Hi,

Signal quality and strength are two different independent parameters.
RSSI is easy to measure, but dbm numbers are not understandable by end users, and
not always correlate with the actual signal quality.
For example one can have very weak signal with high quality, and strong
signal with high interference, thus poor quality.

The signal quality is a estimation to give a simple, user friendly percentage number.
Until Vista, this estimation was done by each vendor's WLAN software.
I don't have the sources right now, but it seems that Vista uses the quality value
provided by the device driver, if available. Otherwise it uses a simple formula to
derive the quality from RSSI.
This can explain why you get negative values for qualiy with some drivers,
it is bug either in the driver or Vista.

The bottom line, you can't directly convert between RSSI and quality, they are
independent. Some formulas for RSSI to percentage conversion can be found in
internet, but they are either device specific, or too simple and wrong.

Hope somebody has Vista docum, or wireless driver source handy, and can correct me.

Regards,
--PA



"WLAN" wrote in message news:279BD898-492D-4778-AA91-07ECCEFE3ECF@microsoft.com...
> Hello ALL,
>
> I am writing a site survey application using wifi api supported by Windows
> Vista. I want to show current wireless connection attributes like SSID,
> BSSID, Signal Strength(dBm) etc.
>
> For querying all the above values, I am using WlanQueryInterface() with
> wlan_intf_opcode_current_Connection opcode. This returns SSID, BSSID and
> Signal Quality in percentage.
>
> How do I get signal strength value in dBm? WiFi API supports another opcode
> called wlan_intf_opcode_rssi which returns rssi values. I am facing some
> difficulties for this opcode. For broadcom adapter, it's returning dBm values
> (-23, -65, -43 etc). But for cisco adapter, it's giving postiive values (23,
> 30, 32 etc). I think for cisco it's giving original rssi values and not dBm
> values.
>
> So How do I convert this value into dBm?
>
> or
>
> Is there anyway to convert signal strength in percentage to dBm?
>
> Any idea is welcome.
>
>