raw to dBm conversion
proski at gnu.org
Wed Jun 28 01:28:07 EDT 2006
On Tue, 2006-06-27 at 13:20 +0200, Valerio, Danilo wrote:
> Hi everybody,
> I searched in the mailing list archive for information about the
> conversion from the raw value of Signal and Noise to a dBm value but i
> didn't find anything really considerable...
There are FIDs 0xFD43 (CommsQuality) and 0xFD51 (dBmCommsQuality), which
are both supported on newer (post-1.3.x) firmwares. I checked both for
the same connections with different signal strength and came to the
following formula, which is used in the Orinoco driver for Intersil
#define RSSI_TO_DBM(x) (10 * ((x) - 317) / 33)
> I'm sniffing via TCPdump, and i need to convert that raw values of the
> prismII header (or AVS header) to dBm values...
I think header RSSI is the same as the one for the connection quality.
> After having a look into the driver code and making some measurement, i
> realized that a correct formula seems to be:
> ((raw_value) - dBmAdjust) * (100/255) - 100
RSSI your formula my formula
27 -89 -88
155 -39 -49
The results are pretty close. But my formula is based on real
measurements with 1.7.4 firmware. The only problem with my approach is
that I don't know if dBmCommsQuality can be trusted. It's possible that
hostap uses something based on closed Intersil documentation.
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