what is Frequency Division Multiplexing (FDM)?

BY ADMIN January 10, 2025

Frequency Division Multiplexing (FDM) is a technique used to send multiple signals over a single communication channel (like a radio wave, cable, or fiber optic line) by dividing the channel into different frequency bands. Each signal is assigned a different frequency range, and they are sent simultaneously without interfering with each other.

Think of FDM Like a Highway with Multiple Lanes:

Imagine a highway where different cars (representing signals) are traveling at the same time. Each lane on the highway represents a different frequency range. Each car in its own lane can move independently, but all of them are still using the same highway at the same time.

In FDM, these different “lanes” are frequency bands, and each “car” is a signal. All signals can travel together without interfering as long as they stay in their assigned lanes.

How FDM Works:

  1. Channel Division: The available communication channel is divided into several frequency bands. These frequency bands do not overlap, so each signal has its own separate band.
  2. Signal Assignment: Each signal (like a phone call, radio station, or TV channel) is assigned a specific frequency range within the channel. For example:

Signal 1 might use frequencies from 100 MHz to 110 MHz.

Signal 2 might use frequencies from 110 MHz to 120 MHz.

And so on…

  1. Simultaneous Transmission: All the signals are transmitted at the same time, but each one is carried on a different frequency. This allows multiple signals to be sent simultaneously through the same communication medium without interference.
  2. Demultiplexing at the Receiver: At the receiving end, a device (called a demultiplexer) separates the different frequency bands, extracting each signal from its specific frequency band, and delivering them to the correct destination (e.g., to different phones, TVs, or other devices).

Example of FDM in Real Life:

  • Radio Broadcasting: FM radio stations use FDM. Each radio station is assigned a unique frequency range (e.g., 88.1 MHz, 88.3 MHz, 88.5 MHz, etc.). All the stations broadcast their signals at the same time, but each station uses its own frequency band, so they don’t interfere with each other. When you tune your radio to 88.1 MHz, you’re listening to the station assigned to that frequency range.
  • TV Channels: Traditional television broadcasting also uses FDM. Different channels (like Channel 1, Channel 2, Channel 3, etc.) are assigned different frequency ranges. The signals for all these channels are broadcast at the same time, but because they are on different frequencies, your TV can receive and display each channel separately.

Advantages of FDM:

  1. Simultaneous Transmission: FDM allows multiple signals to be transmitted at the same time, which makes efficient use of the available bandwidth.
  2. Avoids Interference: By separating signals into different frequency bands, interference between signals is avoided, as long as the frequency bands do not overlap.
  3. Supports Analog and Digital Signals: FDM can handle both analog signals (like FM radio) and digital signals (like internet data over cable).

Disadvantages of FDM:

  1. Requires Larger Bandwidth: FDM requires a large frequency spectrum because each signal needs its own frequency band. This can be inefficient if there aren’t many signals to transmit.
  2. Complex Equipment: The equipment used to separate and combine signals in FDM can be complex and expensive, especially if many signals need to be transmitted.
  3. Guard Bands: To avoid interference, small frequency gaps (called guard bands) are needed between the frequency bands. This can reduce the overall efficiency of the system.

Summary:

  • Frequency Division Multiplexing (FDM) allows multiple signals to be sent over the same channel at the same time by giving each signal its own frequency band.
  • It is like a highway with multiple lanes, where each signal travels in its own lane (frequency band).
  • FDM is used in radio broadcasting, TV channels, and some communication systems.
  • The main advantage is that it allows simultaneous transmission of multiple signals, but it can require more bandwidth and specialized equipment.

In simple terms, FDM is a way of “splitting” a communication channel into smaller channels, each carrying a different signal, so many things can be sent at once without interfering with each other.

 

 

 

 

 

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