Frequency-Division Multiplexing: Advantages & Examples

Lesson Transcript
Instructor: Vignesh Sivabalan

Viignesh has an MS in information technology.

This lesson introduces frequency division multiplexing and explains the process of multiplexing and de-multiplexing in frequency division communication. The advantages, disadvantages and the applications of frequency division multiplexing are also discussed in later parts of this lesson. Updated: 09/26/2021

Frequency Division Multiplexing

Frequency division multiplexing (FDM) is a networking method of sharing the total available bandwidth of any communication channel by dividing them into many non-overlapping bands of frequency. Let's consider an example.

FDM (frequency division multiplexing) can be compared to the operation of radio broadcasting where multiple frequencies are shared among the users and one can tune to any of the available frequency bands, to enjoy their favorite broadcast from that particular station. Frequency division multiplexing allows many users to share the communication channel.

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Multiplexing & De-Multiplexing

In communication networks, multiplexing is a technique that refers to combining many signals (analog or digital) into one and sending them through a communication channel. The main objective of multiplexing is sharing of a scarce resource.

De-multiplexing, on the other hand, refers to the technique of separating these signals or extracting individual channels. Transmitters are devices that perform multiplexing at the sender's end and the receivers perform de-multiplexing at the receiving end.

Many signals get transmitted simultaneously and each signal occupies a different slot of frequency within the available bandwidth (common bandwidth).

Each signal that needs to be sent over a communication channel undergoes modulation with various carrier frequencies, as shown clearly in the diagram here.

Figure 1: FDM Transmitter for Modulation

There are different kinds of modulation such as amplitude modulation, pulse modulation, frequency modulation, etc. As the name suggests, the modulation done here is frequency modulation by the FDM transmitter. These modulated signals are then added up using a linear adder or a mixer, forming a composite signal which gets transmitted over a communication channel (single channel).

At the receiving end, the single composite signal is received by the FDM receiver. The receiver then passes the composite signal through various band pass filters. Each of these band pass filters has a frequency corresponding to the frequencies of one of the carrier waves. Each band pass filter will accept the signal whose frequency matches with the frequency of the carrier signal and rejects all other channels. The signals coming out of band pass filters pass through a demodulator. The demodulator does the work of separating the original signal from the carrier signal.

Frequency overlap is a serious issue when it comes to frequency division multiplexing and it must be completely avoided. Two frequency ranges can be separated by using some narrow frequency ranges called guard bands. The guard bands avoid signal interference and enhance the quality of communication.

Here's an example of frequency division multiplexing and de-multiplexing: Cable televisions use FDM technology. The FDM multiplexer combines multiple channels for maximizing usage of the available bandwidth. The FDM de-multiplexer, found either in a set-top box or a television, separates the transmitted signals and allows the viewers to watch their favorite channel.

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