On Dec 19, 2007, at 6:09 AM, Tal Rusak wrote:
Hi,
I noticed that TOSSIM uses the following formula to compute RSSI:
rcv->strength = (int8_t)(floor(10.0 * log(pow(10.0, power/10.0) +
pow(10.0, noiseStr/10.0)) / log(10.0)));
(in CpmModelC.nc)
I notice that this is adding the signal power (gain) and noise
levels. I am wondering if this is a true reflection of the physical
phenomenon--i.e., in the CC2420, when RSSI is computed
(CC2420Packet.getRssi(packet)), do signal and noise strength
contribute in an additive fashion? Are there any paper or documents
that support this notion?
I appreciate any response in advance.
It's basic wave physics. This is a very simplistic way to compose the
signals. If the signals are completely in phase, it will be additive.
In practice, they're not, so it's less. But trying to capture this
more accurately becomes strange, especially when the two signals are
not precisely the same frequency.
Phil
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