In telecommunication and radio communication, spread-spectrum
techniques are methods by which a signal (e.g., an electrical,
electromagnetic, or acoustic signal) generated with a particular
bandwidth is deliberately spread in the frequency domain, resulting in
a signal with a wider bandwidth. These techniques are used for a
variety of reasons, including the establishment of secure
communications, increasing resistance to natural interference, noise,
and jamming, to prevent detection, to limit power flux density (e.g.,
in satellite down links), and to enable multiple-access
communications.Spread spectrum generally makes use of a sequential
noise-like signal structure to spread the normally narrowband
information signal over a relatively wideband (radio) band of
frequencies. The receiver correlates the received signals to retrieve
the original information signal. Originally there were two
motivations: either to resist enemy efforts to jam the communications
(anti-jam, or AJ), or to hide the fact that communication was even
taking place, sometimes called low probability of intercept
(LPI).Frequency-hopping spread spectrum (FHSS), direct-sequence spread
spectrum (DSSS), time-hopping spread spectrum (THSS), chirp spread
spectrum (CSS), and combinations of these techniques are forms of
spread spectrum. The first two of these techniques employ pseudorandom
number sequencesâ€"created using pseudorandom number generatorsâ€"to
determine and control the spreading pattern of the signal across the
allocated bandwidth. Wireless standard IEEE 802.11 uses either FHSS or
DSSS in its radio interface.
techniques are methods by which a signal (e.g., an electrical,
electromagnetic, or acoustic signal) generated with a particular
bandwidth is deliberately spread in the frequency domain, resulting in
a signal with a wider bandwidth. These techniques are used for a
variety of reasons, including the establishment of secure
communications, increasing resistance to natural interference, noise,
and jamming, to prevent detection, to limit power flux density (e.g.,
in satellite down links), and to enable multiple-access
communications.Spread spectrum generally makes use of a sequential
noise-like signal structure to spread the normally narrowband
information signal over a relatively wideband (radio) band of
frequencies. The receiver correlates the received signals to retrieve
the original information signal. Originally there were two
motivations: either to resist enemy efforts to jam the communications
(anti-jam, or AJ), or to hide the fact that communication was even
taking place, sometimes called low probability of intercept
(LPI).Frequency-hopping spread spectrum (FHSS), direct-sequence spread
spectrum (DSSS), time-hopping spread spectrum (THSS), chirp spread
spectrum (CSS), and combinations of these techniques are forms of
spread spectrum. The first two of these techniques employ pseudorandom
number sequencesâ€"created using pseudorandom number generatorsâ€"to
determine and control the spreading pattern of the signal across the
allocated bandwidth. Wireless standard IEEE 802.11 uses either FHSS or
DSSS in its radio interface.
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