Signal quality

[Aleksander Morgado]

On Tue, Mar 21, 2017 at 5:04 PM, José <Joseddg92 at gmail.com> wrote:
> ModemManager reports look like this:
>
> Status | lock: 'none'
> | unlock retries: 'sim-pin (3), sim-pin2 (3), sim-puk (10), sim-puk2 (10)'
> | state: 'connected'
> | power state: 'on'
> | access tech: 'hsdpa'
> | signal quality: '38' (recent)
>
> I have some questinos about the signal quality quantity:
>
> * Which units does the 'signal quality' use?

It's a percentage value (0-100). The "recent" flag tells us whether
the signal was refreshed in the last 30s IIRC.

> * Is it the same for any technology/modem?
> * How does it relate to RSSI and dbm?

Everywhere should be based on RSSI (dBm), scaled differently depending
on how the value is retrieved from the modem.

E.g. if given in dBm directly, scaled between -113dBm and -51dBm:
https://cgit.freedesktop.org/ModemManager/ModemManager/tree/src/mm-broadband-modem-qmi.c#n2627

Or if already given scaled between 0 and 31 as in +CSQ:
https://cgit.freedesktop.org/ModemManager/ModemManager/tree/src/mm-broadband-modem.c#n1805

Note that if you want "raw" technology-specific values, some modems
(like QMI) provide the "extended" Signal interface, see:
https://www.freedesktop.org/software/ModemManager/api/latest/gdbus-org.freedesktop.ModemManager1.Modem.Signal.html

-- 
Aleksander
https://aleksander.es