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MOBILE COMPUTING CSE 40814/60814 Spring 2017

CellularPosi0oning:CellID

Open-source database of cell IDs: opencellid.org

CellularPosi0oning-CellIDwithTATA: Timing Advance (time a signal takes to travel from mobile device to cell tower)

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CellularPosi0oning-EOTD

Your location is in the zone at the intersection of 3 cell circular bands

EOTD: Enhanced-Observed Time Difference

CellularPosi0oningPerformance

• Mapsoftheareaservedbyindividualcelltowersarecomplex

• GSMsignalrecep0on•  AJenuatedbybarriers•  Changewithcallvolume

•  Cellssizevaries100m-30Km•  Resul0ngposi0oningisinconsistentandunreliable

•  Sufficientforsomeapplica0ons

Cellular Based Location

• Developmentofloca0onsystemsbasedonmobilephasewasdrivenbyUSFederalCommunica0onCommission(FCC)

• Themainpurposewastolocatemobilephonestoassistphonestodeliveremergencyservices

• Lateritwasalsousedfor•  Loca0onBasedservices•  Adver0sement•  Recommenda0onsystems• Gaming

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ComparingCellularandGPSPosi0oning

Wi-FiPosi0oningSystems

• Wi-Fiaccesspoints(hotspots)broadcastsignalsupto100m

• Wi-Fichipsindevicesdetectthenameoftheaccesspoint,signalstrength,and(some0mes)angleofarrival

•  Clientdevicescandetectaccesspointsintwoways•  Passivelylisteningon802.11channelsforbeaconframes

•  Ini0atescanbysendingrequestswhichaccesspointsreply

Location based on 802.11

• 802.11takesadvantagesoftwoproper0esobservedbyclients•  Spa0alvariability:signalstrengthdependsondistance&loca0on•  Temporalconsistency:goodchancethiswillbetrueindays/weeks/months/...

• Mapof“radiofingerprints”canbeestablished

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Wi-Fi Localization • Wi-Fi is everywhere now

•  No new infrastructure •  Low cost •  APs broadcast beacons •  “War drivers” already build AP maps

•  Calibrated using GPS •  Constantly updated

• Position using Wi-Fi •  Indoor Wi-Fi positioning gives 2-3m

accuracy •  But requires high calibration

overhead: 10+ hours per building •  Changes over time (adding/removing/

relocating APs) impact accuracy

Manhattan (Courtesy of Wigle.net)

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AccesstoWirelessPosi0oning

• Skyhookprovideswirelessposi0oningsolu0on(XPS)basedonfusionofGPS,Wi-Fi,andcellular

• Ekahauoffersacommercialsolu0onusingfingerprin0ngmainlyforinternalbuildingposi0oning

Hybrid Positioning System (XPS)

Radio-Naviga0on(LORAN)• Synchronizedsignalsarebroadcastfromcoastalsta0onsoverlargegeographicareas

• Differenceinthe0meofrecep0onofthesignalsisconstantalonghyperboliccurves

• Posi0oncalculatedbyintersec0ngcurvesfrom2setsofsta0ons

• WasseenasanidealbackupforGPSincaseofjamming/outages

• TerminatedinUS/Canadain2010

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OtherIndoorPosi0oningOp0ons• Bluetoothposi0oning

• Usedtosendlocalmessagesaboutloca0on/services• RFIDchipsembeddedintheenvironment

•  RFIDscannerscancheckloca0on/servicesavailable• UWB

• Highprecisionindustrialposi0oningoftagsonitems• TMSI

•  TemporaryIDofGSMphonescanbetrackedforshortperiodwithinsmallareas(e.g.,shoppingcenters)

•  IPposi0oning• UsingstructureofInternettosituateIPaddressgeographically

Indoor Positioning System (IPS)

GPS vs. IPS

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IPS • Beaconing: Wi-Fi, Bluetooth, ... • RFID tags (later lecture) • Magnetic or other sensor data

Positioning Accuracy

iBeacon (Apple, BLE-based)

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iBeacon •  iBeacon is the Apple Trademark for an indoor positioning

system that Apple Inc. calls “a new class of low-powered, low-cost transmitters that can notify nearby iOS devices of their presence.”

•  The iBeacon works on Bluetooth Low Energy (BLE), also known as Bluetooth Smart. BLE can also be found on Bluetooth 4.0 devices that support dual mode.

Estimote iBeacon • An Estimote Beacon is a small wireless device. When

placed in a physical space, it broadcasts tiny radio signals to smart devices

• Smartphones that are in range are able to 'hear' these signals and estimate their location very precisely, as well as to communicate with the beacon to exchange data and information

iBeacon

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iBeacon

iBeacon • Video: http://www.youtube.com/watch?v=sUIqfjpInxY • Video: http://www.youtube.com/watch?v=SrsHBjzt2E8

iBeacon: Advantages • Accuracy (Bluetooth, low-range) • Privacy (beacon DO NOT track users) •  Integration (Apple, Android, ...) • Affordability (low-cost beacons, other devices can be

configured as beacons) • Usability (BLE -> low energy); simple to use (built into OS/

platform)

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Magnetic Positioning • Magnetometer + data connection • Evaluates building’s distortion of Earth’s magnetic field or

“magnetic fingerprint” • Correlates to reference data • More steel improves accuracy (1-2 meters)

Magnetic Positioning

Step 1: Adding floor plans Step 2: Mapping buildings

Step 3: Creating applications

Smartphone Positioning

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FutureforPosi0oning•  Combina0on/fusionofmul0pleposi0oningtechniquesisnownorm•  Focusonenergyefficiency•  Focusonindoorlocaliza0on• Deadreckoning(accelerometer/gyroscope)whennoGPS•  “Snapping”ofloca0on(“natural”boundaries)•  Coopera0velocaliza0on•  Applica0ons:

•  Assettracking:RFID•  Geo-fencing:alerts•  Emergencyresponse•  Socialnetworking•  Health/Wellness