Basic Concept of FDM and TDM

Why do we need Multiplexing technique?
In communication, under the simplest conditions, a medium can carry only one signal at any moment in time.For multiple signals to share one medium, the medium must somehow be divided, giving each signal a portion of the total bandwidth. This is where the concept of Multiplexing comes!
Multiplexing means “sharing a medium”. It is a form of data transmission in which one communication channel carries several transmissions at the same time. In simple words, the method of dividing a single channel into many channels so that a number of independent signals may be transmitted on it is known as Multiplexing.

Multiplexing techniques can be divided into two basic categories:
Frequency Division Multiplexing-FDM
Time Division Multiplexing-TDM
Frequency Division Multiplexing-FDM
In FDM the available bandwidth is divided into a number of smaller independent logical channels with each channel having a small bandwidth. It assigns “frequency ranges” to each “user” or “signal” on a medium. Thus, all signals are transmitted at the same time, each using different frequencies.The method of using a number of carrier frequencies, each of which is modulated by an independent signal is in fact frequency division multiplexing.

Time Division Multiplexing-TDM
In TDM, sharing is accomplished by dividing available “transmission time” on a medium/channel among users.
Each user of the channel is allotted a small time interval during which he transmits a message. Total time available in the channel is divided, and each user is allocated a time slice. In TDM, users send message sequentially one after another. Each user can use the full channel bandwidth during the period he has control over the channel.

Posted by Sadaf Dilshad Khan on 20:13. Filed under , , , . You can follow any responses to this entry through the RSS 2.0. Feel free to leave a response


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