Connected RSSI on iPhone invalid

[jloliveira]

Good Afternoon,

We are using the nRF52840 DevKit with our BLE peripheral app and after connecting on iPhone (iOS11) and trying to read the RSSI (readRSSI() from CoreBluetooth with SWIFT) the values are always invalid, mostly 0. We tried third party apps and the same occurred. When trying to actively read the RSSI on the peripheral side the RSSI is OK.

Is there any reason to justify this? Do you have any suggestion to solve it?

Thank you,

João

[AmbystomaLabs]

That's pretty normal for iOS.  CoreLocation is even worse as with it when the location accuracy goes below a certain threshold it will report 0 for RSSI.  But generally it occurs earlier for CL.  Normally at about 30 feet.  With CB you can normally get out to about 100 feet before it acts up.

I don't have my resources at hand, but the 0 will also get reported at +128dBm depending on how you format the data coming back from the API call.

In our applications, I just reuse the last good value and then keep a rolling average of good values.  Some iPhones are worse than others.  The iPhone 5(c) are the worst of BLE4+. Everything 6 and up is pretty comparable in performance.

I have never seen it to be BLE device dependent.  And have tested many, many different beacon types with the same results.

One thing to remember also is that after about 2 minutes of getting data from CB, the OS will cut back on your resources and you will get many fewer data points from your advertisements.