Tdm & fdm

1. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
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2. 6.2
Bandwidth utilization is the wise use of
available bandwidth to achieve
specific goals.
Efficiency can be achieved by
multiplexing; i.e., sharing of the
bandwidth between multiple users.
Note

3. 6.3
6-1 MULTIPLEXING6-1 MULTIPLEXING
Whenever the bandwidth of a medium linking two Whenever the bandwidth of a medium linking two
devices is greater than the bandwidth needs of the devices is greater than the bandwidth needs of the
devices, the link can be shared. Multiplexing is the set devices, the link can be shared. Multiplexing is the set
of techniques that allows the (simultaneous) of techniques that allows the (simultaneous)
transmission of multiple signals across a single data transmission of multiple signals across a single data
link. As data and telecommunications use increases, link. As data and telecommunications use increases,
so does traffic.so does traffic.
 Frequency-Division Multiplexing
 Synchronous Time-Division Multiplexing
Topics discussed in this section:Topics discussed in this section:

4. 6.4
Figure 6.1 Dividing a link into channels

5. 6.5
FDM is an analog multiplexing technique
that combines analog signals.
It uses the concept of modulation
Note

6. 6.6
Figure 6.4 FDM process

7. 6.7
Figure 6.5 FDM demultiplexing example

8. 6.8
Figure 6.12 Time Division Multiplexing (TDM)

9. 6.9
TDM is a digital multiplexing technique
for combining several low-rate digital
channels into one high-rate one.
Note

10. 6.
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Figure 6.13 Synchronous time-division multiplexing

11. INTERLEAVING
The process of taking a group
of bits from each input line
for multiplexing is called
interleaving.
6.11

12. 6.
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Figure 6.15 Interleaving

13. FREQUENCY DIVISION MULTIPLEX
Separation of spectrum into smaller
frequency bands
Channel gets band of the spectrum for the
whole time
Advantages:
no dynamic coordination needed
works also for analog signals
Disadvantages:
waste of bandwidth
if traffic distributed unevenly
inflexible
guard spaces
Channels
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15. 6.15

16. WHY FDM IS FOR ANALOG SIGNALS AND
TDM IS FOR DIGITAL SIGNALS?
6.16
FDM stnds for frequency division
multiplexing and it is used only in case of
analog signals because analog signals are
continuous in nature and the signal have
frequency.
TDM-stands for time division multiplexing
and it is used only in case of digital
signals because digital signals are
discrete in nature and are in the form of 0
and 1s. and are time dependent.

17. ADVANTAGES & DISADVANTAGES OF
TDM & FDM
6.17
In TDM, different users share the same channel based on
time slots alloted to them. Each user or source is given a
particular time slot to send its information.
1. The entire channel BW is available for a particular time
interval unlike in FDM where the channel BW is split into
smaller segments. This enables higher data rates.
2. All users share the same frequency, so spectrum
efficieny is increased. Available channel BW is no more a
constraint.

18. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
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