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

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Muhamm

ad Uza

ir Rasheed

2009-CPE-0

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UCE&T BZU M

ULTAN

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

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, so link. As data and telecommunications use increases, so does traffic.does traffic.

Frequency-Division Multiplexing Synchronous Time-Division Multiplexing

Topics discussed in this section:Topics discussed in this section:

6.4

Figure 6.1 Dividing a link into channels

6.5

FDM is an analog multiplexing technique that combines analog signals.

It uses the concept of modulation

Note

6.6

Figure 6.4 FDM process

6.7

Figure 6.5 FDM demultiplexing example

6.8

Figure 6.12 Time Division Multiplexing (TDM)

6.9

TDM is a digital multiplexing technique for combining several low-rate digital

channels into one high-rate one.

Note

6.10

Figure 6.13 Synchronous time-division multiplexing

INTERLEAVING

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

6.11

6.12

Figure 6.15 Interleaving

FREQUENCY DIVISION MULTIPLEX

Separation of spectrum into smaller frequency bandsChannel gets band of the spectrum for the whole time Advantages:

no dynamic coordination neededworks also for analog signals

Disadvantages:waste of bandwidth if traffic distributed unevenlyinflexibleguard spaces

Channels ki

k3 k4 k5 k6

t

6.15

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.

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.

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