Vortex radio waves could boost wireless capacity “infinitely” | Hacker News Reader

Vortex radio waves could boost wireless capacity “infinitely”

extremetech.com

244 pointsukdm75 comments

Nature has a clearer report.

http://www.nature.com/news/2011/110222/full/news.2011.114.ht...

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?

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.

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.

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.

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

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.

> 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.

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!

> 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.

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...

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

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

Does launching a wave with OAM require an antenna with spatial extent, or can it be done by a point source?

You're right that multipath is very different from SAM and OAM from a theoretical point of view. Not so much from a practical point of view though.

In current point-to-point systems you often use SAM to give you two "channels" across the link, most often referred to as horizontal and vertical polarity, but you then hook that up to the same MIMO technology that you would use for multipath.

I would expect OAM to be exploited in a similar maner for point-to-point.

The fact that SAM is very difficult to exploit for capacity in cellular applications makes me think it will be even more difficult to exploit OAM. IF you ever see it implemented my money would be on using MIMO to exploit multipath + SAM + OAM, where multipath would dominate in complex radio environments and SAM + OAM in simple more point-to-point like environments.

But that's just an educated guess of course.

The arxiv paper quoted therein: http://arxiv.org/pdf/1101.6015v1.pdf

I, for one, think this is neat stuff. (Practicality might well be a different matter.)

Poynting himself mentioned the angular momentum present -- From the arxiv paper:

Poynting, J. H. The wave motion of a revolving shaft, and a suggestion as to the angular momentum in a beam of circularly polarised light. Proc. Roy. Soc. London A 82, 560–567 (1909).

The presence of "suggestion" in the title is also interesting. Wish I had time to dig through this history.

I'm not sure why anyone writing a science article would ever talk about anything being "potentially infinite". You could claim that the ability to broadcast on different frequencies gives you room for a potentially infinite number of broadcasts, arguing that frequencies are real numbers and there are an infinite number of them between any two points on the radio dial. Unfortunately, you can't simply think in terms of frequencies available, because you need a certain amount of bandwidth around each one to carry information. The more closely you pack the broadcast frequencies, the narrower the slice of bandwidth you have for each, so the more frequencies you transmit on simultaneously, the less information you can transmit on each one.

I suspect that this discovery adds another dimension, as if you took the frequency line and expanded it to a plane, but that each potential transmission "point" on the "airwave plane" would need a finite area around it in which to pack information. This new dimension may allow us to use a lot more capacity that we were previously wasting (maybe), but I'm pretty skeptical that the usable area will be "potentially infinite" except in the limited sense that the usable frequency line was already "potentially infinite".

Even so, any large increase in the effective wireless bandwidth would be cause for celebration.

From that article, it's impossible to understand how this differs from ordinary cirularly polarized radio waves created routinely with helical antennas.

I assume the key difference is that the electric and magnetic field are not 90 degrees out of phase, but some other amount?

It's hard to get a real message through, so many outrageous claims and layers of "popularization" and jargon.

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.

Ah SETI is exatcly what I think when I see things like this.

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-...

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/

You seem to be talking about aliens picking up earth transmissions, while he's talking about receiving alien signals.

Right, but he's saying that if Earth's own signals fail to propagate even outside our solar system, alien signals will have to be exponentially more powerful than ours to even stand a chance of being received. The distance from Earth to Saturn is tiny in comparison to the distance between planetary systems.

Polynomially. Not exponentially. The surface area of a sphere doesn't grow exponentially with radius.

I'm so glad to see you wrote that, seriously. It is absurd how it has become pop-cultural to use "exponentially".

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.

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.

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

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.

Aren't you forgetting diffraction?

You mistake the purpose of SETI. The idea is not to attempt to pick up stray EM transmissions from extra terrestrial civilizations, almost certainly that idea is a non-starter for a wide variety of reasons. Instead, the goal is to pick up signals which are intentionally beamed at Earth.

There are a lot of caveats on whether or not that makes sense, but assuming that an ET civilization has detected our planet (which they could do from across the galaxy) and they want to send us a message then it's not too crazy to imagine they might use radio to do so. Also, looking for such signals is pretty cheap, and the potential impact of such a detection would be enormous, so why not spend a little effort looking?

> assuming that an ET civilization has detected our planet (which they could do from across the galaxy)

The closest galaxy to ours is about 25,000 lightyears away, according to wolframalpha. In other words, we'll have to wait that number of years before an ET civilization from there might pick up on us. I think this makes the whole endeavor completely pointless.

Did you read 'across' as 'outside' or something?

I did, but the milky way has a diameter of 100,000 lightyears, so it doesn't affect my argument.

But a lot if it is really close too.

I said detect our planet not detect our civilization.

For all we know there is some civilization out there which periodically cycles through all the known possibly habitable planets they've detected and beams radio messages at them.

We should do this.

So how do you explain that we're receiving our radio signals bounced back to is from 20+ light years away? http://www.rimmell.com/bbc/news.htm

That story was posted on April 1st in 2009, and isn't hosted on BBC's website. There isn't even a first name given for the researcher (only "Radio astronomer Dr. Venn"). Looks sketchy to me.

I can't find any other information about it, so I'm guessing its a hoax / April Fools joke.

I was actually wondering that too but couldn't find anything definitive saying its a hoax.

I have to think it would have been a huge deal if it were real, no?

> because if our receivers are set up in a different configuration than some potential sender might be, we'll never receive anything.

We'll receive it, but it may be hard to distinguish from noise. But this is already true, for example with spread spectrum - if the transmitters are using that we'll never known, it's almost indistinguishable from noise unless you match the same frequencies they use.

Hasn't SETI been shut down?

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.

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.

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.

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.

I think the author just wanted to throw in the "Verizon pays billions" line. IMHO, they bought it so no one else could have it.

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?

phased arrays etc CAN point the antenna, electronically

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.

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

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!

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.

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

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

That's the first explanation that makes sense so far!

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?).

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

This paper should help: http://www.gla.ac.uk/schools/physics/research/groups/optics/...

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

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

Do electromagnetic waves obey inertia and momentum? Really?

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

Yes, they really do. Start here and keep reading down the page: https://en.wikipedia.org/wiki/General_relativity#Consequence...

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.

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.

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.

the speed of light is independent of the angular momentum... c is still c :)

To me this looks like good old circular polarization.

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

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.

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).

That would be my guess too, especially as two crossed yagis are a well known way to receive circular polarized signals:

http://www.qsl.net/dk7zb/Cross-Yagi/crossyagi.htm

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.

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

http://www.gla.ac.uk/schools/physics/research/groups/optics/...

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