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Table of contents
1.
Introduction 
2.
Time Division Multiplexing (TDM)
2.1.
Types of TDM
2.2.
Advantages of TDM
2.3.
Disadvantages of TDM
2.4.
Time Division Multiplexing (TDM) Applications
3.
Frequency Division Multiplexing (FDM)
3.1.
What is Orthogonal FDM (OFDM)?
3.2.
Advantages of FDM
3.3.
Disadvantages of FDM
3.4.
Frequency Division Multiplexing (FDM) Applications
4.
Difference between TDM and FDM
5.
Example of TDM and FDM
6.
Frequently Asked Questions
6.1.
Where are TDM and FDM commonly used?
6.2.
What are the main advantages of TDM over FDM?
6.3.
Write names of some places around the world that used TDMA frequently.
6.4.
Is TDM faster than FDM?
7.
Conclusion
Last Updated: Mar 27, 2024

Difference Between TDM and FDM

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Introduction 

TDM and FDM are methods to send multiple signals through a single channel. FDM is for analog signals, while TDM can handle digital signals. In TDM, timing is crucial, while in FDM, we need a guard band for separation.

We will learn more about these two, but before that, we will discuss multiplexing.

Multiplexing is a method by which we can transmit a number of signals over one signal. A multiplexed machine is capable of working with a wide variety of devices, and these devices will share the total capacity of that link.

difference between tdm and fdm


This article will discuss the difference between TDM and FDM in detail. We will also discuss their real-world applications along with their advantages and disadvantages.

Time Division Multiplexing (TDM)

Time Division Multiplexing (TDM) deals with digital signals, which are similar to analog signals. The synchronization pulse is very important in TDM. TDM will share a timescale with all the signals it works with. In this type of multiplexing technique, incoming signals are separated into equivalent fixed-length time slots. Once the process of multiplexing is complete, these signals are sent over a shared medium & after the process of demultiplexing, they are reconstructed into their original format.

Time Division Multiplexing

Types of TDM

There are two main types of time division multiplexing:-

  • Synchronous Time Division Multiplexing (STDM): In STDM, each input signal or data stream is allocated a fixed and equal time slot. These time slots are allocated regardless of whether the channel has data to transmit for a particular input or not. There may be unused or idle time slots if some inputs have no data to transmit during their allocated time. This technique is commonly used in scenarios where the timing and synchronization of signals are important.
     
  • Asynchronous Time Division Multiplexing (ATDM): ATDM allocates time slots dynamically based on the actual data arrival from each input source. This means that if an input has no data to transmit, it does not waste a time slot. It is commonly used in networks where data traffic can be bursty and unpredictable.

Advantages of TDM

  • Crosstalk: Crosstalk can be triggered by pulse overlapping. We can reduce it by using guard time. 
     
  • Bandwidth: It has the ability to increase the bandwidth of our system. It does so by allowing multiple signals to be transmitted simultaneously over a single wire or channel, which is much faster than the process of sending them one by one.
     
  • Coordination: Dynamic coordination is a unique feature of TDM.
     
  • High transmission speed: It can transport information at high speeds. A DS0 voice signal used in calling has a data bit rate of nearly 64 kbit/s.
     
  • Usability: Another benefit of TDM is that, mainly, it is used for digital signals, but we can also use TDM for analog signals.
     
  • Hardware simplicity: The hardware for time-division multiplexing is quite simple.
     

Disadvantages of TDM

  • Reliablity: Due to slow and sluggish narrow-band fading, aII TDM channels may get shut down. So, reliability decreases.
     
  • Requirement: A buffer and Address information is essential for the proper working of a TDM system.
     
  • Synchronization issues: As we know that all signal has their own timeslot, and the receiver must know when that timeslot starts and ends. This means that the receiver will need to be synchronized with the sender to decode all of the information correctly. If they are not in sync with each other, then they won’t be able to convey where in the stream a piece of information starts and ends.
     
  • Latency: Generally, TDM has less latency as compared to FDM.
     
  • Time-consuming: There is a lot of time required for range planning. Due to this, the time requirement increases.
     

Time Division Multiplexing (TDM) Applications

  • We can use it on wired telephone lines for the purpose of communication.
     
  • We can use it on Integrated Services Digital Network telephone lines.
     
  • We can use it on public switched telephone networks.
     
  • We can use it for some telephone systems.


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Frequency Division Multiplexing (FDM)

It is a type of multiplexing technique that can be used in different analog systems. It is a technique in which we combine multiple signals over a medium shared by all signals. In FDM, signals of different frequencies and amplitude are combined in one signal for concurrent transmission of signals.

Frequency Division Multiplexing

What is Orthogonal FDM (OFDM)?

Orthogonal Frequency Division Multiplexing (OFDM) is a digital multiplexing technique used in telecommunications to transmit data over wireless and wired communication channels. OFDM divides a wide frequency band into multiple non-interfering subcarriers, each with a lower-rate data stream. These subcarriers are closely spaced and overlap in frequency, which increases the spectrum utilization. OFDM is known for its durability against interference. It is suitable for high-speed data transmission in various applications like Wi-Fi, 4G/5G mobile networks, digital television (DTV), and DSL broadband. 

Advantages of FDM

  • No need for Synchronization: It does not need synchronization between its transmitter and receiver.
     
  • Simpler: FDM is simpler and easy demodulation of the signal is possible.
     
  • Reliability: In FDM, only one channel gets affected due to slow narrow-band fading.
     
  • Synchronization: We can transfer multiple signals simultaneously by using FDM.
     

Disadvantages of FDM

  • We can only use it when a few low-speed channels are required.
     
  • Intermodulation distortion takes place in FDM, which decreases the efficiency of the process.
     
  • It has the problem of crosstalk, due to which it is not able to work properly.
     

Frequency Division Multiplexing (FDM) Applications

  • Broadcasting: In the broadcast of audio signals, video signals, etc., we will use FDM.
     
  • Television: FDM is also used in Television Broadcasting. Here we will use the same concept as in radio broadcasting.
     
  • AM and FM: In broadcasting AM and FM, we can also use FDM for transmitting multiple signals concurrently over a single signal.
     
  • Telephone: We use the FDM system in the telephone system. FDM helps us to transmit multiple signals over a single line through which data is transmitted.
     

Difference between TDM and FDM

Parameters Time Division Multiplexing (TDM) Frequency Division Multiplexing (FDM)
Working In order to transmit multiple signals through a communication channel, TDM typically divides the channel into smaller time intervals. It divides the communication channel into different frequency bands for the transmission of multiple signals.
Types of Signals TDM works with both analog as well as digital signals. It only works with analog signals.

Circuitry

complexity

It has a very simple type of circuitry. The circuitry in FDM is comparatively more complex.
Wiring Used Compared to FDM, the TDM's chip or wiring is perceived as relatively uncomplicated. FDM can support a high number of channels.
Number of channels The number of channel in TDM are limited and less than in FDM. FDM can support a high number of channels.
Input Required The TDM technique demands a prerequisite of the synchronization pulse. The FDM technique makes it imperative to have a  guard band.
Interference The TDM technique has low or negligible interference. More prone to noise and distortion.
Crosstalk TDM has limited crosstalk as signals are time-separated. In FDM, crosstalk can happen due to the shared frequency bands.
Propagation Delay TDM has a low propagation delay as the data is sent sequentially. Propagation delay depends on the frequency allocation.
Efficiency Efficient for synchronous and periodic data streams. Efficient for multiple, continuous data streams.
Applications TDM is commonly used in telecommunications and other digital communication systems. FDM is commonly used in broadcasting and analog communication.

 

Also read - Multiplexers (MUX)

Example of TDM and FDM

The following are some real-world examples of TDM and FDM.

  • Time Division Multiplexing (TDM): In a TDM scenario, consider a telephone exchange system where multiple users share a single communication channel, but each user is assigned a specific time slot within a frame. User A's voice data is transmitted during their allocated time slot, followed by User B's data, and so on.
     
  • Frequency Division Multiplexing (FDM): In an FDM example, think of a cable TV network where Different TV channels are multiplexed onto a single cable by assigning each channel to a specific frequency band. Channel 1 might use the 0-6 MHz band, Channel 2 the 6-12 MHz band, and so on.

Frequently Asked Questions

Where are TDM and FDM commonly used?

TDM is used in digital telephone networks. FDM is more commonly used in radio and television broadcasting because they transfer multiple signals.

What are the main advantages of TDM over FDM?

The main advantages of Time Division Multiplexing (TDM) over Frequency Division Multiplexing (FDM) are -- efficient bandwidth utilization, reduced crosstalk, and suitability for asynchronous data streams, making it ideal for digital communication systems.

Write names of some places around the world that used TDMA frequently.

India, China, South Korea, etc. countries use TDMA the most for communication, but North and South America use CDMA (code-division multiple access). These countries use TDMA because TDMA allows multiple people to share the same frequency by dividing all cellular channels into different time slots. All these countries have large populations. So, TDMA is beneficial for these countries.

Is TDM faster than FDM?

Both TDM and FDM can achieve high-speed data transmission when they are appropriately configured. There is no clear difference in their speeds, it mainly depends on factors like data rate and channel bandwidth.

Conclusion

If we want to use shared communication channels, then we will have to use some optimization through techniques like TDM and FDM. At the same time, TDM proves to be more useful with limited channel availability for sending uneven data. Whereas FDM stands out as better suited for multiple continuous channel transmissions. Selecting which method to use will depend solely on the application's requirements. Keep in mind all factors concerning the advantages and disadvantages of these techniques.

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