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.
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.
- 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.
- A noisy cloud of Bluetooth signals can impede the accuracy of beacon signal measurement. This vulnerability to Bluetooth noise can vary by beacon manufacturer - based on the strength and protocol of the signal - so be sure to test your selected beacons in a live environment.