Finding distance from RSSI value of Bluetooth Low Energy enabled device

iphone objective-c ios7 bluetooth-lowenergy
puneet kathuria picture puneet kathuria · Dec 4, 2012 · Viewed 61k times · Source

I am working on Bluetooth low energy concept project. I am getting the RSSI value between 1 and 100. As I move the tag the RSSI value increase as the peripheral moves away from the iPhone and decreases as it moves closer.

Can anybody help me to get exact distance between the iPhone and the Bluetooth tag based on the RSSI value? Are there any available formulas?

I am getting the RSSI value of the device with the help of this bluetooth Low energy delegate method:

 - (void)centralManager:(CBCentralManager *)central didDiscoverPeripheral:(CBPeripheral   
   *)peripheral advertisementData:(NSDictionary *)advertisementData RSSI:(NSNumber *)RSSI

Answer

henrik picture henrik · Dec 5, 2012

I answered this in another thread, repeating it here.

In line-of-sight (no obstacles causing change in RSSI), -6dB seems to be double the distance.

If you at 1m distance read RSSI -40dB then 2m gives -46dB, 4m gives -52dB, 8m gives -58dB, 16m gives -64dB.

You can not get an exact position, only a circular maximum distance.

Using triangulation with 2-3 or more devices you get a much more accurate positioning result. You can get this purely from Advertisement packages but you must either Disable scan -> Enable scan or tell iOS CoreBluetooth to report all adv packages.

In foreground mode you can do this but in background mode you can't get all adv packages. You must connect and read RSSI to do it in the background.

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