Wireless for Mobile Computing
Transcript of 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.