
Neglected channels could add Wi-Fi capacity - teklaperry
http://spectrum.ieee.org/telecom/wireless/why-wifi-stinksand-how-to-fix-it
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jrockway
Wifi stations only interfere when they're transmitting at the same time, and
other stations can hear it. Channels are a very simplistic way of
understanding WiFi sharing, time and space are also important dimensions. If
Station A and Client A want to communicate, they will not interfere with
Station B and Client B if they pick different times to talk, or cannot "hear"
each other at all.

There is some good work going on to improve this. Faster WiFi speeds mean that
less time is needed to transmit the same number of bytes, meaning that
stations are less likely to interfere. (This is why everyone hates your
802.11b-only client that can do a maximum of 11Mbps. It ties up the entire
channel for no good reason.)

The default rate control built into most APs is awful, and makes things worse
than they need to be. For example, let's say sending at 100Mbps, there's a 50%
chance that the message won't be decodable, and sending at 1Mbps, there's a
99.999% chance that the message will get through. APs will try sending at the
high rate, notice an error, and then go to the low rate. But that's wrong: it
doesn't minimize the use of airtime. Sending 100Mb at 100Mbps twice is much
more time-efficient than sending it at 1Mbps once. Some work is under way to
improve this algorithm and get it in consumer routers.

There is also work to make APs transmit to stations at a transmit power tuned
to be as low as possible. If a station is close, the AP only needs a small
amount of power to send a decipherable message to the station. And, because
the power is low, it interferes with less space. I believe this is now working
under Linux with ath9k chipsets.

Anyway, "channels" is a terrible way to understand WiFi performance, because
space and time are the other critical dimensions. Unfortunately, most "WiFi
analyzers" only show which channels have APs, which is a meaningless metric.

Here's an interesting talk about how this all works in the real world:
[http://apenwarr.ca/diary/wifi-data-
apenwarr-201602.pdf](http://apenwarr.ca/diary/wifi-data-apenwarr-201602.pdf)

~~~
chrisfosterelli
Could WiFi analyzers effectively determine information about space from a
single location? Time is obviously possible, but isn't it inherently providing
information about space by providing power readings from a single point?

~~~
jrockway
Which WiFi analyzer actually looks for traffic? Most of the ones I've seen (a
popular Android app) just show you beacons.

Seeing beacons != seeing traffic.

~~~
nitrogen
Ubiquiti Wifi devices I've used have a built-in spectrum analyzer that can
show channel, time, and intensity (a rough proxy for distance).

~~~
wtallis
The hardware capability Ubiquity is probably using:
[https://wireless.wiki.kernel.org/en/users/drivers/ath9k/spec...](https://wireless.wiki.kernel.org/en/users/drivers/ath9k/spectral_scan)

This is an awesome and useful feature, but it isn't quite the same as monitor
mode packet capturing. The FFT won't do much to help you figure out whether
the interference is coming from a really high traffic volume or just a
talkative 802.11b IoT PoS.

------
specialist
Should I stop hoping that we'll get consumer grade ultra-wide band devices,
mooting the whole frequency licensing issue?

    
    
      "Did the NSA help kill UWB?"
      http://www.cringely.com/2014/05/15/nsa-help-kill-uwb/

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elif
I think as we are continuing to balloon request sizes, stream more and higher
quality video, increasingly populate urban cores, etc. finding more spectrum
to pollute is an untenable long-term solution.

I think a more reasonable approach is to start putting wire in house-wrap, and
perhaps putting a repeater antenna outside the Faraday cage for cell signals.

~~~
DiabloD3
Actually, we sort of already solved it. Wifi was never meant to go insanely
long distances, and now spamming APs inside of even a smaller home is a cheap
and effective way of dealing with signal problems.

60ghz (Added by 802.11ad) can't penetrate sheetrock effectively, let alone
bother your neighbors, a much smaller distance than 5ghz (which has half-
solved the dense urban environment issue on it's own, but not completely; the
article overplays issues significantly).

I support abandoning 2.4ghz for Wifi and anything else that is high bandwidth.
The good news is, the 802.11 Working Group and the major Wifi impl manufs
agree with me, which is why 802.11ac is 5ghz only, and 802.11ad is 60ghz
first, both of them removing 2.4ghz for anything but 802.11 b/g/n legacy
connectivity.

Also, as a side note, I want the FCC to ban the LTE-over-5ghz plan. 5ghz is
ours; they can have 2.4ghz, we're done with it.

~~~
briandear
Except when you live in a 200 year old house like I do with 1 foot thick stone
walls. I don't have to worry about "polluting" my neighbors because my nearest
neighbor is a mile away. Any "standards" ought to not just assume everyone
lives in dense, multi-family residences.

~~~
DiabloD3
Yes, but it's called designing for the most damaging worst case. Both ultra-
dense urban and houses like yours are corner cases, but on opposite ends of
the spectrum.

For you, I'd suggest looking into Unifi AC APs (the lowest end ones are $99
each, the Pros are extremely nice), and then put them everywhere you want
signal.

~~~
briandear
Thanks! Great suggestion. I've actually been running Cat 6/7 all over the
place to mitigate my "problem." I'll check out your suggestion.

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ryao
For those who are unaware, these are the channels that caused the FCC to
effectively ban OSS firmware in wifi routers. As far as I know, Ubiquiti and
Mikrotik could be configured to use them unconditionally, which caused
problems with radar.

