[Make-wifi-fast] [Bloat] Is 5/10MHz wifi bandwidth legal in 2.4GHz (half/quarter-clocking)?
bkil.hu+Aq at gmail.com
Tue Oct 9 01:44:40 EDT 2018
Yes, that was my conclusion as well. There exist spectral masks of
maximal allowed side lobes, but if you are transmitting signals
narrower than that, the side lobes will be much below the limit.
Spectral density in Hungary and some other countries allows for
10mW/MHz, meaning twice the power density for narrow channels.
There can exist a possibility for starvation if two narrow channels
use the two sides of a wider channel in turn, similar to HT40, so a
neighborly mechanism would be nice.
On Tue, Oct 9, 2018 at 5:53 AM Ryan Mounce <ryan at mounce.com.au> wrote:
> 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 at 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  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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> > Bloat at lists.bufferbloat.net
> > https://lists.bufferbloat.net/listinfo/bloat
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