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Spread-spectrum techniques are methods by which energy generated at one or more discrete frequencies is deliberately spread or distributed in time or frequency domains. This is done for a variety of reasons, including the establishment of secure communications, increasing resistance to natural interference and jamming, and to prevent detection. FreQuency is a music video game developed by Harmonix and published by SCEI. It was released in November 2001. ...
Time-domain is a term used to describe the analysis of mathematical functions, or real-life signals, with respect to time. ...
Frequency domain is a term used to describe the analysis of mathematical functions with respect to frequency. ...
Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). ...
Radio jamming is the (usually deliberate) transmission of radio signals that disrupt communications by decreasing the signal to noise ratio. ...
History The concept of frequency hopping was first alluded to in Nikola Tesla's U.S. patents # 723188 and 725605, 1903, the application for which had been filed even earlier in July 1900. Tesla came up with the idea after demonstrating the world's first radio-controlled submersible boat in 1898, when it became apparent the wireless signals controlling the boat needed to be secure from "being disturbed, intercepted, or interfered with in any way." His patents covered two fundamentally different techniques for achieving immunity to interference, both of which functioned by altering the carrier frequency or other exclusive characteristic. The first had a transmitter that worked simultaneously at two or more separate frequencies and a receiver in which each of the individual transmitted frequencies had to be tuned in, in order for the control circuitry to respond. The second technique used a variable-frequency transmitter controlled by an encoding wheel that altered the transmitted frequency in a predetermined manner. These patents describe the basic principles of frequency hopping and frequency-division multiplexing, and also the electronic AND-gate logic circuit. Frequency-hopping spread spectrum (FHSS) is a spread-spectrum method of transmitting signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver. ...
Nikola Tesla (1856-1943)[1] was a world-renowned Serbian inventor, physicist, mechanical engineer and electrical engineer. ...
Frequency hopping is also mentioned in radio pioneer Johannes Zenneck's book Wireless Telegraphy (German, 1908, English translation McGraw Hill, 1915), although Zenneck himself states that Telefunken had already tried it several years earlier. Zenneck's book was a leading text of the time and it is likely that many later engineers were aware of it. A Polish army officer, named Leonard Danielewicz, came up with the idea in 1929.[citation needed] Several other patents were taken out in the 1930s, including one by Willem Broertjes (Germany 1929, US patent # 1,869,695, 1932). During World War II, the US Army Signal Corp was inventing a communication system called SIGSALY for communication between Roosevelt and Churchill, which incorporated spread spectrum, but due to its top secret nature, SIGSALY's existence did not become known until the 1980s. Telefunken is a German radio- and television company, founded in 1903. ...
Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki TÅjÅ Casualties Military dead: 17,000,000 Civilian dead: 33,000...
SIGSALY exhibit at the National Cryptologic Museum In cryptography, SIGSALY (also Green Hornet) was a telephone scrambler used in World War II for the highest-level Allied communications. ...
The most celebrated invention of frequency hopping was that of actress Hedy Lamarr and composer George Antheil, who in 1942 received U.S. patent # 2,292,387 for their "Secret Communications System". Lamarr had learned about the problem at defense meetings she had attended with her former husband Friedrich Mandl, who was an Austrian arms manufacturer. The Antheil-Lamarr version of frequency hopping used a piano-roll to change among 88 frequencies, and was intended to make radio-guided torpedoes harder for enemies to detect or to jam. The patent came to light during patent searches in the 1950s when ITT Corporation and other private firms began to develop Code Division Multiple Access (CDMA), a civilian form of spread spectrum, though the Lamarr patent had no direct impact on subsequent technology. It was in fact ongoing military research at MIT Lincoln Laboratory, Magnavox Government & Industrial Electronics Corporation, ITT and Sylvania Electronic Systems that led to early spread-spectrum technology in the 1950s. Parallel research on radar systems and a technologically similar concept called "phase coding" also had an impact on spread-spectrum development. Hedy Lamarr (November 9, 1913 – January 19, 2000) was an Austrian/Jewish-American actress and communications technology innovator. ...
George Antheil (June 8, 1900 – February 12, 1959) was an American composer and pianist of German and Lutheran descent, born in Trenton, New Jersey. ...
Friedrich Mandl (1900 - 1977) was chairman of Hirtenberger Patronen-Fabrik, a leading Austrian armaments firm founded by his father, Alexander Mandl. ...
It has been suggested that Music roll be merged into this article or section. ...
A modern torpedo, historically called a self propelled torpedo, is a self-propelled guided projectile that (after being launched above or below the water surface) operates underwater and is designed to detonate on contact or in proximity to a target. ...
ITT Corporation, NYSE: ITT is a large American manufacturing company with 2006 revenues of $7. ...
Code division multiple access (CDMA) is a form of multiplexing and a method of multiple access to a physical medium such as a radio channel, where different users use the medium at the same time thanks to using different code sequences. ...
MIT Lincoln Laboratory, also known as Lincoln Lab, is a federally funded research and development center managed by the Massachusetts Institute of Technology and funded by the United States Department of Defense. ...
Magnavox (Latin for loud voice) is a consumer electronics company that is now part of Philips Consumer Electronics. ...
On the morning of July 2, 1956, an explosion involving scrap Thorium occurred at the Sylvania Electric Products Metallurgical Laboratory. ...
Commercial use The 1976 publication of Spread Spectrum Systems by Robert Dixon, ISBN 0-471-21629-1, was a significant milestone in the commercialization of this technology. Previous publications were either classified military reports or academic papers on narrow subtopics. Dixon's book was the first comprehensive unclassified review of the technology and set the stage for increasing research into commercial applications.
Initial commercial use of spread spectrum began in the 1980s in the US with three systems: Equatorial Communications System's very small aperture (VSAT) satellite terminal system for newspaper newswire services, Del Norte Technology's radionavigation system for navigation of aircraft for crop dusting and similar applications, and Qualcomm's OmniTRACS system for communications to trucks. In the Qualcomm and Equatorial systems, spread spectrum enabled small antennas that viewed more than one satellite to be used since the processing gain of spread spectrum eliminated interference. The Del Norte system used the high bandwidth of spread spectrum to improve location accuracy. VSAT is short for Very Small Aperture Terminal. ...
Qualcomm (NASDAQ: QCOM) is a wireless telecommunications research and development company based in San Diego, California. ...
In 1981, the Federal Communications Commission started exploring ways to permit more general civil uses of spread spectrum in a Notice of Inquiry docket. [1]. This docket was proposed to FCC and then directed by Michael Marcus of the FCC staff. The proposals in the docket were generally opposed by spectrum users and radio equipment manufacturers, although they were supported by the then Hewlett-Packard Corp. The laboratory group supporting the proposal would later become part of Agilent. The Hewlett-Packard Company (NYSE: HPQ), commonly known as HP, is a very large, global company headquartered in Palo Alto, California, United States. ...
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The May 1985 decision [2] in this docket permitted unlicensed use of spread spectrum in 3 bands at powers up to 1 Watt. FCC said at the time that it would welcome additional requests for spread spectrum in other bands.The resulting rules, now codified as [3] permitted Wi-Fi, Bluetooth, and many other products including cordless telephones. These rules were then copied in many other countries. Qualcomm was incorporated within 2 months after the decision to commercialize CDMA. Official Wi-Fi logo Wi-Fi is a wireless technology brand owned by the Wi-Fi Alliance intended to improve the interoperability of wireless local area network products based on the IEEE 802. ...
Bluetooth logo This article is about the electronic protocol named after Harald Bluetooth Gormson. ...
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. Copy of the original phone of Alexander Graham Bell at the Musée des Arts et Métiers in Paris Telecommunication is the transmission of signals over a distance for the purpose of communication. ...
This article does not cite any references or sources. ...
FreQuency is a music video game developed by Harmonix and published by SCEI. It was released in November 2001. ...
Spread-spectrum telecommunications is a signal structuring technique that employs direct sequence, frequency hopping or a hybrid of these, which can be used for multiple access and/or multiple functions. This technique decreases the potential interference to other receivers while achieving privacy. 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). For the Irish mythological figure, see Naoise. ...
Narrowband (narrow bandwidth) refers to a signal which occupies only a small amount of space on the radio spectrum -- the opposite of broadband or wideband. ...
Wideband is a relative term used to describe a wide range of frequencies in a spectrum. ...
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. Each of these techniques employ pseudorandom number sequences — created using pseudorandom number generators — to determine and control the spreading pattern of the signal across the alloted bandwidth. Ultra-wideband (UWB) is another modulation technique that accomplishes the same purpose, based on transmitting short duration pulses. Wireless Ethernet standard IEEE 802.11 uses either FHSS or DSSS in its radio interface. Frequency-hopping spread spectrum (FHSS) is a spread-spectrum method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver. ...
In telecommunications, direct-sequence spread spectrum (DSSS) is a modulation technique. ...
This article does not cite any references or sources. ...
A Pseudorandom number sequence is a sequence of numbers that has been computed by some defined arithmetic process but is effectively a random number sequence for the purpose for which it is required. ...
// A pseudorandom number generator (PRNG) is an algorithm that uses arithmetics to generate a sequence of numbers that approximate the properties of random numbers. ...
Ultra-wideband (also UWB, and ultra-wide-band, ultra-wide band, etc. ...
IEEE 802. ...
Notes - Techniques known since 1940s and used in military communication system since 1950s
- "Spread" 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.
- Two main techniques:
- Resistance to jamming (interference). DS is better at resisting continuous-time narrowband jamming, while FH is better at resisting pulse jamming. In DS systems, narrowband jamming affects detection performance about as much as if the amount of jamming power is spread over the whole signal bandwidth, when it will often not be much stronger than background noise. By contrast, in narrowband systems where the signal bandwidth is low, the received signal quality will be severely lowered if the jamming power happens to be concentrated on the signal bandwidth.
- Resistance to eavesdropping. The spreading code (in DS systems) or the frequency-hopping pattern (in FH systems) is often unknown by anyone for whom the signal is unintended, in which case it "encrypts" the signal and prevents the adversary from making sense of it. What's more, for a given noise power spectral density (PSD), spread-spectrum systems require the same amount of energy per bit before spreading as narrowband systems and therefore the same amount of power if the bitrate before spreading is the same, but since the signal power is spread over a large bandwidth, the signal PSD is much lower, often significantly lower than the noise PSD, therefore the adversary may be unable to determine if the signal exists at all. Note that these effects can also be achieved by using encryption and a very low-rate channel code, which can also be viewed as a spread-spectrum method, albeit more complex.
- Resistance to fading. The high bandwidth occupied by spread-spectrum signals offer some frequency diversity, i.e. it is unlikely that the signal would encounter severe multipath fading over its whole bandwidth, and in other cases the signal can be detected using e.g. a Rake receiver.
- Multiple access capability. Multiple users can transmit simultaneously on the same frequency (range) as long as they use different spreading codes. See CDMA.
In telecommunications, direct-sequence spread spectrum (DSSS) is a modulation technique. ...
Frequency-hopping spread spectrum (FHSS) is a spread-spectrum method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver. ...
To eavesdrop is to surreptitiously overhear a private conversation. ...
In physics, the spectral density, or more correctly the power spectral density (PSD) of a given bandwidth of electromagnetic radiation is the total power in this bandwidth divided by the specified bandwidth. ...
Fading (or fading channels) are mathematical models for the distortion that a carrier-modulated telecommunication signal experiences over certain propagation media. ...
PRIMERGY MultiPath PRIMERGY MultiPath supports redundant Fiber Channel paths, the configured connections between server and subsystem that are such an important component of disaster-tolerant servers and clusters. ...
A rake receiver is a radio receiver designed to counter the effects of multipath fading. ...
Code division multiple access (CDMA) is a form of multiplexing and a method of multiple access to a physical medium such as a radio channel, where different users use the medium at the same time thanks to using different code sequences. ...
Spread-spectrum clock signal generation Spread-spectrum clock generation (SSCG) is used in the design of synchronous digital systems, especially those containing microprocessors, to reduce the spectral density of the electromagnetic interference (EMI) that these systems generate. A synchronous digital system is one that is driven by a clock signal and because of its periodic nature, has an unavoidably narrow frequency spectrum. In fact, a perfect clock signal would have all its energy concentrated at a single frequency and its harmonics, and would therefore radiate energy with an infinite spectral density. Practical synchronous digital systems radiate electromagnetic energy on a number of narrow bands spread on the clock frequency and its harmonics, resulting in a frequency spectrum that, at certain frequencies, can exceed the regulatory limits for electromagnetic interference (e.g. those of the Federal Communications Commission (FCC) in the United States, JEITA in Japan and the IEC in Europe). Radio Frequency Interference (RFI) is electromagnetic radiation which is emitted by electrical circuits carrying rapidly changing signals, as a by-product of their normal operation, and which causes unwanted signals (interference or noise) to be induced in other circuits. ...
The FCCs official seal. ...
The Japan Electronics and Information Technology Industries Association (JEITA) is an electronics and IT industry trade organization. ...
The International Electrotechnical Commission (IEC) is an international standards organization dealing with electrical, electronic and related technologies. ...
To avoid this problem, which is of great commercial importance to manufacturers, spread-spectrum clocking is used. This consists of using one of the methods described in the Spread-spectrum telecommunications section in order to reduce the peak radiated energy. The technique therefore reshapes the system's electromagnetic emissions to comply with the electromagnetic compatibility (EMC) regulations. It is a popular technique because it can be used to gain regulatory approval with only a simple modification to the equipment.
Spread-spectrum clocking has become more popular in portable electronics devices because of faster clock speeds and the increasing integration of high-resolution LCD displays in smaller and smaller devices. Because these devices are designed to be lightweight and inexpensive, passive EMI reduction measures such as capacitors or metal shielding are not a viable option. Active EMI reduction techniques such as spread-spectrum clocking are necessary in these cases, but can also create challenges for designers. Principle among these is the risk that modifying the system clock runs the risk of the clock/data misalignment. Active EMI Reduction refers to techniques such as spread spectrum clocking to reduce the effects of electromagnetic interference or EMI. It contrasts with passive techniques such as capacitors or shielding. ...
Many personal computers have a BIOS setting to turn spread-spectrum clocking on or off. See external links at the bottom of this article. This article does not cite any references or sources. ...
It is important to note that this method does not reduce the total energy radiated by the system, and therefore does not necessarily make the system any less likely to interfere with sensitive equipment such as television and wideband receivers. It spreads the energy over a large frequency band which effectively reduces the electrical and magnetic field strengths that are measured within a narrow window of frequencies. Spread-spectrum clocking works because the EMI receivers used by EMC testing laboratories divide the electromagnetic spectrum into frequency bands approximately 120 kHz wide. If the system under test were to radiate all of its energy at one frequency, then this energy would fall into a single frequency band of the receiver, which would register a large peak at that frequency. Spread-spectrum clocking distributes the energy so that it falls into a large number of the receiver's frequency bands, without putting enough energy into any one band to exceed the statutory limits. The usefulness of spread-spectrum clocking as a method of actually reducing interference is often debated, but it is probable that some electronic equipment with sensitivity to a narrowband of frequencies will experience less interference, while other equipment with broadband sensitivity will experience more interference.
FCC certification testing is often completed with the spread-spectrum function enabled in order to reduce the measured emissions to within acceptable legal limits. However, some BIOS writers include the ability to disable spread-spectrum clock generation as a user setting, thereby defeating the object of the EMI regulations. This may be considered a loophole, but is generally overlooked as long as the default BIOS setting provided by the manufacturer has the spread-spectrum feature enabled.
Notes - ^ Notice of Inquiry, General Docket 81-413
- ^ Authorization of Spread Spectrum Systems Under Parts 15 and 90 of the FCC Rules and Regulations
- ^ 47 CFR 15.247
Sources Federal Standard 1037C, entitled Telecommunications: Glossary of Telecommunication Terms is a United States Federal Standard, issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, as amended. ...
Also known as the Red Book, this publication of the Office of Office of Spectrum Management of the National Telecommunications and Information Administration or NTIA, is the official source for all technical regulations relating to the use of the electromagnetic frequency spectrum. ...
MIL-STD-188 is a series of U.S. military standards relating to telecommunications. ...
The National Information Systems Security Glossary, published by the National Security Telecommunications and Information Systems Security Committee of the United States federal government, is an unclassified glossary of Information Systems Security (INFOSEC) terms intended to provide a common vocabulary for discussing INFOSEC. External links Online copy in Adobe Acrobat format...
Howard Rheingold at the Ars Electronica in 2004 Howard Rheingold (born July 7, 1947) is a leading thinker and writer on the cultural, social and political implications of modern communications media such as the Internet, mobile telephony and virtual communities (a term he is credited with inventing). ...
See also Frequency-hopping spread spectrum (FHSS) is a spread-spectrum method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver. ...
In telecommunications, direct-sequence spread spectrum (DSSS) is a modulation technique. ...
Open spectrum (also known as free spectrum) is a movement to get the government to provide more unlicensed spectrum, radio frequency spectrum that is available for use by all. ...
Electromagnetic Compatibility (EMC) is the branch of electrical sciences which studies the unintentional generation, propagation and reception of electromagnetic energy with reference to the unwanted effects that such an energy may induce. ...
Radio Frequency Interference (RFI) is electromagnetic radiation which is emitted by electrical circuits carrying rapidly changing signals, as a by-product of their normal operation, and which causes unwanted signals (interference or noise) to be induced in other circuits. ...
The electromagnetic spectrum is an aspect of the physical world, like land, water, and air. ...
Orthogonal variable spreading factor (OVSF) is an implementation of Code division multiple access (CDMA) where before each signal is transmitted, the spectrum is spread through the use of a users code. ...
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