BLE-RSSI completely noisy signal

I am working on an app for indoor navigation. I am reading the RSSI-values of three Bluetooth beacons, that I placed in my apartment. The TX signal strength of these beacons is 6 dBm, advertising interval 100 ms. I am using a Motorola G7 Plus, Android Version 10. In the room there is also WLAN (mine and that of the neighbours).

I have done a lot of measurements (with self-made beacons and bought ones) and very often there is such a lot of noise in the received RSSI-values! I read some papers about indoor navigation and I did not see that other developers were having the same problem. I also cannot figure out what causes this noise. E.g. I did measurements outdoors (with only one beacon), without any WLAN in reach and the noise was still present (though less intense). Maybe it´s interference with the Smartphone?

Has anyone of you experienced similar measurements?

Solution

I wouldn't call this noise, there is clearly a pattern. Since a myriad of factors can influence the received signal, one can only speculate without further information/measurements.

An example: Bluetooth LE uses three channels for advertising (37, 38 and 39) which are spread over the frequency band. Since the receiver can only receive on one channel at a time, the picture you showed could indicate that the deviations are caused by the different channels/frequencies that find completely different propagation paths in your environment.

The magic word is filtering. You have to average your RSSI measurements over a longer period of time and then use the obtained values to triangulate the position.