On Feb 10, 2007, at 3:43 PM, Madhu Mudigonda wrote:
We have a question on monitoring of environment by reading RSSI
values continuously from RSSI register. We ran an experiment, where
two nodes exchange messages between them and continuously read the
RSSI values from both the received packet and RSSI register. We
could not observe any change in RSSI values, when there is packet
loss between motes. Sometimes, there was not much variation in the
RSSI values, but still there was some packet-loss.
RSSI Values obtained by us are like this:
-99,-99,-99,-99,-98,-65,-56,-86,-99,-99,-98..........
According to our understanding, as the sensitivity threshold of
CC2420 radio is -95dBm, mote should lose packets, if the RSSI is
less than -95dBm ( i.e, -96dBm,-97dBm,...........). But, in reality
though the RSSI values are less than the -95dBm, packets are being
received by the receiver successfully and sometimes though the RSSI
value is something like -76dBm, the packets are getting lost. We
couldnot understand why the RSSI register values are less than
-95dBm even when we are receiving packets?
Any suggestions on how to estimate the channel quality using the
RSSI values?
The -95 dBm number on the datasheet is an approximation. Packet
reception is based on the signal-to-noise ratio. If you noise floor
was say, -94dBm, then in the case of the CC2420 you wouldn't see any
packets at -95dBm.
Phil
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