Download - Spread spectrum
Frequency-hopping spread spectrum
1 Frequency-hopping spread spectrum
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Frequency-hopping spread spectrum
1 Frequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly switching a
carrier among many frequency channels, using a pseudorandom
sequence known to both transmitter and receiver. It is used as a multiple
access method in the frequency-hopping code division multiple
access (FH-CDMA) scheme.https://store.theartofservice.com/the-spread-spectrum-toolkit.html
Frequency-hopping spread spectrum - Civilian use
1 In the US, since the Federal Communications Commission (FCC) amended rules to allow frequency
hopping spread spectrum systems in the unregulated 2.4 GHz band, many consumer devices in that band have employed various spread-spectrum
modes.
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Frequency-hopping spread spectrum - Civilian use
1 Some walkie-talkies that employ frequency-hopping spread spectrum technology have been developed for unlicensed use on the
900 MHz band. Several such radios are marketed under the name eXtreme Radio
Service (eXRS). Despite the name's similarity to the FRS allocation, the system
is a proprietary design, rather than an official U.S. Federal Communications Commission (FCC) allocated service.
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Frequency-hopping spread spectrum - Technical considerations
1 In the US, FCC part 15 on unlicensed system in the 900 MHz and 2.4 GHz bands
permits more power than non-spread spectrum systems. Both frequency hopping and direct sequence systems can transmit
at 1 Watt. The limit is increased from 1 milliwatt to 1 watt or a thousand times increase. The Federal Communications
Commission (FCC) prescribes a minimum number of channels and a maximum dwell
time for each channel.https://store.theartofservice.com/the-spread-spectrum-toolkit.html
Frequency-hopping spread spectrum - Technical considerations
1 Spread spectrum systems rely on excess signal to noise ratios for sharing of spectrum
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Frequency-hopping spread spectrum - Multiple inventors
1 During World War II, the US Army Signal Corps was inventing a communication system called
SIGSALY, which incorporated spread spectrum in a single frequency
context. However, SIGSALY was a top-secret communications system,
so its existence did not become known until the 1980s.
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Frequency-hopping spread spectrum - Variations of FHSS
1 Adaptive Frequency-hopping spread spectrum (AFH) (as used in
Bluetooth) improves resistance to radio frequency interference by
avoiding using crowded frequencies in the hopping sequence. This sort of
adaptive transmission is easier to implement with FHSS than with
DSSS.
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Frequency-hopping spread spectrum - Variations of FHSS
1 The GSM cellular system uses frequency hopping, as a form of
frequency interleaving, in view to avoid that two phone calls in
adjacent cells constantly interfere with each other. However, this is not
considered as spread spectrum, since the two phonecalls within the
same cell never use the same frequency.
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Spread spectrum
1 Spread-spectrum telecommunications This is a
technique in which a telecommunication signal is transmitted on a bandwidth considerably larger than the
frequency content of the original information. Frequency hopping is a basic modulation technique used in
spread spectrum signal transmission.https://store.theartofservice.com/the-spread-spectrum-toolkit.html
Spread spectrum
1 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
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Spread spectrum
1 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
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Spread spectrum - Techniques
1 Techniques known since the 1940s and used in military communication systems
since the 1950s "spread" a radio signal over a wide frequency range several magnitudes
higher than minimum requirement. The core principle of spread spectrum is the use
of noise-like carrier waves, and, as the name implies, bandwidths much wider than
that required for simple point-to-point communication at the same data rate.
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Spread spectrum - Spread-spectrum clock signal generation
1 An ability to disable spread-spectrum clocking in computer systems is
considered useful for overclocking, as spread spectrum can lower
maximum clock speed achievable due to clock skew.
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Spread spectrum - Sources
1 History on spread spectrum, as given in "Smart Mobs, The Next Social
Revolution", Howard Rheingold, ISBN 0-7382-0608-3
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Chirp spread spectrum
1 In digital communications, chirp spread spectrum (CSS) is a spread spectrum
technique that uses wideband linear frequency modulated chirp pulses to encode information. A chirp is a sinusoidal signal whose frequency increases or decreases over time (often with a
polynomial expression for the relationship between time and frequency). In the picture is an example of an upchirp—as you can see, the
frequency increases linearly over time.
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Chirp spread spectrum - Overview
1 Additionally, chirp spread spectrum is resistant to the Doppler effect, which is typical in mobile radio applications.
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Chirp spread spectrum - Uses
1 Chirp spread spectrum was originally designed to compete with ultra-
wideband for precision ranging and low-rate wireless networks in the
2.45 GHz band
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Chirp spread spectrum - Uses
1 Chirp spread spectrum is ideal for applications requiring low power usage and needing relatively low
data rates (1 Mbit/s or less)
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Chirp spread spectrum - Uses
1 Chirp spread spectrum may also be used in the future for military
applications as it is very difficult to detect and intercept when operating
at low power.
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Direct-sequence spread spectrum
1 In telecommunications, direct-sequence spread spectrum (DSSS) is a modulation
technique. As with other spread spectrum technologies, the transmitted signal takes up more bandwidth than the information signal
that modulates the carrier or broadcast frequency. The name 'spread spectrum'
comes from the fact that the carrier signals occur over the full bandwidth (spectrum) of a device's transmitting frequency. Certain IEEE
802.11 standards use DSSS signaling.
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Direct-sequence spread spectrum - Transmission method
1 In contrast, frequency-hopping spread spectrum pseudo-randomly
re-tunes the carrier, instead of adding pseudo-random noise to the data, the latter process results in a
uniform frequency distribution whose width is determined by the output
range of the pseudorandom number generator.
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Channel access method - Code division multiple access (CDMA)/Spread spectrum multiple access (SSMA)
1 The code division multiple access (CDMA) scheme is based on spread
spectrum, meaning that a wider radio spectrum in Hertz is used than
the data rate of each of the transferred bit streams, and several
message signals are transferred simultaneously over the same carrier
frequency, utilizing different spreading codes
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Channel access method - Code division multiple access (CDMA)/Spread spectrum multiple access (SSMA)
1 One form is direct sequence spread spectrum (DS-CDMA), used for
example in 3G cell phone systems. Each information bit (or each symbol)
is represented by a long code sequence of several pulses, called
chips. The sequence is the spreading code, and each message signal (for
example each phone call) use different spreading code.
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Direct sequence spread spectrum
1 In telecommunications, 'direct-sequence spread spectrum' ('DSSS') is a modulation technique.
As with other spread spectrum technologies, the transmitted signal takes up more Bandwidth
(signal processing)|bandwidth than the information signal that modulates the carrier or
broadcast frequency. The name 'spread spectrum' comes from the fact that the carrier
signals occur over the full bandwidth (spectrum) of a device's transmitting frequency. Certain IEEE 802.11 standards use DSSS signaling.
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Miniature helicopter - Spread spectrum
1 Systems such as FHSS (frequency-hopping spread spectrum) used by Futaba Corporation|Futaba employ frequency hopping on the 2.4GHz
band instead of the various frequencies in the lower MHz ranges. The advantage is that radios are no
longer using a fixed frequency during flight, mitigating the risk of
interference on that fixed frequency.https://store.theartofservice.com/the-spread-spectrum-toolkit.html
Miniature helicopter - Spread spectrum
1 Systems such as Spektrum and JR use the DSM2 DSSS(Direct-sequence
spread spectrum) method, where they transmit on a pair of fixed
channels chosen when the radio and receiver are turned on. Any
subsequent systems would avoid using these channels and continue
searching for another unused pair of channels.
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Clandestine HUMINT operational techniques - Steganography, Covert Channels, and Spread Spectrum
1 Basic spread spectrum uses a fixed set of frequencies, but the signal
strength in any one frequency is too low to detect without correlation to
other frequencies.
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Clandestine HUMINT operational techniques - Steganography, Covert Channels, and Spread Spectrum
1 Frequency-hopping spread spectrum is a related technique, which can use
the parallel transmission of true spread spectrum, not using any one frequency long enough for plausible interception. The pattern of variation among channels may be generated
and received using crytographic methods.
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