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Radio | ghz ku band microwave downlink signal rooftop satellite dish antenna subscribers residence.microwave signal converted lower intermediate frequency dish conducted building coaxial cable settop box connected subscribers tv demodulated displayed.subscriber pays monthly fee.time government standard frequency time signal se... |
Radio | one use radio clocks watches include automated receiver periodically usually weekly receives decodes time signal resets watchs internal quartz clock correct time thus allowing small watch desk clock accuracy atomic clock.government time stations declining number gps satellites internet network time protocol ntp provide... |
Radio | radio link may full duplex bidirectional link using two radio channels people talk time cell phone.cell phone – portable wireless telephone connected telephone network radio signals exchanged local antenna cellular base station cell tower.service area covered provider divided small geographical areas called cells serve... |
Radio | cellphones highly automated full duplex digital transceiver using ofdm modulation using two digital radio channels carrying one direction bidirectional conversation well control channel handles dialing calls handing phone another cell tower.older g g g networks use frequencies uhf low microwave range mhz ghz.cell phone... |
Radio | major advantage much higher data rates previous cellular networks gbps times faster previous cellular technology g lte.higher data rates achieved partly using higher frequency radio waves higher microwave band ghz millimeter wave band around ghz.since frequencies shorter range previous cellphone bands cells smaller cel... |
Radio | order phone communicate satellite using small omnidirectional antenna firstgeneration systems use satellites low earth orbit – miles – km surface.orbital period minutes satellite view phone – minutes call handed another satellite one passes beyond local horizon.therefore large numbers satellites required ensure least o... |
Radio | often installed vehicles mobile units communicating dispatcher fixed base station.special systems reserved frequencies used first responder services police fire ambulance emergency services government services.systems made use commercial firms taxi delivery services.vhf systems use channels range – mhz – mhz.uhf system... |
Radio | general vhf systems longer range uhf require longer antennas.fm modulation mainly used digital systems dmr introduced.radiated power typically limited watts.systems fairly limited range usually miles .km depending terrain. |
Radio | repeaters installed tall buildings hills mountain peaks often used increase range desired cover larger area lineofsight.examples land mobile systems cb frs gmrs murs.modern digital systems called trunked radio systems digital channel management system using control channel automatically assigns frequency channels user ... |
Radio | system typical transmission range miles km aircraft flying cruising altitude.flights remote areas transoceanic airline flights aircraft use hf band channels inmarsat iridium satphone satellites.military aircraft also use dedicated uhfam band ..mhz.marine radio – mediumrange transceivers ships used shiptoship shiptoair ... |
Radio | channels halfduplex fullduplex compatible telephone network allow users make telephone calls marine operator.amateur radio – longrange halfduplex twoway radio used hobbyists noncommercial purposes recreational radio contacts amateurs volunteer emergency communication disasters contests experimentation.radio amateurs mu... |
Radio | addition radiotelephony amateurs radio operators still using morse code radiotelegraphy.oneway voice communication one way unidirectional radio transmission called simplex.baby monitor – cribside appliance parents infants transmits babys sounds receiver carried parent monitor baby parts house.transmit fm .. |
Radio | ...mhz low power.many baby monitors duplex channels parent talk baby video cameras show picture baby called baby cam.wireless microphone – batterypowered microphone shortrange transmitter handheld worn persons body transmits sound radio nearby receiver unit connected sound system. |
Radio | wireless microphones used public speakers performers television personalities move freely without trailing microphone cord.analog models transmit fm unused portions television broadcast frequencies vhf uhf bands.models transmit two frequency channels diversity reception prevent nulls interrupting transmission performer... |
Radio | data communication wireless networking – automated radio links transmit digital data computers wireless devices using radio waves linking devices together transparently computer network.computer networks transmit form data addition email web pages also carry phone calls voip audio video content called streaming media.s... |
Radio | wireless routers public places like libraries hotels coffee shops create wireless access points hotspots allow public access internet portable devices like smartphones tablets laptops.device exchanges data using wireless modem wireless network interface controller automated microwave transmitter receiver omnidirectiona... |
Radio | maximum indoor range ft .ghz ft ghz.wireless wan wireless wide area network wwan – variety technologies provide wireless internet access wider area wifi networks – office building campus neighborhood entire city.common technologies used cellular modems exchange computer data radio cell towers satellite internet access ... |
Radio | system uses frequencyhopping spread spectrum transmission successive data packets transmitted pseudorandom order one mhz bluetooth channels ..ghz ism band.allows bluetooth networks operate presence noise wireless devices bluetooth networks using frequencies since chance another device attempting transmit frequency time... |
Radio | node communicates neighboring nodes packets data passed node node reach destination.uses x. network protocol.packet radio systems used limited degree commercial telecommunications companies amateur radio community.text messaging texting – service cell phones allowing user type short alphanumeric message send another ph... |
Radio | since antennas must lineofsight distances limited visual horizon – miles – km.microwave links used private business data wide area computer networks wans telephone companies transmit long distance phone calls television signals cities.telemetry – automated oneway simplex transmission measurements operation data remote ... |
Radio | receives interrogation pulse radio waves nearby reader unit tag transmits back id number used inventory goods.passive tags common type chip powered radio energy received reader rectified diode small grain rice.incorporated products clothes railroad cars library books airline baggage tags implanted skin pets livestock m... |
Radio | ghz ism bands short range.active tags powered battery larger transmit stronger signal giving range hundreds meters.submarine communication – submerged submarines cut ordinary radio communication military command authorities conductive seawater.however radio waves low enough frequencies vlf khz elf khz bands able penetr... |
Radio | communication channel oneway since long antennas needed transmit vlf elf waves cannot fit submarine.vlf transmitters use miles long wire antennas like umbrella antennas.nations use elf transmitters operating around hz communicate submarines lower depths.use even larger antennas called ground dipoles consisting two grou... |
Radio | communication spacecraft involves longest transmission distances radio links billions kilometers interplanetary spacecraft.order receive weak signals distant spacecraft satellite ground stations use large parabolic dish antennas metres ft diameter extremely sensitive receivers.high frequencies microwave band used since... |
Radio | used microwaves used telecommunications travel line sight cannot propagate around curve earth.january communications satellites earth orbit.geostationary orbit miles km equator satellite appears stationary point sky satellite dish antennas ground stations aimed permanently spot move track it.satellite ground station mi... |
Radio | satellite transponder receives signal translates different downlink frequency avoid interfering uplink signal retransmits another ground station may widely separated first.downlink signal demodulated telecommunications traffic carries sent local destinations landlines.communication satellites typically several dozen tr... |
Radio | .ghz ku band transmitted watts received relatively small – cm – satellite dishes mounted outside buildings.radar radar radiolocation method used locate track aircraft spacecraft missiles ships vehicles also map weather patterns terrain.radar set consists transmitter receiver.transmitter emits narrow beam radio waves sw... |
Radio | beam strikes target object radio waves reflected back receiver.direction beam reveals objects location.since radio waves travel constant speed close speed light measuring brief time delay outgoing pulse received echo range target calculated.targets often displayed graphically map display called radar screen.doppler rad... |
Radio | parabolic dish antennas widely used.radars transmitting antenna also serves receiving antenna called monostatic radar.radar uses separate transmitting receiving antennas called bistatic radar.airport surveillance radar – aviation radar main tool air traffic control.rotating dish antenna sweeps vertical fanshaped beam m... |
Radio | – .ghz microwave band.large airports radar image displayed multiple screens operations room called tracon terminal radar approach control air traffic controllers direct aircraft radio maintain safe aircraft separation.secondary surveillance radar – aircraft carry radar transponders transceivers triggered incoming radar... |
Radio | since radar cannot measure aircrafts altitude accuracy transponder also transmits back aircrafts altitude measured altimeter id number identifying aircraft displayed radar screen.electronic countermeasures ecm – military defensive electronic systems designed degrade enemy radar effectiveness deceive false information p... |
Radio | radar mounted aircraft spacecraft radar antenna radiates beam radio waves sideways right angles direction motion toward ground.processing return radar signal motion vehicle used simulate large antenna giving radar higher resolution.groundpenetrating radar – specialized radar instrument rolled along ground surface cart ... |
Radio | speed guns use x band ku band.radiolocation radiolocation generic term covering variety techniques use radio waves find location objects navigationglobal navigation satellite system gnss satnav system – system satellites allows geographical location earth latitude longitude altitudeelevation determined high precision w... |
Radio | satellite onboard atomic clock transmits continuous radio signal containing precise time signal well current position.two frequencies used ..ghz.since velocity radio waves virtually constant delay radio signal satellite proportional distance receiver satellite. |
Radio | receiving signals least four satellites gps receiver calculate position earth comparing arrival time radio signals.since satellites position known precisely given time delay position receiver calculated microprocessor receiver.position displayed latitude longitude marker electronic map.gps receivers incorporated almost... |
Radio | .mhz vhf band.automated navigational instrument aircraft displays bearing nearby vor transmitter.vor beacon transmits two signals simultaneously different frequencies.directional antenna transmits beam radio waves rotates like lighthouse fixed rate times per second. |
Radio | directional beam facing north omnidirectional antenna transmits pulse.measuring difference phase two signals aircraft determine bearing radial station accurately.taking bearing two vor beacons aircraft determine position called fix accuracy metres ft. vor beacons also distance measuring capability called distance measu... |
Radio | allows aircraft determine location fix one vor beacon.since lineofsight vhf frequencies used vor beacons range miles aircraft cruising altitude.tacan similar military radio beacon system transmits – mhz combined vor tacan beacon called vortac.vor beacons worldwide number declining aviation switches rnav system relies g... |
Radio | taking bearings two beacons determine position.ndbs use frequencies khz lf mf bands propagate beyond horizon ground waves skywaves much farther vor beacons.transmit callsign consisting one morse code letters identifier.emergency locator beacon – portable battery powered radio transmitter used emergencies locate airplan... |
Radio | latest generation emergency position indicating rescue beacons epirbs contain gps receiver broadcast rescue teams exact location within meters.cospassarsat – international humanitarian consortium governmental private agencies acts dispatcher search rescue operations.operates network satellites carrying radio receivers ... |
Radio | military forces use rdf locate enemy forces tactical radio transmissions counterintelligence services use locate clandestine transmitters used espionage agents governments use locate unlicensed transmitters interference sources.older rdf receivers used rotatable loop antennas antenna rotated radio signal strength weake... |
Radio | vhf band typically used since antennas band fairly compact.receiver directional antenna typically small yagi rotated received signal strongest point antenna pointing direction animal.sophisticated systems used recent years use satellites track animal geolocation tags gps receivers record transmit log animals location.r... |
Radio | unmanned spacecraft example remote controlled machines controlled commands transmitted satellite ground stations.handheld remote controls used control consumer electronics products like televisions dvd players actually operate infrared light rather radio waves examples radio remote control.security concern remote contr... |
Radio | pilot uses aircraft controls like joystick steering wheel create control signals transmitted drone radio control flight surfaces engine.telemetry system transmits back video image camera drone allow pilot see aircraft going data gps receiver giving realtime position aircraft.uavs sophisticated onboard automatic pilot s... |
Radio | fob must close vehicle typically within meters.north america japan use frequency mhz europe uses .mhz.models also remotely start engine warm car.security concern keyless entry systems replay attack thief uses special receiver code grabber record radio signal opening later replayed open door. |
Radio | prevent keyless systems use rolling code system pseudorandom number generator remote control generates different random key time used.prevent thieves simulating pseudorandom generator calculate next key radio signal also encrypted.garage door opener – shortrange handheld transmitter open close buildings electrically op... |
Radio | recent transmitters use .ghz ism band multiple control channels modulated pwm pcm fsk.wireless doorbell – residential doorbell uses wireless technology eliminate need run wires building walls.consists doorbell button beside door containing small battery powered transmitter.doorbell pressed sends signal receiver inside ... |
Radio | ghz ism band.frequency channel used usually changed owner case another nearby doorbell using channel.jamming radio jamming deliberate radiation radio signals designed interfere reception radio signals.jamming devices called signal suppressors interference generators jammers.during wartime militaries use jamming interfe... |
Radio | jamming usually accomplished powerful transmitter generates noise frequency target transmitter.us federal law prohibits nonmilitary operation sale type jamming devices including ones interfere gps cellular wifi police radars.scientific research radio astronomy scientific study radio waves emitted astronomical objects.r... |
Radio | rf front end electronics receiver often cooled liquid nitrogen reduce thermal noise.multiple antennas often linked together arrays function single antenna increase collecting power.long baseline interferometry vlbi radio telescopes different continents linked achieve resolution antenna thousands miles diameter.remote s... |
Radio | etymology word radio derived latin word radius meaning spoke wheel beam light ray.first applied communications suggestion french scientist ernest mercadier alexander graham bell adopted radiophone meaning radiated sound alternate name photophone optical transmission system.however invention would widely adopted.followi... |
Radio | radio prefix later used form additional descriptive compound hyphenated words especially europe.example early british publication practical engineer included reference radiotelegraph radiotelegraphy french text berlin radiotelegraphic conventions includes phrases radiotélégraphique radiotélégrammes.the use radio standa... |
Radio | although translation berlin convention used terms wireless telegraph wireless telegram began promote use radio instead.term started become preferred general public introduction broadcasting.word broadcasting originated agricultural term meaning roughly scattering seeds widely.british commonwealth countries continued co... |
Time of arrival | history see history radio invention radio timeline radio history broadcasting see also outline radioelectromagnetic radiation healthradio quiet zone references external linksusage many radiolocation systems use toa measurements perform geopositioning via truerange multilateration.true range distance directly calculated... |
Time of arrival | inaccuracy clock synchronization translates directly imprecise location.with two signals different frequency hence different speed.sound ranging lightning strike works way speed light sound velocity.via measurement triggering common reference point.without direct synchronisation compensation clock phase differences two... |
Computer network | contrast faulty explanations concept may applied well ieee ..acss ieee ..auwb modulation.see also angle arrivalgsm localizationrangingtriangulation references external links seminar security mobile communication held communication security cosy group ruhruniversity bochum germanycomputers use common communication proto... |
Computer network | history computer networking may considered branch computer science computer engineering telecommunications since relies theoretical practical application related disciplines.computer networking influenced wide array technology developments historical milestones.in late network computers built u.s. military semiautomati... |
Computer network | mccarthy instrumental creation three earliest timesharing systems compatible timesharing system bbn timesharing system dartmouth time sharing system .in anatoly kitov proposed central committee communist party soviet union detailed plan reorganisation control soviet armed forces soviet economy basis network computing c... |
Computer network | early leonard kleinrock carried mathematical work model performance packetswitched networks underpinned development arpanet.theoretical work hierarchical routing late student farouk kamoun remains critical operation internet today.in commercial services first deployed public data networks europe began using x. late spr... |
Computer network | ethernet supported transmission speeds gbits.subsequently higher speeds gbits added .scaling ethernet contributing factor continued use.use computer network extends interpersonal communications electronic means various technologies email instant messaging online chat voice video telephone calls video conferencing.netwo... |
Computer network | users may access use resources provided devices network printing document shared network printer use shared storage device.network allows sharing files data types information giving authorized users ability access information stored computers network.distributed computing uses computing resources across network accompl... |
Computer network | control information provides data network needs deliver user data example source destination network addresses error detection codes sequencing information.typically control information found packet headers trailers payload data between.with packets bandwidth transmission medium better shared among users network circui... |
Computer network | longer message may fragmented transferred packets arrive reassembled construct original message.network topology physical geographic locations network nodes links generally relatively little effect network topology interconnections network significantly affect throughput reliability.many technologies bus star networks ... |
Computer network | layout used original ethernet called base base.still common topology data link layer although modern physical layer variants use pointtopoint links instead forming star tree.star network nodes connected special central node.typical layout found small switched ethernet lan client connects central network switch logicall... |
Computer network | example fddi network topology ring physical topology often star neighboring connections routed via central physical location.physical layout completely irrelevant however common ducting equipment locations represent single points failure due issues like fires power failures flooding.overlay network overlay network virt... |
Computer network | topology overlay network may often differ underlying one.example many peertopeer networks overlay networks.organized nodes virtual system links run top internet.overlay networks around since invention networking computer systems connected telephone lines using modems data network existed.the striking example overlay ne... |
Computer network | address resolution routing means allow mapping fully connected ip overlay network underlying network.another example overlay network distributed hash table maps keys nodes network.case underlying network ip network overlay network table actually map indexed keys.overlay networks also proposed way improve internet routi... |
Computer network | academic research includes end system multicast resilient routing quality service studies among others.network links transmission media often referred literature physical medium used link devices form computer network include electrical cable optical fiber free space.osi model software handle media defined layers — phy... |
Computer network | wired following classes wired technologies used computer networking.coaxial cable widely used cable television systems office buildings worksites local area networks.transmission speed ranges million bits per second million bits per second.itut g.hn technology uses existing home wiring coaxial cable phone lines power l... |
Computer network | twisted pair cabling comes two forms unshielded twisted pair utp shielded twistedpair stp.form comes several category ratings designed use various scenarios.an optical fiber glass fiber.carries pulses light represent data via lasers optical amplifiers.advantages optical fibers metal wires low transmission loss immunity... |
Computer network | optic fibers used long runs cable carrying high data rates used undersea cables interconnect continents.two basic types fiber optics singlemode optical fiber smf multimode optical fiber mmf.singlemode fiber advantage able sustain coherent signal dozens even hundred kilometers.multimode fiber cheaper terminate limited h... |
Computer network | terrestrial microwave – terrestrial microwave communication uses earthbased transmitters receivers resembling satellite dishes.terrestrial microwaves low gigahertz range limits communications lineofsight.relay stations spaced approximately miles km apart.communications satellites – satellites also communicate via micro... |
Computer network | systems divide region covered multiple geographic areas.area served lowpower transceiver.radio spread spectrum technologies – wireless lans use highfrequency radio technology similar digital cellular.wireless lans use spread spectrum technology enable communication multiple devices limited area.ieee .defines common fla... |
Computer network | cases lineofsight propagation used limits physical positioning communicating devices.extending internet interplanetary dimensions via radio waves optical means interplanetary internet.ip avian carriers humorous april fools request comments issued rfc .implemented real life .the last two cases large roundtrip delay time... |
Computer network | example nic may connector accepting cable aerial wireless transmission reception associated circuitry.in ethernet networks network interface controller unique media access control mac address—usually stored controllers permanent memory.avoid address conflicts network devices institute electrical electronics engineers i... |
Computer network | repeaters hubs repeater electronic device receives network signal cleans unnecessary noise regenerates it.signal retransmitted higher power level side obstruction signal cover longer distances without degradation.twisted pair ethernet configurations repeaters required cable runs longer meters.fiber optics repeaters ten... |
Computer network | result many network architectures limit number repeaters used network e.g.ethernet rule.an ethernet repeater multiple ports known ethernet hub.addition reconditioning distributing network signals repeater hub assists collision detection fault isolation network.hubs repeaters lans largely obsoleted modern network switch... |
Computer network | bridges two ports switch thought multiport bridge.switches normally numerous ports facilitating star topology devices cascading additional switches.bridges switches operate data link layer layer osi model bridge traffic two network segments form single local network.devices forward frames data ports based destination m... |
Computer network | routers router internetworking device forwards packets networks processing addressing routing information included packet.routing information often processed conjunction routing table.router uses routing table determine forward packets require broadcasting packets inefficient big networks.modems modems modulatordemodul... |
Computer network | early modems modulated audio signals sent standard voice telephone line.modems still commonly used telephone lines using digital subscriber line technology cable television systems using docsis technology.firewalls firewall network device software controlling network security access rules.firewalls inserted connections... |
Computer network | vital role firewalls play network security grows parallel constant increase cyber attacks.communication protocols communication protocol set rules exchanging information network.communication protocols various characteristics.may connectionoriented connectionless may use circuit mode packet switching may use hierarchic... |
Computer network | important example protocol stack http world wide web protocol running tcp ip internet protocols ieee .wifi protocol.stack used wireless router home users personal computer user surfing web.there many communication protocols described below.common protocols internet protocol suite internet protocol suite also called tcp... |
Computer network | core protocol suite defines addressing identification routing specifications internet protocol version ipv ipv next generation protocol much enlarged addressing capability.internet protocol suite defining set protocols internet.ieee ieee family ieee standards dealing local area networks metropolitan area networks.compl... |
Computer network | operate mostly layers osi model.for example mac bridging ieee .d deals routing ethernet packets using spanning tree protocol.ieee .q describes vlans ieee .x defines portbased network access control protocol forms basis authentication mechanisms used vlans also found wlans – home user sees user enter wireless access key... |
Computer network | wireless lan wireless lan based ieee .standards also widely known wlan wifi probably wellknown member ieee protocol family home users today.ieee .shares many properties wired ethernet.sonetsdh synchronous optical networking sonet synchronous digital hierarchy sdh standardized multiplexing protocols transfer multiple di... |
Computer network | originally designed transport circuit mode communications variety different sources primarily support circuitswitched digital telephony.however due protocol neutrality transportoriented features sonetsdh also obvious choice transporting asynchronous transfer mode atm frames.asynchronous transfer mode asynchronous trans... |
Computer network | atm similarities circuit packet switched networking.makes good choice network must handle traditional highthroughput data traffic realtime lowlatency content voice video.atm uses connectionoriented model virtual circuit must established two endpoints actual data exchange begins.atm still plays role last mile connection... |
Computer network | routing performed many kinds networks including circuit switching networks packet switched networks.in packetswitched networks routing protocols direct packet forwarding transit logically addressed network packets source toward ultimate destination intermediate nodes.intermediate nodes typically network hardware device... |
Computer network | multipath routing techniques enable use multiple alternative paths.routing narrow sense term often contrasted bridging assumption network addresses structured similar addresses imply proximity within network.structured addresses allow single routing table entry represent route group devices.large networks structured ad... |
Computer network | geographic scale networks may characterized many properties features physical capacity organizational purpose user authorization access rights others.another distinct classification method physical extent geographic scale.nanoscale networka nanoscale communication network key components implemented nanoscale including ... |
Computer network | reach pan typically extends meters.wired pan usually constructed usb firewire connections technologies bluetooth infrared communication typically form wireless pan.local area networka local area network lan network connects computers devices limited geographical area home school office building closely positioned group... |
Computer network | current ethernet ieee .lan technologies operate data transfer rates gbits standardized ieee .currently gbits ethernet developed.a lan connected wan using router.home area networka home area network han residential lan used communication digital devices typically deployed home usually small number personal computers acc... |
Computer network | san typically network storage devices generally accessible local area network devices.cost complexity sans dropped early levels allowing wider adoption across enterprise small mediumsized business environments.campus area networka campus area network made interconnection lans within limited geographical area.networking... |
Computer network | equipment ties together departmental networks constitutes network backbone.designing network backbone network performance network congestion critical factors take account.normally backbone networks capacity greater individual networks connected it.another example backbone network internet backbone massive global system... |
Computer network | wan technologies generally function lower three layers osi reference model physical layer data link layer network layer.enterprise private networkan enterprise private network network single organization builds interconnect office locations e.g.production sites head offices remote offices shops share computer resources... |
Computer network | vpns example used separate traffic different user communities underlying network strong security features.vpn may besteffort performance may defined service level agreement sla vpn customer vpn service provider.generally vpn topology complex pointtopoint.global area networka global area network gan network used support... |
Computer network | private enterprise networks may use combination intranets extranets.may also provide network access internet single owner permits virtually unlimited global connectivity.intranet intranet set networks control single administrative entity.intranet uses ip protocol ipbased tools web browsers file transfer applications.ad... |
Computer network | commonly intranet internal lan organization.large intranet typically least one web server provide users organizational information.intranet also anything behind router local area network.extranet extranet network also administrative control single organization supports limited connection specific external network.examp... |
Computer network | entities necessarily trusted security standpoint.network connection extranet often always implemented via wan technology.internet internetwork connection multiple different types computer networks form single computer network layering top different networking software connecting together using routers.the internet larg... |
Computer network | successor advanced research projects agency network arpanet developed darpa united states department defense.internet utilizes copper communications optical networking backbone enable world wide web www internet things video transfer broad range information services.participants internet use diverse array methods sever... |
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