How to calculate the distance of devices over WI-FI using force and signal frequency?

Question

How can I calculate the distance of a device by wifi, using the strength of the signal of the same?

I’m using tshark (wireshark) to perform this 802.11 scan, capturing only Prob requests (the moment the device searches for Aps). Then filter the fields that interest me as MAC address of the emitter, Signal Strength and among others.

Shell command (With MAC filter):

tshark -l -i wlxe894f617588c -Y "wlan.fc.type_subtype == 4 && wlan.sa == xx:xx:xx:xx:xx:xx" -T fields -e wlan_radio.timestamp -e _ws.col.Source -e _ws.col.Destination -e wlan_radio.signal_dbm  -e wlan_radio.frequency

Output

1614649110  xx:xx:xx:XX:XX:XX   Broadcast   -34 2412
1614751459  xx:xx:xx:XX:XX:XX   Broadcast   -40 2412
1615400027  xx:xx:xx:XX:XX:XX   Broadcast   -74 2412
1615514449  xx:xx:xx:XX:XX:XX   Broadcast   -74 2412
1615672377  xx:xx:xx:XX:XX:XX   Broadcast   -86 2412

From the above columns I use only the last two which are signal strength and frequency. To perform the following calculation:

Distance = 10 ((27.55 - (20 * log10(Frequency)) + signalLevel)/20)

Described as response How to calculate Distance from Wifi router using Signal Strength? He further informs:

Example: Frequency = 2412MHz, signalLevel = -57dbm, result = 7.000397427391188m

But when I perform the calculation with these values the result is totally different:

#include <stdio.h>
#include <math.h>

int main(){
    float r = pow(10.0,((27.55 - (20 * log10(2414))+ -57)/20.0));
    printf("%d\n",r); // resultado 0.000014
    return 0;
}

There are other answers that involve the calculation FSPL (Free Space Path Lost), but it requires variables that I do not have, such as sensitivity of antenna reception or its gain.

It is obviously not easy to get the exact distance of the device, since the signal strength is sensitive to any physical barrier and interference of the same frequency. The very goal is to know how many Vices are next to my antenna in a radius of 5 meters or more if necessary being connected or not.

Answer 1

I tested it here on Matlab:

Frequency in 2412

signallevel in -57

Your code is missing one abs look there in the image formula:

abs(-57)

Correct equation for the above data:

10 ^ ((27.55 - (20 * log10(2412)) + abs(-57))/20)