Re: [Cerowrt-devel] wifi over narrow channels

[dpreed@reed.com]

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Wideband is far better for scaling than narrowband, though.  This may seem counterintuitive, but narrowband systems are extremely inefficient.  They appeal to 0/1 thinking intuitively, but in actual fact the wider the bandwidth the more sharing and the more scaling is possible (and not be "balkanization" or "exclusive channel negotiation").
 
Two Internets are far worse than a single Internet that combines both.  That's because you have more degrees of freedom in a single network than you can in two distinct networks, by a combinatorial factor.
 
The analogy holds that one wide band is far better than two disjoint bands in terms of scaling and adaptation. The situation only gets better because of the physics of "multipath", which creates more problems the more narrowband the signal, and when the signal is a single frequency, multipath is disastrous.
 
The same is true if you try to divide space into disjoint "channels" (as cellular tries to).
 
So in the near term, narrowband wifi might be a short-term benefit, but long-term it is 180 degress away from where you want to go.
 
(the listen-before-talk protocol in WiFi is pragmatic because it is built into hardware today, but terrible for wideband signals, because you can't shorten the 4 usec. pre-transmit delay, and probably need to lengthen it, since 4 usec. is about 1.25 km or 0.8 miles, and  holds 40 bits at 10 Mb/s, or 4000 bits at 1 Gb/sec).
 
Either for distance or for rate, the "Ethernet MAC+PHY" was designed for short "coax" or "hub" domains. Its not good for digital wireless Internet, except for one thing: it is based on distributed control that does not require any advance planning.
 
If you want to improve open wireless, you have to a) go wide, b) maintain distributed control, c) get rid of listen-before-talk to replace it with a mixture of co-channel decoding and propagation negotiation.  Then you can beat cellular trivially.
 
I wish I could attract investment away from the "short term" WiFi thinking, but in the last 15 years, I've failed.  Meanwhile WiFi also attracts those people who want to add bufferbloat into the routers because they don't understand congestion control.
 
Sad.


On Wednesday, October 8, 2014 6:14pm, "Dave Taht" <dave.taht@gmail.com> said:



> https://www.usenix.org/system/files/conference/nsdi12/nsdi12-final142.pdf
> 
> I've had 5mhz channels working in the ath9k at various points in
> cerowrt's lifetime. (using it for meshy stuff) After digesting most of
> the 802.11ac standard I do find myself wishing they'd gone towards
> narrower channels rather than wider.
> 
> The netgear x4 defaults to a 160mhz wide channel. :sigh:
> 
> The above paper has some nifty ideas in it.
> 
> --
> Dave Täht
> 
> https://www.bufferbloat.net/projects/make-wifi-fast
> _______________________________________________
> Cerowrt-devel mailing list
> Cerowrt-devel@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/cerowrt-devel
> 

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