Hi Xiaohui, if you are in an open field and there is not fast fading, then there is a fixed attenuation because of the distance and other factors.
If there is not line of sight (shadow) but the frequency is not very high then the wave is diffracted and the receiver will get some signal. On the other hand, if the frequency is quite high (i.e., I like to think about it like the wavelength is much smaller than the object that is shadowing) then you won't receive any signal at all from the direct path, but you could receive some reflections from a different path. It sounds like you are measuring indoor. If something moves in the room, then the reflected rays will fade and you will see a considerable drift in the RSSI. In summary, are you measuring indoor or outdoor? You should use a more complex model than the log-normal for indoor environments. Also, you are speaking about the channel, but check also that you always transmit and receive with the same radiation pattern (i.e., antennas are oriented the same). Hope this helps! Sergio On Mon, Mar 25, 2013 at 11:43 AM, Xiaohui Liu <[email protected]> wrote: > Hello everybody, > > I have a generic question regarding shadowing effect and hope somebody in > the mailing list can give me a hint, even though it is not TinyOS-specific. > > Given a RF sender and a receiver, suppose the obstacles between them are > fixed, both their material and dielectric properties, does the path loss > caused by their shadowing vary? If yes, what causes the variation? If not, > why is it generally modeled as a log-normal random variable? We can assume > there is only one path between the sender and receiver if this simplifies > the question. > > Thanks and look forward to your reply. > > -- > -Xiaohui Liu > TelosB > TinyOS 2.1.2 > www.cs.wayne.edu/xliu/ > > _______________________________________________ > Tinyos-help mailing list > [email protected] > https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help >
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