What happens when multiple devices scan the same BLE tag

Understand how the platform process information from multiple BLE scanning devices reporting the same tag.

Typical cases

When deploying a BLE scanning solution for a particular area, very often more than one zone anchor needs to be deployed to ensure that all assets are reliable detected. As a result, a single tag may be seen by multiple scanning devices.

Without any additional logic in the platform, this would result in a continuous 'jumping' of the BLE tag from one scanning devices location to the other. The tag would simply be at the location of the scanning device that most recently reported the tag. This location jumping behavior is not acceptable because it would lead to a very 'noisy' location history.

The platform applies extra rules to counter the jumping behavior:

• The RSSI strength at which the BLE tag is taken into account. An incoming scanning observation is compared to the last recent observation. If the strength of the incoming observation is lower or comparable to the last recent observation, then the tag location will not be updated. However, when the RSSI strength is considerable higher, then the new scanning device will 'claim' the tag. It is configurable how much large the RSSI difference should be.
• Distance is also taken into account. If the new observation is sufficiently far away from the previous location (farther than BLE detection radius) , then the new scanning device can claim the tag regardless of the RSSI strength.
• Finally, also the time difference is taken into account. If the observation by a previous scanning device was sufficiently long ago, then the new scanning device can also 'claim' the tag. This time difference is defined as a multitude of the sending interval.

The above logic is described in detail in Enter-Exit locations with BLE zone anchors.

Third party BLE scanning solutions such as HP Aruba and Cisco Meraki have an intermediate gateway server that processes observations from the individual scanning devices. Refer to the user guide of these solutions to understand the exact localization behavior.

Use the same scanning device at a single zone

At a single location, avoid deploying a mix of different scanning device types. Different scanning devices might have different signal sensitivity and different scanning intervals, complicating the interpretation of BLE tag observations.

Note that it is perfectly possible to equip one location with a set of battery powered zone anchors, and another location with fixed zone anchors. Just avoid mixing them at one location.

In cases where vehicle trackers that do BLE scanning are deployed, it may happen that a tag is both in range of the vehicle tracker and a zone anchor (either battery powered or externally powered) . The platform prioritizes the zone anchors over the vehicle tracker: only when the vehicle tracker is sufficiently far away from the zone anchor, it will claim the tag.

Draw geozones

Make good use of geozones. In most cases, perform location analysis on the level of the geozone, not on the level of individual anchors. This also helps in managing the accuracy expectation by the end-users.

• When zone anchors with overlapping ranges are deployed in a single warehouse / room / location, create a single geozone containing all zone anchors.
• When zone anchors are overlapping, but the locations are functionally different, ensure with proper testing that they are sufficiently separated by distance or walls that block the BLE signal. Draw geozones containing the functionally related anchors.