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Frequency-division multiplexing (FDM) is a form of signal multiplexing where multiple baseband signals are modulated on different frequency carrier waves and added together to create a composite signal. In telecommunications, multiplexing (also muxing or MUXing) is the combining of two or more information channels onto a common transmission medium using hardware called a multiplexer or (MUX). ...
All signals are comprised of a whole range of different frequencies added up together. ...
For the musical use of modulation, see modulation (music). ...
A carrier wave, or carrier is a waveform (usually sinusoidal) that is modulated (modified) to represent the information to be transmitted. ...
Historically, telephone networks used FDM to carry several voice channels on a single physical circuit. In this, 12 voice channels would be modulated onto carriers spaced 4 kHz apart. The composite signal, occupying the frequency range 60 – 108 kHz, was known as a group. In turn, five groups could themselves be multiplexed by a similar method into a supergroup, containing 60 voice channels. There were even higher levels of multiplexing, and it became possible to send thousands of voice channels down a single circuit.
Modern telephone systems employ digital transmission, in which time-division multiplexing (TDM) is used instead of FDM. Time-division multiplexing (TDM) is a type of digital multiplexing in which two or more apparently simultaneous channels are derived from a given frequency spectrum, i. ...
FDM can also be used to combine multiple signals before final modulation onto a carrier wave. In this case the carrier signals are referred to as subcarriers: an example is stereo FM transmission, where a 38 kHz subcarrier is used to separate the left-right difference signal from the central left-right sum channel, prior to the frequency modulation of the composite signal. A subcarrier is separate analog or digital signal carried on a main radio transmission, which carries extra information such as voice or data. ...
FM radio is a broadcast technology invented by Edwin Howard Armstrong that uses frequency modulation to provide high-fidelity broadcast radio sound. ...
Where frequency division multiplexing is used as to allow multiple users to share a physical communications channel, it is called frequency-division multiple access (FDMA). A Communications channel (or channel for short), models the medium through which information is transmitted from a sender (or transmitter) to a receiver. ...
FDMA, or frequency-division multiple access, is the oldest and most important of the three main ways for multiple radio transmitters to share the radio spectrum. ...
FDMA is the traditional way of separating radio signals from different transmitters.
The analog of frequency division multiplexing in the optical domain is known as wavelength division multiplexing. In telecommunications wavelength division multiplexing (WDM) is a technology which multiplexes several optical carrier signals on a single optical fibre by using different wavelengths (colours) of laser light to carry different signals. ...
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