wireless for mobile computing

8/8/2019 Wireless for Mobile Computing

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Wireless Protocols for

Mobile Computing

Technology Overview

Paul J. Fong 12 August 2003


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The Impossible Dream

Well have infinitebandwidth in a decades

time. Bill Gates, PCMag, 11/11/94.

computercommunications willbreak down into two

domains - thefibersphere and theatmosphere. - GeorgeGilder, Forbes, 3/29/93.


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Topics

IEEE Standard 802.11: Mobile EthernetShort history

Layer 1: spread spectrumLayer 2: collision avoidanceUpdate on security issues

Layer 3: Wireless Routing

Mobile Ad hoc NetworksSensor Networks

Bluetooth Special Interest Group (SIG)FCC Initiatives


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1941: Hedy Lamarr

UNITED STATES

PATENT OFFICE

2,292,387SECRET

COMMUNICATIONSYSTEM

Hedy Kiesler Markey,

Los Angeles, and GeorgeAntheil, Manhattan

Beach, Cakif.Application June 10,

1941, Serial No. 397,412


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2001:Mic

hael Powell, FCCChairman

Species migrate toescape hostile

conditionsCompanies "seekshelter in regulationsto protect themselvesin the fierce storm of

the market," yet often"attempt to useregulation to harm orburden theircompetitors."


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Industrial Scientific Medical (ISM)Unlicensed Spread Spectrum Bands


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IEEE 802.11 Transmission Modes

Initial SpecificationInfrared

1 or 2 MbpsFrequency HoppingSpread Spectrum (FHSS)

Direct Sequence SpreadSpectrum (DSSS)

802.11aOrthogonal Frequency

Division Multiplexing(OFDM)

54 Mbps/5 GHz

802.11bHigh Rate DSSS

11 Mbps/2.4 GHz802.11g

OFDM

22-54 Mbps/2.4 Ghz


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Allocating Spectrum

Frequency DivisionMultiple Access(FDMA)

Time DivisionMultiple Access

(TDMA)Code DivisionMultiple Access(CDMA)


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CDMA Example: 2-chip Sequence

Station A:

1-bit: +A = [+1 +1]

0-bit: -A = [-1 -1]

Normalized Dot Product:

X * Y =

1/2[(x1)(y1)+(x2)(y2)]

Receiver extracts data:

(+A) * A = 1 (1-bit)(-A) * A = -1 (0-bit)


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CDMA Example (cont)2 stations:

+A=[+1 +1] +B=[-1 +1]

-A=[-1 -1] -B=[+1 -1]Both transmit,receiver hears:

S1 = +A+B = [ 0 +2]

S2 = -A+B = [-2 0]

Extract A=[+1 +1]:

S1*A = 1/2( 0 +2)

= 1 (1-bit)

S2*A = 1/2(-2 +0)

=-1 (0-bit)


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CDMA Example (cont)A & B are orthogonal,

so A*B = B*A = 0

(+A+B)*A = A*A + B*A

= 1 + 0

= 1-bit

(-A+B)*A = -A*A + B*A

= -1 + 0

= 0-bit


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802.11b Dynamic Rate Shifting

Data rate can be automaticallyreadjusted for noise and distance

Data Rate Code Modulation Symbol Rate Bits per

(Mbps) Length (MSps) Symbol1 11 (Barker Sequence) Binary Phase Shift Keying 1 1

2 11 (Barker Sequence) Quadrature Phase Shift Keying 1 2

5.5 8 (Complementary Code Keying) Quadrature Phase Shift Keying 1.375 4

11 8 (Complementary Code Keying) Quadrature Phase Shift Keying 1.375 8


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802.11b Frequency Channels

14 (22 MHz) frequency channels (11 in US)3 non-overlapping channels11 Mbps data rateSpreading codes used


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802.11b Range

Fixed Point to Point:

1w limit (4w EIRP)

Typical Indoor Use:30-100 milliwatts

Omnidirectional:150-300 feet

Timing Modification:72 miles SanClemente Island


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Layer2

Implementations:

Infrastructure (Managed) LAN


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Layer2

Implementations:

Ad Hoc (Unmanaged) LANPeer-to-peer

No access pointsDistributedCoordinationFunction (DCF)


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Layer2: Channel Contention

Point CoordinationFunction (PCF)

Polling by basestation or accesspoint

DistributedCoordinationFunction (DCF)

Mobile Ethernet

CSMA/CA:

Collision AvoidanceNot CSMA/CD


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Point Coordination Function(PCF)Access point pollsclients (2007 max.

per cell)Beacon frames sentfor synchronization

No collisions within

cellAllows guaranteedQuality of ServiceAccess

Point

A

B

C

D


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Hidden Station Problem

A is transmitting to B

C is out of range of AC transmits to B causing collision

DCF attempts to solve this problem

A B C


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Exposed Station

B is transmitting to A

C wants to transmit to DC senses transmission & declines

No 802.11 solution

A B C D


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DCF Virtual Ch

annel Sensing:Request to Send

A B C D

RTS


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DCF Virtual Ch

annel Sensing:

Clear to Send

A B C D

CTS


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Virtual Channel Sensing: Timing

RTS

CTS

DATA

ACK

Netw r All ti Vect r

Netw r All cati Vect r

A

B

C

D

Ti e


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Inter-Frame Spacing (IFS)

ACK

SIFS

PIFS

DIFS

EIFS

Ti

ShortInterframeSpacing (28 usec)

PCF InterframeSpacing (78 usec)

DCF Interface

Spacing (128 usec)Extended InterframeSpacing


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Virtual Ch

annel Sensing:Fragment Burst


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Doonesbury


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Wireless Insecurity

War Driving

Early Security ToolsSSID key & MACfilter

Wireless EquivalentPrivacy (WEP)

War Driving ToolsAirSnort

WepCrack

Rogue Access Point


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Wireless Security

Behind access point:

Gateway

Firewall

At the access point:Tunneled TransportLayer Security (TTLS)

Protected ExtensibleAuthentication Protocol(PEAP)

RADIUS authentication

Encrypted handshake


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Layer 3:

MobileA

dh

ocN

etworks(MANET)


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MANETApplications

Disaster Site

Archeological Site

Battlefield

Fleet of ships

Squadron of aircraft

Outdoor conference

Sensor networks


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Wireless Mobile Routing

Each node alsoroutes

Dynamic topology

Flat networkaddressing

No aggregation

Single port typical


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A

dh

oc On Demand Distance Vector(AODV)On-demand routecalculation

No periodicbroadcasts ofrouting table

Only changes

propagatedSequence numbers

IANA port 654


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Route Discovery

Node A wants tosend a packet to I

Node A broadcasts aroute request.

BC

D

E

F

G

H I

A


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Route Discovery (2)

BC

D

E

FG

B & D propagateroute requests

Duplicate routerequests discardedusing hop count

Reverse routesestablished


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Route Discovery (3)

BC

D

E

FG

C, F & G propagateroute requests

1stroute requestreaches node I


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Route Discovery (4)

Node I sends routereplyB

C

D

E

FG


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Route Maintenance

BC

D

E

F

H I

A Periodic hellomessages are sent

Node G goes offline

Routes for node Gare pruned


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Geographical Routing

Longitude & Latitude

Grid LocationService

Packet forwarded toneighbor nearest to

destination


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Common Wireless Routing Protocols

Destination-SequencedDistance Vector (DSDV)

Dynamic SourceRouting (DSR)

Optimized Link StateRouting (OLSR)

Temporally-OrderedRouting Algorithm(TORA)


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SensorNetworks

1stResponders

Tiny OS

Add-on sensors:

GPS

Temperature

AccelerometersRadar


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Micro Radar Mote

DARPA project

Detect intruderswith micro-poweredradar detectors andrelay data throughmote network

Dropped from UAV(Predator)


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Bluetooth

Viking King Blatand(Bluetooth) united

Denmark & Norway.

So shall theBluetooth wirelessstandard unitepersonal electronicdevices.


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Bluetooth Specifications2.4 Gigahertz ISM

Frequency Hopping

79 frequencies:1 MHz apart

1600 hops/second

625 microsec slots

Time-DivisionDuplex (TDD)

1 Mbps 7 Mbps


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Bluetooth Mouse Application

Bluetooth Mouse

USB antenna

Recharging Cradle

Power Class 3:

1 milliwatt power

10 meter range


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PersonalArea Networks (PAN)Wireless PAN

Bluetooth cell phone

Bluetooth headsetBluetooth Piconet

1 Master

Up to 7 slaves

Same FH channel

ScatternetOverlapping piconets

Different FH channels


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Bluetooth & 802.11b Integration

Bluetooth Piconet

802.11b InternetAccess

CoexistenceSchemes


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Overlapping Frequencies


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FCC Spectrum Scarcity IssuesTime Dimension

License for certain times of a day

Licenses that expire with old technologyFlexible software licenses

Receiver StandardsPoor receivers part of the interference problem

Will not automatically blame transmitters

Wireless Broadband IEEE 802.16Wireless Metropolitan Area Network (WMAN)

Wireless local loop

Point-to-Multipoint/10-66 GHz


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Powell Speech: Boulder, Colorado

30 Oct02..interference is often more a product of receivers;that is receivers are too dumb or too sensitive or too

cheap to filter out unwanted signals...a software defined radio may allow licensees todynamically rent certain spectrum bands when theyare not in use by other licensees.

Spectrum is an essential input in the continuing fightagainst terrorism, a force multiplier for our military

and an everyday necessity for public safety officials.

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