Direct-sequence spread spectrum: Difference between revisions

Revision as of 15:27, 5 September 2005

Revision as of 03:33, 2 November 2005

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# A [[signal]] structuring technique utilizing a [[digital]] code [[sequence]] ([[PN Sequences]]) 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 the data being transmitted by a "noise" signal. This noise signal is a pseudorandom sequence of <code>1</code> and <code>-1−1</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 ([[PN Sequences]]) to the received signal (because 1 &times;× 1 = 1, and -1−1 &times;× -1−1 = 1).

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.