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.
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.
Types of TDM
There are two main types of time division multiplexing:-
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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
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Crosstalk: Crosstalk can be triggered by pulse overlapping. We can reduce it by using guard time.
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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.
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Coordination: Dynamic coordination is a unique feature of TDM.
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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.
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Usability: Another benefit of TDM is that, mainly, it is used for digital signals, but we can also use TDM for analog signals.
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Hardware simplicity: The hardware for time-division multiplexing is quite simple.
Disadvantages of TDM
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Reliablity: Due to slow and sluggish narrow-band fading, aII TDM channels may get shut down. So, reliability decreases.
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Requirement: A buffer and Address information is essential for the proper working of a TDM system.
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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.
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Latency: Generally, TDM has less latency as compared to FDM.
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Time-consuming: There is a lot of time required for range planning. Due to this, the time requirement increases.
Time Division Multiplexing (TDM) Applications
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We can use it on wired telephone lines for the purpose of communication.
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We can use it on Integrated Services Digital Network telephone lines.
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We can use it on public switched telephone networks.
- We can use it for some telephone systems.
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