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Multiplexing and Demultiplexing

Chapter Overview

A communication channel, or link, between two points is established whenever a cable is connected or a radio transmitter and receiver are set up between the two points. When there is only one link, only one function—whether it involves signal transmission or control operations—can be performed at a time. For two-way communication, a half duplex process is set up: Both ends of the communication link can send and receive but not at the same time.

Transmitting two or more signals simultaneously can be accomplished by running multiple cables or setting up one transmitter/receiver pair for each channel, but this is an expensive approach. In fact, a single cable or radio link can handle multiple signals simultaneously by using a technique known as multiplexing, which permits hundreds or even thousands of signals to be combined and transmitted over a single medium. Multiplexing has made simultaneous communication more practical and economically feasible, helped conserve spectrum space, and allowed new, sophisticated applications to be implemented.

Chapter Outline

10-1 Multiplexing Principles
10-2 Frequency-Division Multiplexing
10-3 Time-Division Multiplexing
10-4 Pulse-Code Modulation
10-5 Duplexing

Chapter Objectives

  • Explain why multiplexing techniques are necessary in telemetry, telephone systems, radio and TV broadcasting, and Internet access.
  • Compare frequency division multiplexing with time-division multiplexing.
  • Trace the steps in the transmission and reception of multiplexed signals.
  • List the major subtypes of time-division multiplexing.
  • Define pulse-code modulation, draw the diagram of a typical PCM multiplexer, and state the primary benefit of PCM over other forms of pulse modulation.
  • List the characteristics of the T-carrier system.
  • Explain the difference between time and frequency duplexing.

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