Difference Between FDM and TDM

What is FDM?

FDM is the abbreviation of frequency division multiplexing. It is a technique for sending multiple signals of different frequencies for transmission from a single medium or channel. FDM separates various bands to transmit multiple signals through a single line or channel successfully.

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FDM, after separating these bands, assigns the bands to the unused frequencies called guard bands. So, FDM prevents overlapping signals of different frequencies in a shared medium or channel.

A signal is generated and modulated by a sending device which carries it to other bands of frequencies. The multiplexers (MUX) combine the modulated signals in the sending end. The combined signal is transferred to the communication channel. Thus it allows the transmission of multiple independent data streams simultaneously.

The individual signals are separated from the combined signals at the receiving end by the demultiplexing (DEMUX) process.

The most common example of FDM is broadcasting radio and tv signals of different frequencies through the air simultaneously. Another example is television cable which carries different channels of different frequencies at the same time on a single cable.

What is TDM?

TDM is an abbreviation of time division multiplexing. It is a technique to transmit multiple signals in a single medium or channel in different time slots. It is a digital procedure. This method transmits digital or analog signals by a single or common medium or channel.

It is used when the transmission rate of the medium exceeds the bit rate. Each signal is broken into segments of short duration in TDM. Different signals are transmitted in TDM by utilizing other time slots.

In TDM, each sender is provided the slot or possession of the whole bandwidth for a fixed duration. After this, the control is moved to the next sender. The television broadcast is a prominent example of TDM.

A serial run on television for 10 minutes is followed by ads of 5 minutes. The total frequency is dedicated to the serial when the serial is broadcasted.

Difference Between FDM and TDM

FDM and TDM are both multiplexing techniques used to transmit signals in telecommunication.

  1. FDM uses to transmit multiple signals of different frequencies from the same channel, or it uses analog signals for transmission. On the contrary, the TDM sends various signals of different frequencies in the same channel using different time slots or analog and digital signals for communication.
  2. For the proper working of FDM, the guard band is required. In contrast, in TDM, a synchronization pulse is necessary for the sound transmission of a signal.

Comparison Between FDM and TDM

ParametersFDMTDM
DefinitionIt is a technique for sending multiple signals of different frequencies for transmission from a single medium or channel.It is a technique to transmit multiple signals in a single medium or channel in different time slots.
SignalsFDM works only by using analog signals for transmission.TDM works by using analog and digital signals.
EfficiencyFDM could be more efficient.TDM is more efficient.
Cable or wiringThe Wiring or chip is complex in FDM.Chip or wiring is simpler in TDM.
SharingFDM shares the frequencies of different signals.TDM shares the time slots for different signals.
InputFDM requires a guard band as input.TDM requires the synchronization pulse as input.
ConflictFDM has high conflict due to various frequencies.TDM has less conflict due to different time slots.

References

  1. Lundheim, L., 2002. On Shannon and” Shannon’s Formula”. Telektronikk, 98(1), pp.20-29.
  2. Kessner, D., 1998, March. Design of a time-slot-interchanger and other TDM bus interfacing issues. In 1998 IEEE Aerospace Conference Proceedings (Cat. No. 98TH8339) (Vol. 4, pp. 515-521). IEEE.
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