Mobile Wireless Networking - KU ITTCjpgs/courses/mwnets/lecture-physical-mwn-print.pdf · Mobile...

KU EECS 882 – Mobile Wireless Networking – Physical Layer and Mobile Wireless Environment

– 1 –

© James P.G. SterbenzITTC

James P.G. Sterbenz

Department of Electrical Engineering & Computer ScienceInformation Technology & Telecommunications Research Center

The University of Kansas

[email protected]

http://www.ittc.ku.edu/~jpgs/courses/mwn

Mobile Wireless NetworkingThe University of Kansas EECS 882Physical Layer & MW Environment

22 August 2011 rev. 11.0 © 2004–2011 James P.G. Sterbenz

22 August 2011 KU EECS 882 – Mobile Wireless Nets – Phy. Layer & Env. MWN-MW-2


Mobile Wireless NetworkingPhysical Layer and Mobile Wireless Environment

PL.1 Physical media and spectrumPL.2 Wireless channels and propagationPL.3 Modulation, coding, and error controlPL.4 Mobile wireless environment


– 2 –



Physical LayerPhysical Layer Communication

networkCPU

M app

end system

CPU

M app

end system

R = ∞

D = 0

• Physical layer communicates digital information– through a communication channel in a medium– digital bits are coded as electronic or photonic signals

• digital or analog coding

– over a link between nodes (layer 2)



Mobile Wireless NetworkingPhysical Layer and Mobile Wireless Environment

• EECS 882 is a networking course– but the operation of the network depends on…– characteristics of the communication channels– physical environment

• Therefore– brief non-mathematical introduction to physical layer

details in EECS 865• review for EE folk• important for CS and IT folk to understand why

– discussion of impact of mobility and wireless on network


– 3 –



Mobile Wireless NetworkingPL.1 Physical Media and Spectrum




Physical MediaGuided

• Guided media– wire

• twisted pair• coaxial cable• power line

– fiber optic cable

role in communication networks?


– 4 –



Physical MediaGuided




traditional Internet & PSTN mostly guided mediaEECS 780 and 881



Physical MediaUnguided




• Unguided media– free space

• radio frequency• optical


– 5 –



Physical MediaUnguided




• Unguided media– wireless free space

• radio frequency• optical

networks with unguided media subject for EECS 882



Wireless Free SpaceSpectrum

• Spectrum– range of frequencies available for communication

• λf = c ; c = 3×105 km/s

– only some spectrum usable for communicationwhich parts?

[http://www.ntia.doc.gov/osmhome/allochrt.pdf]


– 6 –





• λf = c ; c = 3×105 km/s

– RF: radio frequency• frequency determines propagation characteristics






• λf = c ; c = 3×105 km/s

– RF: radio frequency– optical

• infrared 800–900 nm = 333–375 THz 41 THz spectrum

why not higher frequencies?



– 7 –





• λf = c ; c = 3×105 km/s

– RF: radio frequency– optical– higher frequencies: UV, x-ray, γ-ray, …

• health risks of radiation exposure• frequency beyond current tranceiver technology• propagation problems




Wireless Free SpaceSpectrum Table

Usage ExamplesPropagationRangeBand

LOS

LOS

LOS

LOS

LOS

LOS

SW

GW

GW

GW

GW

GW

Sight

770–330 nm400– 900THzvisiblevisible

IR

EHF

SHF

UHF

VHF

HF

MF

LF

VLF

VF

ELF

Name Attenuation

300GHz–400THz

30– 300GHz

3– 30GHz

300–3000MHz

30– 300MHz

3– 30MHz

300–3000kHz

30– 300kHz

3– 30kHz

300–3000 Hz

30– 300 Hz

Frequencies

optical comm.1000–770nminfrared

wireless comm.O2, H2O vapor10– 1mmext. high

wireless comm.O2, H2O100– 10mmsuper high

television, cell tel.cosmic noise1000–100mmultra high

television, FM radiotemp, cosmic10– 1 mvery high

transportationdaytime100– 10 mhigh

maritime, AM radiodaytime1000–100 mmedium

maritimedaytime10– 1kmlow

submarineatmos. noise100– 10kmvery low

voice tel., modem1000–100kmvoice

home automation10– 1Mmext. low

WavelengthDescription


– 8 –



Wireless Free SpaceCommunication and Radar Bands

• Communication band designations– UHF, VHF, and SHF bands subdivided– ITU-T B.15 and ITU-R V.431-7– IEEE Std. 251



Wireless Free SpaceCommunication and Radar Bands

television, p2p radio1000–300mm300MHz–1GHzUHF

cordless and mobile phones, satellite300–150mm1–2GHzUHFL

SHF

PSTN relay, satellite, WLAN75– 40mm4–8GHzC

satellite links40– 25mm8–12GHzX

satellite links25– 17mm12–18GHzKu

satellite, µwave links17– 10mm18–27GHzK

satellite, WMAN10– 7.5mm27–40GHzKa

Usage ExamplesRangeBand

future27–.77µm110–300GHzmm

W

V

S

VHF

Name

75–110GHz

40–75GHz

2–4GHz

30– 300MHz

Frequencies

future40– 27µm

emerging WLAN, WMAN7500– 40µmEHF

WLAN, WPAN, WMAN, satellite150– 75mm

television, FM radio10– 1 mVHF

WavelengthPartition


– 9 –



Wireless SpectrumAllocation

• Spectrum allocationwhat is it?




• Spectrum allocation – how to partition among:– application

• broadcast radio, television, data communication, etc.


– 10 –






– user sector• consumer, business, government, military






– user sector• consumer, business, government, military

– assignees• entity that is allowed to transmit into spectrum• service providers and/or end users


– 11 –



Wireless SpectrumAllocation: Governance

• Governance of spectrum allocation• International

– ITU-R: International Telecommunication –Radio Sector www.itu.int/ITU‐R

– began as International Telegraph Union in 1865– now agency under UN mandate

• incentive for UN members to play nice



Wireless SpectrumAllocation: Governance

• Governance of spectrum allocation• International

– ITU-R: International Telecommunication –Radio Sector www.itu.int/ITU‐R

• National: government agency or appointee– US FCC – Federal Communications Commission

www.fcc.gov

– UK Ofcom – Office of Communicationswww.ofcom.org.uk

– India TRAI – Telecom Regulatory Authority of India www.trai.gov.in

– etc.


– 12 –



Wireless SpectrumRegulation

• Regulations for transmission within allocation– determined and enforced by governing bodies

• Parameters for allowed communication, e.g.– transmission power– field strength– interference parameters

• transmission energy permitted outside allocation

– geographic limits– date and time restrictions

• e.g. AM radio clear channel interference



Wireless SpectrumEnforcement

• Enforcement of transmission regulations– enforcement by national entity– e.g. US FCC EB (enforcement bureau) www.fcc.gov/eb

• Can cause international tension– e.g. former border blasters

• e.g. XETRA-AM (Mighty 690) in Tijuana Mexico• now US-Mexico treaty coordinates AM transmission


– 13 –



Wireless SpectrumLicensing

• Licensed spectrum– most frequency bands require license to transmit– generally issued by national authority (FCC, Ofcom, etc.)

• e.g. broadcast TV, radio, amateur radio, GMRS• e.g. mobile telephony






– some unlicensed bands do not require license to transmit• e.g. US CB (citizen band), FRS (family radio system)• e.g. ISM for cordless telephones and wireless LANS


– 14 –






– some unlicensed bands do not require license to transmit• e.g. US CB (citizen band), FRS (family radio system)• e.g. ISM for cordless telephones and wireless LANS

unlicensed ≠ unregulated!



Licensed SpectrumBroadcast Radio and Television

transcontinental broadcast radio2.3 – 26.1 MHzAM short wave

US ch.broadcast television54 – 72 MHz76 – 88 MHz

VHF TV ch. 2–4ch. 5–6

broadcast radio520 – 1610 kHzAM medium wave

512 – 698 MHz698 – 806 MHz806 – 894 MHz

174 – 216 MHz

65.9 – 74 MHz76 – 90 MHz87.5 – 108 MHz

153 – 279 kHz

Frequency Range

ch. 18–51UHF TV ch. 52–69

ch. 70–83

VHF TV ch. 7–13

FM radio

AM long wave

Allocation

phasing outreclaimed

broadcast television

US ch.broadcast television

OIRTJapanInternational

broadcast radio

not USbroadcast radio

NotesTypical Use


– 15 –



Licensed SpectrumSelected Telephony Bands

1710 – 1755 MHzcdma2000, UMTS

Europe890 – 960 MHz1710 – 1880 MHz

GSM

Americas PCS1850 – 1990 MHzIS-95, GSM

2496 – 2690 MHz

2110 – 2155 MHz

824 – 894 MHz

Frequency Band

LTE-A

cdma2000, UMTS, W-CDMA

AMPS, IS-95, GSM

Allocation

Americas

Notes



Wireless Free SpaceUnlicensed Spectrum

• Unlicensed spectrum– regulations for use (FCC Title 47 Part 18 and 15.243–249)

• max transmit power (e.g. 1W)• field strength• spread spectrum parameters

– ISM: industrial, scientific, and medical• … 900 MHz, 2.4 GHz, 5.8 GHz, 24GHz …

– UNII: unlicensed national information infrastructure• 5.8 GHz

– may be use by anyone for any purpose (subject to regulations)

problem?


– 16 –



Wireless Free SpaceUnlicensed Spectrum

• Unlicensed spectrum– regulations for use (FCC 15.243–249)

• e.g. max transmit power• e.g. spread spectrum parameters

– ISM: industrial, scientific, and medical• … 900 MHz, 2.4 GHz, 5.8 GHz, 24GHz …

– UNII: unlicensed national information infrastructure• 5.8 GHz

– may be use by anyone for any purpose (subject to regulations)

– interference a significant problem• e.g. 2.4 GHz FHSS cordless phones against 802.11b• e.g. interference among 802.11 hubs in dense environments



Unlicensed SpectrumISM Bands

802.11ad, millimeter-wave links61.250 ± 0.250 GHz61 GHz

27.120 ± 0.163 MHz27 MHz

40.680 ± 0.020 MHz40 MHz

13.560 ± 0.007 MHz13 MHz

245.000 ± 1.000 GHz

122.500 ± 0.500 GHz

24.125 ± 0.125 GHz

5.800 ± 0.075 GHz

2.450 ± 0.050 GHz

915.00 ± 13.00 MHz

433.92 ± 0.87 MHz

6.78 ± 0.15 MHz

Center & BW Freq

245 GHz

122 GHz

24 GHz

5.8 GHz

2.4 GHz

900 MHz

433 MHz

7 MHz

Band

future

future

Microwave mesh link

cordless phones, WLANs (limited use)

cordless phones, WLANs, WPANs

cordless phones, WLANs (historic)

Europe

NotesTypical Use


– 17 –



Wireless SpectrumAllocation Process

• ITU allocates and regulates international spectrumproblem?




• ITU allocates and regulates international spectrum– competing national interests– agreement can be difficult– compromises are frequently poor solutions


– 18 –




• ITU allocates and regulates international spectrum• Government agencies allocate and regulate spectrum

problem?




• ITU allocates and regulates international spectrum• Government agencies allocate and regulate spectrum

– competing business, consumer, and government interests– agreement can be difficult– compromises are frequently poor solutions


– 19 –




• Spectrum allocated in fixed frequency ranges– exclusive use : spectrum within defined area

• government, military, public safety, public interest




• Spectrum allocated in fixed frequency ranges– exclusive use


– command-and-control : license assignment• comparative bidding

– process: broadcasters and service providers submit proposalsproblem?


– 20 –






– command-and-control• comparative bidding

– process: broadcasters and service providers submit proposals– problem: fairness (real and perception) and appeals






– command-and-control• comparative bidding• lottery

– process: assignees picked by lotteryproblem?


– 21 –






– command-and-control• comparative bidding• lottery

– process: assignees picked by lottery– problem: companies bid with intent to resell spectrum






– command-and-control• comparative bidding• lottery• auction

– process: competitive auction for spectrumproblem?


– 22 –







– process: competitive auction for spectrum– problem: complex process

free market but antitrust issues







– commons : unlicensed (including ISM)• process: anyone can use subject to regulation

problem?


– 23 –







– commons• process: anyone can use subject to regulation• problem: interference

– among applications (e.g. WLANs, cordless phones, µwave ovens– among providers and users of given application (e.g. WLANs)




• Spectrum allocated in fixed frequency rangesproblem?


– 24 –




• Spectrum allocated in fixed frequency ranges– problem: very inefficient use of spectrum

why?





• spectrum reserved for future use• difficult to reclaim unused spectrum

– example: UHF TV reclaimed for GSM in 850MHz

• inability to load balance among different allocations


– 25 –



Wireless SpectrumFCC/NTIA Spectrum Allocation

• FCC allocates and licenses spectrum in US– static allocations lead to significant inefficiency in use









alternative?


– 26 –








– alternative: dynamic spectrum allocation• significant technical, political, and policy challenges• fear of making things worse• currently hot topic for research

– technical and policy



Wireless SpectrumDynamic Allocation

• FCC Spectrum Policy Task Force recommendationwww.fcc.gov/sptf– command-and-control should only be used when needed:

• to accomplish important public interest objectives• conform to treaty obligations

– significant expansion of commons allocation

• Dynamic spectrum management– SDR (software defined radios) a key technology– new algorithms and protocols– significant policy change


– 27 –



Mobile Wireless NetworkingPL.2 Wireless Channels and Propagation

PL.1 Physical media and spectrumPL.2 Wireless channels and propagation

PL.2.1 Digital and analog signalsPL.2.2 Wireless propagationPL.2.3 Channel characteristics and challenges

PL.3 Modulation, coding, and error controlPL.4 Mobile wireless environment



Mobile Wireless NetworkingPL.2.1 Digital and Analog Signals





– 28 –



CommunicationSignal Types

• Transmission of a signal through a medium





• Analog signal: time-varying levels– electrical: voltage levels– photonic: light intensity


– 29 –





• Analog signal: time-varying levels– electrical: voltage levels– photonic: light intensity

• Digital signal: sequence of bits represented as levels– electrical: voltage pulses– photonic: light pulses– two levels for binary digital signal

– more levels in some coding schemes more later



CommunicationDigital vs. Analog

• Digital bits are reconstructed at the receiver

0

1

time


– 30 –




• Digital bits are reconstructed at the receiver– all transmission is actually analog!– frequency response determines

• pulse rate that can be transmitted• shape of pulse → ability for receiver to recognise pulse

0

1

time




0

1

harmonic

harmonictime

• Digital bits are reconstructed at the receiver– all transmission is actually analog!– frequency response determines

• pulse rate that can be transmitted• shape of pulse → ability for receiver to recognise pulse

– high-frequency attenuation reduces quality of pulse

attenuated frequencies

adapted from [Tanenbaum 2003]

0

1

time


– 31 –



CommunicationDigital vs. Analog in Free Space

• Digital transmission is baseband– frequency spectrum begins at 0Hz– only practical for dedicated (guided media)

• wire and fiber optic cable

• Free space transmission generally broadband– digital information modulated over a range of frequencies



Mobile Wireless NetworkingPL.2.1 Wireless Propagation





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Wireless Free SpaceMedium Sharing

• Dedicated– single transmitter attached to medium– signals may be multiplexed by a single transmitter

• link multiplexing



Wireless Free SpaceMedium Sharing

• Dedicated– single transmitter attached to medium– signals may be multiplexed by a single transmitter

• link multiplexing

• Shared: multiple access– multiple transmitters transmit into a the same medium

Lecture ML


– 33 –



Wireless Free SpacePropagation Mechanisms

• Direct signal• Reflection• Diffraction• Scattering

WN



Wireless Free SpacePropagation Mechanisms: Direct

• Direct signal– direct transmission from transmitter to receiver

• Reflection• Diffraction• Scattering

WN


– 34 –



Wireless Free SpacePropagation Mechanisms: Reflection

• Direct signal• Reflection

– reflected off object large relative to wavelength

• Diffraction• Scattering

WN



Wireless Free SpacePropagation Mechanisms: Diffraction

• Direct signal• Reflection• Diffraction

– bending by object comparable to wavelength

• Scattering

WN


– 35 –



Wireless Free SpacePropagation Mechanisms: Scattering

• Direct signal• Reflection• Diffraction• Scattering

– by many objects smaller than wavelength– multiple weaker signals

WN



Wireless Free SpacePropagation Mechanisms: Multipath

• Multipath– multiple signals using different propagation mechanisms

problem?

WN


– 36 –



Wireless Free SpacePropagation Mechanisms: Multipath

• Multipath interference or distortion – multiple signals using different propagation mechanisms– time-shifted versions of signal interfere with one another

WN



Wireless Free SpaceAntennæ and Transmission Pattern

• Omnidirectional antennæ– RF radiated in all directions

advantages and disadvantages?


– 37 –




• Omnidirectional antennæ– RF radiated in all directions– advantage: simple cheap design




• Omnidirectional antennæ– RF radiated in all directions– advantage:

simple cheap design– disadvantage:

no spatial reuse


– 38 –




• Omnidirectional antennæ• Directional antennæ

– focused beam of radiationadvantages and disadvantages?





– focused beam of radiation– advantage

• reduces contention with spatial reuse


– 39 –





– focused beam of radiation– advantage

• reduces contention with spatial reuse– disadvantages

• more complex antenna design• significantly complicates

network design: beam steering MACLecture ML



Wireless Free SpacePropagation Modes

• Ground-wave propagation < 2 MHz• Sky wave propagation 2 – 30 MHz• Line-of-sight propagation > 30 MHz

ionosphere


– 40 –



Wireless Free SpacePropagation Modes: Ground Wave

• Ground-wave propagation < 2 MHz– signals follow curvature of earth– scattered in upper atmosphere

• Sky wave propagation 2 – 30 MHz• Line-of-sight propagation > 30 MHz

ionosphere



Wireless Free SpacePropagation Modes: Sky Wave

• Ground-wave propagation < 2 MHz• Sky wave propagation 2 – 30 MHz

– signals refracted off ionosphere– communication possible over thousands of kilometers

• Line-of-sight propagation > 30 MHz

ionosphere


– 41 –



Wireless Free SpacePropagation Modes: Line of Sight

• Ground-wave propagation < 2 MHz• Sky wave propagation 2 – 30 MHz• Line-of-sight propagation > 30 MHz

– antennæ must be in view of one-another– terrain and earth curvature block signature

ionosphere



Wireless Free SpaceSpectrum Table


LOS

LOS

LOS

LOS

LOS

LOS

SW

GW

GW

GW

GW

GW

Sight


IR

EHF

SHF

UHF

VHF

HF

MF

LF

VLF

VF

ELF

Name Attenuation

300GHz–400THz

30– 300GHz

3– 30GHz

300–3000MHz

30– 300MHz

3– 30MHz

300–3000kHz

30– 300kHz

3– 30kHz

300–3000 Hz

30– 300 Hz

Frequencies














– 42 –



Wireless Free SpaceVelocity

• Velocity v = c /n [m/s]– speed of light c = 3×105 km/s– index of refraction n

Consequences?



Wireless Free SpaceVelocity and Delay

• Velocity v = c /n [m/s]– speed of light c = 3×105 km/s– index of refraction n

• this is why velocity slower than c in fiber and wire

• Delay d = 1/v [s/m]– generally we will express delay in [s] given a path length


– 43 –



Mobile Wireless NetworkingPL.2.3 Channel Characteristics and Challenges






Wireless ChannelCharacteristics and Challenges

• Goal for communications link– receiver reconstructs signal transmitter sent– propagation (PL.2.2)

• Challenges to meeting this goal– path loss and attenuation– fading– noise and interference– Doppler Shift– transmission rate constraints


– 44 –



Wireless Channel ChallengesPath Loss and Attenuation

• Path loss and attenuation• Fading• Noise and interference• Doppler Shift• Transmission rate constraints



Path Loss and AttenuationTransmission Length

• Link Length– distance over which signals propagate– constrained by physical properties of medium

Consequences?


– 45 –




• Attenuation: decrease in signal intensity– over distance expressed as [dB/m]– at a particular signal frequency

how to compute?

dB

m

mdB




• Attenuation– signal strength decreases as 1/r 2 in perfect medium

why?


– 46 –




• Attenuation– signal strength decreases as 1/r 2 in perfect medium– signal may decrease as 1/r x with multipath interference

• rural environments: x > 2• urban environments: x → 4

more later



Path Loss and AttenuationFrequency Response

• Attenuation: decrease in signal intensity– over distance expressed as [dB/m]– at a particular signal frequency

• Frequency response of media– wire: generally falls off above a certain fmax

– fiber optic cable & free space transparent to certain rangesanalogy:UV blocking sunglasses (high attenuation )

vs.standard glass (moderate attenuation )

vs.UV transparent black light glass (low attenuation )


– 47 –



Path Loss and AttenuationSpectrum Table: Frequency Response


LOS

LOS

LOS

LOS

LOS

LOS

SW

GW

GW

GW

GW

GW

Sight


IR

EHF

SHF

UHF

VHF

HF

MF

LF

VLF

VF

ELF

Name Attenuation

300GHz–400THz

30– 300GHz

3– 30GHz

300–3000MHz

30– 300MHz

3– 30MHz

300–3000kHz

30– 300kHz

3– 30kHz

300–3000 Hz

30– 300 Hz

Frequencies















Path Loss and AttenuationFrequency Response

• Atmospheric transparency bands– RF: 10MHz – 10GHz

• VHF meter band, UHF millimeter band– Infrared: N-band

RF

0.5

1.0

0.0

Atm

osph

eric

Opa

city

Wavelength [m] | Frequency [Hz]

10µm0.1nm 10nm 10m 100m 1km1m10cm1cm1mm100µm1µm1nm 100nm

adapted from[coolcosmos.ipac.caltech.edu/cosmic_classroom/ir_tutorial/irwindows.html]

10THz1EHz 10Pz 10MHz 1MHz 100KHz100MHz1GHz10GHz100GHz1THz100THz100PHz 1PHz

IR

UHF VHF

microwave shortwave


– 48 –



Wireless Channel ChallengesFading




Wireless Channel FadingDefinition

• Channel fading– changes of signal intensity over time


– 49 –



Wireless Channel FadingTypes and Cause


• Fast fading– rapid fluctuations in intensity– mobility on the order of 1/2 wavelength






• Slow fading– long-term fluctuations in intensity (seconds to minutes)

causes?


– 50 –






• Slow fading– long-term fluctuations in intensity (seconds to minutes)– causes

• obstructions such as rain (rain fade )• micro-mobility among buildings in urban areas• macro-mobility between base stations





• Flat fading (nonselective)– uniform fade across frequency range

• Selective fading– different frequency components suffer different attenuation


– 51 –



Wireless Channel ChallengesInterference




Noise and InterferenceDefinition

• Superposition interaction of waves is interferenceCauses?


– 52 –



Noise and InterferenceCauses

• Superposition interaction of waves is interference• Causes

– noise– co-channel interference– adjacent channel interference



NoiseCauses

• Noise interferes with signals• Thermal noise [W/Hz]

– caused by agitation of electrons: function of temperature t– independent of frequency: white noise

N = kTB ; k = 1.38×10-23 [J/K] (Boltzmann constant)B = bandwidth [Hz]


– 53 –



NoiseCause and Effect: SNR

• Noise interferes with signals• Thermal noise [W/Hz] = [(J/s)/s–1] = [J]

– caused by agitation of electrons: function of temperature t– independent of frequency: white noise

N = kTB ; k = 1.38×10-23 [J/K] (Boltzmann constant)B = bandwidth [Hz]

• Background noise No– thermal noise + other sources (e.g. cosmic radiation)– No interferes with the signal bit energy Eb

– SNR: signal to noise ratio = 10 log10 (Eb /No ) [db] (decibels)



InterferenceCo-Channel Interference

• Co-channel interference within given frequency bandCauses and solutions?


– 54 –




• Co-channel interference within given frequency band• Multiple users sharing channel

– motivates medium access control (MAC) Lecture ML






• Malicious attack: jamming of channel– faraday cage to repel – spread spectrum techniques Lecture ML– resilience techniques EECS 983


– 55 –






• Malicious attack: jamming of channel– Faraday cage to isolate when possible – spread spectrum techniques Lecture ML– resilience techniques EECS 983

• Natural phenomena– e.g. sunspots



InterferenceAdjacent Channel Interference

Solutions?

• Adjacent channel interference between freq. bands


– 56 –




Guard bands– reserved bandwidth between frequency bands




InterferenceAdjacent Channel Interference

• Spatial partitioning– adjacent channels not used in same geographic area

• e.g. TV broadcast channels (2,4,5,7,9,11,13 vs. 3,6,8,10,12)• e.g. FM broadcast stations • e.g. cellular frequency plan for mobile telephony



– 57 –



InterferenceAdjacent Channel Partitioning: Broadcast TV

• Spatial partitioning example: broadcast television– large cities get channels 2,4,5,7,9,11,13

recall guard band between 4/5 and 6/7– small towns in-between get channels 3,6,8,10,12

• Spatial partitioning example: broadcast FM radio– adjacent frequencies not used in same city

METROPOLISCh. 2,4,5,11GOTHAM

Ch. 2,4,5,7,9,11,13

SmallvilleCh. 10, 12

Elk’s BreathCh. 6

MayberryCh. 3,8



InterferenceAdjacent Channel Partitioning: Cellular

• Spatial partitioning example: cellular telephony– most efficient circular packing is hexagonal– frequency channels mapped to hexagonal tiling– adjacent cells assigned different frequencies Lecture MT

cell


– 58 –



Wireless Channel ChallengesDoppler Shift




Doppler ShiftDefinition

• Doppler shift– explained by Austrian scientist Christian Doppler in 1800s

what is it?


– 59 –



Doppler ShiftDefinition

• Doppler shift– explained by Austrian scientist Christian Doppler in 1800s– wavelength changes with relative velocity– recall decreasing pitch of horn as train passes

• Doppler effectfd = v/λ

Consequences?



Doppler ShiftConsequences

• Doppler shift– explained by Austrian scientist Christian Doppler in 1800s– wavelength changes with relative velocity– recall decreasing pitch of horn as train passes

• Doppler effectfd = v/λ

• Consequences– frequency perceived by receiver different from expected– concern networks with high node mobility


– 60 –



Wireless Channel ChallengesTransmission Rate Constraints

• Path loss and attenuation• Fading• Propagation modes and interference• Doppler Shift• Transmission rate constraints



Transmission Rate ConstraintsOverview

• Transmission rate constraints– transceiver switching frequency– Nyquist rate– Shannon rate


– 61 –



Transmission Rate ConstraintsSwitching Frequency

• Rate constrained by switching frequency– transmitter and receiver [b/s]– dictated by electronic circuits

• switching time of transistors• propagation delay through circuits



Transmission Rate ConstraintsNyquist Rate

• Channel capacity C [b/s]– determined by bandwidth

(max CS bandwidth determined by EE bandwidth)– constrained by number of quantization levels per bit

C = 2B log2 LB = channel bandwidth [Hz] = [1/s]L = number of quantization levels


– 62 –



Transmission Rate ConstraintsShannon Theorem

• Maximum data rate for noisy channel– noise reduces data rate

C = B log2 (1+ S/N ))C = channel capacity [b/s]B = channel bandwidth [Hz] = [1/s]S = signal power [dB]N = noise power [dB]



Mobile Wireless NetworkingPL.3 Modulation, Coding, and Error Control

PL.1 Physical media and spectrumPL.2 Wireless channels and propagationPL.3 Modulation, coding, and error control

PL.3.1 Modulation and codingPL.3.2 Error control

PL.4 Mobile wireless environment


– 63 –



Mobile Wireless NetworkingPL.3.1 Modulation and Coding






Modulation and CodingDigital Communication

• Digital Communication– we consider only digital communication for networking

• transmission of binary data (bits) through a channel

– recall: in free space digital signal is analog modulated• broadband, not baseband


– 64 –



Modulation and CodingLine Coding

• Line coding– way in which bits are encoded for transmission– digital codes (binary, trinary, …)– analog modulation



Modulation and CodingLine Coding and Symbol Rate

• Line coding– way in which bits are encoded for transmission– digital codes (binary, trinary, …) EECS 780– analog modulation

• Symbol rate– baud rate [symbols/s]

• baud = b/s only if one symbol/bit

– clever encodings (e.g. QAM) allow high baud rates


– 65 –



Line CodingAnalog Coding

• Analog line coding– modulate an analog carrier

with a digital signal

0 0 1 0 0 1 0 1 1 1



Analog Line CodingAmplitude Modulation

• Analog line coding– modulate an analog carrier

• Amplitude modulation– each symbol a different level of carrier

• one may be zero voltage

– compare to AM radio• modulate an analog carrier with

an analog signal

0 0 1 0 0 1 0 1 1 1


– 66 –



Analog Line CodingFrequency Modulation

• Analog line coding– modulate a carrier

• Amplitude modulation– each symbol a different level

• Frequency modulation– each symbol a different frequency– FSK (frequency shift keying)– compare to FM radio

• modulate an analog carrier withan analog signal

0 0 1 0 0 1 0 1 1 1



Analog Line CodingPhase Modulation

• Analog line coding– modulate a carrier


• Frequency modulation– each symbol a different frequency

• Phase modulation– each symbol a different phase– e.g. 0°, 180°

0 0 1 0 0 1 0 1 1 1


– 67 –



Analog Line CodingCombination Codes

• Analog line coding: – modulate a carrier



• Phase modulation– each symbol a different phase

• Combinations possiblewhy?

0 0 1 0 0 1 0 1 1 1



Analog Line CodingCombination Codes

• Analog line coding: – modulate a carrier



• Phase modulation– each symbol a different phase

• Combinations possible– e.g. amplitude and phase

0 0 1 0 0 1 0 1 1 1

00 10 01 01 11 00 10 01 01 11


– 68 –



Analog Line CodingQPSK and QAM

• Combination of amplitude- and phase-modulation– allows more bits per symbol

• QAM: quadrature amplitude modulation– quadrature = 4 phases carried on two sine waves– PAM is case for only one phase– QPSK is case for only one amplitude

844QAM-256

643QAM-64

442QAM-16

241QPSK

Bits/SymbolPhasesAmplitudesName



Analog Line CodingQPSK and QAM

• QAM: amplitude- and phase modulation• Represented by constellation diagram

– amplitude is distance from origin– phase is angle

0°180°

90°

270°

0°180°

90°

270°

0°180°

90°

270°

QAM-64QAM-16QPSK


– 69 –



Mobile Wireless NetworkingPL.3.2 Error Control






Error ControlIntroduction and Motivation

Motivation for error control?


– 70 –



Error ControlIntroduction and Motivation

• Motivation for error control– channels are imperfect

• cause: noise and interference• result: bit errors

– components can fail– packets my be dropped due to congestion EECS 780

• Therefore need error controlwhere to perform?

physical layer?link layer?transport layer?



Error ControlHop-by-Hop vs. End-to-End

• Per-hop error control for frame transfersWhy?


– 71 –



Error ControlHop-by-Hop vs. End-to-End

• Per-hop error control for frame transfers• Recall end-to-end arguments:

– if error checking and correction needed E2E …… it must be done end-to-end by transport (or application)

• Hop-by-hop control to improve overall performance– physical layer for bit errors in noisy channel– link layer at frame granularity Lecture ML



Error ControlDetection Techniques

• Byte, word, or (small) block: done at physical layer– parity– 2-dimensional parity– Hamming codes

• Frame: done at link layer Lecture ML– checksum– CRC


– 72 –



Block Error DetectionParity

• Parity: detect single errors– no ability to correct errors– only an odd number of bit errors detected

• only useful if bit error probability very low






• Parity bit covers n bit block• Even parity: even number of 1s (including parity)

– example: 0111 0001 1010 1011 ?

• Odd parity odd number of 1s (including parity)– example: 0111 0001 1010 1011 ?


– 73 –






• Parity bit covers n bit block• Even parity: even number of 1s (including parity)

– example: 0111 0001 1010 1011 1

• Odd parity odd number of 1s (including parity)– example: 0111 0001 1010 1011 0



Block Error Detection & Correction2-Dimensional Parity

• 2-dimensional parity: correct single bit errors– detects which bit flipped and can therefore correct


– 74 –





• n + m parity bits covers n × m bit block– n row parity bits cover m data bits each– m column parity bits cover n data bits each






• Example (odd parity)0111 00001 01010 11011 01000


– 75 –






• Example (odd parity)0111 0 0111 00001 0 0001 01010 1 1110 1 ← detects and can correct flip1011 0 1011 01000 1000



Block Error Detection & CorrectionHamming Codes

• Hamming codes: correct single bit errors– detects which bit flipped and can therefore correct– k parity bits per block cover different sets of n data bits


– 76 –





• SECDED: single error correct double error detect





• SECDED: single error correct double error detect• Example 4 data bits covered by 3 parity bits

– parity bits p2 p1 p0 interleaved with data bits d3 d2 d1 d0

1011010 d3 d2 d1 p2 d0 p1 p0

1‐1‐0‐1 d3 d1 d0 covered by p0

10‐‐00‐ d3 d2 d0 covered by p1

1011‐‐‐ d3 d2 d1 covered by p2


– 77 –





• SECDED: single error correct double error detect• Example 4 data bits covered by 3 parity bits

– parity bits p2 p1 p0 interleaved with data bits d3 d2 d1 d0

1011010 d3 d2 d1 p2 d0 p1 p0 11110101‐1‐0‐1 d3 d1 d0 covered by p0 1‐1‐0‐110‐‐00‐ d3 d2 d0 covered by p1 11‐‐00‐ p1 detects error1011‐‐‐ d3 d2 d1 covered by p2 1111‐‐‐ p2 detects error



Error Detection & CorrectionForward Error Correction

• Forward error correction (FEC)– redundant information added to data– allows detection of errors– also allows correction of errors


– 78 –



Error Detection & CorrectionForward Error Correction

• Forward error correction (FEC)– redundant information added to data– allows detection of errors– also allows correction of errors

• Types of FEC codes– block codes: FEC header over link layer frame Lecture ML– convolutional code: redundant bits interspersed in stream– turbo codes: iterative convolutional coder

• performs closer to theoretical Shannon limit

EECS 869



Forward Error CorrectionConvolutional Coder

• Convolutional code– redundant bits interspersed in stream


– 79 –



Mobile Wireless NetworkingPL.4 Mobile Wireless Environment


PL.4.1 Network impact of wireless channelPL.4.2 Network impact of mobility



Mobile Wireless EnvironmentImpact on the Network

• Recap: brief introduction to physical layerWhy does this matter to the network?


– 80 –




• Recap: brief introduction to physical layer• Network consists of nodes interconnected by links

– characteristics of links and nodes impact network




• Recap: brief introduction to physical layer• Network consists of nodes interconnected by links

– characteristics of links and nodes impact network

• Traditional PSTN and Internet– static (non-mobile) nodes– reliable wired links– many design decisions based on these assumptions

What is different and why does it matter?


– 81 –



Mobile Wireless EnvironmentPL.4.1 Network Impact of Wireless Channel





Impact of Wireless ChannelChannel Connectivity

Impact of wireless channel on connectivity?


– 82 –



Wireless ChannelChannel Connectivity

• Weak time-varying connectivity– limited bandwidth of shared medium– time-varying channel capacity

• noise• interference• fading




• Weak time-varying connectivity• Intermittent and episodic connectivity

– long fades (e.g. rain fades)– interference and jamming


– 83 –




• Weak time-varying connectivity• Intermittent and episodic connectivity• Asymmetric connectivity due to heterogeneous nodes

– unequal transmitter power• design• available power over battery life

– different up/downlink characteristics• mobile phones• satellite links



Wireless ChannelImpact of Weak Connectivity

• Traditional networks– strong symmetric connectivity assumed– weak connectivity treated as failure


– 84 –





Impact of weak connectivity?





• Impact of weak connectivity– bit errors → packet loss → performance impact– link failures → routing reconvergence– loss discrimination important Lecture WI


– 85 –





• Impact of weak connectivity– bit errors → packet loss → performance impact– link failures → routing reconvergence– loss discrimination important Lecture WI

• Mobile wireless networks– weak, asymmetric, intermittent, episodic connectivity routine– network architecture and protocol design for this



• Millimeter-wave links– 60–90 GHz, 1–10 Gb/s– severe rain attenuation

• Mesh architecture– high degree of connectivity– alternate diverse paths

• WDTN solution– reroute before failures occur– avoid high error links– P-WARP, XL-OSPF

[Jabbar Rohrer Oberthaler Çetinkaya Frost Sterbenz 2009]

Example Weak Connectivity ScenarioWDTN Millimeter-Wave Mesh Network

802.163–4G

CO/POP


– 86 –



Wireless ChannelOpen Channel

• Open channelproblems?



Wireless ChannelOpen Channel

• Open channel subject to attack– eavesdropping

• network and traffic analysis

– interference• jamming and denial of service

– injection of bogus signalling and control messages


– 87 –



Wireless ChannelImpact of Open Channel

• Open channel subject to attack– eavesdropping

• network and traffic analysis

– interference• jamming and denial of service

– injection of bogus signalling and control messages

• Security and resilience more importantLecture RSECS 983



Mobile Wireless EnvironmentPL.4.2 Network Impact of Mobility




– 88 –



Impact of MobilityOverview

Impact of mobility?



Impact of MobilityOverview

• Impact of mobility– connectivity– dynamic topologies– QoS


– 89 –



Impact of MobilityConnectivity

• Mobility impacts connectivity– nodes move in and out of range of one another– long fades– episodic and intermittent connectivity

• Design for weak connectivity– as for wireless channel impacts



Impact of MobilityDynamic Topologies

• Mobility means nodes and subnets move– result: dynamic topology– changing links, clustering, and federation topology– difficult to achieve routing convergence– mobility may exceed ability of control loops to react


– 90 –



Impact of MobilityDynamic Topologies

• Mobility means nodes and subnets move– result: dynamic topology– changing links, clustering, and federation topology– difficult to achieve routing convergence– mobility may exceed ability of control loops to react

• Design for mobility– addressing mechanisms must not assume static location– routing algorithms must assume dynamic topologies

• predictive• reactive



Impact of MobilityQuality of Service

• Mobility impacts QoS (quality of service)

1


– 91 –




• Mobility impacts QoS (quality of service)– changes in inter-node distance

• requires power adaptation• changes node density and impacts degree of connectivity

– latency issues (routing optimisations temporary)

2




• Mobility impacts QoS (quality of service)– changes in inter-node distance

• requires power adaptation• changes node density and impacts degree of connectivity

– latency issues (routing optimisations temporary)

3


– 92 –



Airborne Telemetry NetworkingScenario and Environment

• Very high relative velocity– Mach 7 ≈ 10 s contact– dynamic topology

• Communication channel– limited spectrum– asymmetric links

• data down omni• C&C up directional

• Multihop– among TAs– through relay nodes

GSGS

RN

TATA

TAs

Internet

GWGW

TA – test articleRN – relay node

GS – ground stationGW – gateway



Mobile Wireless EnvironmentImpact on Network

• Now we are ready for the rest of the course…


– 93 –



Physical LayerFurther Reading

• William Stallings,Data and Computer Communications, 8th ed.Pearson Prentice Hall, Upper Saddle River NJ, 2007.



Physical LayerAcknowledgements

Some material in these foils is based on the textbook• Murthy and Manoj,

Ad Hoc Wireless Networks:Architectures and Protocols

Significant material in these foils enhanced from EECS 780 foils

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