
Vortex radio waves could boost wireless capacity “infinitely” - ukdm
http://www.extremetech.com/extreme/120803-vortex-radio-waves-could-boost-wireless-capacity-infinitely
======
femto
Nature has a clearer report.

[http://www.nature.com/news/2011/110222/full/news.2011.114.ht...](http://www.nature.com/news/2011/110222/full/news.2011.114.html)

It bears a similarity to MIMO, in that MIMO initially promised "infinite"
capacity. MIMO did give an improvement in capacity, but it wasn't infinite,
the limit being related to the volume occupied by the antenna array (see
papers by Leif Hanlen). One has to think that this technology will turn out to
have a similar limit on fuller analysis. In fact one has to wonder whether the
limit will turn out to be exactly the same, and whether it turns out to be a
form of space-time coding? After all, one could presumably emulate the
"slotted parabolic dish" antenna mentioned by using a suitably coded antenna
array?

~~~
dvdkhlng
Me, too thinks that this is just (a subset of) MIMO in disguise. The advantage
of the antenna array you mention is, that it can precode/decode with any
channel matrix, while these antennas implement one fixed matrix.

~~~
bjornsing
I get the same feeling. MIMO basically exploits that there can be multiple
propagation "paths" over the same frequency and that those can each carry
information up to the Shannon capacity. Paths can be separated by geometry
(reflections etc) or polarity. This Orbital Angular Momentum is probably just
another way to create more "paths" that can be exploited with MIMO.

In complex radio environments (like urban cellular networks) you get so many
reflections that the limitation to MIMO is usually not too few separate paths
but rather too many, with too much correlation between them. I'm not sure this
would help very much there.

But in simple radio environments, like point-to-point links you often are
limited by the number of separate paths (you can have two based on Spin
Angular Momentum aka polarity and there are lots of products out there that do
that).

In short; I think these guys are barking up the wrong tree in trying to adapt
this for cellular, they should stay in point-to-point. They will be very
welcome in that space if they can go from 2x2 to 4x4 MIMO across a point-to-
point link.

~~~
henryaym
This doesn't have to do with different propagation paths. The Orbital Angular
Momentum (OAM) is an inherent wave property, like Wavelength or Frequency.
Just like you can listen to radio on different frequencies (eg 660AM, 1010AM),
you can think about this technology as "listening" on different OAM channels.

The twist in the wavefront can be thought of as a newly available subset of
channels.

This has been a a field of research that has been primarily been developed in
Optics, in fact, my PhD research included creating ultrafast (femtosecond),
supercontinuum (white light) vortices that are capable of transmitting
information over 2^L channels where L is the amount of twist the light has.

~~~
gallamine
Is this "twist" related to the circular polarization of light?

~~~
henryaym
Quick Answer: No. Longer Answer: Sorta.

Circular polarization of light (or waves in general) corresponds to a spin
angular momentum that arises as the polarization of the light is "spinning".

This "twist" is the wavefronts phase rotating or being staggered as it travels
forward. Think of the wavefront of the twisted wave as looking like a piece of
spiral pasta.

It is this spiraling that corresponds to orbital angular momentum.

~~~
jpdoctor
> _orbital angular momentum_

Under what circumstance can you change the OAM in order to exert a torque? (or
maybe vice-versa: What is an example of torque exerting a change in OAM on the
wave?)

TIA.

~~~
henryaym
If I understand your question..

You can prepare waves in such a way that forces them into this spiraled
waveform state. This can be done in a cavity (in the case of lasers) as there
are solutions of the wave equation that give rise to OAM; or this can be done
by using diffractive optics, like a hologram, that somewhat force the wave
into this state. It is this case that you can think of a torque being exerted
onto the waves.

Waves too, can exert torque on small particles (micron sized polystyrene
spheres for instance). Light with spin or orbital angular momentum can be used
to make these small object rotate!

~~~
jpdoctor
> _Light with spin or orbital angular momentum can be used to make these small
> object rotate!_

Thank you, that was exactly the effect I was looking for. Any links handy?
Fascinating stuff, this from an old microwave-digital guy.

~~~
henryaym
Sure! Here's a research group in Glasgow that has a great site:
<http://www.physics.gla.ac.uk/Optics/play/photonOAM/>

And here is the lab where I did my undergrad research (Colgate Univ.):
[http://departments.colgate.edu/physics/research/optics/oamgp...](http://departments.colgate.edu/physics/research/optics/oamgp/gp.htm)

happy to offer up my phd thesis as well: <http://shel.tv/henry_thesis>

~~~
jpdoctor
If you ever find yourself in Santa Monica, the beer is on me.

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DanielBMarkham
This has the feel of one of those articles that promise much more than it
delivers. But the site is good, the idea interesting, and it definitely could
be a game-changer. If this pans out, it also has interesting implications for
SETI, because if our receivers are set up in a different configuration than
some potential sender might be, we'll never receive anything.

~~~
bh42222
I know the idea behind SETI is great, but I have great doubt about the
execution. Here is why:

From: [http://www.damninteresting.com/space-radio-more-static-
less-...](http://www.damninteresting.com/space-radio-more-static-less-talk/)

 _When any non-focused electromagnetic signal is generated– such as a
television broadcast or a cell phone conversation– the energy propagates as a
spherical wavefront at the speed of light. When a sphere is doubled in
diameter, its surface area increases by a factor of four; but in a spherical
wave the “surface area” is the energy itself. This means the signal’s energy
is spread over four times more area at twice the distance, resulting in a 75%
loss in intensity. To put it another way, in order for a broadcasting tower to
double its effective range for a given receiver, it must quadruple its
transmitting power._

 _To demonstrate the degrading effect of distance on an everyday
omnidirectional signal, one might imagine a spacecraft equipped with an
Arecibo-style radio receiver directed towards the Earth. If this hypothetical
spacecraft were to set out for the interstellar medium, its massive 305-meter
wide dish would lose its tenuous grip on AM radio before reaching Mars.
Somewhere en route to Jupiter, the UHF television receivers would spew nothing
but static. Before passing Saturn, the last of the FM radio stations would
fade away, leaving all of Earth’s electromagnetic chatter behind well before
leaving our own solar system._

And: <http://blog.jackadam.net/2011/the-tiny-humanity-bubble/>

~~~
sp332
This isn't a "non-focused" signal. This is being directed by an antenna in one
dimension. A perfect antenna transmitting through empty space would send a
signal that does not diminish at all with distance. The only attenuation would
be due to imperfections in the antenna causing a gradual widening of the beam,
and obstacles in the path of the signal.

~~~
bh42222
Imperfections in the antenna, obstacles in the path of the signal, etc. From
the The Hitchhiker's Guide to the Galaxy:

 _Space... is big. Really big. You just won't believe how vastly hugely
mindbogglingly big it is..._

My point is space is HUGE, and it would take a stupendous amount of effort and
energy to create and send a signal which Earth can correctly receive. And
that's even if you specifically focus it at us.

But why would anyone specifically focus it at us, if our own signals are not
focused and quickly (quickly in term of universe distances) become
indistinguishable from background radiation, how would they know we are here?

What I am ultimately claiming is that even if we have intelligent radio using
alien life "near by" we _still_ would never find each other. Because even if
we both have a SETI equivalent, neither one of us would initiate the huge
effort necessary to send a focused "Hello" signal which the other can receive.

~~~
oscilloscope
Well, to start we could just send signals to nearby stars with planets.
Obviously planets within 20 light years are the low hanging fruit. Since we
know there's life on Earth, nearby stars might have a greater than average
chance of harboring life as well.

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

~~~
sesqu
There is at least one astronomer who's doing exactly that. I didn't find his
name with a quick googling, but I think it was a Russian fellow. Naturally,
not everyone agrees on the step from listening to sending focused, targeted
bursts.

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4rgento
To describe electromagnetic waves, or to write a solution to the wave
equation, you need to use a system of coordinates. The most common by far is
the rectangular system (x,y,z), but there are other ones: cylindrical
coordinates, elliptical, spherical, and more. This is like choosing a base in
a vector space. If you choose rectangular coordinates then your solutions are
expressed as a linear combination of plane waves ( Cos(k*x-wt), k is wave
vector, x is position, w is frequency and t is time ). If you choose
cylindrical coordinates, then your solution will be spanned as a combination
of bessel functions( more exactly cylindrical waves) whose parameters are
called: OAM, spin, and momentum (in z axis). As nature doesn't care which
coordinate system we choose and neither the wave equation, a solution in one
system of coordinates y also a solution in another. In this case, a
cylindrical wave can be expressed as an infinite combination of plane waves.
So what this people seems to be saying is more or less: "Instead of emitting
waves and, in the receiver, just measure the frequency; let's emit more
complex patterns and, in the receiver, measure enough features of the wave (
not just the frequency) so that we can tell it apart from other signals.

I hope this helps.

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JunkDNA
Can we get a sanity check from someone with actual background in this area?
Seems like this would only work point to point in a line of sight manner with
no obstructions. While still cool (satellite TV/Internet comes to mind), it's
hard to see how you could adapt this to something like a mobile phone.

~~~
Stwerp
Radio guy here. You are correct. I just finished reading their paper, and they
describe a technique that creates a spatial null by changing the orbital
angular momentum. In other words, they push the intensity away from the line-
of-sight (LOS) ray out slightly (in space about the ray) so that two antennas
can receive the different signals by spatial diversity. This requires A)
precise tuning and setup B) a decent distance away from the transmitter source
since you need the wavefront to spread out wide enough for antenna location
and C) a re-calibration/tuning anytime the setup or possibly multipath
changes.

This technique should work well for static point-point comms (not with the
claimed infinite bandwidth though since you run into a physical problem of
area and precise location of the receiving array as well as near-field antenna
effects affecting receiver patterns) but in its current form could not be
implemented in a mobile device. Hell, a bunch of the time in WiFi or cell
reception, multipath is your best friend and can be the only way you receive a
signal and this work does not seem to address this issue.

Still though, this is an interesting idea and should not be quickly
discounted, although the article gives it much more hype than it merits imho.

~~~
marshray
Is this completely different than circular polarization?

It's been a long time since I've thought about this, but ISTR polarization
errors gave only 10-20 dB attenuation/separation max.

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joezydeco
My RF knowledge is old and sketchy, but doesn't a dish imply that these RF
signals are point-to-point? How would that work in a mobile handset where we
can't point the antenna?

~~~
JoeAltmaier
phased arrays etc CAN point the antenna, electronically

~~~
joezydeco
Sure, but that's a little exotic and expensive for the consumer market at this
point. I'd be happy with phased array satellite antennas I can stick on the
outside of my house.

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kruhft
Here's a video presentation on Vortex Based Mathematics:

    
    
      magnet:? xt=urn:btih:44b89f9125978a8d0f46cf42de9b2110c9bdd151&dn=Vortex+Based+Mathematics+by+Marko+Rodin&tr=udp%3A%2F%2Ftracker.openbittorrent.com%3A80&tr=udp%3A%2F%2Ftracker.publicbt.com%3A80&tr=udp%3A%2F%2Ftracker.ccc.de%3A80

~~~
Groxx
would you mind putting that on a new line, and indenting it 2 spaces, so it
doesn't break the page's size?

edit: thanks!

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ec429
I strongly suspect that this will prove to be limited by the RF path; it
relies (as far as I can tell) on coherent properties of the wavefront. This
means it will break as soon as the signal passes through heterogeneous
material (such as a building), or as soon as reflections produce multi-path
interference.

And you certainly wouldn't be able to use it at HF - imagine what the
ionosphere will do to your carefully constructed wave!

In general, using more parameters of the wave reduces your resilience to
noise; the usual approach of extracting only amplitude, frequency and
(perhaps) phase is a summation operator that smooths out a lot of
interference. Conceptually, this is like how QPSK needs a higher SNR than BPSK
does - you're using more parameters, so you're reducing the 'distance' between
things you want to distinguish, so you're increasing the chance that a given
amount of noise will produce errors.

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jcarreiro
See also <http://physics.aps.org/story/v17/st15> for a bit more on photon
orbital angular momentum.

~~~
jcarreiro
And <http://physics.aps.org/story/v9/st29>, which is an older Focus story
linked to from my original post.

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Groxx
I can see this being a great improvement in capacity, but wouldn't data from
other 'vortices' leak data into the one you're listening to? Any integer
multiple would add noise to every bit sent to station X, and lots and lots
where isolated bits from other channels leak in (what would that be, divisible
by the station's period?).

------
it
The antenna reminds me of branch cuts in complex analysis. I suspect there is
a connection here.

<http://en.wikipedia.org/wiki/Branch_point#Branch_cuts>

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ars
This paper should help:
[http://www.gla.ac.uk/schools/physics/research/groups/optics/...](http://www.gla.ac.uk/schools/physics/research/groups/optics/research/orbitalangularmomentum/)

------
mnl
I've used his free course on Electrodynamics (tricky subject) while developing
a text for our Uni. This guy knows his stuff...

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jakeonthemove
I was just reading about DIDO (aka MU-MIMO) the other day, and this looks like
a great addition to the technology...

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ck2
Do electromagnetic waves obey inertia and momentum? Really?

How is that possible if they move at the speed of light for any observer?

~~~
sp332
Yes, they really do. Start here and keep reading down the page:
[https://en.wikipedia.org/wiki/General_relativity#Consequence...](https://en.wikipedia.org/wiki/General_relativity#Consequences_of_Einstein.27s_theory)

~~~
ck2
Hmm but with things like gravitational lensing, it happens because space
itself is being bent, not the wave, wave is just traveling "straight ahead"
and doing it's thing.

If waves obeyed momentum, then a wildly spinning pulsar's gamma waves would
not travel just outward but like a curve ball from a baseball pitcher, they'd
be long perpendicular distorted waves.

~~~
sp332
The wave "free-falls" toward the object with exactly the same acceleration as
anything else passing by.

I'm not sure what you meant by the last part. The light beams would form a
spiral expanding through space. (Like "zooming in" to the spiral, not turning
like a screw.) Each photon moves in a straight line, but since the source of
the beam is turning, the beam is a curve though space.

~~~
ck2
Ah you know what - I really wasn't thinking this out.

If waves didn't obey momentum then light being emitted by the very monitor I
am looking at now would probably not make it to my eyes, or at least be
shifted, since the planet and galaxy are moving rapidly.

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dosenwurst
To me this looks like good old circular polarization.

<http://en.wikipedia.org/wiki/Polarization_%28waves%29>

~~~
ars
No, that's well known, and is only half of the rotation. (A rotation of the
angle between the electric and magnetic fields.)

This is apparently something new, not sure what though - it's not something I
ever learned about with photons.

~~~
dvdkhlng
Not sure that this is new. It is known that channel capacity can be scaled up
linearly with the number of receive/transmit antennas by properly de-mixing
the signal at the receiver (or pre-coding it properly at the sender).

This is known as MIMO transmission, see <https://en.wikipedia.org/wiki/MIMO>
for details (also has the capacity formula).

What these people call "vortex wave", is just precoding/decoding done in a
fixed way using fixed antennas. But with non-line-of sight channels and moving
sender/receiver you will need dynamic MIMO coding anyways. This is already
implemented in LTE (2 antennas in the handset, 4 at the base station, AFAIR).

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Porter_423
It is just another encouraging research.I think it will take few more years to
use this technology in communication fields.Its range is still too small.It
must be improved otherwise it will not become cost effective and loss will be
huge.

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ktizo
well, the effect seems real enough, looking to other references;

[http://www.gla.ac.uk/schools/physics/research/groups/optics/...](http://www.gla.ac.uk/schools/physics/research/groups/optics/research/orbitalangularmomentum/)

