First off, there several types of RSSI ``readings'': 1) what the radio returns 2) a value in dBm (normalized from #1) 3) a value in watts (converted from #2)
First off, make sure you have type #3 if you use the following. For a -really- rough estimation of distance (RSSI readings are highly subjective to transmission power, receive sensitivity, antenna lobes, the environment, etc.) you can use the property that: P is proportional to C / R^2, where P is power, in watts (not dB!), R is distance in meters, and C is some constant. The problem is that, in reality, C is not constant. Anyway, with a little math and knowing P1 at distance R1, assuming a constant C, you can find R2 for P2. You'll have to find C based on some playing around and, please do keep in mind that this is very fickle! (But you should be able to tell general "proximity".) EM waves are pesky little guys. There is a whole slew of other approaches to perform more advanced localization techniques with more nodes, more centralization, more hardware, etc. _______________________________________________ Tinyos-help mailing list Tinyos-help@millennium.berkeley.edu https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
