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E6126 : Wireless MultipleAccess Communicationsl Instructor:DrTonyQ.S.Quek*[email protected]

l Office:S1-B1b-71l OfficeHours:Byapptthroughemail

l LectureNotesandAssignments:Availableatwww.edventure.edu.sg

l Pre-requisites:l Digitalcommunications,probability,FourierandZ-transform,matrices.

*Other instructor : A/Prof Erry Gunawan 1


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Text Book & ReferenceslTextbook(highlyrecommended)

lA.Goldsmith,WirelessCommunications,CambridgeUniversityPress,2005.

lReferenceslJ.Proakis,DigitalCommunications,4thedition,McGrawHill,2001.

lT.S.Rappaport,WirelessCommunications,2nd

edition,Prentice-Hall,2002.

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E6126 : Outline (Part I)l OverviewofWirelessCommunicationsSystemsl WirelessChannels

lPathLoss,Shadowing,andFadingModelslCapacityofWirelessChannels

l DigitalModulationlPerformanceinFadingChannels

l DiversitylMIMOSystems

l Equalizationl MulticarrierModulation

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Wireless Channelsl Path Loss (includes average shadowing)l Shadowing (due to obstructions)l Multipath Fading

Pr/Pt

d=vt

PrPt

d=vt

v Very slow

Slow

Fast

4


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Digital Modulationsource source encoder channel encoder modulator

demodulator

discrete

channel

user source decoder channel decoder

channel

Modulation: Convert digital data into a signal waveform to be transmitted over

the channel. . .

Baseband modulation: Transmitted signal at low frequencies

e.g. cables, hard-disks, . . .

Carrier/bandpass modulation: Transmitted signal at high frequencies

e.g. radio channels, . . .


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Diversityl Basic Idea

lSend same bits over independent fading paths Independent fading paths obtained by time, space,frequency, or polarization diversity

lCombine paths to mitigate fading effectsTb

tMultiplepathsunlikelytofadesimultaneously


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MIMO SystemsSIMO case:

Tx Rx

N1 antenna antennas

MISO case:

Tx Rx

Nantennas 1 antenna

MIMO case:

Tx Rx

N Mantennas antennas

channel


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Equalization Visualization of the effect of ISI (for the noise-free case)

Received signal (noise free): r(t) =P

n b[n]x(t nT)

Effective impulse response: x(t) = (gT gC gR)(t)(incl. transmit, channel, and receive filter)

Eye diagram superimpose the waveforms {r(t kT), k = 1, 2, . . .}

Example(a) BPSK signal with ISI free pulse in (open eye);(b) BPSK signal with ISI (closed eye).

[U. Madhow, Fundamentals of Dig. Comm., 2008]


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Multicarrier Modulation

l Breaks data into N substreamsl Substream modulated onto separate carriers

l Substream bandwidth is B/N for B total bandwidthl B/N


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OverviewofWirelessCommunications

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Wireless Historyl Radioinventedinthe1880sbyMarconil ManysophisticatedmilitaryradiosystemsweredevelopedduringandafterWW2

l Cellularhasenjoyedexponentialgrowthsince1988,withalmost3billionusersworldwidetodayl Ignitedthewirelessrevolutionl Voice,data,andmultimediabecomingubiquitousl Useinthirdworldcountriesgrowingrapidly

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Evolution of Current Systemsl Wirelesssystemstoday

l 3GCellular:~200-300Kbps.lWLANs&Wimax:~450Mbps(andgrowing).

lNextGenerationisintheworksl 4GCellular:LikelyOFDM/MIMO,LTEl 4GWLANs:Wideopen,3Gjustbeingfinalized

l TechnologyEnhancementslHardware:Betterbatteries.Bettercircuits/processors.l Link:Antennas,modulation,coding,adaptivity,BW.lNetwork:NWcoding,Co-operativecommunicationslApplication:SoftandadaptiveQoS.

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Design Challengesl Wirelesschannelsareadifficultandcapacity-limitedbroadcastcommunicationsmedium

l Trafficpatterns,userlocations,andnetworkconditionsareconstantlychanging

l Applicationsareheterogeneouswithhardconstraintsthatmustbemetbythenetwork

l Energyanddelayconstraintschangedesignprinciplesacrossalllayersoftheprotocolstack

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Multimedia RequirementsVoice VideoData

Delay

Packet Loss

BER

Data Rate

Traffic


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Crosslayer Designl Applicationl Networkl Channel Accessl Linkl Hardware

Delay Constraints

Rate Constraints

Energy Constraints

Adapt across design layers

Reduce uncertainty through scheduling

Provide robustness via diversity16


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Current Wireless Systemsl Cellular Systemsl Wireless LANsl Satellite Systemsl Paging Systemsl Bluetoothl Ultrawideband radiosl Zigbee radios

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3G Cellular Design:Voice and Datal Data is bursty, whereas voice is continuous

l Typically require different access and routing strategiesl 3G widens the data pipe:

l 384 Kbps (802.11n has 100s of Mbps).l Standard based on wideband CDMAl Packet-based switching for both voice and data

l 3G cellular popular in Asia and Europel Evolution of existing systems in US (2.5G++)

GSM+EDGE, IS-95(CDMA)+HDR 100 Kbps may be enough Dual phone (2/3G+Wifi) use growing (iPhone,Google)

l What is beyond 3G? The trillion dollar question18


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Wireless Local AreaNetworks (WLANs)

l WLANs connect local computers (100m range)l Breaks data into packetsl Channel access is shared (random access)l Backbone Internet provides best-effort service

l Poor performance in some apps (e.g. video)

01011011

Internet

Access

Point

0101 1011

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Wireless LAN Standardsl 802.11b (Old 1990s)

l Standard for 2.4GHz ISM band (80 MHz)l Direct sequence spread spectrum (DSSS)l Speeds of 11 Mbps, approx. 500 ft range

l 802.11a/g (Middle Age mid-late 1990s)l Standard for 5GHz NII band (300 MHz)l OFDM in 20 MHz with adaptive rate/codesl Speeds of 54 Mbps, approx. 100-200 ft range

l 802.11n (Hot stuff, standard close to finalization)l Standard in 2.4 GHz and 5 GHzbandl Adaptive OFDM /MIMO in 20/40 MHz (2-4 antennas)l Speeds up to 600Mbps, approx. 200 ft rangel Other advances in packetization, antenna use, etc.

Many WLANcards haveall 3 (a/b/g)

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Satellite Systems

l Cover very large areasl Different orbit heights

l GEOs (39000 Km) versus LEOs (2000 Km)l Optimized for one-way transmission

l Radio (XM, DAB) and movie (SatTV) broadcastingl Most two-way systems struggling or bankrupt

l Expensive alternative to terrestrial systeml A few ambitious systems on the horizon


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Paging Systemsl Broad coverage for short messagingl Message broadcast from all base

stationsl Simple terminalsl Optimized for 1-way transmissionl Answer-back hardl Overtaken by cellular


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8C32810.61-Cimini-7/98

Bluetoothl Cable replacement RF technology (low

cost)l Short range (10m, extendable to 100m)l 2.4 GHz band (crowded)l 1 Data (700 Kbps) and 3 voice channelsl Widely supported by telecommunications,PC, and consumer electronics companiesl Few applications beyond cable


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Ultrawideband Radio(UWB)l UWB is an impulse radio: sends pulses of tens

of picoseconds(10-12) to nanoseconds (10-9)l Duty cycle of only a fraction of a percentl A carrier is not necessarily neededl Uses a lot of bandwidth (GHz)l Low probability of detectionl Excellent ranging capabilityl Multipath highly resolvable: good and bad

l Can use OFDM to get around multipath problem.


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IEEE 802.15.4 / ZigBeeRadiosl Low-Rate WPANl Data rates of 20, 40, 250 kbpsl Star clusters or peer-to-peer operationl Support for low latency devicesl CSMA-CA channel accessl Very low power consumptionl Frequency of operation in ISM bands


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Future Wireless NetworksWireless Internet accessNext generation CellularWireless Ad HocNetworksSmart GridSmart homes/spacesWireless MultimediaSmart Homes/SpacesAutomated HighwaysAll this and more

Ubiquitous Communication Among People and Devices

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Technical Challenges

28

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Spectral Reuse

Due to its scarcity, spectrum is reused

BS

In licensed bands

Cellular, Wimax Wifi, BT, UWB,

and unlicensed bands

Reuse introduces interference


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Interference: Friend or Foe?

l If treated as noise: Foe

l If decodable (MUD): Neither friend nor foe

l If exploited via cooperation and cognition:Friend (especially in a network setting)

IN

PSNR

+

=Increases BER

Reduces capacity


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Multiuser Detection

Signal 1Demod

Signal 2Demod

- =Signal 1

- =

Signal 2

Code properties of CDMA allow the signal separation and subtraction


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MIMO in Cellular:Performance Benefits

lAntenna gain extended battery life,extended range, and higher throughput

l Diversity gain improved reliability, morerobust operation of services

l Multiplexing gain higher data ratesl Interference suppression (TXBF)

improved quality, reliability, robustness

l Reduced interference to other systems


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Network MIMO. .

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Scarce Wireless Spectrum

$$$


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Intelligence beyondCooperation: Cognitionl Cognitive radios can support new wireless users in

existing crowded spectruml Without degrading performance of existing users

lUtilize advanced communication and signalprocessing techniquesl Coupled with novel spectrum allocation policies

lTechnology couldl Revolutionize the way spectrum is allocated worldwidel Provide sufficient bandwidth to support higher quality

and higher data rate products and services


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Cognitive Radio Paradigms

l UnderlaylCognitive radios constrained to cause minimal

interference to noncognitive radios

l InterweavelCognitive radios find and exploit spectral holes

to avoid interfering with noncognitive radios

l OverlaylCognitive radios overhear and enhance

noncognitive radio transmissions Knowledgeand

Complexity


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Underlay Systems

l Cognitive radios determine the interference theirtransmission causes to noncognitive nodeslTransmit if interference below a given threshold

lThe interference constraint may be metlVia wideband signalling to maintain interference

below the noise floor (spread spectrum or UWB)

lVia multiple antennas and beamforming

NCR

IP

NCRCR CR


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Interweave Systems

l Measurements indicate that even crowded spectrumis not used across all time, space, and frequenciesl Original motivation for cognitive radios (Mitola00)

lThese holes can be used for communicationl Interweave CRs periodically monitor spectrum for holesl Hole location must be agreed upon between TX and RXl Hole is then used for opportunistic communication with

minimal interference to noncognitive users


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Green Communications

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Motivation for Green$ $

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CO2 Annual Emissions( ( ( (

Energy ~2TWh ~60TWh ~3.5TWh ~10TWh

CO2

~1Mt ~30Mt


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Traffic-Revenue Divide-end

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Heterogeneous Networks$ $ $

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Device Challenges

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Software Defined Radio

. . .

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Difference of M2M Cellular mobile networks are designed forhuman communication

Interactive communication between humans (voice, video)

Data communication involving humans (web browsing, file downloads,

etc).

Communication is connection-centric

Cellular mobile networks are optimized fortraffic characteristics ofhuman-based communication applications

Communication with a certain length (sessions) and data volume

Communication with a certain interaction frequency and patterns (talk-

listen, download-reading, etc.)

But: M2M communication is different


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M2M: Smart Grid

Control and reading of metering/infrastructure

Smart Elec.Smart

Water

Appliances

Temperature

Light

Wind Turbine

Solar Panel

Smart

Gas

Meters Coms

Home displays

TV, Computer

In-Home

Energy

Display

Breaker Valves

Gateway

Data

Center

WanCommunication

Image source: ETSI

Small message sizesLow to medium frequent communicationRelaxed delay requirementsHigh requirements on energy efficiency?Large number of devices


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M2M: Intelligent Transport System

Image source: ETSI

Very high

mobility/latency

requirements

High speed

mobility

Car-to-X:High mobilityHigh speedVery low latencySecurity


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M2M Challenges

M2M is an enabler of the Internet of Things. M2M is challenging

Interworking between M2M operator and mobile operator.

Efforts in Standardsnecessary, as less as possible.

Research needs to think beyond this approach M2M applications imply novel network performance metrics

Flexible MAC, low-overhead protocols, virtualization, energy efficiency,

First step: M2M traffic models for popular use cases (e.g. smart meters)!

Talk to industries and users of M2M communications.


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Summary

50

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wireless multiple 1

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