these signals/frequencies are multiplexed and are transmitted in air. A
receiver receives all these signals but tunes only one which is required.
Similarly FM broadcasting uses a bandwidth of 88 to 108 MHz
3. FDM is used in television broadcasting.
4. First generation cellular telephone also uses FDM.

22. Thank you!