Re: WiF Transmit Power Control (TPC) Regulatory Requirements?

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Hi,

The only project I've heard of that implements such functionality is
https://github.com/thuehn/Minstrel-Blues.

On Thu, Jan 4, 2024 at 12:02 PM <b.K.il.h.u+tigbuh@xxxxxxxxx> wrote:
>
> Ideally, TPC should be a fully automatic mechanism that reduces
> transmit power between the two points to as low of a level as possible
> while delivering the same quality of service. The purpose is to reduce
> the excess headroom in each link. I.e., if you could still link with
> 65Mb/s towards a given direction using 14dBmW, you should not transmit
> with 20dBmW.
>
> Some only set the AP TX power globally (i.e., same towards all of its
> connected clients at the moment) to tackle the hidden/exposed node
> problem, but again must do this adaptively and change this constantly
> without human intervention. There exist multiple advanced algorithms
> for this, some proprietary tuned for corporate deployment.
>
> Actually, if we accepted automatically retuning tx power with iw based
> on actual link stats of momentarily connected clients every 60s with
> cron, this could be added to OpenWrt pretty easily.
>
> > Class A devices control their transmit power within ±3 dB and class B devices control their power within ±9 dB.
>
> - https://www.litepoint.com/blog/wi-fi-6-ofdma/
> - https://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/8-3/b_RRM_White_Paper/tpc.html
>
> On Thu, Jan 4, 2024 at 10:42 AM Johannes Berg <johannes@xxxxxxxxxxxxxxxx> wrote:
> >
> > On Thu, 2024-01-04 at 10:07 +0100, b.K.il.h.u+tigbuh@xxxxxxxxx wrote:
> > > You can find a wording in most such regulations that if TPC is not
> > > supported, the maximal TX power must be reduced by 3 dBmW. Hence in
> > > all such cases, the entries in db.txt contain 3 less than the maximum.
> > >
> > > If, on the other hand, you know of a country that specifies that
> > > devices lacking TPC may not use the band at all, all such band entries
> > > must be omitted (commented out along with a URL).
> >
> > Yeah, that's how we (currently) handle things.
> >
> > I'm not even sure what the requirements would be for "TPC" to be
> > implemented, tbh.
> >
> > > > As far as I know the kernel doesn't have facilities to support TPC or
> > > > transmit power control,
> >
> > Right. I have, however, heard the interpretation that the fact that we
> > have - even if nobody uses it - the "iw set txpower" command means that
> > we *do* have TPC ... Not really sure what to make of that though.
> >
> > > > nor does the wireless-regdb database.
> >
> > Correct. With the new regdb format we could add something that would
> > enable these ranges in the kernel only with some additional
> > requirements, but
> >   (a) we don't implement that now, and
> >   (b) I don't know what the requirements would actually be, e.g. would
> >       it be enough that the driver promises it implements "TPC" in some
> >       way? Or even the manual setting?
> >
> > > > And so
> > > > in the database we would either omit rules that require TPC, or include
> > > > alternative rules (as specified by local regulations) not requiring TPC.
> > > > Am I right?
> >
> > Right.
> >
> > johannes
>





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