Beacon
calibration & distance estimation precision
Beacon calibration will help a Bluetooth LE receiver accurately
estimate the distance between itself and that beacon. Calibration
means providing the correct Transmission Power
(txPower) information in the beacon message. With accurate
txPower information, the receiver will be able to
convert the difference between the Received Signal Strength
Indicator (RSSI) and the txPower into a
distance.
Beacon calibration procedures can vary widely so check your
beacon manufacturer's website for information about if and how
calibration is performed. If you are using beacons that can be
calibrated, it is important to calibrate them after onsite
installation, in their final usage conditions.
Different factors can impact the quality of the Bluetooth signal
received by the receiver from a beacon. Signal noise will reduce
the precision of the estimated distance. Some factors influencing
noise
putting two beacons very close to each other
putting two beacons in a straight line from the receiver
changing the rotational orientation of a beacon
Beacons broadcast in all directions but not necessarily with
uniform power
position of the receiver
an external Bluetooth LE USB dongle will have better reception
than an internal Bluetooth LE chipset
holding a tablet in portrait or landscape orientation will
provide different results
placing beacons in an isolated box (doesn't add noise, it
reduces signal strength)
To limit noise, the Beacon Detection
interface asset applies filters on the raw data captured by the
Bluetooth received. These filters will remove unrealistic values
(beacons jumping from 2 meters to 10 meters then coming back) while
introducing a small delay in measurement.
Beacon configuration
Some beacons enable you to configure their broadcasting
power.
high power (eg. -3dB/m, 0dB/m, +3db/m) will enable a receiver
to detect the beacon over a large distance, up to 230 feet / 70
meters away. However, this will add noise to the signal and will
reduce the precision of distance estimation, particularly at short
distances. It also consumes more of the beacon's battery.
low power (eg. -12dB/m) will enable a receiver to only detect
beacons over a small distance, under 35 feet / 10 meters, but will
provide a better signal with less noise.
Some beacons, like those from Estimote, also enable you to configure
the type of beacon. You can therefore use the same
physical beacon as an iBeacon™ or as an Eddystone-UID, for
example.
Other beacons, like the
Radius Networks RadBeacon, can emit multiple signals - iBeacon,
Eddystone-UID, Eddystone-URL - at the same time. This is not
handled by the Beacon Detection
interface asset, thus we recommend only using beacons emitting a
single signal.
Tips
When creating your experience with Composer, you might want your
beacons to be detected and lost without having to run 165 feet / 50
meters away from your desk. Most beacons don't have a "power
on/off" option so the simplest solution is to build a "Faraday
cage" using several antistatic bags and a metal box in which to
store your beacons. Beacons inside such a box and with such
packaging won't be detected.