WLAN signal strength - good or bad ?

Werner Almesberger werner at openmoko.org
Mon Oct 6 19:09:44 CEST 2008


Andy Green wrote:
> I was saying maybe there is an easy patch there going into the IOCTL
> stuff that iwconfig uses and putting something more meaningful in this
> returned member.

Let's see ... for the AR6k, the code is here
drivers/sdio/function/wlan/ar6000/ar6000/wireless_ext.c:ar6000_set_quality

What it does is that it only looks at the SNR, even though it often
calls it the RSSI [1], and the description of that function uses the
two almost interchangeably. The noise floor is just a hard-coded best
guess, as expected.

The chip does return the RSSI as well [2], but it just seems to do
exactly the same calculation as the driver, i.e., reported RSSI =
reported SNR - hard-coded noise.

[1] http://en.wikipedia.org/wiki/RSSI
[2] This is the data structure that comes from the chip:
    drivers/sdio/function/wlan/ar6000/include/wmi.h:WMI_BSS_INFO_HDR

So, short of actually trying to associate, this seems to be as much
information we can get.

- Werner



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