freebsd stable - Sep 2006 - 802.11 RSSI value displayed from ifconfig(8)

Hello, I would like to convert RSSI to dBm (in fact I would love if
ifconfig cound display SNR in dBM), so I would like to know if this
formula is any right:

/* Calculate the RSSI Value */
V_RSSI = 3.0 * (RSSI_VAL/1024);
RSSI_dBM = (int8_t) ((-50.0 * V_RSSI) - 45.5);

And if there are any other tools which can help me finding out signal
stenght, when I am acting as an access point.

> Hello, I would like to convert RSSI to dBm (in fact I would love if
> ifconfig cound display SNR in dBM), so I would like to know if this
> formula is any right:
Take a look here:

http://www.wildpackets.com/elements/whitepapers/Converting_Signal_Strength.pdf

Especially at the top of page 5. RSSI isn't defined to be in particular
units, so the formula will be different for each piece of radio hardware
you have. Unless you have a way of calibrating your specific interface
then you probably cant do it in any meaningful way.

-pete.

Eduardo Meyer wrote:
> Hello, I would like to convert RSSI to dBm (in fact I would love if
> ifconfig cound display SNR in dBM), so I would like to know if this
> formula is any right:
> 
> /* Calculate the RSSI Value */
> V_RSSI = 3.0 * (RSSI_VAL/1024);
> RSSI_dBM = (int8_t) ((-50.0 * V_RSSI) - 45.5);
> 
> And if there are any other tools which can help me finding out signal
> stenght, when I am acting as an access point.
ifconfig reports rssi as whatever the driver provided.  The intent is
that it be a signed value relative to the current noise floor (both in
dBm).  If you look at the output of wlanstats
(tools/tools/net80211/wlanstats) or, for ath devices, athstats
(tools/tools/ath/athstats) you will see the default displays show
"signal" which is rssi+noise-floor in dBm.  The main issue(s) right
now
are that the net80211-driver api does not pass noise floor up so it can
be reported to user apps and drivers reports rssi+nf in varying units.
athstats doesn't have that issue since it queries the driver directly
(hence it's display has a reasonable noise floor).

It's on my todo list to push signal-related data up properly and fix
ifconfig so it displays a proper signal strength in the normal status
display.  The issue of units is more difficult as converting data for
some devices to dBm can be tricky.

	Sam