Determining how far you are from a beacon is a challenge because 1) RF signals degrade unpredictably depending on their environments; 2) Bluetooth beacons do not use a consistent RF transmit power; and 3) the technology does not have enough technical tricks yet.
To date, the only feasible answer to locate a beacon without geo-positioning information is to estimate its distance from the receiver (scanner) based on Received Signal Strength Indicator (RSSI) and RF transmit power. The exercise spits out an approximate proximity, or an “approximity,” if you’ll allow the pun.
Part of the reason is that RF degrades in its environment according to an almost unlimited number of variables (humidity, people density, walls, wall materials, transmit power, adjacent blockers, trees, metal, etc.
Another part is that Bluetooth beacons do not have a single standardized RF output power, and therefore range can vary from under a meter, to a few meters, to more than 500 meters. A final part is that RSSI does very little to indicate directionality.
So in practice, receiving and decoding a beacon packet has limited information for calculating how near it is.
There are some bits of helpful information and techniques. The beacon’s transmit power is included in the packet structure, and most scanners, or receivers, have an RSSI. Using these two inputs, RSSI + TX Power, a receiver can approximate the distance to the beacon. Further, as multiple approximations are calculated it follows that an application can determine if the scanner is getting closer or further from the beacon.
Once the beacon location is determined, smartphone applications can store the information for subsequent encounters. When the beacon identifier and services are decoded, the smartphone or associated application already has its location stored.
Future versions of the Bluetooth specification will likely incorporate Angle-of-Arrival (AoA) and Angle-of-Departure (AoD) features which allow multi-antenna Bluetooth devices to determine the spatial location of another Bluetooth device. AoA and AoD will support high-accuracy location detection, potentially giving position accuracy to within tens of centimeters.
But standards move slowly. Until AoA and AoD are standardized, the RSSI + TX power calculation is the best approximity measurement, and changes unpredictably with the real world of walls, weather, people, and propagation.
Whitepaper on Developing with Bluetooth BLE Beacons
Our experts have put some very relevant information in a whitepaper on developing with Bluetooth beacons. The goal is to help you get to market quickly with the right, stable solution.
It covers a lot of territory:
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