This document summarizes research into factors affecting the positional accuracy of iBeacons. iBeacons use Bluetooth Low Energy signals to enable indoor positioning but signal strength decreases unpredictably with distance from beacons. While triangulating position is possible with 3 or more beacons, distance estimates are difficult due to environmental influences. The presentation examines how the surrounding environment, human presence, and device orientation impact signal reception and the ability to accurately determine distances between beacons and receivers. Further refinement of experimental protocols is needed to better understand inconsistent results.

1. Presentation:
Factors
effecting
positional
accuracy
of
iBeacons
Chris
Thomson
Codepilots.com
31st
March
2014
Commentary
on
the
slides:
1.
2.
3. This presentation concerns indoor localisation and positioning – the target is
to locate a person using a mobile device within a building.
4. The technology under consideration to do this is the iBeacon. Battery powered
is a very important issue, as it means they can be placed anywhere without the
expense of routing power or network connections. So Ideal for quick
deployments, and use in locations inside and outside where we don’t want to
make changes – e.g. heritage locations. Battery’s last up to 2 years, at which
point the unit is replaced.
5. In this research I made use of Beacons by Estimote (estimote.com), who also
produced these graphs. These graphs show the measured power at distances
from a typical iBeacon, we can use power information to estimate the distance
of an receiver. Notice how the measured power does not decrease uniformly
as we move away from the receiver, this is the biggest limiting factor in using
this technology for accurate positioning.
6. If we have at least 3 beacons we can, using geometry/trigonometry work out
the unknown location of the receiver, based on the known location of the
transmitters and their distance from the receiver. Unfortunately finding the
distance is quite difficult!
7. You can express this problem mathematically in a number of ways, this is one
of them. The d, is the distance we want to know, the d0 a measure of distance
for a known power output, the n is the way the signal power degrades over
distance, and squiggle the environmental effect, the environmental effect is
actually quite large!
8. A fair bit of research in measuring distance in this way has been done, lots of
it is to do with wireless sensor networks, three approaches seem common,
these are as listed on the slide. But for iBeacons, we are limited to only the top
approach as real time measurements are two power hungry, and we don’t
have access to the raw radio in iOS to do anything clever.
9. The main issues and limitations are as listed on the slide, the questions we
can actually investigate are underlined. These are: How the signal is received
and transmitted; Now noisy is the environment, and its effect; and Humans
and other objects.
10.
11. It is worth mentioning here, that at this stage, all of the above is basically
standard practice available on the market.
12. If you want to reproduce the results, this information will probably be

2. important. As radio reflection may also be an issue, the room has a concrete
floor, breeze block walls, and a plasterboard ceiling. The presences of 2 doors
and a window may also set up interesting interference patterns.
13. I need to do a statistical analysis of this variation, but have not yet done so.
However the variance does not seem great.
14.
15. These are the main high level, and radio obstructions which could cause a
problem.
16. The way the iPad is held is very important, the receiver seems most sensitive
to being held at the front bottom of the iPad near the home button. So the
orientation of the iPad is rather important. In this experiment the iPad was
held horizontally in front of the person holding it, with hands underneath the
device.
17. In this experiment the iPad was held, operator standing looking towards the
top of each graph, and the iPad rotated in front of the operator.
18. In this case the ipad was placed onto a stool. Something interesting is going
on with the bottom right beacon, why is it so far out?
19. Clearly I need to refine the experimental protocol here, as the changes in the
top right beacon’s distance are rather interesting.
20.
21.
22.
Comments,
advice
and
suggestions
are
invited,
email
me:
chris
(at)
codepilots.com
or
twitter
@codepilots.