Techniques of Indoor Positioning

1. Techniques of Indoor Positioning 蔡智強 副教授 國立中興大學電機工程學系

2. Outline • Introduction • Basic Techniques • Advanced Techniques • Commercial Products • Using the Indoor Map Information • Indoor Positioning Using Femtocell • 4GLTE-ALocalization System • In-Location Alliance • Conclusions

3. Introduction • Location-aware real-time services • Elderly nursing • Child monitoring • Object positioning • Global Positioning System (GPS) is the most well-known positioning service • The restrictions of GPS • Requiring a line of sight (LOS) with satellite systems

4. Introduction (cont.) • GPS signal is easily affected by buildings • Errors up to 10m • Need other techniques for indoor positioning

5. Basic Techniques • Employ some information between beacon nodes and the unknown node

6. Trilateration

7. Trilateration (cont.) • Node A’s coordinate is (xa, ya) • Node B’s coordinate is (xb, yb) • Node C’s coordinate is (xc, yc) • The unknown node D’s coordinate is (x, y) • The distance between A (or B or C) and D is d1 (or d2 or d3)

8. Trilateration (cont.)

9. Triangulation (cont.)

10. Triangulation (cont.) • The unknown node D’s coordinate is (x, y) • Node A’s coordinate is (xa, ya) and the angle to the D is ∠ADB • Node B’s coordinate is (xb, yb) and the angle to the D is ∠ADC • Node C’s coordinate is (xc, yc) and the angle to the D is∠BDC

11. Triangulation (cont.) • Circle center coordinate is , radius is r1 , and α to calculate and r1 • Similarly, calculate and center coordinate and radius • Use trilateration to calculate D’s position

12. Measuring Distance • Three basic properties to measure the distance between a beacon node and a unknown node • Received signal strength indication (RSSI) • Time of flight (TOF) • Angle of arrival (AOA)

13. Received signal strength indication • Two kinds of methods for RSSI location • Database • Radio propagation model

14. Received signal strength indication (cont.) • Database • Measure the relation between distances and RSSI values • Set up a database • According the database, we can calculate the distance between two nodes

15. Received signal strength indication (cont.) • Radio propagation model • In the RADAR system, the Wall Attenuation Factor (WAF) model is: where n indicates the rate at which path loss decreases with distance, P(d0) signal power at some reference d0, and d is the transmitter-receiver distance.

16. Received signal strength indication (cont.) Moreover, C is the maximum number of obstructions (walls), nW the number of obstructions between the transmitter and receiver, and WAF is the wall attenuation factor.

17. Time of flight • Calculate the distance between a transmitter and a receiver by the time of flight • Time of arrival (TOA) • Time difference of arrival (TDOA)

18. Time of flight (cont.) • TOA • The transmitter and receiver must synchronize their time • The transmitter sends a signal to the receiver • Upon receiving the signal, based on the propagation time, the receiver can calculate the distance between the transmitter and it

19. Time of flight (cont.)

20. Time of flight (cont.) • TDOA • Based on the difference of time between different signals from the transmitter arriving at the receiver • The transmitter sends two different signals with propagation speeds α1 , α2, respectively • The receiver receives two such signals at different times, say T1and T2, respectively • The distance is

21. Time of flight (cont.)

22. Angle of arrival • By the propagation direction of radio-frequency waves incident on an antenna array

23. Comparisons • RSSI • Advantage: simple hardware • Disadvantage: unstable, easily impacted by the environment • TOA • Advantage: good accuracy • Disadvantage: time synchronization required, complex hardware

24. Comparisons (cont.) • TDOA • Advantage: no time synchronization, good accuracy • Disadvantage: complex hardware • AOA • Advantage: nice accuracy • Disadvantage: Directional antenna array required

25. Maximum likelihood estimation

26. Maximum likelihood estimation (cont.) • n reference nodes with coordinates • The unknown node in (x, y) • The distances between reference nodes and the unknown node are , respectively, measured by RSSI values

27. Maximum likelihood estimation (cont.) • Subtract the last equation from each equation

28. Maximum likelihood estimation (cont.) • Use the matrix representation AX=b • The coordinate of the unknown node :

29. Self-Calibrating Indoor Positioning System Based On ZigBee Devices • This paper presents a positioning system based on the round-trip time-of-flight (RTT) measurement • RTT can be modeled as:

30. System Architecture • The developed system is composed of three types of transponders: • Mobile node • Calibration node • Fixed node

31. System Architecture (cont.) • Mobile node • Chipcon CC2431 : Zigbeechip • TMS320C6713(DSP) : Timing and control functions • TDC-GP2 : Time interval measurement function, timing and control functions

32. System Architecture (cont.) • Calibration node • Chipcon CC2431 : Zigbee chip • TDC-GP2 : Time interval measurement function, timing and control functions • Fixed node • Chipcon CC2431 : Zigbee chip

33. Measuring procedure • Measuring procedure • Initiated by a mobile node • It transmits a packet to a fixed node • Fixed node retransmits a packet • The master node receives the packet and its TDC determines the RTT • Calibrating procedure • Initiated by a mobile node • It transmits a packet to a calibration node • The calibration node initializes its TDC

34. Measuring procedure (cont.) • The calibration node transmits a packet to a selected fixed node • The selected fixed node received and retransmits the packet • The calibration node receives the packet and its TDC determines the RTT • The calibration node repeats the foregoing procedure to a set of fixed nodes • The results of RTT are sent to the mobile node for calibration

35. Measuring procedure (cont.) • By using the calibration data, the mobile node DSP can determine the unknown position more accurately

36. Tested Result • Three fixed node, one calibration node

37. NTU Indoor Localization • RSSI fingerprinting localization • Training • Collect RSSI values at every specific position • Use all collected RSSI values to build a database • Tracking • Upon receiving RSSI values, an end-device can compare them with those in the database • Then calculate the position by KNN (K-Nearest-Neighbor)

38. NTU Indoor Localization (cont.) Beacon 1 Beacon 2 Beacon 3 Look up the table

39. NTU Indoor Localization (cont.)

40. NTU Indoor Localization (cont.) • Example of KNN AP2 11 10 9 12 5 6 30m 7 8 2 3 4 1 AP3 AP1 50m

41. NTU Indoor Localization (cont.) • STEP1 • The end-device receives the RSSI values and normalizes them • STEP2 • The normalized RSSI values are compared with those in the database, and find the minimum L differences Dn • ST is the received RSSI value • Sn is store at the database • STEP3 • For L nearest neighbors, the location estimate is

42. NTU Indoor Localization (cont.) • STEP1 • PT = (-94dbm -96dbm -95dbm) • PT = (0dbm -2dbm -1dbm) Normalize 正規化

43. NTU Indoor Localization (cont.) • STEP2 • STEP3

44. AeroScout

45. AeroScoutTag Tag using RFID2.4GhzWiFitransmission, MAX read range200M, LF125k precise positioning 1~2M，

46. AeroScout Location Receivers • Location Receivers allow accurately positioning in outdoor or harsh environments • They execute sophisticated radio signal measuring and calculating methods • Then the results are sent to the AeroScout Engine for accurately positioning

47. AeroScoutTDOA • Use TDOA for positioning

48. AeroScout System Architecture

49. AeroScoutEngine • Processes information received from any vendor's wireless Access Points nearby • Allow accurate and reliable positioning for assets equipped with AeroScout's Wi-Fi-based Active RFID Tags

50. AeroScoutMobileView • Customers use MobileView to TRACK, MANAGE and INTEGRATE their assets from a single platform