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	Frequency hopping
		Frequency hopping is one of the various Spread Spectrum techniques that are in use today and is the one that is being is used in the above mentioned applications.
		Fast frequency hopping seems to be a better technique as jamming at even one of the selected frequencies does not effect the quality of received data as each bit has been represented by a large number of frequencies.
		Frequency hopping actually involves transmission in the form of analog signals, however analog circuits involve use of lot of hardware in simple A/D and D/A conversions at the transmitter and the receiver stages.
	www.geocities.com /anujgrover22/techpapers/commproj.html (1841 words)

	frequency-hopping spread spectrum - a Whatis.com definition - see also: FH-CDMA
		Frequency hopping is one of two basic modulation techniques used in spread spectrum signal transmission.
		It is the repeated switching of frequencies during radio transmission, often to minimize the effectiveness of "electronic warfare" - that is, the unauthorized interception or jamming of telecommunications.
		Frequency hopping requires a much wider bandwidth than is needed to transmit the same information using only one carrier frequency.
	searchnetworking.techtarget.com /sDefinition/0,,sid7_gci525695,00.html (599 words)

	Frequency Hopping in radio scramblers
		In the illustration, the input signal is inverted at frequency 3.3kHz.
		The frequencies for this higher block are calculated as the sum of the input signal and the inversion frequency
		The process is often incorrectly called "frequency hopping", but should not be confused with true hopping, where the transmission frequency itself changes (click here for more information).
	www.cescomm.co.nz /about/scrambling.html (756 words)

	Welcome to SkyDSP, OFDM systems, telemetry, software radio
		The main four schemes are to use a group of carriers with a fixed frequency, randomly hopped group of carriers, spread out carriers in a comb pattern and adaptive frequency hopping.
		A new adaptive frequency hopping technique is proposed for multiuser OFDM such that blocks of carriers are hopped based on the current channel conditions.
		Adaptive frequency hopping for multiuser OFDM has been presented and shown to be a powerful technique for reducing the effects of frequency selective fading.
	www.skydsp.com /publications/AdaptMod (3418 words)

	Synchronizer for frequency hopping receiver - Patent 4023103
		Then the receiver compares the half periods of every frequency hopping period for a predetermined number of periods and advances or retards the receiver clock a predetermined small fraction of a period and repeats the process until there is sync to within a predetermined minor fraction of a period.
		The frequency synthesizers 18A and 18B generate carrier and local frequencies, respectively, and each is controlled to generate any one of a population of 2.sup.n frequencies that are equally spaced, within the carrier band and local frequency band, respectively.
		To synchronize the frequency synthesizer 18B and to keep it in sync, a multiphase synchronizer 28 according to this invention is connected between the output of mixer 24 and the receiver clock 14B.
	www.freepatentsonline.com /4023103.html (2773 words)

	Method for frequency sharing and frequency punchout in frequency hopping communications network - Patent 5515369
		If there is traffic at that frequency, the transmitter waits an interval and the transmitter and receiver both hop to the next frequency in the pattern and the transmitter listens again.
		Once a frequency is found with no traffic, the transmitter sends a poll packet, and when that poll packet is acknowledged, the transmitter sends a data packet before the hop to the next frequency.
		Frequency mask 20 is a mask received from an acquiring node indicating channels that are to be eliminated from the channel list, with a zero indicating channels to be eliminated and a one indicating channels used by the source node.
	www.freepatentsonline.com /5515369.html (3016 words)

	Frequency Hopping vs. Direct Sequence Spread Spectrum Techniques (Site not responding. Last check: 2007-10-21)
		The frequency hopping physical layer is required to hop across the 2.4GHz ISM band covering 79 channels.
		Frequency Hopping Spread Spectrum systems may have data speed limitations and be shorter in range.
		Frequency hopping spread spectrum systems are good for high user density areas such as corporate offices, education and healthcare applications.
	www.bazar-e.net /raylink/docs/doc_frecuencehoping.htm (1152 words)

	Bluetooth; What´s the advantage of frequency-hopping?
		The mapping from the input to a particular hop frequency is performed in the selection box.
		A inquiry response sequence covering 32 (16) unique response frequencies that are all in a one-to-one correspondence to the current inquiry hopping sequence.
		A channel hopping sequence with very long period, which does not show repetitive patterns over a short time interval, but which distributes the hop frequencies equally.
	www.swedetrack.com /images/bluet11.htm (398 words)

	Frequency hopping communication method and apparatus for modifying frequency hopping sequence in accordance with ...
		The spectrum is arranged into a plurality of segments, with each segment corresponding to a subset of the frequencies, preferably a contiguous subset of the frequencies.
		The communication device receives data over a sequence of hopping frequencies from the other party, with each of the hopping frequencies being part of a used segment from the plurality of segments.
		A method for performing frequency hopping communication with another party over an available spectrum of frequencies, the spectrum being arranged into a plurality of segments, each of the segments comprising a subset of the available spectrum including multiple possible hopping frequencies, the method comprising the steps of:
	www.delphion.com /details?pn=US06115407__ (571 words)

	Frequency Hopping verus Direct Sequence Spread Spectrum (Site not responding. Last check: 2007-10-21)
		Frequency hop systems generally possess a large processing gain which allows the systems to operate with a low signal-to-noise ratio at the input of the receiver.
		Since a frequency hop signal generally has numerous frequency slots, the only time a narrow band jammer affects signal reception is when the signal hops to a frequency slot that is occupied by the jammer.
		Frequency hop systems can be used for multiple access systems; time division, frequency division and code division multiple access systems can all employ frequency hop signals.
	www.qsl.net /n9zia/wireless/fhss_vs_dsss.html (1461 words)

	Automatic transmission power level control method in a frequency hopping communication system (US6115408)
		The present invention is an apparatus and method thereof for performing frequency hopping communication with another party over a subset of hopping frequencies from available frequencies.
		The spectrum is arranged into a plurality of segments, with each segment corresponding to a subset of the spectrum of frequencies, preferably a contiguous subset of the spectrum.
		Frequency hopping communication method and apparatus changing a hopping frequency as a result of a counted number of errors
	www.delphion.com /details?pn=US06115408__ (550 words)

	Frequency Hopping Spread Spectrum - Wikipedia
		Frequency Hopping Spread Spectrum (FHSS) ist ein Frequenzspreizverfahren für die drahtlose Datenübertragung.
		Generell wechselt hier die Trägerfrequenz frequentiv und diskret.
		Fast Hopping: Hier wird maximal 1 bit pro Frequenzsprung übertragen, es können aber durchaus auch 3 Frequenzsprünge innerhalb eines Bits stattfinden.
	de.wikipedia.org /wiki/FHSS (135 words)

	BluetoothNews: Cover Story
		Suddenly she realized that if the radio on the ship and the radio in a torpedo could keep switching frequencies in sync with each other, it would be impossible for an enemy to jam unless they knew the pattern.
		The first implementation of frequency hopping was used to secure ship-to-ship communications during the blockade of Cuba in what has become known as “The Cuban Missile Crisis”.
		Today, frequency hopping, and its more complex sibling: direct sequence spread spectrum, are no longer classified government secrets, but common elements of modern electronic communications.
	www.bluetoothnews.com /hedy_lamarr_story.htm (1890 words)

	Encyclopedia: Frequency-hopping spread spectrum (Site not responding. Last check: 2007-10-21)
		Spread-spectrum telecommunications This is a technique in which a signal is transmitted in a bandwidth considerably greater than the frequency content of the original information.
		Carrier frequency is the fundamental frequency used in both amplitude modulation and frequency modulation i.
		Although it is widely used as a measure of the loudness of sound, the decibel (dB) is more generally a measure of the ratio between two quantities, and can be used to express a wide variety of measurements in acoustics and electronics.
	www.nationmaster.com /encyclopedia/Frequency_hopping-spread-spectrum (1415 words)

	Bluetooth Glossary
		This is a pseudo-random sequence of 79 (23 for the 23MHz system) frequencies, The frequency is calculated using the BD_ADDR of the master of the piconet.
		The channel hopping sequence has a very long period length, does not show repetitive patterns over a short time interval, but which distributes the hop frequencies equally over the 79 (23 for the 23MHz system) MHz during a short time interval.See also Frequency sequence.
		This is a sequence of 32 (16 for the 23MHz system) frequencies, The frequency is calculated using the GIAC LAP or the DIAC LAP.
	www.palowireless.com /infotooth/glossary.asp (5094 words)

	Fixed frequency transceiver for use in a frequency hopping system - US Patent 6751251 (Site not responding. Last check: 2007-10-21)
		Because of this pattern of frequency changes or hops, to an unintended receiver, FHSS signals appear to be short-duration interference bursts.
		Even though frequency synthesizers represent a significant portion of the overall system cost, they are necessary for full performance of the FHSS systems (or also referred to as frequency-hopping systems).
		Therefore, when node 302 is ready to transmit data at one of the frequency channels in its frequency hop pattern, node 302 first verifies the availability of that frequency channel for transmission.
	www.patentstorm.us /patents/6751251.html (3675 words)

	Omnispread Communications, Inc. - Direct Sequence vs. Frequency Hopping (Site not responding. Last check: 2007-10-21)
		The direct sequence and frequency hopping are the most commonly used methods for the spread spectrum technology.
		The frequency hopping technique does not spread the signal, as a result, there is no processing gain.
		The frequency hopper is also more difficult to synchronize the receiver to the transmitter because both the time and frequency need to be in tune.
	www.omnispread.com /TECHNOLOGY/ds-fh.html (914 words)

	Frequency Hopping (Site not responding. Last check: 2007-10-21)
		Frequency hopping, which today is used extensively in military communications, means broadcasting a signal (which might carry commands for directing a torpedo) over a seemingly random series of radio frequencies, switching from frequency to frequency at split-second intervals.
		A receiver hopping between frequencies in sync with the transmitter can pick up the message, while any eavesdroppers will only hear random blips.
		An attempt to jam such a signal—jamming was and remains a drawback to radio control—will knock out only bits of it, often leaving enough untouched to do no harm at all.
	www.inventions.org /culture/female/popups/frequency.html (92 words)

	What is FHSS? - A Word Definition From the Webopedia Computer Dictionary
		FHSS is a transmission technology used in LAWN transmissions where the data signal is modulated with a narrowband carrier signal that "hops" in a random but predictable sequence from frequency to frequency as a function of time over a wide band of frequencies.
		The receiver must be set to the same hopping code and must listen to the incoming signal at the right time and correct frequency in order to properly receive the signal.
		Current FCC regulations require manufacturers to use 75 or more frequencies per transmission channel with a maximum dwell time (the time spent at a particular frequency during any single hop) of 400 ms.
	www.webopedia.com /TERM/F/FHSS.html (296 words)

	Frequency Hopping
		If the network were able to move us from slot to slot, and from frequency to frequency, then we could randomize the effects of interference.
		By jumping from frequency to frequency we may only experience problematic multipath for very short periods of time, once again giving the error correction algorithms the chance to clean it up.
		From what I’ve been able to gather from testing Microcell Connexions in the areas where Frequency Hopping is implemented, and by comparing that to areas where it is not, I would have to say that it works exceedingly well.
	www.arcx.com /sites/FrequencyHopping.htm (772 words)

	Frequency Hopping vs Direct Sequence
		The frequency of the carrier is periodically modified (hopped) following a specific spreading code.(In FHSS systems, the spreading code is a list of frequencies to be used for the carrier signal).
		Redundancy is achieved in FHSS systems by the possibility to execute re-transmissions on frequencies (hops) not affected by noise.
		The FHSS receiver will not be able to operate at that specific hop, but, after hopping to a different frequency, the narrow filter will reject the interfering signal, and the hopper will execute reception without being disturbed...
	www.cs.technion.ac.il /Labs/Lccn/projects/spring99/wireless/frequenc.htm (2882 words)

	Frequency hopping (Site not responding. Last check: 2007-10-21)
		Frequency Hopping The Patent Wiring Diagrams of distribution the torpedo guidance signal over several frequencies to thus protect it from enemy jamming.
		Frequency hopping is one of spread spectrum technique, Spreading process on Frequency hopping, with canged carrier frequency perodically.
		Frequency hopping means the repeated frequency change during a single call.
	rfid.sitesarea.com /q/rfid-frequency-hopping.htm (973 words)

	What is this frequency-hopping?
		By changing frequencies every 20 milliseconds, the GeneralCommunications.com FHSS radios avoid most interference that may be present within its frequency band, and by sending data over and over again, gets the data through, even if some packets may have been lost to interference.
		The spreading of a direct sequence signal is a function of the chips per bit and the information transmitted by a spread spectrum radio using this method is recovered by multiplying the received signal with a copy of the code sequence.
		A pre-determined algorithm is utilized to maintain the synchronization between radios as they hop sequentially through a set pattern of frequencies determined by the algorithm.
	www.oksolar.com /communications/frequency_hopping.htm (2721 words)

	Story: FCC Permits Frequency Hopping Spread Spectrum Devices in the 2.4 GHz Band, 9/4/00.
		Story: FCC Permits Frequency Hopping Spread Spectrum Devices in the 2.4 GHz Band, 9/4/00.
		"Frequency hopping systems in the 2400 - 2483.5 MHz band may utilize hopping channels whose 20 dB bandwidth is greater than 1 MHz provided the systems use at least 15 non-overlapping channels.
		The total span of hopping channels shall be at least 75 MHz.
	www.techlawjournal.com /internet/20000904.asp (588 words)

	Frequency-hopping spread spectrum : Frequency hopping (Site not responding. Last check: 2007-10-21)
		Frequency-hopping spread spectrum (FHSS) is a spread-spectrum method of transmitting signals by rapidly switching a carrier among many frequency channels, using a sequence known to both transmitter and receiver.
		By virtue of these properties, spread-spectrum communication offers a third benefit: spread-spectrum transmissions can share a frequency band with conventional transmissions with minimal interference.
		Use of the Shannon-Hartley law shows that the signal to noise ratio (SNR) required for the carrier relative to the background decreases the wider the range of frequencies used for transmission.
	www.termsdefined.net /fr/frequency-hopping.html (394 words)

	Adaptive Frequency Hopping for Reduced Interference between Bluetooth® and Wireless LAN
		Version 1.2 of the Bluetooth Specification, being adopted in 2003, includes Adaptive Frequency Hopping, a technique proven to be an effective remedy to the problem of interference in WLAN and similar environments.
		This is done to avoid instances where the master transmits on a “good” channel while the slave responds on a “bad” one (or vice versa), as this would lead to several retransmissions.
		Devices using frequency hopping, however, such as other Bluetooth devices, are likely to cause just as much interference as they normally would.
	www.us.design-reuse.com /articles/article5715.html (1928 words)

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