**2. Analog multiplexing**

The most commonly used analog multiplexing techniques are frequency division multiplexing (FDM) and wavelength division multiplexing.

### **2.1 Frequency division multiplexing**

**Frequency division multiplexing** [1–4] is a networking technique which combines many signals into a single one and then transmitted the combined signal through a common communication channel. In the receiver side, the opposite process is carried out which is known as demultiplexing which extracts the individual channel signals. Here the transmitter side performs multiplexing, and the receiver side performs demultiplexing. In FDM the total bandwidth available in a communication medium is divided into a series of nonoverlapping frequency bands. Each of these bands is used to carry a separate signal. In FDM all users use the same common channel at full time. But each of the users is allocated with different frequencies for transmission for avoiding the signal interference. Sometimes there is a possibility of cross talk because all the users use the transmission medium at the same time.

FDM is used for analog signal transmission. It does not need synchronization between the transmitter and receiver. Here a large number of signals can be transmitted simultaneously. It suffers the problem of cross talk, and intermodulation distortion may take place.

FDM is used in amplitude modulation (AM) and FM broadcasting, public telephone networks, and cable TV network systems. The allocation of frequency bands to different users is shown in **Figure 2**.

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plexer and demultiplexer.

through a prism as shown in **Figure 4**.

*Multiplexing*

**Figure 3.**

**Figure 4.**

*Representation of WDM multiplexing.*

*DOI: http://dx.doi.org/10.5772/intechopen.85866*

**2.2 Wavelength division multiplexing**

*Refraction of light through prism.*

Fiber-optic communications require a different kind of multiplexer called a wavelength division multiplexer (WAD) [2, 4]. It is an analog multiplexing technique. It is designed for high data rate capability fiber cable. In this technique the bandwidth of the communication channel should be greater than the combined bandwidth of the individual channels. Here signals are converted to light signals; each light which has different wavelengths is transmitted through the same fiber cable. WDM transmission system divides the optical fiber bandwidth into a number of nonoverlapping optical wavelengths; these are referred to as WDM channels. WDM mixes all incoming signals having different wavelengths and are transmitted over a common channel. A demultiplexer does the reverse operation and separates the wavelengths. This multiplexing mechanism provides a much higher available transmission capacity. **Figure 3** shows the representation of WDM system that consists of both multi-

WDM multiplexing and demultiplexing are similar to the refraction of light

**Figure 2.** *Allocation of different frequencies to different users in FDM.*

*Multiplexing*

**1.1 Types of multiplexing**

**2. Analog multiplexing**

**2.1 Frequency division multiplexing**

to different users is shown in **Figure 2**.

*Allocation of different frequencies to different users in FDM.*

Even though the transmission occurs on the same channel, they do not necessarily occur at the same instant. In general multiplexing is a technique in which several message signals are combined into a composite signal so that these can be transmitted over a common channel. In order to transmit various signals over the same channel, it is essential to keep the signals apart to avoid the interference between

Domains in which multiplexing can be accomplished are time, phase, frequency

Multiplexers are mainly classified as shown in **Figure 1**. Analog multiplexing

The most commonly used analog multiplexing techniques are frequency division

FDM is used for analog signal transmission. It does not need synchronization between the transmitter and receiver. Here a large number of signals can be transmitted simultaneously. It suffers the problem of cross talk, and intermodulation distortion may take place. FDM is used in amplitude modulation (AM) and FM broadcasting, public telephone networks, and cable TV network systems. The allocation of frequency bands

**Frequency division multiplexing** [1–4] is a networking technique which combines many signals into a single one and then transmitted the combined signal through a common communication channel. In the receiver side, the opposite process is carried out which is known as demultiplexing which extracts the individual channel signals. Here the transmitter side performs multiplexing, and the receiver side performs demultiplexing. In FDM the total bandwidth available in a communication medium is divided into a series of nonoverlapping frequency bands. Each of these bands is used to carry a separate signal. In FDM all users use the same common channel at full time. But each of the users is allocated with different frequencies for transmission for avoiding the signal interference. Sometimes there is a possibility of cross talk because all the users use the transmission medium at the same time.

them, and then it can be easily separated at the receiving end.

and digital multiplexing are the major classification.

multiplexing (FDM) and wavelength division multiplexing.

wavelength, etc. Multiplexing circuits are called multiplexer or MUX.

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**Figure 2.**

**Figure 3.** *Representation of WDM multiplexing.*

**Figure 4.**

*Refraction of light through prism.*
