[Tinyos-help] Outdoor Range with Tmote sky

[David Gay]

On 2/20/07, Philip Levis <pal at cs.stanford.edu> wrote:
> On Feb 20, 2007, at 10:42 AM, Jacob Sorber wrote:
>
> > You are asking for a simple answer where none exists.  Wireless
> > channels are tricky.  While line-of-sight is straightforward, "not
> > in line of sight" could mean a lot of things.  What is obstructing
> > the signal?  A building?  A person?  A hill of dirt and rock?  Is
> > it raining?  What is the humidity?  I have yet to find a radio that
> > is immune to obstructions.  If you find one, I would love to see
> > it.  My experience has been that the 2.5Ghz radios are usually more
> > robust to obstructions than the CC1000 radios on the Mica2/Mica2Dot
> > motes, but not always.  When one mote is a meter under water the
> > CC1000 seems to do much better than the CC2420, though neither work
> > very well in that situation.  Also a rain storm can reduce the
> > range some.  The best thing to do is to program two motes and take
> > them outside and see.  It will only take a few minutes.  If you
> > need a more technical explanation for why node A can't hear node B,
> > then you need to do some reading in the wireless comm literature.
> > This might be a good place to start ( www.eecs.berkeley.edu/~dtse/
> > cu_day1.ppt).
> >
>
> My understanding is that the waves which are really resistant to
> obstructions are extremely low frequency (ELF) ones: think < 100Hz.
> That's what submarines use to communicate when submerged, for example
> [1].

Lower frequencies propagate better through water (which is why a
CC1000 at 400 or 900MHz is better than a CC2420 at 2.4GHz). And
propagation through fresh water is significantly better than through
salt water (if I remember the numbers correctly, salt water ==
essentially no range at the frequencies under discussion, while fresh
water might get a few meters).

Lots more detail on all this is available if you look up electrical
engineering source materials rather than sensor network ones... (i.e.,
tinyos-help is probably not the best place to find out about this, try
finding a friendly professor with RF knowledge).

David Gay