Hi. For distance estimation, I just use RSSI. I do experiment and tabulate the data. Data of the distance and its RSSI Value. Then from the tabulated data, I plot the graph and get the equation from the graph(distance vs RSSI). As the signal is fluctuating, i will do average for the received data. I'm doing it for distance estimation using xbee. but the idea is like that. Just note that it will not get the accurate distance. Just the suggestion.