Carrier wave
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In telecommunications, a carrier wave, or carrier is a waveform (usually sinusoidal) that is modulated (modified) with an input signal for the purpose of conveying information, for example voice or data, to be transmitted. This carrier wave is usually of much higher frequency than the baseband modulating signal (the signal which contains the information).
Carrier waves are used when transmitting radio signals to a radio receiver.
- Frequency modulation (FM) and amplitude modulation (AM) are common methods of sending information over carrier waves.
- In the case of single-sideband modulation (SSB) the carrier is suppressed (and in some forms of SSB eliminated). The carrier must be reintroduced at the receiver by a beat frequency oscillator (BFO).
The frequency for a given radio station is actually the carrier wave's center frequency.
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[edit] Modern modulation systems & the carrier wave
Newer forms of radio communication, such as spread spectrum and ultra wide band, do not transmit a conventional carrier wave, nor does COFDM, which is used in DSL and in the European standard for HDTV.
- COFDM should be thought of as an array of symmetrical carrier waves. The rules governing carrier wave propagation affect COFDM differently than 8VSB.
- Some forms of spread spectrum transmission and most forms of ultra wide band transmission are mathematically defined as being devoid of carrier waves.
[edit] Definition of carrier waves
In telecommunication, the term carrier (cxr) or carrier wave has the following meanings:
- A waveform suitable for modulation by an information-bearing signal.
- An unmodulated emission. Note: The carrier is usually a sinusoidal wave or a uniform or predictable series of pulses. Synonym: carrier wave.
- Sometimes employed as a synonym for a carrier system, or a synonym for a telecommunications provider company (operator), such as a common carrier.
Source: mostly from Federal Standard 1037C and from MIL-STD-188
[edit] References
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