Spread spectrum .

• spread spectrum

https://store.theartofservice.com/the-spread-spectrum-toolkit.html

Frequency-hopping spread spectrum

1 Frequency-hopping spread spectrum


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.


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.


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


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.


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.


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.


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


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


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.


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.


Spread spectrum - Sources

1 History on spread spectrum, as given in "Smart Mobs, The Next Social

Revolution", Howard Rheingold, ISBN 0-7382-0608-3


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.


Chirp spread spectrum - Overview

1 Additionally, chirp spread spectrum is resistant to the Doppler effect, which is typical in mobile radio applications.


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



1 Chirp spread spectrum is ideal for applications requiring low power usage and needing relatively low

data rates (1 Mbit/s or less)



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.


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.


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.


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


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.


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.


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.


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.


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.


For More Information, Visit:

• https://store.theartofservice.com/the-spread-spectrum-toolkit.html

The Art of Servicehttps://store.theartofservice.com






Spread spectrum .

Documents

Transcript of Spread spectrum .