On May 25, 2007, at 6:38 AM, Matthias Gauger wrote:
Hello,
Is there a way to detect and log the occurrence of collisions
causing packet loss in TOSSIM when using Tinyos 2.0? I couldn't
find any information on that in the TOSSIM tutorial.
Because TOSSIM in 2.0 uses an SNR model, doing this in a precise way
is non-trivial. E.g., it's possible to have a noise floor of -93 dBm,
a packet (which can't be received due to its low signal) comes in at
-94 dBm, raising the noise floor to -92 dBm, which then causes a
packet at -87 dBm to be lost that might not have been had the first
weak packet not arrived. This gets trickier in 2.0.1, when there
isn't a fixed SNR threshold but rather an SNR/PRR curve.
That being said, there are conditions when it's pretty clear. E.g.,
Noise floor is -95 dBm
Start (successfully) receiving packet A at -80 dBm
Halfway through packet A, start receiving packet B at -70 dBm
- B corrupts A, and since there is not continuous start symbol
detection, B is lost as well
In 2.0.1, the best way to figure this out is to enable the dbg
channel "SNRLoss". It won't tell you exactly what you want -- there's
some additional information in there -- but I think that if you trim
its output a bit (e.g., add another channel to some of the dbg
statements that only report collisions) then you should be able to
get the information you need.
Phil
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