
Wi-FM listens to FM signals to determine best times to send and receive data - zw123456
http://www.mccormick.northwestern.edu/news/articles/2015/11/using-fm-to-improve-wireless-networks.html
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resoluteteeth
The article is somewhat confusingly worded (the actual paper it links is more
clear:
[http://networks.cs.northwestern.edu/publications/wifm/icnp20...](http://networks.cs.northwestern.edu/publications/wifm/icnp2015-flores.pdf))
and I initially thought it was describing something like Microsoft's White
Spaces project where devices would automatically transmit over unused
spectrum. In reality, the idea is that the devices all automatically select
timing relative to an FM Radio Data System transmission and then can infer
each other's chosen timing without actually communicating (or they "implicitly
communicate" in the words of the paper's author as quoted in the article).

~~~
Natanael_L
So a transmission time slot selector seeded by FM signals. I haven't read it
yet, but is there a good summary for how it handles varying loads? As the
number of users and packets go up, you have to select smaller timeslots from
the same FM signal seed.

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vdm
Paper
[http://networks.cs.northwestern.edu/publications/wifm/icnp20...](http://networks.cs.northwestern.edu/publications/wifm/icnp2015-flores.pdf)

> We show that the digital signal that accompanies broadcast FM radio has
> sufficient structure to enable effective scheduling relative to it. It thus
> provides a common reference for neighboring devices to harmonize their
> transmissions, yet without requiring any explicit communication among them.

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zw123456
The link to the paper provide more detail. The basic idea is to use the FM
radio RDS sub-channel as a sort of control plane or control channel. One of
the things that differentiates LTE for example from 802.11 (WiFi) is that LTE
has a control channel that coordinates the activities, when to transmit an on
which channel via a control plane and hence achieves a higher spectral
efficiency. Wifi uses CSMA/CD to sense and detect collisions. But sensing when
they happen is not as good as just avoiding it all together. But to do that
you need a control channel. The idea of using something as ubiquitous as the
RDS sub-channel as a control channel has a lot of potential applications
beyond Wifi, it could also be used for white space control to open up vast
amounts of un-used spectrum potentially.

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jamstruth
Doesn't the WiFi standard already do this for devices running in the same
channel? I.e. if 3 devices are on Channel 1 they will talk to each other to
avoid conflicts. Hence why you should only use one of 3 channels (the only 3
which never overlap)

~~~
alphapapa
That is the popular wisdom, but in my experience it's not universally true. I
have had good results in an apartment building by choosing channels between 1,
6, and 11. Signal strength sometimes went up quite a bit.

For example, if there are 3 APs on each of the three non-overlapping channels,
using a channel between those channels may provide better results than
directly competing with 3 other APs for the entire channel.

However, it also depends on the observed signal strength for each of the
competing APs. For best results, you should probably test your equipment.

But if you really want decent transfer rates between devices, just use
Ethernet. I've given up on ever reaching even 50% of rated speeds on wifi.
With competing APs, walls, distance, etc, it's just never going to happen.

~~~
mikexstudios
I think this is a bad idea... to use non-standard channels. See:
[http://superuser.com/questions/443178/is-it-better-to-
use-a-...](http://superuser.com/questions/443178/is-it-better-to-use-a-
crowded-2-4ghz-wi-fi-channel-1-6-11-or-unused-3-4-8)

~~~
alphapapa
You should read the links you cite before you cite them. Among the answers
found on that page are these:

"The 1-6-11 recommendation contained in Cisco's whitepaper about IEEE 802.11
deployment in the corporate environment certainly does not apply to all
circumstances! For example, in moderately congested neighbourhoods, one stands
a very good chance to benefit from not sticking to this proposed scheme."

"the situation usually gets worse when one voluntary abides to the 1-6-11 non-
overlapping channel scheme. Doing so will expose your devices to the IEEE
802.11 RTS/CTS/ACK (Request to Send / Clear to Send / Acknowledge) of alien
devices, effectively silencing your devices and hence forcedly lowering your
bandwidth. This problem is known as the exposed node problem. In a corporate
setting this problem can be solved by synchronising the nodes. In the wild,
this is not readily achievable."

"In big corporate networks it's common practice to use channels 1,6 & 11
because it is fairly straightforward (at least on a diagram) to design non-
overlapping cells of coverage. As a home user you don't have the same
constraints so it makes sense to experiment and look for the best channel."

"I am a Ham Radio operator. I have done extensive testing. On my Actiontec or
ZyXcel, channel 1 is abysmal! Channel 11 is a close second to the death of
channel 1. ACTUAL power readings put 3 and 4 as the strongest signal output
and throughput. Channels 6 and 9 are the standard preset. so actually avoid
1,6,9,11. I am a DSL tech also. I have walked people through changing channels
from 9-10-11 to 3 or 4. They are amazed at the doubling of the wifi signal on
all devices across the board."

"Hence, I call for actually measuring one's own signal-to-noise level...The
Quality value takes into account noise from overlapping channels."

The bottom line is as I said: test your own equipment in your own environment
and find what works best for you.

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xlm1717
Is this still a problem for 5Ghz wifi?

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dang
Url changed from [http://phys.org/news/2015-11-wi-fm-
fm.html](http://phys.org/news/2015-11-wi-fm-fm.html), which points to this.

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zump
There is a MAC you know...

