FDM vs TDM: Difference and Comparison

FDM and TDM are multiplexing techniques. FDM, called Frequency Division Multiplexing, is a multiplexing technique used in an analog system. FDM requires a guard band, and it has low spectral efficiency.

TDM is called Time Division Multiplexing, which works with both digital signals and analog signals. TDM requires a synchronization pulse and shares the timescale with various signals.

Key Takeaways

  1. Frequency Division Multiplexing (FDM) separates signals by assigning different frequencies, while Time Division Multiplexing (TDM) allocates time slots for each signal.
  2. FDM is more suitable for analog communication, whereas TDM is better for digital communication.
  3. FDM can result in crosstalk and signal interference, while TDM avoids these issues by strictly separating time slots.


FDM stands for Frequency Division Multiplexing and consists of complex wiring or chips used to share the frequency available for analog signals. TDM means Time Division Multiplexing, and it shares timescales available for the signals, working with analog and digital signals with simple circuitry.


FDM is a Frequency Division Multiplexing that shares the frequency available for the signals. It works with analog signals and has complex circuitry.


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It is made of complex chips or wiring. This technique requires a guard band and has a very high level of interference. FDM has low spectral efficiency and higher conflict.

TDM is a Time Division Multiplexing that shares the timescale available for the signals. It works with both analog signals and digital signals. It has very simple circuitry.

It is made up of simple chips or wiring. It requires a synchronization phase and has a low level of interference. TDM has two types of timescale signals: synchronous TDM and asynchronous TDM.

Comparison Table

Parameters Of ComparisonFDMTDM
DefinitionFDM is a multiplexing technique that shares or sends frequency with the available signals, preferably analog signals.TDM is a multiplexing technique that shares the timescale with the available signals, preferably both digital signals and analog signals.
Circuitry and WiringFDM has a complex form of circuitry. It has complex wiring or chips used.TDM has a simple form of circuitry. It is made of simple wiring or a chip.
Conflict and EfficiencyFDM has higher conflict, and this technique is quite inefficient.TDM has very conflict, and this technique is very efficient.
PrerequisitesFDM requires Guard Band as a prerequisite.TDM requires the synchronization phase as a prerequisite.
InterferenceFDM has a very high level of interference.TDM has a very low level of interference.

What is FDM?

FDM is the acronym for Frequency Division Multiplexing. It is an analog technique that is used for analog signals only. It is used when the bandwidth of the link is higher than that of the bandwidth of the signals that are to be transmitted.

Carrier frequencies are used to modulate the signals from the donor devices. They are isolated with adequate bandwidth to modulate the signals.

FDM uses the signals and transfers them into one single compound of the signal by the link. The signals transferred travel through the channel. FDM also controls overlapping signals.

The signal overlapping is controlled by the unutilized bandwidth strips that are used for segregating the channels. They are known as Guard Bands, which are essential and prerequisites for the FDM technique.

FDM deals only with analog signals and has a complex circuitry system. They are made up of complex chips and wiring. It also has a very high level of interference.

There should not be any overlapping of carrier frequencies with the original frequencies, leading to a failure condition where the original signals cannot be recovered from the system.

FDM involves the distribution of frequencies with the respective bandwidths. Guard Bands are used to separate the signals and prevent overlapping various signals.

They also require different bandpass filters to help in doing the mechanism. It divides the link into multiple channels, which is not in the case of other multiplexing techniques, making it less efficient than others.

What is TDM?

TDM is an acronym for Time Division Multiplexing that is used in sharing the timescale to both analog and digital signals as well.

This technique is used when the transmission rate quantity is higher when compared to the rate of transmitting and receiving signal devices. The signals are transmitted from different sources that require a synchronization pulse.

TDM has different frames that consist of different sets of time slots to which the time slot is assigned to different frames. There are two different types of TDM.

The first would be Synchronous Time Division Multiplexing, which assigns the time slot individually to the device that either sends or does not send the signals. If there is no signal sent, the time slot will be empty.

TDM uses Framing Bits to synchronize at the beginning of each time frame. Bit stuffing is a mechanism used to equalize the speed between the devices that appends into the source system.

Synchronous Time Division Multiplexing uses interleaving between the frames, where one can take the data units at a particular time from each device.

TDM has a second type called Asynchronous Time Division Multiplexing that uses unused space wasted in Synchronous Time Division Multiplexing.

Asynchronous means were flexible and not fixed, where several low-rate input lines were multiplexed into a single line of the frame. The number of slots is less than the number of data lines in ATDM.

Main Differences Between FDM And TDM

  1. FDM is called Frequency Division Multiplexing, which shares the frequencies through channels divided into various bandwidths. In contrast, TDM is called Time Division Multiplexing, which shares the timescale through various time slots for the signals.
  2. FDM uses only analog signals and has complex chips and wiring, whereas TDM uses analog signals and digital signals and has simple chips and wiring.
  3. FDM uses guard bands to separate the signals and prevent overlapping, whereas TDM uses Framing Bits or synchronous pulse to trigger the synchronization mechanisms.
  4. FDM is less efficient as it manually divides the link into multiple channels with empty spaces, making it less efficient. In contrast, TDM is more efficient as it properly utilizes the physical link.
  5. FDM has a non-linear character in its distortion as it has various amplifiers and a high level of interference. In contrast, TDM has a low level of interference as it has separate time slots for individual signals.
  1. https://ieeexplore.ieee.org/abstract/document/1092391/
  2. https://ieeexplore.ieee.org/abstract/document/923482/

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