Factors effecting positional accuracy of iBeacons
Chris Thomson - Factors effecting positional accuracy of iBeacons In September 2013 Apple Computer Inc. popularized the idea of using Bluetooth LE to indicate locational presence, the technology branded as iBeacon. iBeacons advertise frequently their presence with a unique identifier, a receiver can use this information to approximate the distance to the iBeacon based on the measured signal strength. Using the trilateration technique and a table of iBeacon locations it is possible to locate the receiver in three-dimensional space as long as three iBeacons are within range. The measurement of the distance between the iBeacon and the receiver is imperfect due to interference. In particular a significant factor is the absorption of the radio carrier by water within an operators body, and other people near by. Using prototype iBeacons provided by Estimote Inc. I have investigated this effect. I will report on my initial findings and present proposals on the best placement for iBeacons and how accuracy might be improved by taking local environmental factors into account when estimating distance. You can cite this presentation as: Thomson, C. (2014) "Factors effecting positional accuracy of iBeacons" Presentation at R08 Associate Lecturer Scholarship Showcase, Open University, Manchester, 29th March I have commentary available for the slides on my blog: http://bit.ly/1iSdh6L Please email me if you have any questions chris@codepilots.com
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Factors effecting positional accuracy of iBeacons
- 4. Codepilots.comComputer Consulting iBeacons Small (50x30mm) Cheap (£8-30 per beacon) Range of up to 75m Battery powered Supported by Apple (unlike RFID tags)
- 5. Codepilots.comComputer Consulting Distance to a iBeacon Anon (2014) 'Adjust beacon range with Estimote’s new App and change UUID using Estimote’s new SDK', Reality matters [Online]. 28/1/2014. Available at http://blog.estimote.com/post/74816977799/estimote-app-v1-2 (Accessed 19/3/2014).
- 6. Codepilots.comComputer Consulting iBeacon localization Estimote iBeacons, from http://estimote.com
- 7. Codepilots.comComputer Consulting The only maths: distance Qiu, T, Zhou, Y, Xia, F, Jin, N, & Feng, L 2012, 'A localization strategy based on n-times trilateral centroid with weight', International Journal Of Communication Systems, 25, 9, pp. 1160-1177, Academic Search Complete, EBSCOhost, viewed 18 March 2014. Bulusu, N, Heidemann, J, & Estrin, D n.d., 'GPS-less low-cost outdoor localization for very small devices', Ieee Personal Communications, 7, 5, pp. 28-34, Science Citation Index, EBSCOhost, viewed 18 March 2014.
- 8. Codepilots.comComputer Consulting Overcoming Environmental factors Bayesian learning (Öktem & Aydin, 2010) Real-time reference measurements (Hyo-Sung & Wonpil 2009) Clever uses of the radio (Wu et al, 2013) Öktem R, & Aydin, E 2010, 'An RFID based indoor tracking method for navigating visually impaired people', Turkish Journal Of Electrical Engineering & Computer Sciences, 18, 2, pp. 185-196, Academic Search Complete, EBSCOhost, viewed 18 March 2014. Hyo-Sung, A, & Wonpil, Y 2009, 'Environmental-Adaptive RSSI-Based Indoor Localization', IEEE Transactions On Automation Science & Engineering, 6, 4, pp. 626-633, Business Source Complete, EBSCOhost, viewed 18 March 2014. Wu, K, Xiao, J, Yi, Y, Chen, D, Luo, X, & Ni, L 2013, 'CSI-Based Indoor Localization', IEEE Transactions On Parallel & Distributed
- 9. Codepilots.comComputer Consulting Practical issues to consider Differences in devices: Tablets, Smart phones and iBeacons Noisy environments Objects in the environment Cost of deployment and maintenance Limited access to raw hardware
- 11. Codepilots.comComputer Consulting Experimental setup 4mx3m Test ‘Lab’ IPad Air (2013 wi-fi only model) 3 Estimote pre-production iBeacons (early 2014) Core Location SDK and Estimote SDK Trilateration algorithm (wwnick &Austin, 2010) wwnick, Austin, J. (2010) 'Trilateration using 3 latitude and longitude points, and 3 distances', Geographic Information Systems Stack Exchange [Online]. 26/6/2012. Available at http://gis.stackexchange.com/a/415 (Accessed 18/3/2014).
- 12. Codepilots.comComputer Consulting Technical stuff Estimotes x 3 Hardware: D3.2, Software: A1.9 Power: 4 dBm, Interval 200ms Estimote API dated 19/02/2014 Elevation: 210cm (wall) or 240cm (celling) iPad Air Elevation: 130cm (held) or 70cm (on stool) Held flat, home button to left of operator, hands under the device.
- 13. Codepilots.comComputer Consulting Estimote Uniformity Measured power levels (typical) at 1 meter. Receiver iPad Air, home button towards Estimote spot. Typical RSSI values: -65 dBm, -71 dBm, -66 dBm Levels fluctuated approximately ±5 dBM Stayed within this range with other WiFi and Bluetooth devices disabled.
- 14. Codepilots.comComputer Consulting Test ‘lab’ Operator and facing direction Trilateration location Beacon and reported distance
- 15. Codepilots.comComputer Consulting Test ‘lab’ obstructions WiFi access point Lamp shade Mac with WIFI Beacon on bookshelf, obstructed to left Shelf below beacon Window Door Door
- 19. Codepilots.comComputer Consulting Rotation of iBeacon Bottom right beacon rotated only, stuck to wall, vertical orientation facing iPad, operator stood in front of iPad, iPad at 70cm elevation on stool.
- 20. Codepilots.comComputer Consulting Rotation of iBeacon Bottom right beacon rotated only, stuck to wall, Horizontal orientation, base facing iPad
- 21. Codepilots.comComputer Consulting Rotation of iBeacon Bottom right beacon rotated only, stuck to celling, horizontal orientation facing iPad, operator stood in front of iPad
- 22. Codepilots.comComputer Consulting Recommendations Ceiling mounting of Estimotes reduces variance and may also help with blocking by the operator Signal transmission and reception are dependent on the orientation of both the transmitter and receiver. So this should be built into positioning models. Radio absorption by the operator is significant in determining distance. Again models should take account of the direction of the operator. Other radio interference does not seem significant in practice.
- 23. Codepilots.comComputer Consulting Future research Does other hardware suffer from the same directionality issues? Improve experimental protocol to eliminate operator issues, and take more accurate measurements. Collect further data on the variation in signal strength, to check for statistical significance of effects observed. Experiment with a predictive model to take observed effects into account.