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L ocation B ased S ervices for Mobile Devices. Embedded Computing Seminar Shay Horovitz. Technologies. Location Technologies. GPS - Global Positioning System AGPS - Assisted GPS Cell ID Cell ID + Timing Advance Signal Strength Based AOA - Angle Of Arrival TOA - Time Of Arrival

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L ocation b ased s ervices for mobile devices l.jpg

Location Based ServicesforMobile Devices

Embedded Computing Seminar

Shay Horovitz

Location technologies l.jpg
Location Technologies

  • GPS - Global Positioning System

  • AGPS - Assisted GPS

  • Cell ID

  • Cell ID + Timing Advance

  • Signal Strength Based

  • AOA - Angle Of Arrival

  • TOA - Time Of Arrival

  • TDOA - Time Difference of Arrival

  • EOTD - Enhanced Observed Time Difference

  • Keypad based (click the address yourself)

  • Camera based (taking pictures of signs)

  • Hybrid solutions

  • RF Fingerprinting (on phones that will support WLAN)

History l.jpg

  • Mariners relied upon the sun for latitude, and clocks for longitude

  • With the launch of Sputnik in 1957, radio-based global positioning became a (theoretical) possibility

Transit l.jpg

  • This was a very crude form of GPS using only one satellite (1960s)

    • Submarines used it

    • Could only be used every 35-45 minutes

    • Submarine had to be still

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TIMATION (1960s)

  • Another satellite (TIMATION I) was launched to enhance the TRANSIT system

  • Major innovation was the inclusion of an atomic clock

  • Submarines could now be in motion and use the system

Navstar l.jpg

  • In 1973, NAVSTAR began research & development

  • 1978 – the first 4 satellites were launched

  • Operated by the Department of Defense

    • Primary mission is to provide exact coordinates for land, sea & air-based military forces

    • Cost about $18,000,000,000 to develop… so far

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There are three components of GPS

  • 1.) Space (e.g. satellites)

  • 2.) Control (i.e. a ground station at a known geographic location)

  • 3.) User

Satellites l.jpg

  • The GPS receiver precisely measures the time it takes a signal to travel from a satellite to the receiver

  • There are lots and lots of satellites

  • Anyone want to guess how many?

Details l.jpg

  • 6 orbital planes, included at 55 degrees to the equator, each with 4 satellites

    • 21 active satellites, 3 backups

  • Orbit the earth at 12,541 miles and have an orbital period of 11 hrs. 56 min.

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How many points do you need?

  • Using one satellite narrows the distance to a sphere around the satellite

  • Using two satellites, you’ll find your location within a circle (previous slide)

  • Using three satellites limits your location to only 2 points

    • Usually, it is possible to determine which point

  • Using four satellites confirms your location and gives you 2 readings for altitude

    • Usually you can determine which is correct

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The importance of time

  • Both satellites and receivers generate Pseudo Random Noise (PRN)

    • A Link 1 (L1) carrier signal is generated at 1575.42 MHz and Link 2 (L2) carrier signal is generated at 1227.60 MHz

      • Carrier signals are modulated to produce coded signals, such as C/A code (at 1.023 MHz) and the P code (at 10.23 MHz)

    • The frequencies are frequency-modulated to produce step-functions

    • The codes repeat every millisecond

  • The satellites come with cesium or rubidium clocks

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Selective Acquisition

  • The US military was concerned about the possibility of terrorists or other unfriendly people using GPS to precisely guide a missile (or other unfriendly device)

  • The deliberately introduced errors in the time embedded in the signal

  • This caused locations to be up to 100m off

  • Turned off on 2 May 2000

Slide19 l.jpg

  • GPS III system will launch

  • Should be even more accurate than the 8m accuracy limit currently in place

Tech agps l.jpg
Tech: AGPS

  • GPS has a slow time to fix unless it is permanently tracking satellites

  • To solve the inherent restrictions with GPS, Assisted GPS was proposed

  • Assisted GPS is based upon providing GPS satellite information to the handset, via the cellular network

Tech agps21 l.jpg
Tech: AGPS

  • Assisted GPS gives improvements in

    • Time to First Fix

    • Battery Life

    • Sensitivity

    • Cost

  • Assistance Data

    • Satellite Position

    • Time information

    • Visible GPS List

    • Sensitivity

Tech cell id l.jpg
Tech: Cell ID

  • Cell ID: the cell that the mobile is connected to

  • Operator’s know where their cell sites are

  • Accuracy is dependent on cell density

  • Can be implemented both network based or device based

Tech cell id23 l.jpg
Tech: Cell ID

Tech cell id timing advance ta l.jpg
Tech: Cell ID + Timing Advance (TA)

  • TA is the time delay between the mobile and serving base station

  • Resolution is 500 meters

  • Serving cell identity and TA are available in networks

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Tech: Signal Strength Based

  • Measure signal strength from the control channels of several Base Stations

  • If signal levels from 3 different BSs are known, it’s possible to calculate the location

Tech signal strength based26 l.jpg
Tech: Signal Strength Based

Tech aoa angle of arrival l.jpg
Tech: AOA - Angle Of Arrival

  • Measure the angle of arrived signal between base station and mobile station

  • Location error increases as mobile is far from BSs

Tech toa time of arrival l.jpg
Tech: TOA - Time Of Arrival

  • Measure the time of arrived signal between base station and mobile station

  • Mobile station locates at the intersection point which will be made by more than 3 circles

Tech tdoa time difference of arrival l.jpg
Tech: TDOA – Time Difference Of Arrival

  • Measure the time difference of arrived signal between base station and mobile station : Minimum three base stations

  • Mobile station locates at the intersection point which will be made by more than 3 hyperbolas

Tech tdoa time difference of arrival30 l.jpg
Tech: TDOA – Time Difference Of Arrival

Tech eotd enhanced observed time difference l.jpg
Tech: EOTD – Enhanced Observed Time Difference

  • Added device, LMU (Location Measurement Unit), whose location is known

  • LMU and mobile station measure the time difference of arrived signal from base station at the same time

  • Mobile station locates at the intersection point which will be made by more than 3 hyperbolas

Tech eotd enhanced observed time difference32 l.jpg
Tech: EOTD – Enhanced Observed Time Difference

Tech keyboard based l.jpg
Tech: Keyboard Based

  • You set your location!

  • Example: Navigation Software:

    • Manually set origin

    • Manually set destination

    • Approve when each step is completed to get the next step instructions

Tech camera based l.jpg
Tech: Camera Based

  • Take a picture of road signs and send by MMS to a server

  • 2D Barcodes

Tech lamposts based l.jpg
Tech: Lamposts Based

  • Last Mile, a British company plans to offer Internet & LBS using street lampposts…

  • A flash memory will be installed inside the lampposts and store info about local pubs, shops.

  • Cost: about £500 per lamppost

Tech hybrid solutions based l.jpg
Tech: Hybrid Solutions Based

  • Improve effectiveness

  • Extends the coverage of a solution e.g. AGPS

  • Common Hybrids

    • EOTD / AGPS

    • Cell ID / AGPS

  • Benefits of both systems realized increasing the accuracy and availability of any single method

Tech rf fingerprint based l.jpg
Tech: RF Fingerprint Based

  • Pinpointing wireless clients makes it easier to secure and manage wireless LANs

  • WLANs typically have used closest access point (closest AP) or triangulation technologies to track location

  • RF fingerprinting improves by taking into account the effects that a building or people will have on an RF signal - characteristics such as reflection, attenuation and multi-path

Tech rf fingerprint based38 l.jpg
Tech: RF Fingerprint Based

Range of coverage l.jpg
Range Of Coverage

5 m


100 m



300 m

Cell ID + TA

500 m

Cell ID


Applications l.jpg

  • Network Optimization

  • In-Car & Personal Navigation and wayfinding

  • Emergency (E911)

  • Monitoring traffic flow using device location & optimization

  • Automated Mapping

  • Family Tracking/ Find-A-Friend

  • Find the Nearest Store/place

  • Tourist Information/Automated Guide

  • Live public transport info

  • Games

  • Fleet Management

  • Location-based Billing

  • Demographic Statistics

  • Target Marketing

  • Other applications

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Game: Glofun RayGun

  • Location: US

  • Target: Ghost-Hunting!

  • Use of GPS for location of player

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Game: SS+K Conqwest

  • Location: 5 cities in the USA

  • Team-based treasure hunt in the urban jungle

  • 5 teams searching for treasure in the form of “printed codes” – 2d barcodes that can be captured by phonecam

  • 1 code=1$. First team to find $5000 worth codes wins and earns a $5000 scholarship for their school…

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Game: Blisterent Swordfish

  • GPS based game

  • You play against a virtual school of Swordfish

  • See where’s the nearest school of virtual fish

Game blisterent torpedo bay l.jpg
Game: Blisterent Torpedo Bay

  • A-GPS based game

  • No GPS reception? - Predictive positioning…

  • Use of real map

  • 360 degrees view

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Game: NewtGames Mogi

  • Location: Tokyo, Japan

  • GPS based

  • Pick up virtual items spread on the whole of Japan

  • At a range of 400m, you’re able to collect an item

Game mikoishi gunslingers l.jpg
Game: Mikoishi GunSlingers

  • Location: Singapore

  • Cell-ID based

  • Multiplayer shooting game

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HP Labs City Tags

  • Location: Bristol, UK

  • iPaq PocketPC with GPS, Wifi needed

  • Social interaction: Tag people

  • When got tagged, need to find a friend to free you

Geocaching l.jpg

  • Take something from the cache

  • Leave something in the cache

  • Write about it in the logbook

Developer toolkits l.jpg
Developer Toolkits

  • Chips:

    • HammerHead

    • TI

    • Intel

  • APIs:

    • Sun J2ME Location API

    • Qualcomm BREW LBS API

Chips market l.jpg
Chips Market

"The mobile GPS semiconductor market is expected to exceed 180 million units in 2008 …" Will Strauss, president of Forward Concepts[http://www10.edacafe.com/nbc/articles/view_article.php?section=ICNews&articleid=223846]

Hammerhead pmb 2520 l.jpg
HammerHead: PMB 2520

  • Single chip solution

  • A-GPS Implementation

  • Size: 80 mm2

  • Low Power

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TI Chip: NaviLink 4.0 GPS5300

  • Single chip solution

  • Smallest A-GPS (50 mm2)

  • Low Power, Power Management

  • Production: 2Q, 2006

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Intel’s Plans

  • “Notebook chips will likely support location-based services by 2006, Intel says. “ PCWorld [http://www.itworld.com/Comp/2085/041025pentiumm/]

Sun j2me lbs l.jpg

  • Location API for J2ME (JSR 179)

  • A set of generic APIs for developing LBS

  • Can support GPS/A-GPS/Cell-ID/any other method [by implementing a location provider]

Some interesting numbers l.jpg
Some interesting numbers…

  • Most popular chipset – SiRF

  • Smallest modules:

    • SyChip GPS2020: 13x15x3.8

    • Trimble M-Loc MPM: 25x25x6.5

    • Fastrax iTrax02: 26x26x6.5

  • Smallest module with integrated Antenna – Axiom Swift A1: 41x41x11

Use one l.jpg
Use One?

  • Ready made External boxes with integrated antennas or separate

  • Support USB / RS232

  • Available as both PCMCIA and Compact Flash cards

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GPS Building Blocks 1

  • Antenna element

    • Cost: $3 to $300 (depends on single/double frequency reception & phase center stability)

    • Diameter: 2cm to 15cm

  • Low Noise Amplifier (LNA)

    • Amplifies GPS signals

    • Cost: $5 to $100 (depends on number of frequencies & quality of filters)

    • Power consumption: 20mW to 200mW

  • RF section

    • Converts received signal to digital form

    • Cost: $5 to $200 (depends on number of frequencies & quality of filters)

    • Size: 2-20 cm

    • Power consumption 100mW to 1 Watt

Gps building blocks 2 l.jpg
GPS Building Blocks 2

  • Digital section

    • Processes the digital samples and provides tracking measures

    • Cost: $5 to $15

  • Microprocessor

    • Control the tracking elements based on measurements and doppler (range rate change)

    • Collects navigation data about the orbit and clock of each satellite

    • Compute position

    • Support interfaces to the user

    • Cost: $5 to $50

    • Power consumption: 200mW to 3W

Gps building blocks 3 l.jpg
GPS Building Blocks 3

  • Processor Peripherals

    • Provide memory for program and data storage

    • Cost: $5 to $100 (depending on capacity and speed)

    • Power consumption: 100mW to 2W

  • I/O & Drivers

    • Serial/ Parallel/ USB/ Ethernet/ other comm ports

    • Cost: $2 to $20

    • Power consumption: 10mW to 100mW

References l.jpg

  • Ronald Azuma et el., “Recent Advances in Augmented Reality”, IEEE Computer Graphics and Applications, vol.21, no.6, Nov/Dec 2001, pp.34-47

  • Mohammad S. Sharawi et el., “Investigation into the performance of EOTD for GSM users in Telematics applications”, Proceedings of SPIE, vol. 5084, Aug. 2003, pp.6-18

  • http://yona_n.tripod.com/gps/gps-survey.html#chips

  • EDN: http://www.edn.com/article/CA243219.html

  • GPSWorld: http://www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=15100&pageID=1

  • HowStuffWorks: http://electronics.howstuffworks.com/gps.htm

  • http://www.symbian.com/developer/techlib/papers/messaging/LocalAwareness_LBS_01.pdf

  • http://www.terena.nl/conferences/tnc2005/core/getfile.php?file_id=453

  • LBS Market: http://www.trueposition.com/lrc/LBSLongTimeComing.pdf

  • LBS Forecast: http://mms.ecs.soton.ac.uk/mms2002/papers/4.pdf

  • Location Technologies: http://developer.openwave.com/omdtdocs/location_studio_sdk/pdf/Intro_to_Location_Technologies.pdf

  • GSM LBS: http://www.ftw.at/ftw/events/telekommunikationsforum/WS2001/WS01docs/020111.ppt

  • E-911: http://www.sss-mag.com/e911.html

  • Solutions: http://www.wirelessdevnet.com/channels/lbs/features/mobilepositioning.html

  • GPS Based games: http://www.glofun.com/

  • LBS in Europe: http://www.hottelecom.com/berginsight-lbs.html

Slide82 l.jpg

Thank You

For Listening