RANGING AND POSITIONING OF UHF RFID TAGS

Transcription

1 RANGING AND POSITIONING OF UHF RFID TAGS H. Arthaber, K. Witrisal RFID Real-Time Localization for Flexible Production Environments (REFlex) Ass.Prof. Dr. Holger Arthaber Vienna University of Technology Institute of Electrodynamics, Microwave and Circuit Engineering Microwave Engineering Group Gusshausstrasse 25/ Vienna, Austria Assoc.Prof. Dr. Klaus Witrisal Graz University of Technology Signal Processing and Speech Communication Lab Inffeldgasse 16c 8010 Graz, Austria

2 Contents Ranging/Positioning Applications The UHF RFID Radio Szenario Passive UHF RFID Ranging/Positioning Methods Positioning with Multiple Antennas A new Time-of-Flight Ranging Method for Passive UHF Tags Summary 2

3 Contents Ranging/Positioning Applications The UHF RFID Radio Szenario Passive UHF RFID Ranging/Positioning Methods Positioning with Multiple Antennas A new Time-of-Flight Ranging Method for Passive UHF Tags Summary 3

4 Applications for Accurate Indoor Positioning Systems Manufacturing Process monitoring Process control Retail Real-time inventory Recommender system Theft control Manufacturing Logistics Positioning / Navigation Safety Flexible processes Pick-and-place Error detection Flexible processes Assisted Living Fall detection Medication management Behavior monitoring Emergency response systems Safety Coordination Monitoring Objectives: Positioning and navigation; activity recognition; control Requirements: Accuracy (5 20 cm); Reliability (90 100%) Technologies: RFID; active transponders (IoT; UWB); 5G wireless systems Images: Ubisense, SSI Schaefer, brighamyen.com, Witrisal, Jungheinrich, slashgear.com 4

5 Ranging/Positioning Applications Potential future applications for RFID Positioning of massive tag populations Activity recognition (humans interacting with goods) Sales floor Recommender systems for brick and mortar stores Warehouses Pick-and-place stations Requirements: large read volumes (entire rooms); decimeter-range accuracies Images: SSI Schaefer, brighamyen.com 5

6 Ranging/Positioning Applications Traditional RFID applications domains ranging allows for: RFID Gates distance bounding, range gating reduce false detects movement direction detection Conveyor belts ordering on conveyor belt distance bounding for parallel belts Requirements: confined read volumes; m accuracy; (typically) ~100 % reliability Images: intermec 6

7 Contents Ranging/Positioning Applications The UHF RFID Radio Szenario Passive UHF RFID Ranging/Positioning Methods Positioning with Multiple Antennas A new Time-of-Flight Ranging Method for Passive UHF Tags Summary 7

8 The UHF RFID Radio Szenario Monostatic configuration: Bistatic configuration: red. unmodulated signal from reader green signal with tag-modulation on it line of sight path other paths, e.g. via reflectors Problems: Multipath : several ways/paths from antenna to tag Reflectors : introduce multipath and/or blind the RFID reader Dead spots : no communication zones due to interference 8

9 The UHF RFID Radio Szenario How does the signal look like at the RX-antenna? Radio waves are described by Frequency (e.g. 868 MHz) Magnitude Phase RX antenna receives unmodulated TX signal and tag s modulated response + = large signal (dominated by TX-RX-coupling) very small signal, shown enlarged (dominated by line-of-sight path) combined signal (tag response almost invisible) 9

10 Contents Ranging/Positioning Applications The UHF RFID Radio Szenario Passive UHF RFID Ranging/Positioning Methods Positioning with Multiple Antennas A new Time-of-Flight Ranging Method for Passive UHF Tags Summary 10

11 Passive UHF RFID Ranging/Positioning Overview 2D Positioning Methods 1) Angle based (Triangulation) requires at least 2 RFID readers at exactly known positions and orientations 2) Distance based (Trilateration) requires at least 2(3) RFID readers at exactly known positions 3) Combination of Angle + Distance works with a single reader 11

12 Passive UHF RFID Ranging/Positioning Received Signal Strength (RSSI) Received Signal Strength (RSSI) Uses the received signal power Gives a distance estimate Problems: Multipath results in inaccuracy Antenna pattern influence Tag s reflection is not constant Many RFID reader chipsets aren t capable of vector measurements (they either use real or imaginary part)?? 12

13 Passive UHF RFID Ranging/Positioning Angle of Arrival (AoA) Angle of Arrival (AoA) Uses at least two antennas phase difference of tag s signal gives an angle estimate Problems: Multiple antennas needed Multipath will result in wrong power readings Many RFID readers aren t capable of vector measurements? 13

14 Passive UHF RFID Ranging/Positioning Time of Flight (ToF) Time of Flight (ToF) An experiment: Transmission of an ultra-short pulse in an indoor environment Signal reflections lead to multipath propagation 14

15 Passive UHF RFID Ranging/Positioning Time of Flight (ToF) Influence of bandwidth: Time/range resolution changes vastly Impact of multipath propagation onto ToF ranging: Ultra-wideband (> 500 MHz): line-of-sight signal is clearly seen MHz: signal distortions and fading Narrowband (<= 1 MHz): flat fading (only) Conclusion: (very) large bandwidth is needed 15

16 Contents Ranging/Positioning Applications The UHF RFID Radio Szenario Passive UHF RFID Ranging/Positioning Methods Positioning with Multiple Antennas A new Time-of-Flight Ranging Method for Passive UHF Tags Summary 16

17 Positioning with Multiple Antennas Multi-antenna systems improve the ranging and positioning performance Three reader configurations with 2 reader positions are compared. Each reader has: Error ellipses: 95% of measurements are inside positioning error at 50 MHz ranging bandwidth 1) combined TX/RX antenna 2 range measurements 2) separated TX/RX antennas 2 range + 2 bistatic meas. 3) 2 pairs of separated TX/RX ant. 2 x 4 independent range plus 8 independent bistatic meas range 4 1range 28 bistatic TX; TX, TRX 12RX RX 21 TX, 1TX; TRX 21RX 17

18 Positioning with Multiple Antennas Comparison of numeric results over entire test area: 95% error 99% error 2 x monostatic 34 cm 38 cm 4 x bistatic 26 cm 30 cm 16 x bistatic 13 cm 15 cm Always statistical errors There is no 100% guarantee! Multiple antennas improve performance dramatically, but Require complex infrastructure (antennas mounted at exact positions) Positioning performance with 50 MHz bandwidth sufficient for most applications 18

19 Contents Ranging/Positioning Applications The UHF RFID Radio Szenario Passive UHF RFID Ranging/Positioning Methods Positioning with Multiple Antennas A new Time-of-Flight Ranging Method for Passive UHF Tags Summary 19

20 A new Time-of-Flight Ranging Method for Passive UHF Tags What s new? Direct time-of-flight measurement with 50 MHz bandwidth Works with standard EPC Gen2 tags Independent on tag chip manufacturer Performs ranging with a single antenna Measures the echo from the tag s antenna and suppresses other echos 20

21 A new Time-of-Flight Ranging Method for Passive UHF Tags How does the ranging signal look like? Spectrum of RFID and ranging signal: RFID communication unattenuated ranging signal reduced power ranging signal Without any changes, the signal violates EPC standard and radio standards an extremely low power ranging signal must be used this reduces signal to noise ratio expect noisy distance measurements 21

22 A new Time-of-Flight Ranging Method for Passive UHF Tags Nice theory But can this work? Ranging Enabled RFID Reader Prototype: EPC compliant 868/915 MHz reader Real-time positioning of standard UHF EPC tags FPGA implementation Research platform: RF-Frontend not yet optimized Positioning algorithms SPS IPC Drives 2015, Nuremburg 22

23 A new Time-of-Flight Ranging Method for Passive UHF Tags Measurement results NXP UCODE 7 tags 5 tags in different distances 95 (0.5) ± 1.2 cm 1.14 ± 4.8 cm 2.06 ± 4.2 cm 2.84 ± 6.2 cm 4.22 ± 8.8 cm 23

24 Contents Ranging/Positioning Applications The UHF RFID Radio Szenario Passive UHF RFID Ranging/Positioning Methods Positioning with Multiple Antennas A new Time-of-Flight Ranging Method for Passive UHF Tags Summary 24

25 Summary Basic ranging principles explained Distance based Angle based Ranging/positioning accuracy is limited by multipath transmission Always statistical errors, no 100% guarantee More bandwidth better accuracy More antennas more accuracy New ToF-based ranging method Promising results for standard EPC Gen2 tags 25

26 Thank You For Your Attention! parts of the shown results were done in the funded research project: RFID Real-Time Localization for Flexible Production Environments (REFlex)