How to calculate distance from Wifi router using Signal Strength?

Question

I would like to calculate the exact location of a mobile device inside a building ( so no GPS access)

I want to do this using the signal strength(in dBm) of at least

Answer 1

In general, this is a really bad way of doing things due to multipath interference. This is definitely more of an RF engineering question than a coding one.

Tl;dr, the wifi RF energy gets scattered in different directions after bouncing off walls, people, the floor etc. There's no way of telling where you are by trianglation alone, unless you're in an empty room with the wifi beacons placed in exactly the right place.

Google is able to get away with this because they essentially can map where every wifi SSID is to a GPS location when any android user (who opts in to their service) walks into range. That way, the next time a user walks by there, even without a perfect GPS signal, the google mothership can tell where you are. Typically, they'll use that in conjunction with a crappy GPS signal.

What I have seen done is a grid of Zigbee or BTLE devices. If you know where these are laid out, you can used the combined RSS to figure out relatively which ones you're closest to, and go from there.