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Factors effecting positional accuracy of iBeacons Chris Thomson ([email protected])

Factors effecting positional accuracy of iBeacons

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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 [email protected]

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Page 1: Factors effecting positional accuracy of iBeacons

Factors effecting positional

accuracy of iBeacons

Chris Thomson ([email protected])

Page 2: Factors effecting positional accuracy of iBeacons

Background

Page 3: Factors effecting positional accuracy of iBeacons

Indoor localization

?Where

am I

Page 4: Factors effecting positional accuracy of iBeacons

iBeacons

Small (50x30mm)

Cheap (£8-30 per beacon)

Range of up to 75m

Battery powered

Supported by Apple (unlike RFID tags)

Page 5: Factors effecting positional accuracy of iBeacons

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).

Page 6: Factors effecting positional accuracy of iBeacons

iBeacon localization

Estimote iBeacons, from http://estimote.com

Page 7: Factors effecting positional accuracy of iBeacons

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.

Page 8: Factors effecting positional accuracy of iBeacons

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 Systems, 24, 7, pp. 1300-1309, Business Source Complete, EBSCOhost, viewed 18 March 2014.

Page 9: Factors effecting positional accuracy of iBeacons

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

Page 10: Factors effecting positional accuracy of iBeacons

Solutions?

Page 11: Factors effecting positional accuracy of iBeacons

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).

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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.

Page 13: Factors effecting positional accuracy of iBeacons

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.

Page 14: Factors effecting positional accuracy of iBeacons

Test ‘lab’

Operator and facing direction

Trilateration location

Beacon and reported distance

Page 15: Factors effecting positional accuracy of iBeacons

Test ‘lab’ obstructions

WiFi access point

Lamp shade

Mac with WIFI

Beacon on bookshelf,obstructed to left

Shelf belowbeacon

Window

Door

Door

Page 16: Factors effecting positional accuracy of iBeacons

Operator Rotation

Page 17: Factors effecting positional accuracy of iBeacons

iPad rotation

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No Operator

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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.

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Rotation of iBeacon

Bottom right beacon rotated only, stuck to wall, Horizontal orientation, base facing iPad

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Rotation of iBeacon

Bottom right beacon rotated only, stuck to celling, horizontal orientation facing iPad, operator stood in front of iPad

Page 22: Factors effecting positional accuracy of iBeacons

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.

Page 23: Factors effecting positional accuracy of iBeacons

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.