Carrier wave

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.[1] This carrier wave is usually of much higher frequency than the input signal. The purpose of the carrier is usually either to transmit the information through space as an electromagnetic wave (as in radio communication), or to allow several carriers at different frequencies to share a common physical transmission medium by frequency division multiplexing (as is used in, for example, a cable television system).

Frequency modulation (FM) and amplitude modulation (AM) are commonly used methods to modulate the carrier. 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 or television station is actually the carrier wave's center frequency.

Contents

Definition of carrier waves

In telecommunication, the term carrier (cxr) or carrier wave has the following meanings:

  1. A waveform suitable for modulation by an information-bearing signal.
  2. An unmodulated emission. Note: The carrier is usually a sinusoidal wave or a uniform or predictable series of pulses. Synonym: carrier wave.
  3. Sometimes employed as a synonym for a carrier system, or a synonym for a telecommunications provider company (operator), such as a common carrier.
Source: Federal Standard 1037C and MIL-STD-188

Carrierless modulation systems

Newer forms of radio communication, such as spread spectrum and ultra-wideband, do not transmit a conventional carrier wave, nor does OFDM, which is used in DSL and in the European standard for HDTV.

  • OFDM should be thought of as an array of symmetrical carrier waves. The rules governing carrier wave propagation affect OFDM differently than 8VSB.
  • Some forms of spread spectrum transmission and most forms of ultra-wideband transmission are mathematically defined as being devoid of carrier waves.

See also

References

  1. ^ "Carrier wave with no modulation transports no information.". University Of Texas. http://www.utexas.edu/research/cemd/nim/Agif/CarrWave.html. Retrieved 2008-05-30. 

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