Computer Networks

Lecture38:

WirelessStandards,Network

Architectures,andModulationSchemes

ElementsofaWirelessNetwork

network

infrastructure

wirelesshosts

laptop,tablet,

smartphone

runapplications

maybestationary(non-mobile)or

mobile

wirelessdoesnotalwaysmean

mobility,couldbejustnomadic

network

infrastructure

basestation

typicallyconnected

towirednetwork

actasrelay-responsiblefor

sendingpacketsbetweenwired

networkandwirelesshost(s)in

its“area”

e.g.,celltowers,802.11accesspoints

ElementsofaWirelessNetwork

network

infrastructure

ElementsofaWirelessNetwork

down-orforward-link(↓):basestationtowirelesshost

up-orreverse-link(↑):wirelesshosttobasestation

wirelesslink

typicallyusedtoconnect

mobile(s)tobasestation

alsousedasbackbonelink

multipleaccessprotocol

coordinateslinkaccess

variousdatarates,

transmissiondistance

network

infrastructure

infrastructuremode

basestationconnectsmobiles

intowirednetwork

handoff:mobilechanging

basestation

ModeofOperation

adhocmode

nobasestations

nodescanonlytransmitto

othernodeswithinlink

coverage

nodesorganizethemselves

intoanetwork:routeamong

themselves

ModeofOperation

Mobile

Switching

Center

publictelephone

network,and

Internet

Mobile

Switching

Center

CellularNetworkArchitecture

•  connectsbasestationstowideareanet

•  managescallsetup

•  handlesmobility

MSC•  coversgeographicalregion•  basestation(BS)analogousto802.11accesspoint(AP)

•  mobileusersattachto

networkthroughBS

•  airinterface:physicalandlinklayerprotocolbetween

mobileandBS

cell

wirednetwork

[wikipedia:dori]

Wirelesscapacity/throughput

1970 1980 1990 2000 2010

Firstcell

phones

AMPS

GSM

CDMA

Wi-Fi (802.11) WiMAX (802.16)

LTE

UMTS/HSxPA2G

3G

4G

IEEE 802

[Mlinarsky,Turner]

WirelessTechnologiesTimeline

30,000 ftview

1G

2015

LTEAdvanced

5G?

CorrespondingDataRates

UMTS(pico cell)

GSM

HSCSD/GPRS

EDGE

UMTS(macro cell)

Satellites

DECT

LTE (uplink) / HSDPA+

LTE (downlink)

WLAN

HSUPA+

[Schill]

3 Gbps

300Mbps

200Mbps

100Mbps

50Mbps

10Mbps

1Mbps

100Kbps

10Kbps

1995 2000 2005 2010 2015

LTEAdvanced

CellularNetworkStandards

Standard ModulationData rate (avg) in Kbps, K2=M

Multiple Access

1G AMPS FM - FDMA

2G

GSM GMSK 9.6-14.4

TDMA

GPRS GMSK 115 (20-30)

EDGE 8PSK 384 (100-130)

EDGE Evolution 16QAM/32QAM 1.89K (400)

IS-136 DQPSK 9.6

IS-95 (cdmaOne) QPSK/OQPSK 9.6CDMA

cdma2000 1xRTT QPSK 114 (50-70)

3G

cdma2000 1xEVDO (Rel 0)QPSK/8PSK/16QAM

2K/150 (500/80)CDMA w/ TDM

cdma2000 1xEVDO rev A 3K/1.8K (700/350)

WCDMA/UMTS QPSK/BPSK 2K (220-320)

CDMAUMTS HSPA 64QAM/16QAM+MIMO 28K/11K (500-1K)

UMTS HSPA+ 64QAM/64QAM+MIMO 336K/72K (14K)

UMTS LTE QPSK/QAM/OFDM+MIMO 73K-300K/36-75K OFDMA

WiMAX Rel 1 (802.16e) OFDM+MIMO 128K/56K SOFDMA

4GWiMAX Rel. 2 (802.16m) OFDM+MIMO 100K SOFDMA

LTE-Advanced OFDM+MIMO 1M/375-568K SC-FDMA

Range: < 2-8 kmSpeed: < 250 km/h

GSM — Global System for Mobile communication

SS7BTS

BSC MSCVLR

HLR AuC

GMSC

BSS

PSTN

NSS

AE

CD

PSTNAbis

B

H

MS

BSS — Base Station SystemBTS — Base Transceiver StationBSC — Base Station ControllerMS — Mobile Station

NSS — Network Sub-SystemMSC — Mobile-service Switching ControllerVLR — Visitor Location RegisterHLR — Home Location RegisterAuC — Authentication ServerGMSC — Gateway MSC

GSM (2G) and GPRS (2.5G) Network Architecture

IP

2G+ MS (voice & data)

PSDNGi

SGSN

Gr

Gb

Gs

GGSN

Gc

Gn

2G MS (voice only)

[Turner&Orange]

SGSN — Serving GPRS Support NodeGGSN — Gateway GPRS Support Node

GPRS — General Packet Radio Service

2.5G requires a separate packet switched network for data

UMTS (R99) Network Architecture

SS7

IP

BTSBSC MSC

VLR

HLRAuC

GMSC

BSS

SGSN GGSN

PSTN

PSDN

CN

C

D

Gc

Gr

Gn Gi

Abis

Gs

B

H

BSS — Base Station SystemBTS — Base Transceiver StationBSC — Base Station ControllerMS — Mobile Station

RNS — Radio Network SystemUTRAN — UMTS Terrestrial Radio Access NetworkRNC — Radio Network ControllerUE — User Equipment

CN — Core NetworkMSC — Mobile-service Switching ControllerVLR — Visitor Location RegisterHLR — Home Location RegisterAuC — Authentication ServerGMSC — Gateway MSC

SGSN — Serving GPRS Support NodeGGSN — Gateway GPRS Support Node

AE PSTN

2G MS (voice only)

2G+ MS (voice & data)

UMTS — Universal Mobile Telecommunication System

Gb

3G UE (voice & data)Node B

RNC

RNS/UTRAN

Iub

IuCS

ATMIuPS

[Turner&Orange]

[Olssonetal.]

Overall3GPPNetworkArchitecture

[Motorola, Mlinarsky&Turner]

4G

EPC — Evolved Packet CoreSAE — System Architecture EvolutionMME — Mobility Management EntityHSS — Home Subscriber ServerSPR — Subscriber Profile RepositoryPCRF — Policy and Charging Rules

FunctionPDN — Packet Data Network

MMEServing

GWPDN GW

eNode-B IP Services (IMS), WiFi,, and trusted non-3GPP IP access (CDMA, TD-SCDMA, WiMAX)

Compatible with

everything!!!

Evolved Packet System (EPS)

EPC

SAE

All IP!

Band Uplink Downlink TotalFDD Comments

800 MHz 832-862 791-821 2 x 30 MHz establishedornew

900 MHz 880-915 925-960 2 x 35 MHz originallyGSM,

recentlyUMTS

1800 MHz 1710-1785 1805-1880 2 x 75 MHz GSM

2100 MHz 1920-1980 2110-2170 2 x 60 MHz originalUMTS

2600 MHz 2500-2570 2620-2690 2 x 70 MHz LTE

RFSpectrum

Whyare800,1800and2600bandspopular?

IEEEWireless802.1xStandardsStandard Year

Frequency Band (GHz) Air Interface

Mbps (actual) Range (m) Speed

802.111987 (started)1997 (standard)

2.4

DS-SS/DBPSKDS-SS/DQPSK

12

walking802.11b(WiFi) 1999

CCK-BPSKCCK-QPSK

5.511 (5)

< 30/300 (outdoors)

802.11a 1999 5 OFDM/24QAM 54 (27) < 10/100

802.11g 2003 2.4 OFDM/64QAM 1-54 (22) < 30/300

802.11n 2010 (est) 2.4 and 5 64QAM+MIMO 300 (144) < 10/100

802.11ac 12/2013 5 256QAM+MUMIMO 1.3K

802.11ad (WiGig, Wireless USB) 12/2012 2.4, 5, and 60 MIMO 7K LoS

802.15.1(Bluetooth)

1994 (started)1999 (standard) 2.4 TDM-FHSS .721-4 < 10 m

N/A802.16a (Line Of Sight) 2001 10-66 OFDM

QPSK16QAM 64QAM

4-70 (1-4)

< 50 km

802.16d (Non LOS) 2003 2-11 < 6-10 km

802.16e(Mobile WiMAX,S. Korea WiBro)

2005, 2009 2.3, 2.5, 3.3, 3.5ScalableOFDMA+MIMO < 1-5 km

< 120 km/h

802.16m(WiMAX II) 2011 2.3, 2.5, 3.3, 3.5

ScalableOFDMA+MIMO

100 mobile1K fixed < 50 km

M

S

Master device

Slave device

Parked device (inactive)P

802.15:PersonalAreaNetwork

Replacementforcables(mouse,keyboard,

headphones)

Adhoc:noinfrastructure

Lessthan10mdiameter

Master/slaves:

•  slavesrequestpermissiontosend(tomaster)

•  mastergrantsrequests

802.15:evolvedfromBluetoothspecification

•  abluetoothnetwork(piconet)supports2-7gadgets•  eachgadgetgivena12-bitaddress•  supportsgadgetauthenticationanddataencryption•  usesfrequencyhoppingspreadspectrum(signaloccupies

differentfrequencies,inagivenpatternandduration,as

transmissionprogresses)

•  usesFEC,CRC,andARQ

M radius of coverage

S

S S

P

P

P

P

CharacteristicsofSelectedWireless

LinkStandards

Indoor10-30m

Outdoor50-200m

Mid-rangeoutdoor

200m – 4 Km

Long-rangeoutdoor

5Km – 20 Km

.056

.384

1

4

5-11

54

IS-95, CDMA, GSM 2G

UMTS/WCDMA, CDMA2000 3G

802.15

802.11b

802.11a,g

3.5G

802.11a,g point-to-point

200 802.11n

Dat

a ra

te (M

bp

s) data

UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO

4G: LTE, WiMAX

InternetProtocolStack

application:supportingnetworkapplications

• HTTP,SMTP,FTP,etc.

transport:endhost-endhostdatatransfer

•  TCP,UDP

network:routingofdatagramsfromsource

todestination

•  IP,routingprotocols

link:datatransferbetweenneighboring

networkelements:multipleaccesscontrol

•  Ethernet,WiFi

physical:modulationmethods,bitsintheair

application

transport

network

link

physical

airinterface

Frequency-ShiftKeying

BinaryFrequency-ShiftKeying(BFSK):uses2fixed-amplitude(A)carriersignals,differentinfrequency(f ),torepresent1and0

Halsall

Datasignalvd(t)

Carrier1v1(t)

Carrier2v2(t)

vBFSK(t)

Phase-ShiftKeyingPhaseshiftoccursateachbittransition

BinaryPhase-ShiftKeying(BPSK):Aandfarefixed,1and0aredifferentphases(ϕ)ofthesignal,e.g.,startat180º=0,at0º=1

DifferentialPhase-ShiftKeying(DPSK):phasedifferenceisrelative

topreviousbit,e.g.,signalshiftedby90º=0,by270º=1

Halsall

Datasignalvd(t)

CarriervC(t)

Phasecoherent

vPSK (t)

Differential v’PSK(t)

DPSK:

•  simplertoimplement

•  butmoreproneto

errors

We’renotlimitedtousingonly2phasesQuadraturePhase-ShiftKeying(QPSK):eachphase

ofthesignalrepresents2bits,giving4values

• 8PSK:eachphaserepresents3bits,giving8values• reducingphasedifferencesmakesthesignalmore

pronetonoiseandinterference

DifferentialQPSK(DQPSK):phasedifferenceis

relativetopreviousbit

M-aryPhase-ShiftKeying

Halsall

Amplitude+PhaseShiftKeying

Quadrature*AmplitudeModulation(QAM):

• usesamplitude,inadditiontophase,forbitencoding

• acombinationofAmplitudeShiftKeying(ASK)andPhaseShiftKeying(PSK)usedtoencode/representmultiplebits

t

PSK(ϕ=270°=¾)ASK(A=½)

t

PSK(ϕ=90°=¼)

t

PSK(ϕ=180°=½)

t

QAM:ASK+PSK

(A=½, ϕ=90°)

t

[Schill]*The“quadrature”inthenamereferstotheuseof“inquadrature”componentsignal

Bitvalue 000 001 010 011 100 101 110 111

amplitude(A) 1 ½ 1 ½ 1 ½ 1 ½

phaseshift(ϕ) 0 0 ¼ ¼ ½ ½ ¾ ¾

kQAM

64QAM16QAMQPSK*

*QuadraturePhase-ShiftKeying=4QAM(noinfofromamplitude)

Example:8QAM,3bits/symbol(8codablestates)

16QAM:4bits/symbol

•  morestates,moresensitive

tointerference

[Fujitsu,Schill]

PolarandI/QRepresentationDifficulttomodulateamplitudeandphase

simultaneouslyandseparately,e.g.,phase

changecancauseamplitudemodulationandviceversa

Easiertorepresenttheamplitudeandphase

ofsignalasavectorinpolarcoordinate:

•  the0º-axisiscalledthe“in-phase”(I )axis•  the90º-axisisorthogonalor“inquadrature”(Q)totheIaxis

•  projectionsofthesignalvectorontheseaxesisarectangularrepresentationofthepolardiagram

•  I -value:A cos θ• Q-value:A sin θ

[HP, Cisco]

θ

θ

SignalChangesontheI/QPlane

Magnitude/

Amplitude

Change

Phase

ChangeMagnitude

andPhase

Change

[Donadio,Keithley]

Q

I

Q

I

BPSK 8PSK

Constellationdiagrams:

modulator

demodulator

I/QSignalModulation

Datainthemodulatorisseparatedinto2channelsIandQ• eachchannelmodulatesacarrier

• thetwocarriershavethesamefrequencyandamplitude

butthephaseisoffsetby90º(“inquadrature”)

Thetwocomponentsaresummedinamodulatorcircuit

andtransmittedasonecompositesignal

[Langton,HP,Cisco,wikipedia]

compositesignal

PolarandI/QRepresentationTheIandQsignalsaretwoindependentcomponents

ofthesignal,changingonedoesn’tchangetheother

Signalsthatareinquadraturedonotinterferewith

eachother

[HP,Cisco,wikipedia]

modulated

carrier

composite

signal

QPSKontheI/QPlane

[Cisco]

The4valuesofQPSKcanberepresented

ontheI/Qplane:• withphases45º,135º,225º,and315º• theoreticalbandwidthefficiency:2bits/sec/Hz

QPSKconstellation:

00

01

10

11

16QAM

AswithQPSK,dataissplitintoIandQchannels,buteachchannelcantakeon2phasesand2amplitude

values!

FourIvaluesandfourQvalues:4bitspersymbol,24 = 16statesTwobitsareroutedtoeachchannelsimultaneously,

whichareaddedandappliedtothecarriers

Theoreticalbandwidthefficiency:4bits/sec/Hz

16QAMConstellationQ

0000

0001

0010

0011

At0,there’snovoltagepresent:• whensignalisamplified,zerocrossing

causesartifacts(e.g.,audioclicks)in

thenon-zeropartoftheoutputsignal

whengainisabruptlyswitchedbetweengainsettings

• whensignalisfiltered,voltageneedstimetorampup/down,

zerocrossingcausesamplitudechange

•  ingraphicsrendering,zerocrossingshowsupasblacklines

•  inimageprocessing,zerocrossingusuallymarksboundary/edge

offeatures�don’twantextraneouszerocrossings

ZeroCrossing

[wikipedia]

InQPSK,carriersignalcanphaseshiftby180º,encounteringzerocrossing,causingcarrier

amplitudechangewhenfilteredoramplified

QPSKandZeroCrossing

IdealQPSK

FilteredQPSK

[Donadio]

signal

stretchedout

signal

stretchedout

OffsetQPSK(OQPSK)a.k.a.StaggeredQPSK(SQPSK):

limitphaseshiftto90ºeveryhalf-symboltime(T )(bytime-shiftingtheQcomponent)

OQPSK

[Hull]

timeshift

I

Q

OffsetQPSK(OQPSK)a.k.a.StaggeredQPSK(SQPSK):

limitphaseshiftto90ºeveryhalf-symboltime(T )(bytime-shiftingtheQcomponent)

QPSKvs.OQPSK

[wikipedia]

QPSK

OQPSK

modulated

carrier

composite

signal

modulated

carrier

composite

signal

QPSKvs.OQPSK

QPSKcanphaseshiftby180º,whereasOQPSKis

limitedto90ºperhalfsymboltime

[Donadio]

QPSK OQPSK

peaksymbolpower

zerocrossing

MinimumShiftKeying(MSK):

OQPSKwithhalf-cyclesinusoid

componentsignal,insteadof

rectangularpulse,tomakethe

phasechangelinear

• resultturnsouttobeequivalenttoFSKwithonly1bit/symbol

GaussianMSK(GMSK):

MSKoutputpassedthroughaGaussianfilter,resultingin

narrowerbandwidthrequirement;usedinGSM

GMSK

[Langton,HP]

Differencesfromwiredlink….

Decreasingsignalstrength:

• radiosignaldispersesasittravelsgreaterdistances

• andattenuatesasitpropagatesthroughmatter(pathloss)

Interferencefromothersources

• standardizedwirelessnetworkfrequencies(e.g.,2.4GHz)sharedbyotherdevices(e.g.,cordlessphones)

• electromagneticnoise

(e.g.,microwaveoven,

motors)interferesaswell

WirelessLinkCharacteristics

Multi-pathpropagation

• radiosignalreflectsoffobjects,walls,ground

• takingmanypathsofdifferentpathlengths,

arrivingatdestinationatslightlydifferenttimes

• causingblurringofsignalatthereceiver

makecommunicationacross(evenapointtopoint)

wirelesslinkmuchmore“difficult”

receiver

transmitter

WirelessLinkCharacteristics WirelessLinkCharacteristics

Givenairinterface:increased

power→ increasedSNR→

decreasedBER

• SNR:signal-to-noiseratio

• BER:biterrorrate

Fundamentaltrade-off:

energy-savingvs.ratevs.range•  givenSNR:chooseairinterfacethatmeets

BERrequirementathighestthroughput

•  SNRmaychangewithmobility:dynamically

adapttheairinterfacetocompensate

(modulationtechnique,rate)

•  allthelateststandardshaverateadaptation,including802.11,802.16,andLTE

QAM256(8Mbps)

QAM16(4Mbps)

BPSK(1Mbps)

10 20 30 40

SNR(dB)

BE

R

10-1

10-2

10-3

10-5

10-6

10-7

10-4

DealingwithBitErrors

Wiredvs.wirelesslinks

• wired:mostlossisduetocongestion

• wireless:higher,time-varyingbit-errorrate

Dealingwithhighwirelessbit-errorrates

• sendercouldincreasetransmissionpower

•  requiresmoreenergy(badforbattery-poweredhosts),and

•  createsmoreinterferencewithothersenders

• strongererrordetectionandrecovery• morepowerfulerrordetection/correctioncodes

•  link-layerretransmissionofcorruptedframes

ManyTCPalternatives/extensionsforwireless

• e.g.,TCPWestwoodusesanExplicitLossNotification(ELN)bit

Multi-antenna(MIMO)

WithbandwidthreachingShannon’slimit,futuregainin

bandwidthwillcomefromsmarterantennause:

Beamforming(a.k.a.,smartantenna/adaptiveantennasystem

(AAS)):generateinterferingpatternsfrommultipleantennae

suchthattheintendedsignalisstrengthened,inthedirection

intended(Cf.noisecancellationheadphones)

Spatialmultiplexing:organizeddataintospatialstreamsthat

aretransmittedsimultaneously,onthesamefrequency,using

multipleantennae;streamsreceivedovermultipleantennae

andseparatedusingvariousdetectionalgorithms

•  increaseinspectralefficiency(andresultingdatarate)

andqualityoftransmission

MIMOAntennaTechnique

MIMO:Multi-Input/Multi-Output

• there’sapropagationpathbetweeneachtransmit(Tx)and

receive(Rx)antenna(a“MIMOpath”)

• N×MMIMO(e.g.,4×4, 2×2, 2×3)•  Ntransmitantennas

•  Mreceiveantennas

•  totalofN×Mpaths

• MIMOtransmissionincreasesthroughputbybeamforming,error

correctionacrossTxantennae,signalinterpolationacrossRxantennae,

networkcodingacrossmultiplehosts(co-MIMO)

[Mlinarsky&Turner,Schill]

TxMIMO

ReceiverInput Output

Rx1

Rx2

2×3MIMO

Rx32×3