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

1. 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

2. 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

3. 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.

4. 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

5. 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

6. §8.2 LBS Technologies LBS App. Location Management Localization Module Geographic Information System

7. 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

8. LBS System based on GSM

9. 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

10. Mobile Positioning System of GSM • 图9-10， p262

11. Mobile Positioning System of GSM • MTGMLC • GMLCauth.HLR • GMLCloc. req.MT/VLR • MT/VLRloc. rep.GMLC

12. WebSphere LBS

13. Location Component • To collect and process client location records

14. §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.

15. Cell Identity • A naive solution • Location of BS  Location of MT • Accuracy • Depending on the density and coverage of BS • ~100m to ~10km

16. 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

17. CGI + TA • Cell Global Identity, CGI • A standard identifier for mobile phones cells • TA: within a cell • CGI+TA: global

18. 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

19. Time Difference of Arrival (TDOA) • TDOA = TOA1 – TOA2

20. 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

21. 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

22. 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.

23. Enhanced Observed Time Difference (E-OTD) • TOA at mobile terminal • But the MT makes the time measurements instead of BS

24. Enhanced Observed Time Difference (E-OTD) • Values to measure • OTD: observed time difference • RTD: real time difference • GTD: geographic time difference

25. 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.

26. Three Segments of GPS Space Segment User Segment Control Segment GroundAntennas Monitor Stations Master Station

27. 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.

28. 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 T 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”

29. Three Satellites (2D Positioning)

30. Three Dimensional (3D) Positioning

31. GPS • 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

32. 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

33. 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.

34. Comparisons

35. §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.

36. GIS

37. 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

38. 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