Re: [Bloat] Is 5/10MHz wifi bandwidth legal in 2.4GHz (half/quarter-clocking)?

[Ryan Mounce <ryan@mounce.com.au>]

I'm not aware of anywhere this would be illegal. Worst case you will
need to reduce power by 3/6dB (10/5MHz) if there is a power spectral
density limit in a given jurisdiction and max EIRP @ 20MHz is already
at that limit.

On Tue, 9 Oct 2018 at 06:48, bkil <bkil.hu+Aq@gmail.com> wrote:
>
> If this is not the right forum to discuss, could you please point me
> in the right direction?
>
> After all, channel spacing is indeed 5MHz here. Although using a new
> raster instead of the 20MHz channel center frequencies would allow
> full utilization of the band (16 or 8 channels respectively), using
> the standard set of 11 (13) channels is better than nothing.
>
> Is it a good idea to use HT instead of g for such links?
>
> =
> Some background and links for those who do not know this mode:
>
> "the 2007 version of the IEEE 802.11 standard [1] specifies 5 and 10
> MHz wide channels for use in the 4.9 GHz public safety bands"
>
> Although according to my reading of section 17.1, it applies to the
> 5GHz bands as well:
>
> >> 17. Orthogonal frequency division multiplexing (OFDM) PHY specification
> for the 5 GHz band
> [...]
> The OFDM system also provides a “half-clocked” operation using 10 MHz
> channel spacings with data
> communications capabilities of 3, 4.5, 6, 9, 12, 18, 24, and 27 Mb/s.
> The support of transmitting and
> receiving at data rates of 3, 6, and 12 Mb/s is mandatory when using
> 10 MHz channel spacing. The half-
> clocked operation doubles symbol times and clear channel assessment
> (CCA) times when using 10 MHz
> channel spacing. The regulatory requirements and information regarding
> use of this OFDM system in
> 4.9 GHz and 5 GHz bands is in Annex I and Annex J.<<
>
> They probably did not highlight 2.4GHz usage because of mixed-mode
> (non-OFDM) crowding, although nowadays we could actually move this
> band to OFDM-only as well.
>
> It is unfortunate that this allowance has disappeared in newer
> versions of the standard. Was that intentional?
>
> Reasons why downclocking is advantageous (up to +9dB link budget):
>
> * longer GI = better protection against multipath fading;
> * higher power density allowed (2x here) = better SNR;
> * less chance for (adjacent-channel) interference;
> * reduced TX & RX power consumption for idling and low load.
>
> I know that 802.11ah/af are here, but there exist literally millions
> of devices potentially supporting this old and trusty mode, software
> permit.
>
> Many Atheros chipsets support it, both old and new. OpenWrt has
> debugfs patches applied to enable this, while Linux has some other
> patches as well, although it is not user visible.
>
> If this is a legal and preferred mode, it would be nice if we could
> unify access.
>
> https://openwrt.org/docs/guide-user/network/wifi/basic?s[]=chanbw
> http://ccr.sigcomm.org/online/files/p135-chandra.pdf
> https://kabru.eecs.umich.edu/papers/publications/2011/xyzhang_kgshin_mobicom11.pdf
> https://www.etsi.org/deliver/etsi_en/300300_300399/300328/01.08.01_60/en_300328v010801p.pdf
> https://www.cwnp.com/forums/posts?postNum=305220
> https://forum.archive.openwrt.org/viewtopic.php?id=38590
> https://forum.openwrt.org/t/5-mhz-bandwith-option/3615
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