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Date:   Mon, 27 Mar 2023 14:40:35 -0500
From:   Seth Forshee <sforshee@kernel.org>
To:     Keshav <the.ridikulus.rat@gmail.com>
Cc:     wireless-regdb@lists.infradead.org, linux-wireless@vger.kernel.org
Subject: Re: wireless-regdb: Please correct the regulatory rules for India
 (IN) on 2.4 GHz
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On Fri, Mar 24, 2023 at 06:30:32PM -0500, Keshav wrote:
> Hello Seth,
> 
> Thank you for your reply. Please find below my comments.
> 
> On Tue, Mar 21, 2023 at 11:38 AM Seth Forshee <sforshee@kernel.org> wrote:
> >
> > On Sat, Mar 04, 2023 at 05:13:44PM -0600, Keshav wrote:
> > > Hello,
> > >
> > > I noticed that wireless-regdb db.txt [1] has restricted India's 2.4
> > > GHz maximum power to only 20 dBm:
> > >
> > > country IN:
> > >         (2402 - 2482 @ 40), (20)
> > >
> > > However the Official Gazette of Government of India (PDF [3] linked in
> > > URL [2]) mentions that upto 30 dBm is allowed in the 2.4 GHz band.
> > >
> > > 2.4 GHz Rules for India (IN): Pages 87 to 88 of PDF [3]
> > >
> > > I would like to mention that I am not an expert in this topic. I am
> > > not sure if there's any other reason to restrict 2.4 GHz for India to
> > > 20 dBm in the db.txt. I also couldn't find any other official
> > > Government of India document that restricts the maximum power to 20
> > > dBm (due to some other reason). Please look into this and correct the
> > > regulatory rules for India if needed. Thank you.
> > >
> > > Although not the topic of this email, you can also find the 5 GHz
> > > Rules for India in the same PDF [3] (pages 94 to 97) if interested.
> > >
> > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/sforshee/wireless-regdb.git/tree/db.txt?id=7f7a9f7bc6011b072b5427eced1ff19261764e95#n853
> > >
> > > [2] https://dot.gov.in/spectrummanagement/gazette-notifications-delicensed-band
> > >
> > > [3] https://dot.gov.in/sites/default/files/Gazette_Notifications.pdf
> >
> > Sorry for the slow response. I've been attempting to research this as
> > time allows, but I haven't had a lot of time for it, and the information
> > is not well organized.
> >
> > [1] was the most complete summary I found for spectrum use in India. In
> > particular Annex 1 has a table of GSR numbers relevant for unlicensed
> > spectrum, which for 2.4 GHz is GSR No. 45(E) [2] and for 5 GHz is GSR
> > No. 1048(E) [3]. It looks like the document you linked to just bundles
> > these and other GSRs together, so as far as I can tell the information
> > you provided looks accurate.
> >
> > The database stores maximum EIRP, not transmitter output power, so I
> > think that 36 dBm is the correct value for 2.4 GHz (GSR No. 45(E) shows
> > an ERP of 36dBm, but based on the maximum transmitter power of 30 dBm I
> > think this is probably meant to be the EIRP).
> >
> > The 5 GHz rules look mostly right, except that it looks like 5250-5350
> > and 5470-5725 MHz both require DFS. They also require TPC, which Linux
> > doesn't support, but the PSD limit restricts our max EIRP to below the
> > threshold where TPC is required.
> >
> > So I think these are the correct rules for India:
> >
> > country IN:
> >         (2400 - 2482 @ 40), (36)
> >         (5150 - 5250 @ 80), (30)
> >         (5250 - 5350 @ 80), (24), DFS
> >         (5470 - 5725 @ 160), (24), DFS
> >         (5725 - 5875 @ 80), (30)
> >
> > If this looks right to you, I can send the patch to update the rules.
> >
> > Thanks,
> > Seth
> >
> > [1] https://dot.gov.in/sites/default/files/NFAP%202018.pdf
> > [2] https://dot.gov.in/spectrummanagement/delicensing-24-24835-ghz-band-gsr-45-e-5150-5350-ghz-gsr-46-e-and-5725-5875-ghz
> > [3] https://dot.gov.in/spectrummanagement/license-exemption-5-ghz-gsr-1048e-dated-22102018
> 
> Based on your explanation, the numbers look right to me. However, I am
> not an RF expert and I do not have enough knowledge to interpret these
> rules correctly myself. Therefore I will defer to your judgement here.

I am not an RF expert either.

> There's one thing I forgot to mention in my previous email. I noticed
> this discrepancy in db.txt because I came across the embedded regdb
> rules defined in an ath11k wifi router running OpenWrt
> (https://openwrt.org/toh/hwdata/dynalink/dynalink_dl-wrx36), and
> noticed that they are different from wireless-regdb db.txt rules. The
> "iw" outputs from the ath11k device are pasted below for your
> reference.
> 
> # iw reg get
> global
> country IN: DFS-UNSET
>         (2402 - 2482 @ 40), (N/A, 20), (N/A)
>         (5150 - 5250 @ 80), (N/A, 30), (N/A)
>         (5250 - 5350 @ 80), (N/A, 24), (N/A)
>         (5470 - 5725 @ 160), (N/A, 24), (N/A)
>         (5725 - 5875 @ 80), (N/A, 30), (N/A)
> 
> phy#1 (self-managed)
> country IN: DFS-FCC
>         (2402 - 2472 @ 40), (N/A, 30), (N/A)
>         (5170 - 5250 @ 80), (N/A, 30), (N/A), AUTO-BW
>         (5250 - 5330 @ 80), (N/A, 24), (0 ms), DFS, AUTO-BW
>         (5490 - 5730 @ 160), (N/A, 24), (0 ms), DFS, AUTO-BW
>         (5735 - 5835 @ 80), (N/A, 30), (N/A), AUTO-BW
> 
> phy#0 (self-managed)
> country IN: DFS-FCC
>         (2402 - 2472 @ 40), (N/A, 30), (N/A)
>         (5170 - 5250 @ 80), (N/A, 30), (N/A), AUTO-BW
>         (5250 - 5330 @ 80), (N/A, 24), (0 ms), DFS, AUTO-BW
>         (5490 - 5730 @ 160), (N/A, 24), (0 ms), DFS, AUTO-BW
>         (5735 - 5835 @ 80), (N/A, 30), (N/A), AUTO-BW
> 
> # iw list
> Wiphy phy1
> Frequencies:
>                         * 2412 MHz [1] (30.0 dBm)
>                         * 2417 MHz [2] (30.0 dBm)
>                         * 2422 MHz [3] (30.0 dBm)
>                         * 2427 MHz [4] (30.0 dBm)
>                         * 2432 MHz [5] (30.0 dBm)
>                         * 2437 MHz [6] (30.0 dBm)
>                         * 2442 MHz [7] (30.0 dBm)
>                         * 2447 MHz [8] (30.0 dBm)
>                         * 2452 MHz [9] (30.0 dBm)
>                         * 2457 MHz [10] (30.0 dBm)
>                         * 2462 MHz [11] (30.0 dBm)
>                         * 2467 MHz [12] (disabled)
>                         * 2472 MHz [13] (disabled)
>                         * 2484 MHz [14] (disabled)
> 
> Wiphy phy0
> Frequencies:
>                         * 5180 MHz [36] (30.0 dBm)
>                         * 5200 MHz [40] (30.0 dBm)
>                         * 5220 MHz [44] (30.0 dBm)
>                         * 5240 MHz [48] (30.0 dBm)
>                         * 5260 MHz [52] (24.0 dBm) (radar detection)
>                         * 5280 MHz [56] (24.0 dBm) (radar detection)
>                         * 5300 MHz [60] (24.0 dBm) (radar detection)
>                         * 5320 MHz [64] (24.0 dBm) (radar detection)
>                         * 5500 MHz [100] (24.0 dBm) (radar detection)
>                         * 5520 MHz [104] (24.0 dBm) (radar detection)
>                         * 5540 MHz [108] (24.0 dBm) (radar detection)
>                         * 5560 MHz [112] (24.0 dBm) (radar detection)
>                         * 5580 MHz [116] (24.0 dBm) (radar detection)
>                         * 5600 MHz [120] (24.0 dBm) (radar detection)
>                         * 5620 MHz [124] (24.0 dBm) (radar detection)
>                         * 5640 MHz [128] (24.0 dBm) (radar detection)
>                         * 5660 MHz [132] (24.0 dBm) (radar detection)
>                         * 5680 MHz [136] (24.0 dBm) (radar detection)
>                         * 5700 MHz [140] (24.0 dBm) (radar detection)
>                         * 5720 MHz [144] (24.0 dBm) (radar detection)
>                         * 5745 MHz [149] (30.0 dBm)
>                         * 5765 MHz [153] (30.0 dBm)
>                         * 5785 MHz [157] (30.0 dBm)
>                         * 5805 MHz [161] (30.0 dBm)
>                         * 5825 MHz [165] (30.0 dBm)
>                         * 5845 MHz [169] (disabled)
>                         * 5865 MHz [173] (disabled)
> 
> Looks like ath11k restricts the maximum EIRP to 30 dBm for 2.4 GHz.
> Again I am not an expert so I can't comment on whether 30 dBm vs 36
> dBm is the correct maximum EIRP value for 2.4 GHz.

I find the rules in GSR No. 45(E) unclear and a little confusing.
Broadly you can think of EIRP(dBm) = tx_output_power(dBm) +
antenna_gain(dBi). If you look at the US rules [1] you can see that it
specifies EIRP assuming an antenna gain of 6 dBi or less, with
adjusments for antennas with larger gains.

GSR No. 45(E) does not define things as clearly, but when I see a
transmitter output power of 30 dBm and a maximum effective radiated
power of 36 dBm it leads me to think that it has a similar model of
assuming an antenna gain <= 6 dBi. I could be wrong, but from what I see
this interpretation makes the most sense to me.

30 dBm is certainly a safe value though, as the max EIRP should be at
least that much under any interpretation.

[1] https://www.ecfr.gov/current/title-47/chapter-I/subchapter-A/part-15/subpart-C/subject-group-ECFR2f2e5828339709e/section-15.247

Thanks,
Seth