data communication chapter 06(1), Slides of Data Communication Systems and Computer Networks

Download data communication chapter 06(1) and more Slides Data Communication Systems and Computer Networks in PDF only on Docsity!

Chapter 6

Bandwidth Utilization:

Multiplexing and

Spreading

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

Figure 6.1 Dividing a link into channels

Figure 6.2 Categories of multiplexing

FDM is an analog multiplexing technique

that combines analog signals.

It uses the concept of modulation

discussed in Ch 5.

Note

Figure 6.4 FDM process

Figure 6.5 FDM demultiplexing example

Assume that a voice channel occupies a bandwidth of 4 kHz. We need to combine three voice channels into a link with a bandwidth of 12 kHz, from 20 to 32 kHz. Show the configuration, using the frequency domain. Assume there are no guard bands. Solution We shift (modulate) each of the three voice channels to a different bandwidth, as shown in Figure 6.6. We use the 20 to 24kHz bandwidth for the first channel, the 24 to 28kHz bandwidth for the second channel, and the 28 to 32kHz bandwidth for the third one. Then we combine them as shown in Figure 6.6.

Example 6.

Five channels, each with a 100-kHz bandwidth, are to be multiplexed together. What is the minimum bandwidth of the link if there is a need for a guard band of 10 kHz between the channels to prevent interference? Solution For five channels, we need at least four guard bands. This means that the required bandwidth is at least 5 × 100 + 4 × 10 = 540 kHz, as shown in Figure 6.7.

Example 6.

• Figure 6.6 Example 6.
• Figure 6.7 Example 6.
• Figure 6.8 Example 6.

Figure 6.9 Analog hierarchy

Figure 6.10 Wavelength-division multiplexing (WDM)

WDM is an analog multiplexing

technique to combine optical signals.

Note