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==Transmission method==
Direct-sequence spread-spectrum transmissions multiply the data being transmitted by a pseudorandom spreading sequence that has a much higher bit rate than the original data rate. The resulting transmitted signal resembles bandlimited [[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 spreading sequence (because {{nowrap|1 × 1 {{=}} 1}}, and {{nowrap|−1 × −1 {{=}} 1}}). This process, known as despreading, is mathematically a [[correlation]] of the transmitted spreading sequence with the spreading sequence that the receiver already knows the transmitter is using. After the despreading, the [[signal-to-noise ratio]] is approximately increased by the spreading factor, which is the ratio of the spreading-sequence rate to the data rate.
While a transmitted DSSS signal occupies a much wider bandwidth than a simple modulation of the original signal would require, its frequency spectrum can be somewhat restricted for spectrum economy by a conventional analog bandpass filter to give a roughly bell-shaped envelope centered on the [[carrier frequency]]. In contrast, [[frequency-hopping spread spectrum]] pseudorandomly retunes the carrier and requires a uniform frequency response since any bandwidth shaping would cause amplitude modulation of the signal by the hopping code.
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