Direct-sequence spread spectrum: Difference between revisions

Revision as of 10:58, 5 June 2018

Revision as of 10:59, 5 June 2018

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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</code> values; at a frequency much higher than that of the original signal.

The resulting signal resembles [[white noise]], like an audio recording of "static". However, this noise-like signal is used to exactly reconstruct the original data at the receiving end, by multiplying it by the same pseudorandom sequence (because 1 × 1 = 1, and −1 × −1 = -1). This process, known as "de-spreading", mathematically constitutes a [[correlation]] of the transmitted PN sequence with the PN sequence that the receiver already knows the transmitter is using.

The resulting effect of enhancing [[signal to noise ratio]] on the channel is called ''[[process gain]]''. This effect can be made larger by employing a longer PN sequence and more chips per bit, but physical devices used to generate the PN sequence impose practical limits on attainable processing gain.