wireless-regdb: Wrong ETSI tranmit power without TPC

wireless-regdb: Wrong ETSI tranmit power without TPC

[Alexander Wilhelm]

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.

Is there inconsistencies between dBm/mW conversions? Please give me a feedback.


Best regards
Alexander Wilhelm

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

[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?

> 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

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

[Johannes Berg]

On Fri, 2025-05-16 at 16:15 +0800, Chen-Yu Tsai wrote:
> 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.

While technically true, I'd think it's probably hard to even measure
that accurately, 27 dBm is 501.187 mW?

> Or, if we understand 3 dBm reduction to be halving the power,

That's fairly precise, a factor of 0.501.

> 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.

I don't think _drivers_ (or firmware) would support both units, so
that'd just shift the rounding issue elsewhere?

Though I think in some places we use "mBm" instead of dBm? But then we
also just convert to dBm in many places so that'd likely not make it any
better.

johannes

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

[Johannes Berg]

On Fri, 2025-05-16 at 16:15 +0800, Chen-Yu Tsai wrote:
> > The frequencies 5470 - 5725 have a power of 500 mW. It results in 26 dBm. But I
> > believe 27 dBm are allowed.

Seems like. But units are hard...

The link in the db went stale, but the current versions

https://www.bundesnetzagentur.de/SharedDocs/Downloads/DE/Sachgebiete/Telekommunikation/Unternehmen_Institutionen/Frequenzen/Allgemeinzuteilungen/MobilfunkDectWlanCBFunk/WLAN_5GHz_pdf.pdf?__blob=publicationFile&v=1

states (page 5):

--------------------
Frequenzband 5470–5725 MHz
...
Maximale mittlere EIRP für
bandinterne Aussendungen

1 W
Ausnahmen:
für Anlagen in Straßenfahrzeugen gilt eine maximale
mittlere EIRP von 200 mW.

...

Maximale mittlere EIRP-Dichte für
bandinterne Aussendungen

50 mW/MHz in jedem 1 MHz-Band

...

Sendeleistungsregelung (TPC)

TPC muss durchschnittlich einen Abschwächungsfaktor von
mindestens 3 dB gegenüber der höchstzulässigen
Sendeleistung der Systeme erbringen; oder ohne TPC muss die
höchstzulässige mittlere EIRP und die Obergrenze für die
entsprechende mittlere EIRP-Dichte um 3 dB verringert
werden.
--------------------


So to be _really_ precise you'd end up with 1W reduced by 3dB which of
course _is_ precisely 27dBm since 1W is 10^30 or precisely 30 dBm.

(Except in "street vehicles", apparently. Rail has its own things, so I
guess that really does mean cars/trams/etc.)

But given the unit conversions are hard, we should probably just do this
in the db in dBm?

johannes

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

[Johannes Berg]

On Fri, 2025-05-16 at 10:38 +0200, Johannes Berg wrote:
> 
> So to be _really_ precise you'd end up with 1W reduced by 3dB which of
> course _is_ precisely 27dBm since 1W is 10^30 or precisely 30 dBm.
> 

Obviously 1W isn't 10^30, the latter is just a large number. I meant to
write

1 W is 10^(30/10) mW

johannes

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

[Alexander Wilhelm]

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

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

[Alexander Wilhelm]

Am Fri, May 16, 2025 at 10:38:04AM +0200 schrieb Johannes Berg:
> On Fri, 2025-05-16 at 16:15 +0800, Chen-Yu Tsai wrote:
> > > The frequencies 5470 - 5725 have a power of 500 mW. It results in 26 dBm. But I
> > > believe 27 dBm are allowed.
> 
> Seems like. But units are hard...
> 
> The link in the db went stale, but the current versions
> 
> https://urldefense.com/v3/__https://www.bundesnetzagentur.de/SharedDocs/Downloads/DE/Sachgebiete/Telekommunikation/Unternehmen_Institutionen/Frequenzen/Allgemeinzuteilungen/MobilfunkDectWlanCBFunk/WLAN_5GHz_pdf.pdf?__blob=publicationFile&v=1__;!!I9LPvj3b!Hih48oBC7IPvu59VI1FRTqSb45uwWEnAELFqlK_ubfJdtkTnODDPuyA5gG6olCgbiPxC6m0zQdcuNJ3nzRJ1RJ_PT6ux0w$ 
> 
> states (page 5):
> 
> --------------------
> Frequenzband 5470–5725 MHz
> ...
> Maximale mittlere EIRP für
> bandinterne Aussendungen
> 
> 1 W
> Ausnahmen:
> für Anlagen in Straßenfahrzeugen gilt eine maximale
> mittlere EIRP von 200 mW.
> 
> ...
> 
> Maximale mittlere EIRP-Dichte für
> bandinterne Aussendungen
> 
> 50 mW/MHz in jedem 1 MHz-Band
> 
> ...
> 
> Sendeleistungsregelung (TPC)
> 
> TPC muss durchschnittlich einen Abschwächungsfaktor von
> mindestens 3 dB gegenüber der höchstzulässigen
> Sendeleistung der Systeme erbringen; oder ohne TPC muss die
> höchstzulässige mittlere EIRP und die Obergrenze für die
> entsprechende mittlere EIRP-Dichte um 3 dB verringert
> werden.
> --------------------
> 
> 
> So to be _really_ precise you'd end up with 1W reduced by 3dB which of
> course _is_ precisely 27dBm since 1W is 10^30 or precisely 30 dBm.
> 
> (Except in "street vehicles", apparently. Rail has its own things, so I
> guess that really does mean cars/trams/etc.)
> 
> But given the unit conversions are hard, we should probably just do this
> in the db in dBm?
> 
> johannes

I referred to the following EU Rules:

* ETSI EN 300 328 V2.2.2 (2.4 GHz)
* ETSI EN 301 893 V2.1.1 (5 GHz)
* ETSI EN 300 440 V2.2.1 (5.8 GHz)

The problem with them is that almost always the unit _mW_ is used. And the
reduction without TPC then is given in _dBm_. However, for 5.8 GHz (SRD devices)
the transmission power is stated as 25 mW. Does the EU Rules means 14 dBm or
only 13 dBm are allowed?


Best regards
Alexander Wilhelm

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

[Johannes Berg]

On Fri, 2025-05-16 at 11:22 +0200, Alexander Wilhelm wrote:
> 
> I referred to the following EU Rules:
> 
> * ETSI EN 300 328 V2.2.2 (2.4 GHz)
> * ETSI EN 301 893 V2.1.1 (5 GHz)
> * ETSI EN 300 440 V2.2.1 (5.8 GHz)

Is that really all that relevant? I don't think ETSI has normative
power, that's left to the per-country regulators, IIRC. Who in Germany,
as demonstrated, did a mix of units for the range you were talking about
before.

> The problem with them is that almost always the unit _mW_ is used. And the
> reduction without TPC then is given in _dBm_. However, for 5.8 GHz (SRD devices)
> the transmission power is stated as 25 mW. Does the EU Rules means 14 dBm or
> only 13 dBm are allowed?

It means just that, 25 mW is allowed? I'm not sure you should read more
into it than written.

You could argue that 14 dBm is "close enough" at 25.11886 mW (0.47% too
much), but perhaps that's not something the computer should do, but
rather whoever updated the database. It might even differ slightly per
country, I guess, technically - though here the German document [1]
states the same.

[1] https://www.bundesnetzagentur.de/SharedDocs/Downloads/DE/Sachgebiete/Telekommunikation/Unternehmen_Institutionen/Frequenzen/Allgemeinzuteilungen/FunkanlagenGeringerReichweite/2018_05_SRD_pdf.pdf?__blob=publicationFile&v=2


So perhaps the database could state 14 dBm with an appropriate
justification, but the conversion from 25 mW to eventually rounded down
13 dBm also seems right.

johannes