Re: wireless-regdb: Wrong ETSI tranmit power without TPC

Alexander Wilhelm
2025-05-16T09:14:33Z

Am Fri, May 16, 2025 at 04:15:40PM +0800 schrieb Chen-Yu Tsai:
> On Thu, May 8, 2025 at 1:25 AM Alexander Wilhelm
> <alexander.wilhelm@westermo.com> wrote:
> >
> > Hello devs,
> >
> > please correct me if I'm wrong. Since TPC is not used, the EU Rules dictates to
> > decrease the transmit power by 3 dBm on some sub-bands. For the most of the EU
> > countries the mW instead of dBm is used. Therefore they are halved (e.g for
> > Germany (DE) in commit 81d251dda3985e1088bd89f5d9f565e63ba5a30f). The problem is
> > that the values are then converted to dBm and rounded down and result in a wrong
> > supported value. Take a look at example (Germany again):
> >
> > country DE: DFS-ETSI
> > (2400 - 2483.5 @ 40), (100 mW)
> > (5150 - 5250 @ 80), (200 mW), NO-OUTDOOR, AUTO-BW, wmmrule=ETSI
> > (5250 - 5350 @ 80), (100 mW), NO-OUTDOOR, DFS, AUTO-BW, wmmrule=ETSI
> > (5470 - 5725 @ 160), (500 mW), DFS, wmmrule=ETSI
> > # short range devices (ETSI EN 300 440-1)
> > (5725 - 5875 @ 80), (25 mW)
> > # WiFi 6E
> > (5945 - 6425 @ 320), (23), NO-OUTDOOR, wmmrule=ETSI
> > # 60 GHz band channels 1-4 (ETSI EN 302 567)
> > (57000 - 66000 @ 2160), (40)
> >
> > For the frequencies 5250 - 5350 the power of 100 mW results it 20 dBm. Correct.
> > The frequencies 5470 - 5725 have a power of 500 mW. It results in 26 dBm. But I
> > believe 27 dBm are allowed. For the frequncies 5725 - 5875 the value of 25 mW is
> > also dictated. I'm not sure if I should expect 14 dBm, but I get 13 dBm.
>
> Are you reading the converted numbers from the system, not the database
> text file?

From the system itself. I'm using the 'iw phy info' tool.

Regards
Alexander Wilhelm

>
> > Is there inconsistencies between dBm/mW conversions? Please give me a feedback.
>
> The conversions don't always produce round numbers, and since we can't let
> the system exceed the _actual_ limit, the values can only be rounded down.
> For example, 500 mW converts to roughly 26.9897 dBm. We can't use 27 dBm,
> since if the system outputs at 26.999 dBm, it would be in violation of
> the rules.
>
> Or, if we understand 3 dBm reduction to be halving the power, we could
> fix up any rules that "have their base limit in mW and were converted to
> dBm to apply the reduction" be rewritten in mW with the numbers halved.
> That would require someone to go through the entries though. But if
> the rules are already written in mW, and what you observe is the kernel
> rounding down the numbers, then perhaps the kernel may need to support
> both units.
>
>
> Thanks
> ChenYu