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see also Frequency-hopping spread spectrum |
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<b>2.</b> 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 add pseudorandom "noise" to the data being transmitted, which is then removed by the receiver. The resulting signal resembles the result of a sender transmitting an audio recording of static, except that the "static" can be filtered out at the receiving end to recover the original data. 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.
By contrast, [[Frequency-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.
Source: from [[Federal Standard 1037C]] and from the [[NTIA Manual of Regulations and Procedures for Federal Radio Frequency Management]]
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