

Wi-Fi and Neighborhood Conflicts: An Algorithm to Keep the Peace - Wookai
http://actu.epfl.ch/news/wi-fi-and-neighborhood-conflicts-an-algorithm-to-k/

======
rayiner
These sorts of technologies are really interesting, and will play a big part
in getting the most out of limited wireless spectrum. But the big picture
problem is that we're shoe-horning all this incredibly useful technology into
the ghetto that is ISM band. We need more unlicensed spectrum, and we need
better rules for that unlicensed spectrum that prohibit anti-social behavior:
[http://esd.mit.edu/WPS/esd-wp-2006-01.pdf](http://esd.mit.edu/WPS/esd-
wp-2006-01.pdf).

------
Wookai
Link to technical paper: [http://infoscience.epfl.ch/record/186014/files/saw-
infocom13...](http://infoscience.epfl.ch/record/186014/files/saw-
infocom13.pdf)

------
jdthomas
Hmm, I have not read his paper, but based on the article's mention of "divided
into 13 channels" this is clearly speaking of the 2.4Ghz spectrum. Rather than
try to distribute that evenly, you are FAR better off upgrading your AP and
switching to a 5Ghz channel. First, there are far more potential channels in
5Ghz. Second, they are wider bandwidth (40Mhz, 80Mhz if 80211ac). And third,
5Ghz does not propagate through walls as well (a _feature_ when you have
neighbors also using the spectrum).

My other thoughts: if he is using 8 channels instead of the standard 3
(1,6,11) then there will be some overlap; 80211 devices tends to better handle
in-channel interference.
[http://en.wikipedia.org/wiki/List_of_WLAN_channels](http://en.wikipedia.org/wiki/List_of_WLAN_channels)

~~~
ar_turnbull
I switched to 5g last year, but all of my neighbours have caught up. Worse
still — we all have legacy networks on the 2.4ghz spectrum so that our older
devices can access the Internet. There are probably two dozen networks
accessible from my couch. It's crazy in apartment buildings.

I would suggest that it should become part of our condo fees / building
management, but I have little confidence in our board.

~~~
ajhodges
Not to mention there are many devices that still don't support 5ghz (a
notable/annoying example being Chromecasts). Switching to 5ghz is not a
solution to the problem outlined in this paper, it's a bandaid.

------
cpitman
I'm glad someone at least seems to be addressing congestion. Every 802.11
standard seems to have hopped on the "multiple bandwidth by 2x" bandwagon,
which is great if I live in a single family house with tons of space.

I don't, I live in a city, in an apartment building, surrounded by apartment
buildings. I can frequently see 30+ networks. I'm sure there are wireless
phones and other devices crowding the spectrum as well. Give me more channels,
or better ways to share spectrum, anything other than dividing the number of
usable channels with every update.

~~~
cesarb
> Every 802.11 standard seems to have hopped on the "multiple bandwidth by 2x"
> bandwagon, [...] anything other than dividing the number of usable channels
> with every update.

It might use 2x the bandwidth, but it will use it for half the time for the
same amount of data, so it all evens out (almost; there's an unused "border"
between channels, so 2x the bandwidth is a bit more than 2x faster, and it
will use a bit less than half the time).

And the 802.11ac standard has a way to better share the wide channels and the
narrow channels; see the "Dynamic Bandwidth Operation" chapter of the
"802.11ac: A Survival Guide" book at
[http://chimera.labs.oreilly.com/books/1234000001739/ch03.htm...](http://chimera.labs.oreilly.com/books/1234000001739/ch03.html#section-
mac-dynbw)

------
exelius
I actually had a similar idea recently but assumed it must have already been
part of the protocol. Obviously it wasn't, and truly good ideas are never
unique, so kudos to this guy for doing the work and coming up with a
functional algorithm.

One question I have is how this would perform in an incredibly congested area
like an apartment building. The author only modeled out 2-way conflict; I have
no idea how this algorithm would react if placed in a situation with 15
competing Wi-Fi access points.

Overall a good, nerdy read - this is the kind of shit I keep coming to HN for.

~~~
hrzn
I'm the main inventor. Thanks a lot for the positive feedback!

You are actually right, similar ideas have already been proposed before. The
main novelty here is that the algorithm adapts not only the channel (center
frequency), but also the bandwidth (i.e., the actual amount of spectrum that
is consumed).

Adapting the bandwidth gives a precious additional degree of freedom; in
particular, in a case with many competing WLANs, the algorithm would typically
tend to reduce the bandwidth consumed by each WLAN (assuming the interfering
WLANs are not idle and actually sending traffic). Reducing the bandwidth
potentially reduces the available capacity (if you were alone), but it's still
much more efficient than letting Wi-Fi use the time domain to avoid
interference, so it results in increased throughput compared to current
situations.

It turns out that adapting the bandwidth is becoming a necessity, because
newer versions of Wi-Fi consume more and more bandwidth. This is better if you
are alone, but may be harmful if you have many neighbors.

~~~
cesarb
> in a case with many competing WLANs, the algorithm would typically tend to
> reduce the bandwidth consumed by each WLAN

Wouldn't that use more battery, since for a narrower channel the radio would
have to be kept on for longer to transmit (or receive) the same amount of
data?

~~~
hrzn
Usually, 802.11 devices don't turn off between transmissions, so this has no
effect. In fact, it's actually the opposite; using a narrower channel requires
a slower clock rate, which also significantly reduces power consumption of the
wireless device.

------
hroi
Dynamic Frequency Selection and Transmit Power Control (part of 802.11h) is
already a requirement for 5GHz in many countries:
[http://en.wikipedia.org/wiki/Channel_allocation_schemes#DCA_...](http://en.wikipedia.org/wiki/Channel_allocation_schemes#DCA_and_DFS)

~~~
rayiner
Kind of. DFS is about sharing the 5 GHz band with incumbent radar
installations. Basically how it works is that you have to listen for radars
using the channel, and if you hear one, you have to get off the channel within
a certain number of milliseconds. But DFS systems don't switch channels in
response to other Wi-Fi networks, nor do they switch channels in order to
optimize aggregate bandwidth.

------
BoppreH
When I chose a channel for my router, there was a clear option labelled
"auto". If this algorithm for channel selection is novel, what does "auto" do?

Also, kudos for the idea. This is a much needed feature in today's crowded
condos.

~~~
mikecarlton
Auto usually just means scan channels at boot time and pick one that seems
good (presumably the least amount of traffic).

And on at least one SoC I worked with (Realtek) I swear the algorithm was
"return 6".

