On Wed, May 13, 2009 at 5:51 PM, Sudha Krishna <[email protected]> wrote: > Hi, > > We are doing some localization expts for which we are collecting RSSI > values using the Xbow micaz motes. We use a transmitter and receiver, > with their power level set to 31 (0dBm) using the TinyOS makefile > (CC2420_DEF_RFPOWER=31). We are essentially using the RssiDemo code > with an additional field in the beacon message. I have attached a plot > that displays the RSSI values (y-axis, in dBm) taken at different > distances (X-axis in feet) in a free space outside environment. The > distances are [6,9,12,15,12,18,21,24,30,36]ft. We subtract -45 from > the raw RSSI values output by the RSSIdemo code to get the value in > dBm. Both the motes are in line of sight and placed well above ground > level and there is no other known source of interference. > > Generally the RSSI values are supposed to decrease with distance and > follow a log-linear path loss model. Strangely, as you can see from > the plot after some distance the RSSI values are higher. We are unable > to explain this behaviour, especially given that the multipath effect > is minimal in free space. We are not sure if this an artifact of the > micaz mote hardware or the CC2420 radio or something else we have > overlooked in the software. Has anyone else observed this behaviour > with micaz motes? If someone has an idea why this may be occurring > and how to fix this problem, we would be interested in knowing.
You might want to look at figure 5 on Joe Polastre's paper: http://www.polastre.com/papers/spots05-telos.pdf - om_p _______________________________________________ Tinyos-help mailing list [email protected] https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
