Multiplexing is transmission of information from one or more sources to one or more destinations using the same medium. Transmission medium can be a metallic wire pair, a coaxial cable, a microwave radio system, a satellite microwave or optical fiber cable. To accomplish multiplexing, signals can be either divided by time, frequency, space, phase or wavelength. Some more complicated ways can ignore these conventional limitations.

Frequency-division multiplexing utilize a certain bandwidth with signals sharing the bandwidth, that is, the signalís operating frequency are different and they occupy a certain amount of space in the bandwidth. Frequency-division multiplexing can be seen with local television channeling schemes. Like any broadcast, television station signals are also limited and are only allowed to broadcast at a particular frequency range.

Time-division multiplexing, on the other hand, permits a signal to occupy the whole bandwidth but not the all the time, in fact, only for a few microseconds. Telephone systems use this technique such that the line is not stagnant even for so little a time. A voice signal first comes in the line but only stays for a short burst and reappears after a set number of epochs. Our ear is not sensitive to the periodic voice disruptions because of the speed of transition. In effect, the same amount of information can be delivered plus the insurance that the line is always in use.

Wavelength-division multiplexing is a technique used in fiber optics. The electromagnetic spectrum permits light components to travel at different speeds depending on the wavelength. Thus, it creates a similar effect as that of frequency-division multiplexing but uses wavelength differences to divide the light signals entering the fiber cable.

Posted 2010-12-14 and updated on Dec 14, 2010 1:53pm by crisd

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