frequency division multiplexing

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frequency division multiplexing (FDM) A form of multiplexing in which the bandwidth of the transmission medium is divided into logical channels over which multiple messages can be simultaneously transmitted. FDM is commonly used worldwide to combine multiple voice-grade telephone signals: 4000 hertz (Hz) is allocated for each channel, 3000 Hz per signal plus a 500 Hz guard band (unused frequency band) on either side of the signal. Many such channels are transmitted simultaneously, making effective use of the bandwidth available.

See also broadband networking, time division multiplexing.