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 logicalchannels 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 amessage. 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.
