Convert RSSI to distance

how to convert RSSI to distance?. i have three coordinate RFID reader : Reader1(0,0). reader2(0,8), reader3(8,5). Transponder get RSSI, 156 from reader1, 115 from reader2 and 124 from reader3. how i can get distance between Transponder to reader1, reader2 and reader3? also coordinate of Transponder. Signal strength from RFID Reader is 0-255. 255 if so close, 0 if so far. i got RSSI formula from internet, but i confused to translate the parameters of A and NAi. can u help me?

thx u :-)

Buddy, let me clarify it: RSSI (received signal strength indicator) do not relates with the distance. We must understand that the RSSI value is given in decibel, a logarithm relation with the power ratio expressed in watt. The formula is Db = 10*Log(Watt).

And why it does not relates with distance? Its because a signal strength ratio depends on the environment (such walls, deep, structures, and so on) that makes the signal propagate more easily or more hardly. In other words, you can have different RSSI values for the same distance, as we can experiment if we use a cellphone at an open area, or inside a road tunnel.

Again, RSSI is not related with distance. The only situation where you can freely convert these two values is in theoretical non-practical situations, where environment (earth form, structures, air density, etc) do not takes relevance. In these situations, you fall in physics context, and not in stackoverflow (programming) context.