Elements Of A Wireless Network
Elements of a Wireless Networkwireless hostslaptop, tablet,smartphoneComputer Networksrun applicationsnetworkinfrastructureLecture 38:Wireless Standards, NetworkArchitectures, and Modulation SchemesElements of a Wireless Networknetworkinfrastructuremay be stationary (non-mobile) ormobilewireless does not always meanmobility, could be just nomadicElements of a Wireless Networkbase stationwireless linktypically connectedto wired networktypically used to connectmobile(s) to base stationact as relay - responsible forsending packets between wirednetwork and wireless host(s) inits “area”e.g., cell towers, 802.11access pointsnetworkinfrastructurealso used as backbone linkmultiple access protocolcoordinates link accessvarious data rates,transmission distancedown- or forward-link ( ): base station to wireless hostup- or reverse-link ( ): wireless host to base station
Mode of OperationMode of Operationad hoc modeno base stationsinfrastructure modenetworkinfrastructure5G?to 802.11 access point (AP) mobile users attach tonetwork through BS air interface: physical and linklayer protocol betweenmobile and BSWireless Technologies TimelineMSC30,000 ft view connects base stations to wide area net manages call setup handles mobilityMobileSwitchingCenterpublic telephonenetwork, andInternetMobileSwitchingCenterwired networkWireless capacity / throughputcellnodes organize themselvesinto a network: route amongthemselveshandoff: mobile changingbase stationCellular Network Architecture covers geographical region base station (BS) analogousnodes can only transmit toother nodes within linkcoveragebase station connects mobilesinto wired networkLTE Advanced4GIEEE 8023G2G1GLTEWiMAX (802.16)Wi-Fi (802.11)UMTS/HSxPACDMAGSMAMPSFirst cellphones197019801990200020102015[wikipedia: dori][Mlinarsky, Turner]
Corresponding Data RatesCellular Network StandardsStandardLTE Advanced3 Gbps1GLTE (downlink)300 Mbps200 MbpsLTE (uplink) / HSDPA 100 Mbps2G50 MbpsHSUPA 10 MbpsWLAN1 MbpsGSM10 Kbps200020052G MS (voice only)20104G2015Gs2.5G requires a separatepacket switched networkfor dataBSS — Base Station SystemBTS — Base Transceiver StationBSC — Base Station ControllerMS — Mobile StationDQPSK9.6IS-95 (cdmaOne)QPSK/OQPSK9.6cdma2000 1xRTTQPSK114 (50-70)VLRPSTNCDGrHLRTDMACDMA2K/150 (500/80)QPSK/8PSK/16QAM3K/1.8K (700/350)QPSK/BPSK2K (220-320)UMTS HSPA64QAM/16QAM MIMO28K/11K (500-1K)UMTS HSPA 64QAM/64QAM MIMO336K/72K (14K)SS7QPSK/QAM/OFDM MIMO73K-300K/36-75KOFDMAOFDM MIMO128K/56KSOFDMAWiMAX Rel. 2 (802.16m)OFDM MIMO100KSOFDMALTE-AdvancedOFDM MIMO1M/375-568KSC-FDMAEBBSC2G MS (voice & data)GbMSCGsVLRAuCPSDNGGSNNSS — Network Sub-SystemSGSN — Serving GPRS Support NodeMSC — Mobile-service Switching ControllerGGSN — Gateway GPRS Support NodeVLR — Visitor Location RegisterHLR — Home Location RegisterAuC — Authentication ServerGSM ervicecommunicationGMSC — Gateway MSC[Turner&Orange]GrIuPSNode B3G UE (voice & data)BSS — Base Station SystemBTS — Base Transceiver StationBSC — Base Station ControllerMS — Mobile StationGcGiIPCN — Core NetworkMSC — Mobile-service Switching ControllerVLR — Visitor Location RegisterHLR — Home Location RegisterAuC — Authentication ServerGMSC — Gateway MSCRNS — Radio Network SystemUTRAN — UMTS Terrestrial Radio Access NetworkRNC — Radio Network ControllerUE — User /UTRANGiPSTNAIubIPCDMACNPSTNGMSCGnCDMA w/ TDMWiMAX Rel 1 (802.16e)AbisHSGSN1.89K (400)BTSGb2G MS (voice & data)16QAM/32QAM2G MS (voice only)BMSC384 (100-130)BSSEABSC115 (20-30)8PSKUMTS (R99) Network ArchitectureNSSBTSGMSKEDGE[Schill]BSSMSGPRSUMTS LTEGSM (2G) and GPRS (2.5G)Network 4cdma2000 1xEVDO rev A3GFDMAFMcdma2000 1xEVDO (Rel 0)UMTS(macro cell)MultipleAccessGMSKIS-136DECTData rate (avg)in Kbps, K2 MAMPSEDGE EvolutionUMTS(pico cell)EDGEHSCSD/GPRS100 KbpsModulationRange: 2-8 kmSpeed: 250 km/hPSDNGGSNSGSN — Serving GPRS Support NodeGGSN — Gateway GPRS Support NodeUMTS — Universal Mobile Telecommunication System[Turner&Orange]
Overall 3GPP Network ArchitectureEPC — Evolved Packet CoreSAE — System Architecture EvolutionMME — Mobility Management EntityHSS — Home Subscriber ServerSPR — Subscriber Profile RepositoryPCRF — Policy and Charging RulesFunctionPDN — Packet Data NetworkEvolved Packet SystemAll IP!(EPS)EPCServingGWMMESAEPDNGWithle wpatib g!!!Com erythinev4GeNode-B[Olsson et al.][Motorola, Mlinarsky&Turner]IEEE Wireless 802.1x StandardsRF SpectrumStandardBandUplinkDownlinkTotal FDDComments800 MHz832-862791-8212 x 30 MHzestablished or new900 MHz880-915925-9602 x 35 MHzoriginally GSM,recently UMTS1800 MHz1710-17851805-18802 x 75 MHzGSM2100 MHz1920-19802110-21702 x 60 MHzoriginal UMTS2600 MHz2500-2570IP Services (IMS), WiFi,, andtrusted non-3GPP IP access(CDMA, TD-SCDMA, WiMAX)2620-26902 x 70 MHzWhy are 800, 1800 and 2600 bands popular?LTE802.11Year1987 (started)1997 (standard)FrequencyBand (GHz)2.4Air K-BPSKCCK-QPSK802.11a1999802.11g2003802.11n2010 (est)802.11ac12/20135802.11ad (WiGig,Wireless USB)12/20122.4, 5, and 60802.15.1(Bluetooth)1994 (started)1999 (standard)802.16a(Line Of Sight)200110-66802.16d(Non LOS)20032-11802.16e(Mobile WiMAX,S. Korea WiBro)2005, 20092.3, 2.5, 3.3, 3.5ScalableOFDMA MIMO802.16m(WiMAX II)20112.3, 2.5, 3.3, 3.5ScalableOFDMA MIMO5OFDM/24QAM2.42.4 and 52.4Mbps(actual)Range (m)125.511 (5) 30/300(outdoors)54 (27) 10/100OFDM/64QAM1-54 (22) 30/30064QAM MIMO300 (144) 10/100256QAM MUMIMOMIMOTDM-FHSSOFDMQPSK16QAM 64QAMSpeedwalking1.3K7K.721-4LoS 10 m 50 km4-70 (1-4) 6-10 km 1-5 km100 mobile1K fixedN/A 50 km 120km/h
Characteristics of Selected WirelessLink Standards802.15: Personal Area NetworkReplacement for cables (mouse, keyboard,headphones)PLess than 10 m diameterSP slaves request permission to send (to master) master grants requestsa bluetooth network (piconet) supports 2-7 gadgetseach gadget given a 12-bit addresssupports gadget authentication and data encryptionuses frequency hopping spread spectrum (signal occupiesdifferent frequencies, in a given pattern and duration, astransmission progresses) uses FEC, CRC, and ARQ radius ofcoverageMMaster/slaves:802.15: evolved from Bluetooth specificationPSSPM Master deviceS Slave deviceP Parked device (inactive) HTTP, SMTP, FTP, etc.transport: endhost-endhost data transfer TCP, UDPnetwork: routing of datagrams from sourceto destination IP, routing protocolslink: data transfer between neighboringnetwork elements: multiple access control Ethernet, WiFiphysical: modulation methods, bits in the air545-11802.11n802.11a,g41802.11a,g point-to-point802.11bdata4G: LTE, WiMAXUMTS/WCDMA-HSPDA, CDMA2000-1xEVDO3.5G802.15.3843GUMTS/WCDMA, CDMA2000.0562GIS-95, CDMA, GSMIndoor10-30mOutdoor50-200mMid-rangeoutdoor200m – 4 KmLong-rangeoutdoor5Km – 20 KmFrequency-Shift KeyingInternet Protocol Stackapplication: supporting network applications200Data rate (Mbps)Ad hoc: no infrastructureapplicationtransportBinary Frequency-Shift Keying (BFSK): uses 2 fixedamplitude (A) carrier signals, different in frequency (f ),to represent 1 and 0networkData signal vd(t)linkphysicalair interfaceCarrier 1 v1(t)Carrier 2 v2(t)vBFSK(t)Halsall
M-ary Phase-Shift KeyingPhase-Shift KeyingPhase shift occurs at each bit transitionWe’re not limited to using only 2 phasesBinary Phase-Shift Keying (BPSK): A and f are fixed, 1 and 0 aredifferent phases (ϕ) of the signal, e.g., start at 180º 0, at 0º 1Quadrature Phase-Shift Keying (QPSK): each phaseof the signal represents 2 bits, giving 4 valuesDifferential Phase-Shift Keying (DPSK): phase difference is relativeto previous bit, e.g., signal shifted by 90º 0, by 270º 1Data signal vd(t)HalsallDPSK: simpler to implement but more prone toerrorsCarrier vC(t)Phase coherentvPSK (t) 8PSK: each phase represents 3 bits, giving 8 values reducing phase differences makes the signal moreprone to noise and interferenceDifferential QPSK (DQPSK): phase difference isrelative to previous bitDifferential v’PSK(t)HalsallkQAMAmplitude Phase Shift KeyingExample: 8QAM, 3 bits/symbol (8 codable states)Quadrature* Amplitude Modulation (QAM):Bit value uses amplitude, in addition to phase, for bit encoding a combination of Amplitude Shift Keying (ASK) and PhaseShift Keying (PSK) used to encode/represent multiple bitsASK(A ½)PSK(ϕ 90 ¼)PSK(ϕ 180 ½) PSK(ϕ 270 ¾)QAM: ASK PSK(A ½, ϕ 90 )000 001 010 011 100 101 110 111amplitude (A)1½1½1½1½phase shift (ϕ)00¼¼½½¾¾16QAM: 4 bits/symbol more states, more sensitiveto interferencettttt64 QAM16 QAMQPSK** The “quadrature” in the name refers to the use of “in quadrature” component signal* Quadrature Phase-Shift Keying 4QAM (no info from amplitude)[Schill][Fujitsu, Schill]
Polar and I/Q RepresentationSignal Changes on the I/Q PlaneDifficult to modulate amplitude and phasesimultaneously and separately, e.g., phasechange can cause amplitude modulation and vice versaEasier to represent the amplitude and phaseof signal as a vector in polar coordinate: the 0º-axis is called the “in-phase” (I ) axisPhaseChangeMagnitudeand PhaseChangeMagnitude/AmplitudeChangeθ the 90º-axis is orthogonal or“in quadrature” (Q) to the I axisConstellation diagrams:Q projections of the signal vector on these axesis a rectangular representation of the polar diagram I -value: A cos θQIIθ Q-value: A sin θBPSK8PSK[Donadio, Keithley][HP, Cisco]I/Q Signal ModulationPolar and I/Q RepresentationData in the modulator is separated into 2 channels I and Q each channel modulates a carrier the two carriers have the same frequency and amplitudebut the phase is offset by 90º (“in quadrature”)The two components are summed in a modulator circuitand transmitted as one composite signaldemodulatormodulatorThe I and Q signals are two independent componentsof the signal, changing one doesn’t change the otherSignals that are in quadrature do not interfere witheach othermodulatedcarriercompositesignalcomposite signal[Langton, HP, Cisco, wikipedia][HP, Cisco, wikipedia]
QPSK on the I/Q Plane16QAMThe 4 values of QPSK can be representedon the I/Q plane :As with QPSK, data is split into I and Q channels, buteach channel can take on 2 phases and 2 amplitudevalues! with phases 45º, 135º, 225º, and 315º theoretical bandwidth efficiency: 2 bits/sec/HzFour I values and four Q values: 4 bits per symbol, 24 16 statesQPSK constellation:01Two bits are routed to each channel simultaneously,which are added and applied to the carriers11Theoretical bandwidth efficiency: 4 bits/sec/Hz0010[Cisco]16QAM ConstellationQZero CrossingAt 0, there’s no voltage present: when signal is amplified, zero crossingcauses artifacts (e.g., audio clicks) inthe non-zero part of the output signalwhen gain is abruptly switched between gain settings0010000000110001 when signal is filtered, voltage needs time to ramp up/down,zero crossing causes amplitude change in graphics rendering, zero crossing shows up as black lines in image processing, zero crossing usually marks boundary/edgeof features don’t want extraneous zero crossings[wikipedia]
OQPSKQPSK and Zero CrossingOffset QPSK (OQPSK) a.k.a. Staggered QPSK (SQPSK):limit phase shift to 90º every half-symbol time (T ) (byItime-shifting the Q component)In QPSK, carrier signal can phase shift by 180º,encountering zero crossing, causing carrieramplitude change when filtered or amplifiedQIdeal QPSKtime shiftFiltered QPSKsignalstretched outsignalstretched out[Hull][Donadio]QPSK vs. OQPSKQPSK vs. OQPSKOffset QPSK (OQPSK) a.k.a. Staggered QPSK (SQPSK):limit phase shift to 90º every half-symbol time (T ) (bytime-shifting the Q component)QPSK can phase shift by 180º, whereas OQPSK islimited to 90º per half symbol timepeak symbol arrierOQPSKQPSKcompositesignal[wikipedia]zero crossingOQPSK[Donadio]
Wireless Link CharacteristicsGMSKMinimum Shift Keying (MSK):OQPSK with half-cycle sinusoidcomponent signal, instead ofrectangular pulse, to make thephase change linearDifferences from wired link .Decreasing signal strength: radio signal disperses as it travelsgreater distances and attenuates as it propagatesthrough matter (path loss) result turns out to be equivalent toFSK with only 1 bit/symbolInterference from other sourcesGaussian MSK (GMSK):MSK output passed through a Gaussian filter, resulting innarrower bandwidth requirement; used in GSM standardized wireless network frequencies (e.g., 2.4 GHz)shared by other devices (e.g., cordless phones) electromagnetic noise(e.g., microwave oven,motors) interferes as well[Langton, HP]Wireless Link CharacteristicsWireless Link CharacteristicsGiven air interface: increasedpower increased SNR decreased BER radio signal reflects off objects, walls, ground taking many paths of different path lengths,arriving at destination at slightly different times causing blurring of signal at thereceiver SNR: signal-to-noise ratio BER: bit error rate10-210-310-410-5Fundamental trade-off:energy-saving vs. rate vs. rangereceivertransmitter given SNR: choose air interface that meetsBER requirement at highest throughput SNR may change with mobility: dynamicallymake communication across (even a point to point)wireless link much more “difficult”10-1BERMulti-path propagationadapt the air interface to compensate(modulation technique, rate) all the latest standards have rate adaptation,including 802.11, 802.16, and LTE10-610-7102030SNR(dB)QAM256 (8 Mbps)QAM16 (4 Mbps)BPSK (1 Mbps)40
Multi-antenna (MIMO)Dealing with Bit ErrorsWith bandwidth reaching Shannon’s limit, future gain inbandwidth will come from smarter antenna use:Wired vs. wireless links wired: most loss is due to congestion wireless: higher, time-varying bit-error rateBeamforming (a.k.a., smart antenna/adaptive antenna system(AAS)): generate interfering patterns from multiple antennaesuch that the intended signal is strengthened, in the directionintended (Cf. noise cancellation headphones)Dealing with high wireless bit-error rates sender could increase transmission power requires more energy (bad for battery-powered hosts), and creates more interference with other sendersSpatial multiplexing: organized data into spatial streams thatare transmitted simultaneously, on the same frequency, usingmultiple antennae; streams received over multiple antennaeand separated using various detection algorithms stronger error detection and recovery more powerful error detection/correction codes link-layer retransmission of corrupted framesMany TCP alternatives/extensions for wireless e.g., TCP Westwood uses an Explicit Loss Notification (ELN) bitMIMO Antenna TechniqueMIMO: Multi-Input/Multi-Output there’s a propagation path between each transmit (Tx) andreceive (Rx) antenna (a “MIMO path”) N M MIMO (e.g., 4 4, 2 2, 2 3) N transmit antennas M receive antennas total of N M paths MIMO transmission increases throughput by beam forming, errorcorrection across Tx antennae, signal interpolation across Rx antennae,network coding across multiple hosts (co-MIMO)2 3 MIMOInputRx1TxRx22 3Rx3MIMOReceiverOutput[Mlinarsky&Turner, Schill] increase in spectral efficiency (and resulting data rate)and quality of transmission
Computer Networks Lecture 38: Wireless Standards, Network Architectures, and Modulation Schemes Elements of a Wireless Network . CDMA w/ TDM cdma2000 1xEVDO rev A 3K/1.8K (700/350) WCDMA/UMTS QPSK/BPSK 2K (220-320) UMTS HSPA 64QAM/16QAM MIMO 28K/11K (500-1K) CDMA UMTS HSPA 64QAM/64QAM MIMO 336K
Wireless# Guide to Wireless Communications Chapter 1 Introduction to Wireless Communications . Wireless Local Area Network (WLAN) - Extension of a wired LAN Connecting to it through a device called a wireless . network Each computer on the WLAN has a wireless network interface card (NIC) - With an antenna built into it .
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