Principles Digital Communication System & Computer Networks (Charles River Media Computer Engineering)

In a communication system, the costliest element is the transmission medium. To make the best use of the medium, we have to ensure that the bandwidth of the channel is utilized to its fullest capacity. Multiplexing is the technique used to combine a number of channels and send them over the medium to make the best use of the transmission medium. We will discuss the various multiplexing techniques in this chapter.

7.1 MULTIPLEXING AND DEMULTIPLEXING

Use of multiplexing technique is possible if the capacity of the channel is higher than the data rates of the individual data sources. Consider the example of a communication system in which there are three data sources. As shown in Figure 7.1, the signals from these three sources can be combined together (multiplexed) and sent through a single transmission channel. At the receiving end, the signals are separated (demultiplexed).

Figure 7.1: Multiplexing and demultiplexing.

At the transmitting end, equipment known as a multiplexer (abbreviated to MUX) is required. At the receiving end, equipment known as a demultiplexer (abbreviated to DEMUX) is required. Conceptually, multiplexing is a very simple operation that facilitates good utilization of the channel bandwidth. The various multiplexing techniques are described in the following sections.

A multiplexer (MUX) combines the data of different sources and sends it over the channel. At the receiving end, the demultiplexer (DEMUX) separates the data of the different sources. Multiplexing is done when the capacity of the channel is higher than the data rates of the individual data sources.