Locations are normally estimated with a certain level of uncertainty, referred to as accuracy. This is true regardless of the technique used to determine that location. Higher accuracy means lower uncertainty.
In this page you can find information regarding all the factors that influence the Bluetooth Low Energy signals detected by the BLE nodes and thus the level of accuracy provided by Bluetooth Beacon Tracker. Being aware about these factors will allow you to know what to expect from each installation and how to bring out the most from Bluetooth Beacon Tracker to get the highest positioning accuracy.
1 – Environment
1.1 – Number of obstacles
The best results with Accuware Bluetooth Beacon Tracker are obtained when there is an high attenuation of the Bluetooth signals (RSSI) detected by the BLE nodes. Accuware Accuware Bluetooth Beacon Tracker determines the position of BLE devices by measuring the attenuation of the Bluetooth signal they transmit. This means that, as strange as it might sound, it works better inside building with walls because, since the attenuation of the radio signals is stronger, it is easier for the algorithm to trilaterate the position of BLE devices. In open spaces the attenuation of Bluetooth radio signal is weaker and this leads to a lower accuracy.
- You should expect an average radius of accuracy of 3 meters when tracking BLE devices inside a shopping mall, hospital, school campus, airport, hotels, train station, subway, museum, corporate building (with cubicles or offices), jail, retail store and in general inside buildings with walls.
- You should expect an average radius of accuracy of 5 meters when tracking BLE devices inside a large warehouse, trade show, industrial plant, stadium etc.. and in general inside buildings with only few walls.
1.2 – Types of obstacles
Although Bluetooth Beacon Tracker works well in environments with walls, it must be said that different type of obstacles made of different materials affect the accuracy of Bluetooth Beacon Tracker:
- Thick walls – even if Bluetooth Beacon Tracker works better inside building with walls, if walls are too thick (and the Wi-Fi signal absorption of the walls is too high) there can be some communication problems between the BLE nodes and the Wi-Fi network used by the BLE nodes to communicate with the Accuware server). This means that the BLE nodes will not be able to send their reports to the Wi-Fi network and so the Accuware server will have less data for the computation of the locations of the BLE devices. Anyway this is quite rare because the average spacing between the BLE nodes suggested by us is usually small enough to avoid these kind of communication problems.
- People – one source of interference is the human body that, with its high percentage of water, attenuates the RF signal. This means that if you make your tests while keeping your BLE devices in your pockets or your hands, you will see variations of the RSS depending on how you hold the device and the orientation of your body with respect to the BLE nodes. These RSS variations lead to small variations of the locations of the BLE devices. It should be kept in mind that this effect is more evident in open spaces where there is no attenuation introduced by the walls and the attenuation introduced by the human body can have a great influence on the RSS.
- Metal objects and mirrors – big metal objects and/or mirrors affect negatively the level of accuracy because of the reflection of these kind of objects on the Bluetooth signal propagation.
Anyway, even if you have to be aware about the important notions just reported, you do not have to worry too much because the Accuware Bluetooth Beacon Tracker algorithm is able to adapt itself to the environment in which the BLE nodes are installed.
2 – Nodes
2.1 – Amount
Increasing the BLE nodes density will always increase the system accuracy. Anyway be aware that the number of BLE nodes is a function of the objectives of your project as explained inside this support page.
2.2 – Deployment model
The best results are obtained when the BLE nodes are installed uniformly (ideally in a grid pattern) and diminishing the spacing between the BLE nodes will always increase the system accuracy. Even if the accuracy is affected by multiple factors (and not just by the spacing), here is a rough estimate of how the level of accuracy varies with the spacing between the BLE nodes:
- ~10 meters of spacing between the BLE nodes -> average accuracy of ~2 meters
- ~15 meters of spacing between the BLE nodes -> average accuracy of ~4 meters
Please keep in mind also these notions:
- placing the BLE nodes too close to each other in the same room, does not improve the accuracy because all the BLE nodes will receive the same signal strengths from the BLE devices regardless the location of the BLE devices.
- if you do not need the same level of accuracy everywhere, you can use a different spacing for different areas.
Anyway be aware that the spacing between the BLE nodes is in function of the objectives of your project as explained inside this support page.
2.3 – Physical location
The physical location of the BLE nodes affects the system accuracy. For this reason we suggest to install the BLE nodes in these physical locations (in order of preference):
- on the ground.
- on the lower part of a wall/column.
- on an item that is very close to the ground. Please make sure the signal source is attached to an object that won’t be moved.
- on the ceiling.
- inside a false-ceiling.
- on the upper part of a wall/column.
- an an item that is very close to the ceiling. Please make sure the signal source is attached to an object that won’t be moved.
Do not place the BLE nodes halfway between ceiling and floor (e.g. on desks) and completely avoid mixed configurations (e.g. half of the BLE nodes on the ground and half of the BLE nodes on the ceiling) because in both cases the performances will be negatively affected due to a different propagation of the Bluetooth signal.
There is not a maximum height for the ceiling installation but it should be noted that the accuracy drops as the height increases. From our experience, we do not recommend to install the nodes at a height over 4 meters. The fact that the height of the ceiling is not uniform is not a problem as long as the difference between the min and max height is not higher than 1 meter.
3 – Usage conditions
3.1 – Position with respect to the BLE nodes
Another factor that affects the accuracy is the relative location of the BLE devices compared to the area covered by the BLE nodes. The BLE nodes are able to detect BLE devices up to 30 meters away. Despite the fact that the detection radius is pretty large, you need to be aware that the accurate locations computed by the algorithm are ONLY those related to BLE devices that are physically located inside the ideal perimeter defined by connecting the most outer BLE nodes. The locations of the BLE devices that are physically outside the perimeter defined by the nodes will be wrong (the locations of those BLE devices will be show along the perimeter defined by the nodes).