- Frequency-division multiplexing
Frequency-division multiplexing (FDM) is a form of signal
multiplexingwhere multiple basebandsignals are modulatedon different frequency carrier waves and added together to create a composite signal.
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 FMtransmission, 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 television channel is divided into subcarrier frequencies for video, color, and audio. DSL uses different frequencies for voice and for upstreamand downstreamdata transmission on the same conductors, which is also an example of frequency duplex.
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) [ cite book
last = White
first = Curt
year = 2007
title = Data Communications and Computer Networks
publisher = Thomson Course Technology
location = Boston, MA
pages = 140-143
isbn = 1-4188-3610-9
FDMA is the traditional way of separating
radiosignals from different transmitters.
In the 1860 and 70s, several inventors attempted FDM under the names of
Acoustic telegraphyand Harmonic telegraphy. Practical FDM was only achieved in the electronic age. Meanwhile their efforts led to an elementary understanding of electroacoustic technology, resulting in the invention of the telephone.
long distancetelephone connections, 20th century telephone companies used L-carrierand similar co-axial cablesystems carrying thousands of voice circuits multiplexed in multiple stages.
For short distances, cheaper balanced pair cables were used for various systems including
Bell SystemK- and N-Carrier. Those cables didn't allow such large bandwidths, so only 12 voice channels (Double Sideband) and later 24 (Single Sideband) were multiplexed into four wires, one pair for each direction with repeaters every several miles, approximately 10 km. See 12-channel carrier system. By the end of the 20th Century, FDM voice circuits had become rare. Modern telephone systems employ digital transmission, in which time-division multiplexing(TDM) is used instead of FDM.
Since the late twentieth century
Digital Subscriber Lines have used a Discrete multitone (DMT) system to divide their spectrum into frequency channels.
The concept corresponding to frequency division multiplexing in the optical domain is known as
wavelength division multiplexing.
Orthogonal frequency-division multiplexing(OFDM),
Time-division multiple access
Code division multiple access
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Look at other dictionaries:
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Frequency Division Multiplexing — FDM (Frequency Division Multiplex) ist ein nachrichtentechnisches Multiplexverfahren, mit dem gleichzeitig mehrere Signale auf mehrere Träger verteilt übertragen werden können. Die Träger sind mehreren unterschiedlichen Frequenzen zugeordnet,… … Deutsch Wikipedia
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frequency division multiplexing — See FDM … Dictionary of telecommunications
frequency division multiplexing — … Useful english dictionary
frequency-division multiplexing access — (FDMA) Technique for sharing a single transmission channel among two or more users by allocating each an exclusive frequency band within the channel … IT glossary of terms, acronyms and abbreviations
Orthogonal frequency-division multiplexing — Passband modulation v · d · e Analog modulation AM · … Wikipedia