How to get distance from beacons

Question

I am using Moko H2 beacon and using this library to get beacon list I am getting beacon list successfully

I am getting this type of response after scan

[
  {
    "mac": "F2:EE:97:63:1B:B6",
    "validDataHashMap": {
      "20": {
        "data": "20000bc117c0006673d201552aa1",
        "type": 2
      }
    },
    "rssi": -53
  },
  {
    "name": "BeaconX",
    "mac": "C4:7D:65:69:95:B7",
    "validDataHashMap": {
      "0afcc47d656995b7220164426561636f6e58": {
        "data": "0afcc47d656995b7220164426561636f6e58",
        "type": 4
      }
    },
    "rssi": -58
  },
  {
    "name": "BeaconX",
    "mac": "D0:24:EA:4E:1F:B3",
    "validDataHashMap": {
      "0afcd024ea4e1fb3220164426561636f6e58": {
        "data": "0afcd024ea4e1fb3220164426561636f6e58",
        "type": 4
      },
      "20": {
        "data": "20000bd91980005b4af60130014a",
        "type": 2
      }
    },
    "rssi": -59
  },
  {
    "mac": "D3:B9:AF:E1:D7:D3",
    "validDataHashMap": {
      "1000016d6f6b6f736d61727400": {
        "data": "1000016d6f6b6f736d61727400",
        "type": 1
      }
    },
    "rssi": -61
  },
  {
    "name": "BeaconX",
    "mac": "CB:4C:90:6C:E7:43",
    "validDataHashMap": {
      "1000016d6f6b6f736d61727400": {
        "data": "1000016d6f6b6f736d61727400",
        "type": 1
      },
      "0afccb4c906ce743220163426561636f6e58": {
        "data": "0afccb4c906ce743220163426561636f6e58",
        "type": 4
      }
    },
    "rssi": -61
  },
  {
    "mac": "CF:EB:82:02:6A:78",
    "validDataHashMap": {
      "20": {
        "data": "20000ba51b40006675dd0155316e",
        "type": 2
      }
    },
    "rssi": -61
  }
]

my requirement is how can I get distance from a distance

I have a rssi value and txPower calculation int txPower = Integer.parseInt(data.substring(2, 4), 16);

so how can I calculate distance using these 2 value rssi and txPower

I tried this but getting the wrong result

Adapter

holder.itemView.tvDistance.text = "${model.rssi.toInt().getDistance(model.measure_power.toInt()).convertMeterToFt().toRoundString()} ft" 

Extension function

fun Int.getDistance(txPower: Int): Double {
    return Math.pow(10.0, ((Math.abs(this) - Math.abs(txPower)) / (10 * 2)).toDouble())
}

fun Double.convertMeterToFt(): Double {
    return (3.281 * this) // to ft
}

fun Double.toRoundString(): String {
    return DecimalFormat("#0.##").format(this)
}

rssi@1m is -59

calculate distance

fun calcDistbyRSSI(rssi: Int, measurePower: Int = -59): String? {
        val iRssi = Math.abs(rssi)
        val iMeasurePower = Math.abs(measurePower)
        val power:Double = (iRssi - iMeasurePower)/(10*2.0)
        // ft = m * 3.2808

        if (Math.pow(10.0,power) * 3.2808 < 1.0){
            return String.format("%.2f ft(Immediate)", Math.pow(10.0,power) * 3.2808)
        }else if (Math.pow(10.0,power) * 3.2808 > 1.0 && Math.pow(10.0,power) * 3.2808 < 10.0){
            return String.format("%.2f ft(Near)", Math.pow(10.0,power) * 3.2808)
        }else{
            return String.format("%.2f ft(Far)", Math.pow(10.0,power) * 3.2808)
        }
    }

Please help me Any Help Would be Highly Appreciated.

Kc

Answer 1

You don't need to use txPower if you have RSSI value of beacons. You can calculate the distance information from RSSI value with this formula:

Distance = 10^((Measured Power - Instant RSSI)/(10*N)).

N is the constant for the environmental factor. It takes a value between 2-4. The measured power is the RSSI value at one meter.

So when you get a new beacon info. You can calculate the current distance. Let's assume your RSSI information is -61 and your N factor is 2.4. You measured RSSI value -44 at one meter.

When you get -61 RSSI. It corresponds to 10^((-44-(-61))/(10*2.4)) = 5.10 meter distance between rssi sender and receiver.

Flame

i don't understand how to calculate Measured Power and N please put equation – Kc

You won't calculate measured power. You should observe it manually. Keep your beacon 1 meter away from receiver and observe the beacons rssi values. Also you don't need to calculate N factor. It's a factor that attenuation of signal. It's changing in different environments you can try different values until you find the value that gives the most accurate distance. Because this is about the air in the environment. You can read Equation 3 explanations from here. – Flame

so the measured power is rssi from 1 meter ridht? – Kc

i am geeting rssi like -65,-66,-70,-72,-73,-74 in 1 meter these are multiple beacons – Kc

Yes, right. If you read the article which I referenced you can see "where the distance d0 is a unit distance (i.e., 1 m) and A represents the RSSI of the unit distance." line. And ^ is exponential number symbol. For 10^x, you can use Math.pow(10, x). And finally, you can use arithmetic mean of different RSSIs for 1 meter RSSI. If my answer is helpful you can upvoting so others can read it. – Flame

Math.pow(10.0, ((-44 - model.rssi.toInt()) / 10 * 2.4)) like this? this is right? – Kc

Yes but I gave -44 as example number. You should use average rssi value of different beacons rssi at 1 meter. – Flame

so every time Measured Power is different? – Kc

this is my final equation Math.pow(10.0, ((Math.abs(-65) - Math.abs(model.rssi.toInt())) / 10 * 2.0)) this is right? – Kc

It's so normal cause it's depended to environmental factors. Therefore, your measured power shouldn't be static. You can use the measured power value for hours. Because air behavior and conditions not changes very quickly. But when you observed your results getting bad you can check instant "measured power". If the difference between previous measured power and your instant measured power is very big, you should update your measured power. – Flame

so how can i stable measured power or make dynamic – Kc

i get this result on 1 meter -65,-66,-70,-72,-73,-74 so i use 65 in measured power – Kc

still not getting accurate distance – Kc

can you help me remotely? – Kc

If the distance is not true you should check your parameters. Also note that: You can't get the exact distance with RSSI. Generally, distance values has error tolerance. RSSI values can be affect from anything easily. So distance info can be misleading. I'm suggesting you that should search similar works. – Flame

hello what happens if Measured Power is lower then rssi? because in equation it shows masured power - rssi – Kc

let's remember that measured power is rssi at 1 meter. If your measured power is lower than instant rssi it means the distance between your beacon and signal receiver is less than 1 meter. The equation is "measured power - rssi" means that: let's assume that your measured power is -44 and your rssi is -30 in this case the distance would be: 10^((-44+30)/10*2.4) = 0.26 m is less than 1 meter. In a nutshell: if measured power is lower then rssi, the calculated distance will be less than 1 meter. – Flame

i am doing like this is it right? github.com/MokoBeaconX/MokoBeaconX_Android/issues/13 – Kc

please check my updated question i added a function for getting distance and rssi@1m is -59 – Kc

@Flame the equation, if copied directly into a compiler, did not produce the correct results. I've edited the response, Chirag; pseudo-code would be pow(10, (measuredRssi - instantRssi) / (10.0 * N)... plugging in -44, -61, and 2.4 should give the expected 5.1 meter result cited in the original answer. The equation is also expressed this way in this article, for reference: medium.com/beingcoders/… – Canotas