[Tinyos-devel] Lqi and CC2420

[Omprakash Gnawali]

On Mon, Mar 3, 2008 at 1:00 AM, Andreas Koepke <koepke at tkn.tu-berlin.de> wrote:
> >>
>  >>  Pragmatically: something that delivers a comparable performance.
>  >
>  > Phil can elaborate more because he has looked at RSSI and LQI in
>  > detail but it is not clear if one can get comparable performance using
>  > RSSI vs LQI.
>  >
>  > - om_p
>
>  Well, his published results afaik lack a QQ-Plot using the packet
>  delivery ratio PDR of RSSI vs. LQI. There may exist a cost function such
>  that PDR = cost(RSSI) = cost'(LQI). Theoretically, RSSI and LQI must be
>  strongly correlated in the absence interferers (both in system and out
>  of system like microwave ovens). So I believe that there is such a
>  function, and I would not be surprised if it is linear at least for the
>  relevant interval. Excluding interferers is the difficult part here...
>

Figure 5 on Joe's Spots 2005 paper has plots for PDR vs distance, LQI
vs distance, and RSSI vs distance. If you use a lookup table (in the
worst case) you can come up with a way to translate RSSI to PDR.
However, it is thought to be more difficult to estimate PDR with RSSI
than with LQI even though LQI can not predict PDR terribly accurately
either. From what I have heard from Phil, RSSI and LQI can be used to
classify links at a high granularity at different ranges but computing
a compatible cost that predicts PDR might be non-trivial.

- om_p