[Tinyos-help] collision or interfere in TOSSIM

[Tie Luo]

Thanks for your pointer. In the paper I did see TOSSIM models packet
corruptions (Sec. 3), and the simulation in Sec. 4.2 Fig. 9 also shows
packet loss due to CRC failures.  However I did not see how to distinguish
between the causes to CRC failures, i.e. collision and bit errors.  In Sec.
6 you mentioned that RadioCRCPacket as a simulator has been developed which
can model packet loss due to bit errors but does not model packet
collision.  Perhaps in a simulator like TOSSIM we can identify collision
since we have global knowledge of which nodes are sending simultaneously (
e.g., the paper Sec. 3.7.2 mentioned something similar to this), but in
reality how can a mote itself distinguish these two?

I modified TinyOS MAC layer to pass up packets even if CRC is error.
However in experiments I never detected such CRC error, though I can detect
packet loss.  Is that because the error bits always occur at the start
symbol and thus prevent reception?

Regards,
Tie

On 11/11/06, Philip Levis <pal at cs.stanford.edu> wrote:
>
> On Nov 10, 2006, at 7:14 PM, Tie Luo wrote:
>
> > Thank you for your clarification.
> > I think to detect collision in reality becomes difficult, since
> > both collisions and channel error lead to packet CRC error.  Other
> > methods like using RSSI and LQI cannot clearly distinguish either,
> > although they may help to some extent.
> >
>
> Please read the TOSSIM paper.
>
> Phil
>
>


-- 
Regards,
Tie
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