1TDC 363TDC 363Introductions to Introductions to LANsLANs02/21/081TDC363-07Lecture 7Lecture 7Wireless LANWireless LANOutlineOutline•• WLAN Markets and Business CasesWLAN Markets and Business Cases•• WLAN StandardsWLAN Standards••WLAN Physical Layer WLAN Physical Layer 02/21/082TDC363-07WNy yWNy y•• WLAN MAC LayerWLAN MAC Layer•• WLAN SecurityWLAN Security•• WLAN Design and DeploymentWLAN Design and DeploymentThe Mobile Environment The Mobile Environment (ubiquitous)(ubiquitous)HeadquartersBranchOfficesSOHO02/21/083TDC363-07Wireless LANHomeHotSpotsConventionCentersHotelCustomerSites2Why Wireless LAN?Why Wireless LAN? MobilityMobility FlexibilityFlexibility Ease of deploymentEase of deployment Places where there is no cabling infrastructurePlaces where there is no cabling infrastructure02/21/084TDC363-07 CostCost Relatively low cost of deploymentRelatively low cost of deployment Continual drop in price for WLAN equipmentContinual drop in price for WLAN equipment PerformancePerformance Higher speed standardsHigher speed standards802.11 Protocol standards802.11 Protocol standardsLogical Link Control (LLC)02/21/085TDC363-07802.11infrared802.11FHSS802.11DSSS802.11aOFDM802.11bHR-DSSS802.11gOFDMMedia Access Control (MAC)802.11nMIMO802.11 Standards802.11 Standards 802.11 802.11 –– operations at 2.4 GHzoperations at 2.4 GHz 802.11a802.11a –– operations at 5GHzoperations at 5GHz 802.11b802.11b –– operations at 2.4GHzoperations at 2.4GHz 802.11d 802.11d –– aim to promote worldaim to promote world--wide use of 802.11wide use of 802.11 802.11e802.11e –– Supplement of Supplement of QoSQoS over 802.11over 802.11 802.11f 802.11f –– To achieve WAP interoperabilityTo achieve WAP interoperability 802.11g802.11g –– Improvement of 802.11b with 54MImprovement of 802.11b with 54M802 11h802 11hSliiiESliiiE02/21/086TDC363-07802.11h 802.11h ––Support regulatory provision in EuropeSupport regulatory provision in Europe 802.11i802.11i –– Support WLAN security (802.1X + more)Support WLAN security (802.1X + more) 802.11n802.11n -- Higher throughput improvements (theoretically up to 500M, Higher throughput improvements (theoretically up to 500M, practically up to 150M)practically up to 150M) 802.11s 802.11s –– metro wirelessmetro wireless 802.15 802.15 –– Personal Area NetworkPersonal Area Network 802.15.1802.15.1 -- BluetoothBluetooth 802.16 802.16 –– Broadband Wireless (aka Broadband Wireless (aka WiMaxWiMax)) 802.20 802.20 –– Wireless Metro LANWireless Metro LAN3802.11 Physical layer802.11 Physical layer Diffused Infrared (IR)Diffused Infrared (IR) 850 850 –– 950nm 950nm  Limitation: short physical distanceLimitation: short physical distance Line of sight (direct) or ceiling reflection (diffused)Line of sight (direct) or ceiling reflection (diffused) Spread Spectrum Spread Spectrum 02/21/087TDC363-07pppp Unlicensed Radio Frequency (RF)Unlicensed Radio Frequency (RF) Industry, Scientific, and Medical Applications (ISM)Industry, Scientific, and Medical Applications (ISM) 2.4 2.4 –– 2.485 GHz2.485 GHz Frequency Hopping Spread Spectrum (FHSS)Frequency Hopping Spread Spectrum (FHSS) Direct Sequence Spread Spectrum (DSSS)Direct Sequence Spread Spectrum (DSSS) Orthogonal Frequency Division Multiplexing (OFDM)Orthogonal Frequency Division Multiplexing (OFDM)Wireless TransmissionInfrared(IR)Radio Frequency(RF)Sd02/21/088TDC363-07Spread SpectrumFrequencyHoppingDirectSequenceOFDM MIMOOFDM: Orthogonal Frequency Division MultiplexingMIMO: Multiple Input and Multiple OutputSpread SpectrumThe bandwidth of spread spectrum is several times of the original bandwidth.Original BandwidthAmplitude02/21/089TDC363-07Original BandwidthSpread Spectrum BandwidthAmplitude4Why Spread Spectrum?Why Spread Spectrum? It is the foundation used in the ISM bands.It is the foundation used in the ISM bands. It is a requirement for unlicensed device.It is a requirement for unlicensed device. It makes the transmission look like noise to a It makes the transmission look like noise to a traditional narrowband receiver.traditional narrowband receiver.02/21/0810TDC363-07traditional narrowband receiver.traditional narrowband receiver. It alleviates interference, but does not eliminate It alleviates interference, but does not eliminate it.it. How do you address the issue of interference:How do you address the issue of interference: Limit the power of transmission.Limit the power of transmission.Frequency Hopping Spread Spectrum (FHSS)2.422.432.442.45requency )GHz)1st2nd4th5th02/21/0811TDC363-071. Use multiple frequencies to send the data.2. Instead of using a bandwidth of 10MHz, the above FHSS uses 50MHz.3. 1stbit (or group of bits) is sent on 2.44G, the 2ndbit is sent on 2.41G, and the 3rdbit is sent on 2.40G, etc.123452.402.41Fr2nd3rdDirect Sequence Spread Spectrum (DSSS)Each bit (0 or 1) is replaced by a sequence of bits, called chip code, and then sent out.0: 11001 1:00110 complement of 0’s chip code01101002/21/0812TDC363-07If the original bit steam is 1M bps, the data rate will be 5M bps (chip code = 5 bits in the above diagram).01101011001 11001 1100100110 00110 001105Orthogonal Frequency Orthogonal Frequency Division Multiplexing (OFDM)Division Multiplexing (OFDM) It is a technique to increase transmission speed It is a technique to increase transmission speed by multiplexing.by multiplexing. It uses one wide frequency channel by breaking It uses one wide frequency channel by breaking 02/21/0813TDC363-07it up into several subit up into several sub--channels. channels.  All small subAll small sub--channels are multiplexed into one channels are multiplexed into one “fat” channel. “fat” channel.  Orthogonal: overlapping but distinguishableOrthogonal: overlapping but distinguishableOFDMOFDM02/21/0814TDC363-07Ref. http://www.iec.org/online/tutorials/ofdm/MIMOMIMO(multiple antennas for transmission and reception)(multiple antennas for transmission and reception)0010110001011002/21/0815TDC363-07Ref: http://www.dia.unisa.it/isit2000/tutorials/spacetime.pdf6WLAN Operation ModeWLAN Operation ModeWireless AccessPoint02/21/0816TDC363-07Ad hoc ModeInfrastructure ModeWLAN Topology