Data Multiplexing: FDM, WDM, and TDM Explained

Posted on May 23, 2025 in Communication

FDM (Frequency Division Multiplexing)

Definition: FDM is a technique where the available bandwidth of a communication channel is divided into several frequency bands. Each frequency band is assigned to a different signal or user. The signals are transmitted simultaneously but on different frequency channels, avoiding interference.

  • Key Concept: Different signals are transmitted simultaneously, but each on a different frequency within the available bandwidth.

Process:

  • Multiple signals (e.g., voice or data) are modulated onto different carrier frequencies.
  • These signals are combined and transmitted over the same communication channel (e.g., radio spectrum).
  • At the receiver’s end, filters separate the combined signals based on their frequencies.

Advantages of FDM:

  • Multiple signals transmitted simultaneously.
  • Continuous data flow for each channel.

Disadvantages of FDM:

  • Requires more bandwidth as multiple frequency bands need to be allocated.
  • Can suffer from crosstalk between closely spaced frequency bands.

WDM (Wavelength Division Multiplexing)

Definition: WDM is similar to FDM but used specifically for fiber optic communication. It multiplexes data by using different wavelengths (or colors) of light for different signals on the same optical fiber. Each signal operates at a distinct wavelength (color), allowing multiple data streams to share the same fiber.

  • Key Concept: Different signals use different wavelengths (colors) of light.

Process:

  • Multiple optical signals, each at a different wavelength, are combined and transmitted through a single optical fiber.
  • At the receiver’s end, a demultiplexer separates the signals based on their wavelengths.

Advantages of WDM:

  • High bandwidth and data capacity.
  • Efficient use of fiber optic infrastructure.

Disadvantages of WDM:

  • More expensive due to the need for precise lasers and optical filters.
  • Complexity in managing and maintaining multiple wavelengths.

TDM (Time Division Multiplexing)

Definition: TDM divides the communication channel into time slots. Each signal or user is assigned a specific time slot, during which they can transmit their data. All users share the same frequency range but take turns in transmitting data in an alternating pattern.

  • Key Concept: Multiple signals share the same frequency but take turns in transmitting data based on allocated time slots.

Process:

  • The communication channel is divided into time slots.
  • Each signal is assigned a time slot, during which it can transmit data.
  • This process is repeated in a cyclic fashion, so every signal gets regular access to the medium.

Advantages of TDM:

  • Efficient use of bandwidth when the number of active signals is constant.
  • No interference between different signals since they occupy different time slots.

Disadvantages of TDM:

  • If a signal has no data to send, its time slot is wasted (in synchronous TDM).
  • Latency can be higher if many signals are multiplexed.