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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Indoor localization
?Where
am I

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iBeacons
Small (50x30mm)
Cheap (£8-30 per beacon)
Range of up to 75m
Battery powered
Supported by Apple (unlike RFID tags)

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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).

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iBeacon localization
Estimote iBeacons, from http://estimote.com

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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.

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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

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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

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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.

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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.

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Test ‘lab’
Operator and
facing direction
Trilateration
location
Beacon and
reported distance

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Test ‘lab’ obstructions
WiFi access point
Lamp shade
Mac with WIFI
Beacon on bookshelf,
obstructed to left
Shelf below
beacon
Window
Door
Door

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Operator Rotation

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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

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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.

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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.