Direct-sequence spread spectrum: Difference between revisions

Revision as of 18:31, 18 April 2005

Revision as of 19:32, 13 July 2005

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# A [[signal]] structuring technique utilizing a [[digital]] code [[sequence]] having a [[chip rate]] much higher than the [[information]] signal [[bit rate]]. Each information bit of a [[digital signal]] is transmitted as a pseudorandom sequence of chips.

Put simply, direct-sequence spread-spectrum transmissions multiply a "noise" signal to the data being transmitted by a "noise" signal. This noise signal is a pseudorandom sequence of <code>1</code> and <code>-1</code> values, at a frequency much higher than that of the original signal, thereby spreading the energy of the original signal into a much wider band.

The resulting signal resembles [[white noise]], like an audio recording of "static", except that this noise can be filtered out at the receiving end to recover the original data, by again multiplying the same pseudorandom sequence to the received signal (because 1 &times; 1 = 1, and -1 &times; -1 = 1).

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As this description suggests, a plot of the transmitted waveform has a roughly bell-shaped envelope centered on the carrier frequency, just like a normal [[Amplitude modulation|AM]] transmission, except that the added noise causes the distribution to be much wider than that of an AM transmission.

ByIn contrast, [[Frequencyfrequency-hopping spread spectrum]] pseudo-randomly retunes the carrier, instead of adding pseudo-random noise to the data, which results in a uniform frequency distribution whose width is determined by the output range of the [[Pseudo-random number|pseudo-random]] number generator.

==References==