rssi values using xbee

i am doing indoor localisation project with xbee. i want to determine the position of a mobile node where all other three static nodes . i need to get no. of RSSi values with different positions of mobile nodes .
your help will be highly appereciated

Look in your XBee manual. It documents an ATDB command which returns an RSSI for the most recent RX frame.

Any given reading is unlikely to be completely accurate. At minimum you would likely want to take multiple readings, throw out some number of high/low values, and either average the rest or run some more advances statistics to ensure you are using a solid value.