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Lecture08 Mobile Positioning and LBS 第 8 讲 移动定位与服务. §8.1 LBS Basics §8.2 LBS Technologies §8.3 Mobile Positioning §8.4 Geographic Information System. Location Based Services (LBS). What is it? Allow you to report real time current location to a given platform

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Lecture08 mobile positioning and lbs 8

Lecture08 Mobile Positioning and LBS第8讲 移动定位与服务

§8.1 LBS Basics

§8.2 LBS Technologies

§8.3 Mobile Positioning

§8.4 Geographic Information System

Location based services lbs
Location Based Services (LBS)

  • What is it?

    • Allow you to report real time current location to a given platform

    • Information service accessible using mobile devices through mobile network

    • Ability to make use of geographical position of mobile device

  • Why need it?

    • Location is important

Evolution of lbs
Evolution of LBS

  • First generation

    • Manually input location info.

      • E.g. zip code, a city name or street address.

    • Customized content

      • E.g. driving directions, nearby restaurant or store locations, or weather information.

  • Second generation

    • Automatically determine location info.

      • Usually accurate to within a few kilometers (1 to 2 miles), similar accuracy as in first-generation applications.

      • Similar services to those in first-generation applications.

Evolution of lbs1
Evolution of LBS

  • Third generation

    • Can obtain more accurate location info.

    • Can initiate services based on location.

    • Can provide timely updates

      • nearby brick-and-mortar services,

      • asset tracking information, and

      • street-level mapping and routing.

    • Feature-rich and user-friendly

Lbs applications
LBS Applications

  • What are the top uses?

    • Emergency services

    • GPS Navigation

    • Weather alerts

    • Traffic updates

    • Find-it services

    • Wireless advertising

    • Access control

    • Social networking

  • Notable players

    • Google Maps

    • Foursquare

    • Facebook Places

    • 街旁

8 2 lbs technologies
§8.2 LBS Technologies

LBS App.

Location Management

Localization Module

Geographic Information System

Lbs technologies
LBS Technologies

  • Localizing or Positioning Methods

    • Global Positioning System (GPS)

    • Cellular, WiFi, NFC, RFID, Bluetooth

  • � Geographic Information Systems (GIS)

    • Provide tools to provision and administer base map data

    • Manage point-of-interest data

  • Location Management

    • Process positioning and GIS data

    • Acts as gateway between positioning equipment and LBS infrastructure

Mobile positioning system of gsm
Mobile Positioning System of GSM

  • Specified by ANSI and ETSI

  • Extend classical GSM system

  • Hardware and Software

    • LMU: Location Measurement Unit

      • To measure the time difference between BSs

    • MLC: Mobile Location Center

      • SMLC: Service MLC

        • Measurement and calculation

      • GMLC: Gateway MLC

        • Interface to others

Mobile positioning system of gsm2
Mobile Positioning System of GSM


  • GMLCauth.HLR

  • GMLCloc. req.MT/VLR

  • MT/VLRloc. rep.GMLC

Location component
Location Component

  • To collect and process client location records

8 3 mobile positioning
§8.3 Mobile Positioning

  • Positioning

    • To capture the location of a mobile device

  • Considerations: Accuracy vs. Cost

  • Categories: based on where the calculation is done

    • Network-based

      • For both new and legacy handsets.

      • Quite cost-effective

      • Low accuracy: from hundred meters to several kilometers

    • Terminal-based

      • High accuracy: several meters

      • High cost, for both the terminal and network.

Cell identity
Cell Identity

  • A naive solution

  • Location of BS  Location of MT

  • Accuracy

    • Depending on the density and coverage of BS

    • ~100m to ~10km

Timing advance ta
Timing Advance (TA)

  • TA:

    • The time of a round trip between base station and mobile terminal.

    • Usually between 0 and 63 bit period (~ 3.69 microseconds).

  • TA  distance

    • 1 bit 550m

    • 63 × 550m 35km

  • Pros and cons

    • Low accuracy: 0.2~10km

      • Multipath fading

    • Simple:

      • no change at MT, minor change at BS

Cgi ta

  • Cell Global Identity, CGI

    • A standard identifier for mobile phones cells

  • TA: within a cell

  • CGI+TA: global

Time of arrival toa
Time of Arrival (TOA)

  • d = v * t

  • Distance values to >3 base stations

  • High accuracy

    • 100~150m

  • High complexity

    • Synchronization among BSs

    • Special LMU

    • Computation

  • Work flow

    • MT sends to BSs

    • Each BS measures time

Time difference of arrival tdoa
Time Difference of Arrival (TDOA)

  • TDOA = TOA1 – TOA2

Angle of arrival aoa
Angle Of Arrival (AOA)

  • Input data:

    • Angle with two BSs,

    • Distance between the two BSs

  • Two BSs for 2D location

  • Three BSs for 3D location

  • Need special antenna

Multipath fingerprinting
Multipath Fingerprinting

  • RF pattern match

  • Based on the characteristics of multipath signal

  • Collecting fingerprinting

    • Dedicated learning phase

    • Store the fingerprint in a database

  • Locating mobile device

    • collect the current signal pattern

    • Match it with those in database

Mobile terminal based positioning
Mobile Terminal based Positioning

  • More accuracy than network-based technologies

  • Terminal participant in the location calculation

  • Suitable for 3rd generation of LBS

  • Popular technologies

    • E-OTD: uses BSs

    • GPS: uses satellites.

Enhanced observed time difference e otd
Enhanced Observed Time Difference (E-OTD)

  • TOA at mobile terminal

  • But the MT makes the time measurements instead of BS

Enhanced observed time difference e otd1
Enhanced Observed Time Difference (E-OTD)

  • Values to measure

    • OTD: observed time difference

    • RTD: real time difference

    • GTD: geographic time difference

Global positioning system gps
Global Positioning System (GPS)

  • History

    • Feasibility studies begun in 1960’s.

    • First satellite launched in 1978.

    • System declared fully operational in April, 1995.

  • Consists of 24 MEO satellites that transmit precise microwave signals

    • About 20,200km above the Earth’s surface.

Three segments of gps
Three Segments of GPS

Space Segment

User Segment

Control Segment


Monitor Stations

Master Station

Four basic functions of gps
Four Basic Functions of GPS

  • Position and coordinates.

  • The distance and direction between any two waypoints, or a position and a waypoint.

  • Travel progress reports.

  • Accurate time measurement.

Position is based on time
Position Is based on Time

The satellites constantly broadcast signals that can be read by GPS-enabled devices.

Line of sight : suitable for outdoor only


Signal leaves satellite at time “T”

T + 3

Signal is picked up by the receiver at time “T + 3”

Distance between satellite and receiver = “3 times the speed of light”

Lecture08 mobile positioning and lbs 8

  • Accuracy

    • 5m-40m

    • Highly relying on the accuracy of clock

      • Atomic clock at each satellite

      • 1ms300km

  • Limitations

    • Line of sight to the satellites  outdoor only

      • Solution:

        • Backup method: cell based ones

    • Long delay of positioning: 20s-40s

A gps

  • Network-assisted GPS

  • GPS + assistance from

  • Additionally uses network resources to locate and use the satellites in poor signal conditions.

  • To alleviate both restrictions of GPS

Assistance of location server in a gps
Assistance of Location Server in A-GPS

  • Information used to more quickly acquire satellites

    • It can supply information of GPS satellites, enabling the GPS receiver to lock to the satellites more rapidly.

    • The network can provide precise time.

  • Calculation of position by the server using information from the GPS receiver

    • The assistance server has a good satellite signal, and plentiful computation power, so it can compare fragmentary signals relayed to it.

    • Accurate, surveyed coordinates for the cell site towers allow better knowledge of conditions affecting the GPS, enabling more precise calculation of position.

8 4 geographic information system
§8.4 Geographic Information System

  • GIS, mapping software that

    • Relates the location information with other pertinent information to give it meaning and value.

    • Such as building locations, street layouts, population densities, and a plethora of other information.

  • A GIS can provide information and insight to both mobile users and people at fixed locations.

Common uses of gis
Common Uses of GIS

  • Uses the location coordinates provided by positioning technologies to give details that are relevant to the user at that specific moment.

  • Finding what is nearby

  • Routing information

  • Information alerts

  • Mapping densities

  • Mapping quantities

A summary
A Summary

  • Concepts

    • LBS

    • Mobile device positioning

  • Mobile positioning system

  • Positioning technologies

    • Network-based

      • CGI, TA, CGI+TA

      • TOA, TDOA

      • AOA

      • Fingerprint

    • Terminal-based

      • E-OTD

      • GPS, A-GPS