iOS proximity changes for stationary beacons - why?

[rvaessen]

I am working with nRF51822 beacons and an iOS 9 application that I am developing. I am testing on an iPhone 6. My application uses the CLLocationManager's beacon ranging functionality to determine if the distance to a beacon is immediate, near, far, or unknown. When I have my application running and there are 3 beacons sitting right beside the iPhone, the CLLocationManager reports that their proximity is (mostly) immediate. But, as I sit and watch, the proximity of any given beacon occasionally changes to unknown (sometimes near) and then back to immediate. I expect that there is a good explanation for this but I am unaware of it. Will someone please enlighten me? Thank you.

[Marius Heil]

Hello,

when you are broadcasting iBeacon messages, there's a calibratedTXpower field in the packet. This should be set to the average received RSSI in about 1m distance I believe. If you set that one correctly and have the beacons right next to the iPhone, it should do the ranging correctly I guess.

But RSSI values are never exact and there is a very high jitter over time which is why always multiple measurements must be taken into account to provide a measurement that is usable