On Mar 25, 2006, at 9:21 AM, Sara B. wrote:
Hi all,I'm using MicaZ platform and I'm trying to get LQI and RSSI values. I get correctly LQI values (Msg->lqi), but when trying to get RSSI (power level received) value by Msg->strength I obtain values around 250 at -10 dBm with the 2 motes very near. If I have to substract the offset of -45 to get the final value on dBm, 250 - 45 it's not a good value for RSSI...
-45 is a pretty reasonable value. If you bring the nodes very close at full transmit power (0dBm, you might get an RSSI reading of +3 or +5, which after the -42 offset is -39 or -37. Telos motes have similar behavior (it's the chip, not the platform). The important thing to realize is how much power the chip is consuming to put out that signal: you could always amplify it, but doing so would increase power draw.
The receive sensitivity of the CC2420 is at worst -91 dBm, and more typically -93 dBm. Even in 802.11 environments, this is usually the more important factor than environmental noise. Here's a plot Kannan Srinivasan (a student here at Stanford) collected of PRR vs RSSI on the Intel Mirage testbed:
<<attachment: PRRVsSSI_BurstTx.jpg>>
Our unvalidated hypothesis for the three outliers at -81 dBm is that they're due to 802.11 interference.
Phil
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