Wireless LAN Technology - Lecture 32

Wireless LAN TechnologyLecture 32Wireless LAN IntroductionThe proliferation of laptop computers and other mobile devices (PDAs and cell phones) created an obvious application level demand for wireless Local Area Networking.Companies jumped in, quickly developing incompatible wireless products in the 1990’s.Industry decided to entrust standardization to IEEE committee that dealt with wired LANs IEEE 802 committee!!2Defining a WLAN(Wireless Local Area Network) A communications network that provides connectivity to wireless devices within a limited geographic area. "Wi-Fi" is the universal standard for wireless networks and is the wireless equivalent of wired Ethernet networks. In the office, Wi-Fi networks are adjuncts to the wired networks. At home, a Wi-Fi network can serve as the only network since all laptops and many printers come with Wi-Fi built in, and Wi-Fi can be added to desktop computers via USB.Wi-Fi is achieved with a wireless base station, called an "access point." Its antennas transmit and receive a radio frequency within a range of 30 to 150 feet through walls and other non-metal barriers. 3WLAN Design GoalsGlobal, seamless operationLow power for battery use No special permissions or licenses needed to use the LAN Robust transmission technologySimplified spontaneous cooperation at meetings Easy to use for everyone, simple management Protection of investment in wired networks Security (no one should be able to read my data), privacy (no one should be able to collect user profiles), safety (low radiation)Transparency concerning applications and higher layer protocols, but also location awareness if necessary45Early Wireless LANsMany standards = No standardsLimited or no encryption.5 to 2 Mbps throughputHigh NIC costHigh AP costLimited roaming6Modern Wireless LANsIEEE standards based128 bit encryption≥ 11 Mbps throughputLow NIC costLow AP costIntegrated roaming7Pro and Cons of WLANAdvantagesVery flexible within the reception area Ad-hoc networks without previous planning possible(almost) no wiring difficulties (e.g. historic buildings, firewalls)More robust against disasters like, e.g., earthquakes, fire - or users pulling a plug... DisadvantagesTypically very low bandwidth compared to wired networks due to shared mediumMany proprietary solutions, especially for higher bit-rates, standards take their time (e.g. IEEE 802.11n)Products have to follow many national restrictions if working wireless, it takes a vary long time to establish global solutions like, e.g., IMT-20008WLAN DeploymentsMedical ProfessionalsEducationTemporary SituationsAirlinesSecurity StaffEmergency Centers910Wireless LAN ApplicationsLAN ExtensionCross-building interconnectNomadic Access Ad hoc networking11LAN ExtensionWireless LAN linked into a wired LAN on same premisesWired LAN BackboneSupport servers and stationary workstations Wireless LANStations in large open areasManufacturing plants, stock exchange trading floors, and warehouses12Single Cell LAN Extension13Multiple-cell Wireless LAN14Cross-Building InterconnectConnect LANs in nearby buildingsWired or wireless LANsPoint-to-point wireless link is usedDevices connected are typically bridges or routers1516Cross-Building InterconnectConnect LANs in nearby buildingsWired or wireless LANsPoint-to-point wireless link is usedDevices connected are typically bridges or routersCisco Aironet 1300 and 1400 SeriesWireless Bridges AccessWireless link between LAN hub and mobile data terminal equipped with antennaLaptop computer or notepad computerUses:Transfer data from portable computer to office serverExtended environment such as campususers move around with portable computersaccess to servers on wired LAN17Nomadic Access – Example18Ad Hoc NetworkingTemporary peer-to-peer network set up to meet immediate needExample:Group of employees with laptops convene for a meeting; employees link computers in a temporary network for duration of meeting19Wireless LAN RequirementsThroughputNumber of nodesConnection to backbone LANService areaBattery power consumptionTransmission robustness and securityCollocated network operationLicense-free operationHandoff/roamingDynamic configuration20Wireless LAN RequirementsThroughput. The medium access-control (MAC) protocol should make as efficient use as possible of the wireless medium to maximize capacity. Number of nodes. Wireless LANs may need to support hundreds of nodes across multiple cells. Connection to backbone LAN. In most cases, interconnection with stations on a wired backbone LAN is required. For infrastructure wireless LANs, this is easily accomplished through the use of control modules that connect to both types of LANs. There may also need to be accommodation for mobile users and ad hoc wireless networks. Service area. A typical coverage area for a wireless LAN has a diameter of 100 to 300 m. 21Wireless LAN RequirementsBattery power consumption. Mobile workers use battery-powered workstations that need to have a long battery life when used with wireless adapters. This suggests that a MAC protocol that requires mobile nodes to monitor access points constantly or engage in frequent handshakes with a base station is inappropriate. Typical wireless LAN implementations have features to reduce power consumption while not using the network, such as a sleep mode. 22Wireless LAN RequirementsTransmission robustness and security. Unless properly designed, a wireless LAN may be interference-prone and easily eavesdropped. The design of a wireless LAN must permit reliable transmission even in a noisy environment and should provide some level of security from eavesdropping. 23Wireless LAN RequirementsCollocated network operation. As wireless LANs become more popular, it's quite likely that two or more wireless LANs will operate in the same area or in some area where interference between the LANs is possible. Such interference may thwart the normal operation of a MAC algorithm and may allow unauthorized access to a particular LAN. 24Wireless LAN RequirementsLicense-free operation. Users would prefer to buy and operate wireless LAN products without having to secure a license for the frequency band used by the LAN. Handoff/roaming. The MAC protocol used in the wireless LAN should enable mobile stations to move from one cell to another. Dynamic configuration. The MAC addressing and network management aspects of the LAN should permit dynamic and automated addition, deletion, and relocation of end systems without disruption to other users.25Wireless LAN CategoriesInfrared (IR) LANsSpread spectrum LANsNarrowband microwave26Wireless LANsspread spectrum WLANsmostly operate in ISM (industrial, scientific, and medical) bandsno Federal Communications Commission (FCC) licensing is required in USAOFDM WLANsorthogonal frequency division multiplexingsuperior to spread spectrumoperate in 2.4 GHz or 5 GHz bandinfrared (IR) WLANsindividual cell of IR LAN limited to single roomIR light does not penetrate opaque walls27Strengths of Infrared Over Microwave RadioSpectrum for infrared virtually unlimitedPossibility of high data ratesInfrared spectrum unregulatedEquipment inexpensive and simpleReflected by light-colored objectsCeiling reflection for entire room coverageDoesn’t penetrate wallsMore easily secured against eavesdroppingLess interference between different rooms28Drawbacks of Infrared MediumIndoor environments experience infrared background radiationSunlight and indoor lightingAmbient radiation appears as noise in an infrared receiverTransmitters of higher power requiredLimited by concerns of eye safety and excessive power consumptionLimits range 29IR Data Transmission TechniquesDirected Beam InfraredOminidirectionalDiffused30Directed Beam InfraredUsed to create point-to-point linksRange depends on emitted power and degree of focusingFocused IR data link can have range of kilometersCross-building interconnect between bridges or routers31OminidirectionalSingle base station within line of sight of all other stations on LANStation typically mounted on ceilingBase station acts as a multiport repeaterCeiling transmitter broadcasts signal received by IR transceiversIR transceivers transmit with directional beam aimed at ceiling base unit32DiffusedAll IR transmitters focused and aimed at a point on diffusely reflecting ceilingIR radiation strikes ceiling Reradiated omnidirectionally Picked up by all receivers3334Spread Spectrum WLANConfigurationusually use multiple-cell arrangementadjacent cells use different center frequenciesConfigurationshubconnected to wired LANconnect to stations on wired LAN and in other cellsmay do automatic handoffpeer-to-peerno hubMAC algorithm such as CSMA used to control accessfor ad hoc LANs35Spread Spectrum WLANsTransmission Issues licensing regulations differ between countriesUSA FCC allows in ISM band:spread spectrum (1W), very low power (0.5W)902 - 928 MHz (915-MHz band)2.4 - 2.4835 GHz (2.4-GHz band)5.725 - 5.825 GHz (5.8-GHz band)2.4 GHz also in Europe and JapanInterferencemany devices around 900 MHz: cordless telephones, wireless microphones, and amateur radiofewer devices at 2.4 GHz; microwave ovenlittle competition at 5.8 GHz3637Narrowband Microwave LANsUse of a microwave radio frequency band for signal transmissionRelatively narrow bandwidthLicensedUnlicensed38Licensed Narrowband RFLicensed within specific geographic areas to avoid potential interferenceMotorola - 600 licenses in 18-GHz range Covers all metropolitan areasCan assure that independent LANs in nearby locations don’t interfereEncrypted transmissions prevent eavesdropping39Unlicensed Narrowband RFRadioLAN introduced narrowband wireless LAN in 1995Uses unlicensed ISM spectrumUsed at low power (0.5 watts or less)Operates at 10 Mbps in the 5.8-GHz bandRange = 50 m to 100 m4041Original 802.11 Physical Layer-DSSSDirect-sequence spread spectrum (DSSS)2.4 GHz ISM band at 1 Mbps and 2 Mbpsup to seven channels, each 1 Mbps or 2 Mbps, can be useddepends on bandwidth allocated by various national regulations13 in most European countriesone in Japaneach channel bandwidth 5 MHzencoding scheme DBPSK for 1-Mbps and DQPSK for 2-Mbps using an 11-chip Barker sequence42Original 802.11 Physical Layer-FHSSFrequency-hopping spread spectrum makes use of multiple channelssignal hopping between multiple channels based on a pseudonoise sequence1-MHz channels are usedhopping scheme is adjustable2.5 hops per second in United States6 MHz in North America and Europe5 MHz in Japantwo-level Gaussian FSK modulation for 1 Mbpsfour-level GFSK modulation used for 2 Mbps43Original 802.11 Physical Layer-Infraredomnidirectionalrange up to 20 m1 Mbps uses 16-PPM (pulse position modulation)4 data bit group mapped to one of 16-PPM symbolseach symbol a string of 16 bitseach 16-bit string has fifteen 0s and one binary 12-Mbps has each group of 2 data bits is mapped into one of four 4-bit sequenceseach sequence consists of three 0s and one binary 1intensity modulation is used for transmission44Comparison: infrared vs. radio transmissionInfrareduses IR diodes, diffuse light, multiple reflections (walls, furniture etc.)Advantagessimple, cheap, available in many mobile devicesno licenses neededsimple shielding possibleDisadvantagesinterference by sunlight, heat sources etc.many things shield or absorb IR light low bandwidthExampleIrDA (Infrared Data Association) interface available everywhereRadiotypically using the license free ISM band at 2.4 GHz Advantagesexperience from wireless WAN and mobile phones can be used coverage of larger areas possible (radio can penetrate walls, furniture etc.) Disadvantagesvery limited license free frequency bands shielding more difficult, interference with other electrical devicesExampleMany different products45Comparison: Infrastructure vs. ad-hoc Networksinfrastructure networkad-hoc networkAPAPAPwired networkAP: Access Point4647In response to lacking standards, IEEE developed the first internationally recognized wireless LAN standard – IEEE 802.11 IEEE published 802.11 in 1997, after seven years of workMost prominent specification for WLANsScope of IEEE 802.11 is limited to Physical and Data Link Layers.IEEE 802.11 Wireless LAN Standard48Appliance InteroperabilityFast Product DevelopmentStable Future MigrationPrice ReductionsThe 802.11 standard takes into account the following significant differences between wireless and wired LANs:Power ManagementSecurityBandwidthBenefits of 802.11 Standard49IEEE 802 LAN Standards FamilyIEEE 802.3CarrierSenseIEEE 802.4TokenBusIEEE 802.5TokenRingIEEE 802.11WirelessIEEE 802.2Logical Link Control (LLC)PHYOSI Layer 1(Physical)MacOSI Layer 2(Data Link)50802.11 Protocol Stack Part of the 802.11 protocol stack.51LiFiLiFi is transmission of data through illumination by taking the fiber out of fiber optics by sending data through a LED light bulb that varies in intensity faster than the human eye can follow.Li-Fi is the term some have used to label the fast and cheap wireless communication system, which is the optical version of Wi-Fi. The term was first used in this context by Harald Haas in his TED Global talk on Visible Light Communication. “At the heart of this technology is a new generation of high brightness light-emitting diodes52LiFiLIFI Solid-State Plasma Lighting53Comparison Between Current and Future Wireless Technology54SummaryWLAN ApplicationsWireless RequirementsWLAN ClassificationsDSSS and Frequency Hopping in WLANsIEEE Standardization802.11 Physical Layer FHSS802.11 Physical Layer DSSSComparison of Infrared with Radio TransmissionInfrastructure vs. ad-hoc Network802.11 Benefits802.11 Protocol Stack552nd Part of the LectureGNU Radio5657What is GNU Radio?Basic ConceptsGNU Radio Architecture & PythonDial Tone Example57What is GNU Radio?Software toolkit for signalprocessingSoftware radio constructionRapid developmentCognitive radioUSRP (Universal Software Radio Peripheral)‏Hardware frontend for sendingand receiving waveforms58GNU Radio ComponentsHardware FrontendHost ComputerRF Frontend(Daugtherboard)‏ADC/DAC andDigital Frontend(USRP)‏GNU RadioSoftware59GNU Radio SoftwareOpensource software (GPL)Don't know how something works? Take a look!Existing examples: 802.11b, Zigbee, ATSC (HDTV), OFDM, DBPSK, DQPSKFeaturesExtensive library of signal processing blocks(C++/ and assembly)‏Python environment for composing blocks (flow graph)‏60GNU Radio HardwareSends/receives waveformsUSRP FeaturesUSB 2.0 interface (480Mbps)‏FPGA (customizable)‏64Msps Digital to Analog converters (receiving)‏128Msps Analog to Digital converteres (transmitting)‏Daughterboards for different frequency rangesAvailable Daughterboard400-500Mhz, 800-1000Mhz, 1150-1450Mhz, 1.5-2.1Ghz, 2.3-2.9Ghz61GNU Radio Hardware SchematicRX/TXDaughterboardADC/DACHost ComputerFPGAUSBInterface6263Basics: BlocksSignal Processing BlockAccepts 0 or more input streamsProduces 0 or more output streamsSource: No inputnoise_source,signal_source,usrp_sourceSink: No outputsaudio_alsa_sink,usrp_sink64Basics: Data StreamsBlocks operate on streams of data1533794121265Basics: Data TypesBlocks operate on certain data typeschar, short, int, float, complexVectorsInput Signature:Data types for input streamsOutput Signature:Data types for output streamsTwo streamsof floatOne streamof complex66Basics: Flow GraphBlocks composed as a flow graphData stream flowing from sources to sinks6768GNU Radio Architecture68GNU radio has provided some useful APIsWhat we are interested in at this time is how to use the existing modules that has been provided in GNU radio project to communicate between two end systemsGNU Radio Architecture69GNU Radio Architecture - softwareHow these modules co-work?Signal processing block and flow-graphC++: Extensive library of signal processing blocksPerformance-critical modulesPython: Environment for composing blocks Glue to connect modulesNon performance-critical modules70GNU Radio Architecture – software(2)Python scripting language used for creating "signal flow graphs“C++ used for creating signal processing blocksAn already existing library of signaling blocksThe scheduler is using Python’s built-in module threading, to control the ‘starting’, ‘stopping’ or ‘waiting’ operations of the signal flow graph.71GNU Radio Architecture – software(3)72GNU Radio Companion73GNU Radio Companion (Cont'd)GNU Radio CompanionDesign flow graphsgraphicallyGenerate runnable codeDemonstration74Dial Tone Example Sine Generator (350Hz)‏Sine Generator (440Hz)‏Audio Sink75Dial Tone Example#!/usr/bin/env pythonfrom gnuradio import grfrom gnuradio import audiofrom gnuradio.eng_option import eng_optionfrom optparse import OptionParserclass my_top_block(gr.top_block): def __init__(self): gr.top_block.__init__(self)‏ parser = OptionParser(option_class=eng_option)‏ parser.add_option("-O", "--audio-output", type="string", default="", help="pcm output device name. E.g., hw:0,0")‏ parser.add_option("-r", "--sample-rate", type="eng_float", default=48000, help="set sample rate to RATE (48000)")‏ (options, args) = parser.parse_args ()‏ if len(args) != 0: parser.print_help()‏ raise SystemExit, 1 sample_rate = int(options.sample_rate)‏ ampl = 0.1 src0 = gr.sig_source_f (sample_rate, gr.GR_SIN_WAVE, 350, ampl)‏ src1 = gr.sig_source_f (sample_rate, gr.GR_SIN_WAVE, 440, ampl)‏ dst = audio.sink (sample_rate, options.audio_output)‏ self.connect (src0, (dst, 0))‏ self.connect (src1, (dst, 1))‏if __name__ == '__main__': try: my_top_block().run()‏ except KeyboardInterrupt: pass76SummaryWhat is GNU Radio?Basic ConceptsGNU Radio Architecture & PythonDial Tone Example77