Calculate the distance between two bluetooth devices using RSSI value, in swift?

Question

Created Jul ’20

Replies 3

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I get the RSSI value from the searched bluetooth device in list.
But didn't know how to Calculate the distance.
We need txPower to calculate that but from where I get this txPower.

I'm using this code but don't know it's correct.
func calculateNewDistance(txCalibratedPower: Int, rssi: Int) -> Double{
      if rssi == 0{ return -1 }

      let ratio = Double(exactly:rssi)!/Double(txCalibratedPower)
      if ratio < 1.0{
        return pow(10.0, ratio)
      }else{
        let accuracy = 0.89976 * pow(ratio, 7.7095) + 0.111
        return accuracy
      }
    }

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Answer 1

Claude31 OP

Jul ’20

There are many references on the web for this (seems you inspired from https://gist.github.com/eklimcz/446b56c0cb9cfe61d575)function calculateDistance(rssi) {

Code Block 	var txPower = -59 //hard coded power value. Usually ranges between -59 to -65
	
	if (rssi == 0) {
		return -1.0; 
	}
	var ratio = rssi*1.0/txPower;
	if (ratio < 1.0) {
		return Math.pow(ratio,10);
	}
	else {
		var distance =	(0.89976)*Math.pow(ratio,7.7095) + 0.111;		
		return distance;
	}
}

As explained

Code Block 	var txPower = -59 //hard coded power value. Usually ranges between -59 to -65

txPower (you called it txCalibratedPower) is the transmission power of the beacon or device. Its range is between -59 and -65. For the real value you need to get directly.
So, just do as done here, set at -59.
Then you can try to calibrate:
Modify in calculateNewDistance to loop through different values for txCalibratedPower, from - 56 to - 70

turn device BT on
install in free space from the measuring point
measure the distance and compare with the list of computed values
the closest to real distance will give you an estimate of txPower for THIS device

1

Answer 2

VishalWagh OP

Aug ’20

@Claude Thanks for your answer. I'm done with distance but now the distance which I get is not current.

For Android they use the Kalman filter to remove the noise and get accuracy so similar to that how can i use the Kalman filter in iOS (swift).
Thanksss

0

Answer 3

Claude31 OP

Aug ’20

Kalman on what ? RSSI I guess.

have a look here: https://stackoverflow.com/questions/47883492/ios-swift-calculate-distance-from-rssi

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