Demonstration of an Indoor Real-Time Location System with Optical Fibre BackboneChin-Pang Liu, Yanchuan Huang, Tabassam Is...
Outline<br />Introduction<br />Principle of location finding and algorithm<br />The active transmit-only tag<br />Experime...
Introduction<br />Tracking of individuals and goods is often required for safety, security and asset management purposes.<...
Location Finding by Multilateration<br />AU 2<br />Parabola betweenAU 1 and AU 2<br />Parabola betweenAU 2 and AU 3<br />R...
Finally find x and y so that E(x,y) is minimised.  Corresponding x and y are then the tag’s coordinates.</li></li></ul><li...
Only the 80 s down-chirp is used for the TDOA measurement.</li></ul>Battery powered Analog Devices AD9910 direct digital ...
Experimental Arrangement<br />Test venue: A 6.6m-by-15.6m area within a large café.<br />
Measurement of TDOA<br />RFID<br />tag<br />AU 1<br />AU 2<br />Time difference of arrival between two similar chirp signa...
Key Signal Processing Steps<br />Peak amplitude<br />Line-of-sight<br />Well separated<br />indirect signals<br />AU 1, Am...
After FFT, line-of-sight signal has the lowest frequency.</li></li></ul><li>Screen Capture of the Labview Interface<br />M...
Location System Result Summary<br /><ul><li>30 measurements taken @ each of 30 chosen locations
Mean error distance: 1.1 m or better @ 29 out of 30 locations
Overall positional error: 0.72 m RMS</li></ul>Upper no.: Mean error distance (m)<br />Lower no.: Standard deviation (m)<br />
TINA Showcase Demonstration<br />Extension of existing single tag detection to two tags using both positive and negative c...
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TINA showcase: Active RFID

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This video forms part of the showcase event held by the Intelligent Airport (TINA) project: http://intelligentairport.org.uk.

University College London (UCL) developed a passenger tracking system based on active RFID tags.

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TINA showcase: Active RFID

  1. 1. Demonstration of an Indoor Real-Time Location System with Optical Fibre BackboneChin-Pang Liu, Yanchuan Huang, Tabassam Ismail, Paul Brennan and Alwyn SeedsUCL Department of Electronic and Electrical EngineeringUniversity College LondonTorrington Place, London WC1E 7JE, United Kingdomchliu@ee.ucl.ac.uk<br />
  2. 2. Outline<br />Introduction<br />Principle of location finding and algorithm<br />The active transmit-only tag<br />Experimental arrangement, signal processing & results<br />Conclusion and acknowledgements<br />
  3. 3. Introduction<br />Tracking of individuals and goods is often required for safety, security and asset management purposes.<br />GPS works fine outdoors but not indoors, e.g. airport passenger terminal.<br />WLAN, cellular and Bluetooth do not have sufficient accuracy (>50m)<br />In The Intelligent Networked Airport (TINA) project, it is envisaged that<br />An optical fibre backbone will carry growing amount of data traffic at airports;<br />Air passengers will be given RFID embedded boarding passes so they can be tracked.<br />First demonstration of an indoor location system with optical fibre backbone<br />
  4. 4. Location Finding by Multilateration<br />AU 2<br />Parabola betweenAU 1 and AU 2<br />Parabola betweenAU 2 and AU 3<br />RFID<br />tag<br />AU 1<br />AU 3<br />Parabola betweenAU 1 and AU 3<br />A process of finding the tag location from the measured time difference of arrival (TDOA) of the tag signal at known coordinates.<br />Each TDOA between two AUs represents all possible locations along a parabola in 2-D.<br /><ul><li>An optimisation method is employed to find the tag position.</li></li></ul><li>Multilateration Algorithm<br /><ul><li>First pre-calculate the three sets of TDOAs (td12, td13, td23) on a grid representing the venue.</li></ul>AU1 (0,0) & AU2 (0,15.6)<br />AU1 (0,0) & AU3 (6.6,7.8)<br />AU2 (0,15.6) & AU3 (6.6,7.8)<br /><ul><li>Then form an error function E(x,y) with the measured TDOAs (TD12, TD13, TD23)
  5. 5. Finally find x and y so that E(x,y) is minimised. Corresponding x and y are then the tag’s coordinates.</li></li></ul><li>The Transmit-Only Tag<br /><ul><li>Measured output frequency variation with time.
  6. 6. Only the 80 s down-chirp is used for the TDOA measurement.</li></ul>Battery powered Analog Devices AD9910 direct digital synthesizer (DDS) evaluation board.<br />Programmed FM chirp from 216.5 MHz to 300 MHz with 900 MHz sampling clock.<br />900 MHz<br />Clock<br />Bandpass filtered and amplified<br />DDS output spectrum<br />Frequency (Hz)<br />Fundamental chirp<br />Image chirps<br />
  7. 7. Experimental Arrangement<br />Test venue: A 6.6m-by-15.6m area within a large café.<br />
  8. 8. Measurement of TDOA<br />RFID<br />tag<br />AU 1<br />AU 2<br />Time difference of arrival between two similar chirp signals can be found by multiplying them together.<br />Freq.<br />T2<br />T1<br />T2  T1 = t<br />Time<br />FFT<br />Amplitude<br />However, if the received signals contain multipath interference, this method will fail!<br />Freq.<br />
  9. 9. Key Signal Processing Steps<br />Peak amplitude<br />Line-of-sight<br />Well separated<br />indirect signals<br />AU 1, Amplitude (V2)<br />Frequency (Hz)<br />Peak amplitude<br />Line-of-sight<br />Nearby<br />indirect signal<br />AU 2, Amplitude (V2)<br />Frequency (Hz)<br />Peak amplitude<br />Line-of-sight<br />AU 3, Amplitude (V2)<br />Frequency (Hz)<br /><ul><li>Each AU received signal is first multiplied with a pre-recorded “perfect” reference chirp in a matched filter operation.
  10. 10. After FFT, line-of-sight signal has the lowest frequency.</li></li></ul><li>Screen Capture of the Labview Interface<br />Measuredtag coordinates (m)<br />Actualtag coordinates (m)<br />Measured frequency differences between antennas provide TDOA information used to calculate the tag location.<br />Map of the measurement area and visualisation of the tag location. <br />
  11. 11. Location System Result Summary<br /><ul><li>30 measurements taken @ each of 30 chosen locations
  12. 12. Mean error distance: 1.1 m or better @ 29 out of 30 locations
  13. 13. Overall positional error: 0.72 m RMS</li></ul>Upper no.: Mean error distance (m)<br />Lower no.: Standard deviation (m)<br />
  14. 14. TINA Showcase Demonstration<br />Extension of existing single tag detection to two tags using both positive and negative chirp rates simultaneously.<br />This demo lays the foundation for future location systems capable of identifying and locating large numbers of active tags carried by air-passengers, staff, vehicles and/or equipment at airports.<br />
  15. 15. Conclusions<br />First indoor real-time location system with an optical fibre backbone.<br />Overall positional error: 0.72 m RMS.<br />Dedicated ICs can reduce tag size, costs and power consumption.<br />An additional AU can improve accuracy and reliability by providing information redundancy.<br />Use of smart antennas could provide angle of arrival (AOA) information and together with the TDOA data make the system more robust.<br />
  16. 16. Acknowledgements<br />UK EPSRC Grant (EP/D076722/1) as part of The INtelligent Airport (TINA) project. <br />The authors would like to thank ZinWave for providing the hub and antenna units.<br />

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