
Blame baby monitors, not congestion, for your WiFi woes - terpua
http://arstechnica.com/tech-policy/news/2009/05/blame-baby-monitors-not-congestion-for-your-wifi-woes.ars
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tc
_WiFi has become important enough—and the interference problem bad enough—that
the report recommends creating a new "2.4GHz friendly" logo program to brand
devices that are good radio-frequency citizens._

Are they kidding? Since 802.11_ protocols are 'smart' in the sense that wifi
nodes exercise congestion avoidance with other nodes running the same
protocol, the next wifi standard just needs to be allocated dedicated space in
the spectrum, rather than having to share the same narrow common space with
baby monitors and AV extenders. Alternatively, the band of less-regulated
spectrum needs to be expanded wide enough that manufacturers can create some
informal standards to avoid stepping on each others toes.

(And yes, trust me, I know why this is politically difficult, and that it
wouldn't immediately help the enormous number of users with current-generation
hardware. But really, their recommendation isn't likely to make much short-
term difference either.)

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muon
In 2.4GHz band, there are only three non-overlapping channels (1,6,11). For
the optimal use the wifi and baby monitors need to far apart.

Current wifi access points detects these interference and do not settle in a
channel where baby monitors are operating. For better performances people
should start moving to 5GHz band.

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spkthed
I've been a ham operator since I was 10 so I have a _little_ experience on the
subject. Interference can come from anything. Lots of power supplies for
surprising devices are culprits. The little cheap universal AC/DC adapters are
one of worst offenders. Power-lines, bad transformers, any business that has
massive electrical devices.

TV's, (especially older) microwaves, vacuum cleaners... pretty much anything
can cause interference. One of the worst culprits are the cordless handsets.

The biggest offenders aren't devices that use the same rough frequencies, it's
ones that either splatter all over the place or have harmonic issues
(multiples of frequencies, a 500MHz device can splatter 1,000MHZ, 1.5GHz, etc)

It would be nice to have more spectrum for use for digital devices. Hopefully
in the US they continue moving the TV stations off and eventually provides
more spectrum for growing wireless devices.

~~~
bmj
Yes. At home, I had to muck with the channel on our router/access point so our
cordless handset wouldn't interfere with it. Nothing worse than losing network
connectivity because the phone rings...

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bcl
Not all baby monitors are at fault for WiFi interference. In the US you can
look up the product's FCCID in the FCC database and it will tell you what
frequency it uses.

<http://www.fcc.gov/oet/ea/fccid/>

I'm not sure if the UK has a similar licensing system search or not.

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enomar
Wouldn't making baby monitors that use Wifi mitigate the issue?

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bcl
That would drastically increase the cost of baby monitors. Right now they use
very simple analog RF techniques. Switching to 802.11 would increase the
design complexity and cost.

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varenc
wifi access points sense the wireless medium around them before transmitting.
If they find it busy, they do an exponential wait, and try again. Thats why
everyone can be on channel 11 and things won't be too bad. If they could sense
the medium perfectly, routers would always be able to guarantee service
regardless of the network congestion just throughput would decrease. However,
they can't sense the medium perfectly, so we run into the hidden terminal
problem, where wireless packets clobber mid route because they're transmitted
by routers far way from each other enough that they can't sense each other.
Thats the reason why wifi congestion stops traffic in congested parts of
london.

Baby monitors/any-analogue device doesn't do this, and that's where the
problem comes from. The 5GHZ band (802.11n) is a good alternative.

<http://en.wikipedia.org/wiki/Hidden_terminal_problem>

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zwieback
There's a great low-cost (sort of) spectrum analyzer called "Wi-Spy" (no
affiliation) for anyone who wants to track down what's ruining the 2.4GHz
spectrum. With that and WireShark running on a Linux machine with monitor-mode
capable Wi-Fi interface you can pinpoint what your Wi-Fi problem is quite
well.

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muon
>> "We have found that it is rare for the user data frame rate to exceed 10
percent of the total frame rate,"

Do not know how they came to this conclusion, beacon frames are the only
periodic management frame.

~~~
zwieback
There are lots of probes and probe responses in addition to the beacons. If
you have CTS/RTS enabled (most don't) then you have those frames as well.

Each packet has to be ACKed by the receiver so there's lots of those.

Management frames are usually short, though.

~~~
muon
Agreed, the probe requests and probe responses do not hog the medium. As noted
most of us do not enable RTS/CTS, it would be clear if the researches pointed
out the exact conditions under which they performed their tests. With out
which the statement has no weight.

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skwiddor
We haev free Wifi in our cafe bar, so do the other 3 cafe bars on our street.
All four use Ch. 11! I told our techs but they can't work out how to change it
_sigh_.

~~~
aristus
On a busy day, stand on the bar and yell "Free latte to the first geek who can
fix our wireless!" It'll be sorted in five minutes.

