
A fundamental radio tech breakthrough that could double throughput - DiabloD3
http://www.extremetech.com/extreme/187190-full-duplex-a-fundamental-radio-tech-breakthrough-that-could-double-throughput-alleviate-the-spectrum-crunch
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allegory
_" The receiver “listens” to determine the RF environment and uses algorithms
to predict how the transmission will be altered by the environment and cancel
it out from data received from the receiver. By doing so, the problem of self-
interference goes away, and the receiver can “hear” the signal it is supposed
to hear while the transmitter is active."_

That's a little simplistic IMHO and akin to magic.

The 'RF environment' changes drastically as you move (depending in the
propagation of your waves and reflections etc) and as other things operate so
even with adaptive algorithms there is going go be a period of learning that
will reduce this back to half duplex periodically. With the masses of noise
and interference and harmonics around I'm not sure I believe the claims
entirely. Maybe in ideal conditions it won't spend 100% of the time learning?

A link to a paper would be nice...

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shanon
I think a very good paper solving this problem very clearly with a cool
execution is by Katti Group.

[http://web.stanford.edu/~skatti/pubs/sigcomm13-fullduplex.pd...](http://web.stanford.edu/~skatti/pubs/sigcomm13-fullduplex.pdf)

It deals with all the issue and shows the 2x throughput as well.

~~~
jhallenworld
It's interesting to think of the side uses for this technology, should it
become widespread. The future WIFI radio in your cellphone will end up being a
precise measuring device for the RF environment. I mean you've basically got a
TDR instrument in your phone sensitive to 110 db system loss..

For sure it will work as a motion detector (search for gunn diode motion
detectors- long used by alarm systems).

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VLM
No EE input in this story at least WRT docsis.

Too many HFC plants with enormous capital and labor investment in
bidirectional amps which boil down to amplify 30 MHz and down and send
upstream that direction while amplify 50 MHz and up and set downstream the
opposite direction.

Maybe in all new construction or retrofit or after a hurricane rebuild...
Maybe.

The biggest problem I see is Shannons Law will not be denied, and if the DSP
to pull this off burns more watts than just transmitting a couple more
milliwatts to get a better SNR you can spend on higher speed...

What I'm getting at is if you want a TX RX ratio of 50:50 then merely
increasing TX power by a cheap 3 DB will give you enough SNR margin to double
your speed, making it possible to run "full speed" while listening half the
time. The real world is never quite that simple. Then again real DSP
processing is neither free or low power.

(Let me expound on Shannon's Law... If you double your transmitted data by
doubling your power to double your SNR at the same bit error rate for less
power than perhaps a couple watts of DSP, then you're better off doubling your
power. For, say, wifi, or bluetooth, or cellphones. Or if its cheaper to spend
a couple watts on DSP than to double your tx power, maybe for satellites, then
the DSP obviously wins. I'm thinking low power wifi is perhaps the worst case
scenario for this new tech despite the implications in the article...)

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nardi
People always react to new RF technologies with "SHANNON'S LAW!!!" and ignore
the fact that Shannon's Law refers to _channels_ , not _frequencies_. If you
create a new channel through active interference, you get more bandwidth.

~~~
wirelessjunkie
That's absolutely right. By isolating the transmitter and receiver, you are
able to create an independent channel for the receiver, which can operate
independently of the transmit channel, while each of those channels obey
Shannon's law. Another correction -- Shannon's law is logarithmic -- C
(bit/sec/Hz) = logbase2(1+SNR) ~= logbase2(SNR) for high SNR. Thus a 3dB
increase in SNR is a 1 bit increase in capacity. Clearly, there is a low ROI
on increasing tx power beyond a certain point.

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jhallenworld
A "hybrid" circuit for RF? Interesting.. One of the founders of a past start-
up I worked at wanted to use hybrid circuits for digital I/O cells for ICs (at
year 2000 LVDS rates- they ended up using plain LVDS instead). I've made them
myself using discrete RS-485 drivers for 10 MHz rates. Of course gigabit
ethernet on RJ45 uses this technology: [http://embedded-
computing.com/pdfs/CDT.Fall00.pdf](http://embedded-
computing.com/pdfs/CDT.Fall00.pdf)

RADAR systems have had to deal with a similar problem for a long time. In
RADAR you don't have to receive and transmit at the same time, but you do want
to share the antenna, and the transmitter is very powerful.

[http://www.radartutorial.eu/06.antennas/an19.en.html](http://www.radartutorial.eu/06.antennas/an19.en.html)

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frankus
It seems like newly-allocated spectrum is going to be used for narrowcast
applications, so I think the approach used by the Artemis folks
([http://www.artemis.com](http://www.artemis.com)) is probably more promising
in the long run.

