Hi Matthew, RSSI is a measure af the signal strength with respect to a received message, so it is highly subject to disturb coming from other objects/people. This implies a quite unpredictable fluctuation which can be faced only updating regularly (2/3 times per second) the RSSI samples. You will need N nodes called anchors with known positions, which exchange messages in order to estimate the relationship between RSSI and distance in a given time instant. Then you will use this relationship to convert the RSSI sampled by the moving node (target node) to estimate the distance between itself and a given number of anchors. Finally, triangulation or other geometric methods can help you to estimate the target's coordinates. You should search in literature for "RSSI WSN localization".
Hope this helps, Marco On 14 June 2011 21:18, Matthew Jacques <mjac...@pride.hofstra.edu> wrote: > Hello, > > I am currently trying to build a WSN using MicaZ motes and I need to know, > to a fair degree of accuracy, how far apart one node is from another. I was > reading up on how it is possible in some cases to use RSSI and LQI to > achieve this. I tried taking measurements of average RSSI when the nodes > were 1.5, 2 and 2.5 meters apart but the results were very erratic. While I > did notice that the RSSI tended to be higher when the nodes were further > away from each other, the results were not accurate enough to place the node > within even 4 meters of its actual location. > > Is RSSI not an accurate enough way to get the precision I need? If not is > there any other method I can use to get the distance between nodes? > > I was also thinking of maybe using the system time of the nodes to time how > long a signal took to travel between them but I figured that with the time > to send and the turnaround time of the message in the other node this would > be a pretty inaccurate way to do it. Is that even worth trying? > > Thanks, > > Matthew Jacques > > _______________________________________________ > Tinyos-help mailing list > Tinyos-help@millennium.berkeley.edu > https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help >
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