What is Frequency Division Multiplexing – FDM: A Brief Review

what is Frequency Division Multiplexing - FDM

Nowadays, the exchange of information is an inseparable part of society. With the great advances in communication technologies, communication has become more affordable and faster. A technology that is widely used in telephony, data communications, and audio/video broadcasting is multiplexing which can combine multiple communication signals for them to traverse an otherwise single signal communication medium simultaneously. This article will discuss what Frequency Division Multiplexing – FDM and its application. Follow this new blog in Linquip to find out more. 

What is Frequency Division Multiplexing – FDM?

Frequency division multiplexing (FDM) is a multiplexing technique that divides the available bandwidth into multiple sub-bands each of which can carry a signal. Therefore, FDM enables concurrent transmissions over a shared communication medium. As another common use, FDM enables the system to send a huge amount of data through several segments transmitted over independent frequency sub-bands.

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Frequency Division Multiplexing Working Principle

In FDM, the total bandwidth is divided into a set of frequency bands that do not overlap. Each of these bands is a carrier of a different signal that is generated and modulated by one of the sending devices. The frequency bands are separated from one another by strips of unused frequencies called the guard bands, to prevent overlapping of signals.

The modulated signals are combined using a multiplexer (MUX) in the sending end. The combined signal is transmitted over the communication channel, thus allowing multiple independent data streams to be transmitted simultaneously. At the receiving end, the individual signals are extracted from the combined signal by the process of demultiplexing (DEMUX).

FDM can be used with analog signals. The spectrum of the FDM signal is illustrated in the figure below.

what is Frequency Division Multiplexing - FDM


What Is Guard Band?

For FDM to work properly, frequency overlap must be avoided. A guard band is a narrow frequency range that separates two ranges of wider frequency. This ensures that simultaneously used communication channels do not experience interference which would result in decreased quality of both transmissions. The guard band is shown in the figure below.

what is Frequency Division Multiplexing - FDM

Frequency Division Multiplexing Diagram

The following diagram conceptually represents multiplexing using FDM. It has 4 frequency bands, each of which can carry a signal from 1 sender to 1 receiver. Each of the 4 senders is allocated a frequency band. The four frequency bands are multiplexed and sent via the communication channel. At the receiving end, a demultiplexer regenerates the original four signals as outputs.

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what is Frequency Division Multiplexing - FDM

Frequency Division Multiplexing Application

The applications of FDM are as follows.

  • FDM is commonly used in TV networks.
  • FDM is used in Radio Broadcasting. Every Radio Station has its frequency band. When we turn on our radio then signals from all radio stations are coming on our radio. We can choose the frequency band by rotating the knob to connect our radio with a particular radio station.
  • The first-generation cellular telephone uses FDM. 
  • Frequency Division Multiplexing System is also used in Satelite Communication system. It helps to transmit multiple channels of data in satellite communication.
  • Frequency Division Multiplexing System is used in the telephone system. FDM helps to transmit multiple phone calls over a single transmission line or a single link.
  • In our broadband connection system, FDM is also used. The FDM system is used in Digital Subscriber Line or DSL Modems, which helps to transmit a huge amount of computer data for accessing the Internet over a single transmission line. It is a very important application of FDM.
  • FDM is used in stereo Frequency Modulation or FM transmission systems.
  • FDM is also used in Amplitude Modulation or AM radio transmission system.
  • Frequency Division Multiplexing or FDM system is used for multimedia data such as video, audio, image transmission.
  • In earlier days, FDM was used in harmonic telegraphy communication systems.
  • In earlier days, FDM was used in the cellular telephone system.

Frequency Division Multiplexing Advantages

The important advantages of FDM are given below.

  •  Frequency Division Multiplexing or FDM does not need synchronization but TDM or Time Division Multiplexing needs synchronization. It is an advantage of FDM over TDM.
  • FDM provides more latency than TDM.
  • The demodulation process in FDM is very easy and simple.
  • Using the FDM system a large amount of data can be transmitted than TDM. It is a great advantage of FDM over TDM.
  • Using the FDM system multimedia data can be transferred with very high efficiency and low noise and distortion.
  • FDM system has high reliability.

what is Frequency Division Multiplexing - FDM


Frequency Division Multiplexing Disadvantages

Some disadvantages of FDM are given below.

  • The Frequency Division Multiplexing system needs a carrier wave or carrier signal but the Time Division Multiplexing system does not need a carrier signal.
  • The circuitry for FDM is complex than TDM. FDM requires more hardware than TDM.
  • The Frequency Division Multiplexing system extremely expensive.
  • There is intermodulation distortion that occurs in FDM.
  • There is a need for a large number of system modulators and filters in FDM.
  • FDM provides less throughput.
  • The full bandwidth of a channel cannot be used in the Frequency Division Multiplexing system.
  • FDM has not dynamic coordination.


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