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'Twisted' Waves Could Boost Capacity of Wireless Spectrum

Soulskill posted more than 2 years ago | from the make-them-squirm dept.

Wireless Networking 147

New submitter Ogi_UnixNut writes "In Venice, Italy, physicists have shown that it is possible to use two beams of incoherent radio waves, transmitted on the same frequency but encoded in two different orbital angular momentum states, to simultaneously transmit two independent radio channels. In principle this allows the implementation of an infinite number of channels in a given, fixed bandwidth, even without using polarization, multiport or dense coding techniques. It's potentially a boon for congested spectrum problems, although at the moment I suspect it would only work for directional links."

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Multipath (5, Insightful)

rullywowr (1831632) | more than 2 years ago | (#39219723)

What about the issue of multipath, where one wave inverses the phase because its reflection arrives at the antenna slightly delayed from the original direct LOS (line of sight) signal?
I work with wireless microphones and deal with spectrum issues on a daily basis. With the shrinking spectrum, this would be extremely good news if it actually was feasible and practical in the real world. As it stands right now, two transmitters operating on the same frequency is simply a recipe for disaster.
oh yeah, first!

Re:Multipath (4, Funny)

Forty Two Tenfold (1134125) | more than 2 years ago | (#39219983)

Leeloo Dallas multipath!

Re:Multipath (2)

Sponge Bath (413667) | more than 2 years ago | (#39220407)

Milla Jovovich with a lisp... very sexy.

Re:Multipath (1)

Mister Transistor (259842) | more than 2 years ago | (#39220475)

Less Thermal Tape, Please...

Re:Multipath (2)

tibit (1762298) | more than 2 years ago | (#39220059)

GPS transmitters on the space segment all share the same channels and it's not a recipe for a disaster. Your GPS receiver works just fine listening to all those satellites all jabbering on the same channels. You engineer the whole system for it. Let's put it this way: wireless microphones are not anywhere near state-of-the-art in digital data transmission techniques. Extraterrestrial links are where the state of the art is at, and mostly has been, too, for a good while.

Re:Multipath (1)

camperslo (704715) | more than 2 years ago | (#39220447)

Hmmmm, so now we have a way to take those companies that have gobbled up most of the U.S. broadcast frequencies, and have them put all of their operations in one city on just one channel? Sounds great. Let's do it tomorrow.

Actually with that HD radio technology that nobody but them seem to want (proprietary codec and all), we've already got a way to tell them to put everything in one r.f. channel. Maybe we can bring back some locally owned diverse broadcasting to the U.S. []

Re:Multipath (1)

rullywowr (1831632) | more than 2 years ago | (#39221513)

GPS transmitters on the space segment all share the same channels and it's not a recipe for a disaster. Your GPS receiver works just fine listening to all those satellites all jabbering on the same channels. You engineer the whole system for it. Let's put it this way: wireless microphones are not anywhere near state-of-the-art in digital data transmission techniques. Extraterrestrial links are where the state of the art is at, and mostly has been, too, for a good while.

That may be true for GPS, however you must remember that GPS signal they are multiplexing on the same frequency certainly is not tasked with carrying real-time, high fidelity audio that one expects from wireless microphones, radio, TV, etc. They are simply using a time-based location receiver to determine positioning.

Any engineer worth his salt will tell you that there is "no free lunch" when it comes to transmitting high fidelity audio in real-time over the electromagnetic spectrum.

Re:Multipath (4, Insightful)

YoopDaDum (1998474) | more than 2 years ago | (#39221795)

That's completely different. GPS uses CDMA, which is a way to multiplex several users on the same channel. Here it's a way to create additional independent channels. The former is sharing one channel capacity, the later is adding channels and capacity. If you want to compare this to an existing technology, it's closer in spirit to MIMO with spatial multiplexing.

But as the grand-parent remarked, and if I understand correctly, this shouldn't be robust to multipath (i.e. all the reflections that adds up at the receiver). And all practical use cases you care about as an end user must support multipath (OFDMA used in WiMAX and LTE main strength is its robustness to multipath) as they must operate in non line of sight (NLOS) conditions. So that would limit the application to line of sight (LOS) systems like microwave trunking. Possibly still useful, but not for you and me.

And by the way, although you're correct that wireless microphones are basic tech, satellites links are by no mean state of the art. Satellite is LOS, the challenge is very low signal level but the channel is easy. The state of the art is in terrestrial broadband (mostly LTE and its evolutions now) with mobility and multipath to handle with a constrained (size and power) receiver in a smartphone.

Multiple transmitters on same freq is a reality (1)

Viol8 (599362) | more than 2 years ago | (#39220077) []

AFAIK however its only used for digital transmission where you can do a lot of signal processing. I don't think it would work well with analog - look what happens on AM at night.

However SFNs are used with the DAB digital radio system in europe.

Re:Multiple transmitters on same freq is a reality (2)

rullywowr (1831632) | more than 2 years ago | (#39221585) []

AFAIK however its only used for digital transmission where you can do a lot of signal processing. I don't think it would work well with analog - look what happens on AM at night.

However SFNs are used with the DAB digital radio system in europe.

All transmissions are inherently analog in nature. The phrase "digital" only refers to the processing before and after (companding etc). AM refers to a modulation scheme. FM also refers to a modulation scheme. FM is more reliable and has better consistency than AM, however both are analog technologies.

Re:Multiple transmitters on same freq is a reality (1)

YoopDaDum (1998474) | more than 2 years ago | (#39221835)

As I explained above, this is different. What you mention share the same channel, while here it adds new independent channels. A closer analogy, although it's different, would be MIMO spatial multiplexing. This said, if it doesn't work with multipath it won't change your life.

Re:Multipath (1)

ArsenneLupin (766289) | more than 2 years ago | (#39220117)

oh yeah, first!

Mod parent Insightful!

Not really new (2, Interesting)

scsirob (246572) | more than 2 years ago | (#39219761)

This has been used for ages by HAM radio operators. Horizontal and vertical polarization antenna's can be used independently, or even together to create circular polarization. See: [] and []

Re:Not really new (1)

nedlohs (1335013) | more than 2 years ago | (#39219785)

Surely the "without using polarization" part means it isn't that?

Re:Not really new (4, Insightful)

virgil_disgr4ce (909068) | more than 2 years ago | (#39219861)

Try reading the article. The innovation is to use orbital angular momentum, NOT spin angular momentum (polarization).

not really (1)

Shavano (2541114) | more than 2 years ago | (#39219979)

Em waves don't HAVE orbital angular momentum.

Re:not really (2)

NicknameAvailable (2581237) | more than 2 years ago | (#39220013)

Probably sounds insane to cite, but Rodin coils put out em fields with orbital angular momentum - I've measured it personally from them.

Re:not really (3, Informative)

jo_ham (604554) | more than 2 years ago | (#39220029)

Photons do.

Photons are part of the EM spectrum.

So what are they orbiting then? (1)

Viol8 (599362) | more than 2 years ago | (#39220031)

Some random fixed point in space? The antenna? What?

Re:So what are they orbiting then? (3, Informative)

Anonymous Coward | more than 2 years ago | (#39220069)

Around the propagation direction of the beam. Read this:

Re:So what are they orbiting then? (0)

Anonymous Coward | more than 2 years ago | (#39220413)

That sounds like circular polarization.

Take a scope, signals to horizontal or vertical only trace a line. Both at once a diagonal line, one of those inverted draws a diagonal flipped the other way. 90 degrees out of phase draws a circle. Vary the phase it starts to flatten to an ellipse, reaching lines again at the angles already mentioned.

I'm getting a headache.

Are you sure radio vortex doesn't just mean radio sucks?

Re:So what are they orbiting then? (3, Informative)

Baloroth (2370816) | more than 2 years ago | (#39220149)

See Wikipedia [] for details. It isn't polarization, but I can't exactly explain how it isn't.

Re:So what are they orbiting then? (1)

X0563511 (793323) | more than 2 years ago | (#39220363)

My head just exploded [] , and it's your fault.

Re:So what are they orbiting then? (4, Informative)

tibit (1762298) | more than 2 years ago | (#39220177)

The notion of "what are they orbiting" is nonsensical here -- we're talking about quantum objects. It's like saying that electrons "orbit" the nucleus: in the description of their motion, the concept of a classical "path" doesn't quite apply either, and classical mechanics can't describe what an electron does when bound to the nucleus! Now, Maxwell's theory is "classical" in a way, but it describes AFAIK an aggregate (macroscopic) behavior of inherently non-classical, quantum objects, the photons. To get the behavior at the quantum level right, you need quantum electrodynamics (QED).

It is well known from Maxwell's theory that electromagnetic radiation carries both energy and momentum. The momentum may have both linear and angular contributions; angular momentum has a spin part associated with polarization and an orbital part associated with spatial distribution

- from "Orbital angular momentum of light and the transformation of Laguerre-Gaussian laser modes" by Allen et al. In the same paper, you can read that you can measure those properties of light using fairly simple opto-mechanical instruments:

A suspended lambda/2 birefringent plate undergoes torque in transforming right-handed into left-handed circularly polarized light. Suspended cylindrical lenses undergo torque in transforming a Laguerre-Gaussian mode of orbital angular momentum -l*hbar per photon, into one with +I*hbar per photon.

Re:So what are they orbiting then? (0)

Anonymous Coward | more than 2 years ago | (#39221045)

What's all this? I stopped reading after Q.E.D.

Re:not really (1)

Chris Burke (6130) | more than 2 years ago | (#39221869)

Photons are the EM spectrum, you probably meant to say. :)

Re:Not really new (1)

camperslo (704715) | more than 2 years ago | (#39220101)

I'm not following this. How does one generate such a signal, and receive it, and if it realy works, why demonstrate with only two signals?

Simple cross polarization people can see with polarized sun glasses. And it's used in LCD displays when a plastic sheet allows light at one polarization, and the liquid crystal can flip its polarization when exposed to a field, the light passing through when it agrees with the filter, blocked when at 90 degrees. If the angles aren't quite right there's bleed through. To make the apparent "dynamic" contrast ratio seem better, many vendors dim the backlight on dark scenes, but the the maximum light output is also reduced. So the improvement is a bit of an illusion a bit like most audio noise reduction systems (the noise comes up when the audio does, some hidden from perception by the louder audio).

Horizontal and vertical antenna fed at once in phase produce what amounts to diagonal. Feed the second one inverted, is is diagonal flipped the other way.. receive antennas don't get signal (it's nulled) right at 90 degrees, but a horizontal or vertical antenna would both pick up diagonal (either way) at once, just weaker. Typical satellite transponders have the full frequency range used with the odd channels at one polarization, the even channels are half a channel higher in frequency, polarized at 90 degress (I forget which one is vertical). The receive polarization has to be correct to null out the other signals.
Offsetting the flipped channels just makes things a little more tolerant of being slightly misaligned from 90 degrees isolation, but doesn;t change the principle at all.

If horizontal and vertical are fed 90 degrees out of phase, the polarization rotates. flip the phase 90 degrees the other way it rotates the other way. The advantage of that type of signal is that the antennas can be turned and still get the signal they were intended for. Polarizate flips when bouncing a signal, like off the moon. They call those right hand and left hand circular polarization. And they work well for two signals on the same frequency especially from the same place where the strength is the same. But since reflections can reverse the spin, signals from separate sources that don't experience the same reflections may still interfere because one might get flipped when the other hasn't etc. All that is still about TWO signals on the same channel.

Now to what they're doing in the article? I couldn't envision what's happening (it's early, maybe coffee will help..), but obviously since circular polarization already can do two signals at once, their demo with two signals doesn't prove that they've done something new. So what;s going on, and if it really works, why not demo with more than two signals???

Re:Not really new (1)

squidflakes (905524) | more than 2 years ago | (#39220401)

If I'm understanding this correctly, there is no polarization. The receiving antenna is getting it's voltage changes from the amount of spin energy in the beam and it's location in space, sort of like the way a QAM signal uses phase shift and amplitude changes to create a waveform that wouldn't be possible with either method alone.

Italian translated to english by reporters (1)

Casandro (751346) | more than 2 years ago | (#39220157)

It could mean anything from plain circular polarization (which has been used for ages) to whatever.
I'm not sure what kind of problem it should solve. After all MIMO system can separate different sources of radio just as well.

Besides there are always frauds out there, often those don't even understand what they are doing.

Onlive (-1)

Anonymous Coward | more than 2 years ago | (#39219793)

I believe OnLive is working on something similar.

infinite number of signals (2)

nopainogain (1091795) | more than 2 years ago | (#39219795)

and still nothing but talk on the radio. I know it's about cell communications i just couldn't resist. I live in Philadelphia and we've got one rock station that uses more than 70% of its time to transmit mindless banter that appeals to adolescent mindsets like urination and flatulence jokes... then another 10% committed to a burned out hippie who talks incessantly from 10am til 2pm. then a couple minutes of actual rock music in the mid afternoon when every possible listener is at work.

Re:infinite number of signals (0)

Anonymous Coward | more than 2 years ago | (#39219929)

What's the purpose of analog radio? It's broadcast, so it has to make economical sense to be fed to the masses instead of serving specialized demands. Night shift workers use radio to stay awake, depressed people use it to drown out the destructive chatter of their own minds, or to have someone to "talk to". They don't want long pieces of music, they want talk. Radio music is only an advertisement for music you're supposed to buy. If you want good music, meet the Web.

This is Myron Evans O(3) electrodynamics in action (0)

Anonymous Coward | more than 2 years ago | (#39219815)


Interesting but not convincing. Circ Polarization? (1)

Muad'Dave (255648) | more than 2 years ago | (#39219821)

As I said in the other, non-annointed article on this subject:

I'm not an EM genius, but this sounds an awful lot like circular polarization [] with perhaps a selectable 'twist' rate. I'd love to see a 3D diagram of a vortex wave vs a circularly polarized wave propagating - that would help me understand what's happening.

Re:Interesting but not convincing. Circ Polarizati (0)

Anonymous Coward | more than 2 years ago | (#39219889)

Maybe this helps. I'm still trying to grasp the concept.

Re:Interesting but not convincing. Circ Polarizati (1)

buchner.johannes (1139593) | more than 2 years ago | (#39219895)

Polarization is not spatially twisted -- that is just a visualization using the electric field strength on one spatial axis and the magnetic field strength on the second spatial axis, while the radiation travels in the third (real) spatial axis.

Here is a wikipedia article: []

Re:Interesting but not convincing. Circ Polarizati (1)

Muad'Dave (255648) | more than 2 years ago | (#39220205)

Thanks for the pointer - that helps. My concept of 'twist rate' seems to be borne out as |m|, although what's shown seems to be the whole EM wave spiraling vs the E and M components being polarized. That's cool!

The images in the right column of the diagram look suspiciously like propagation modes in circular waveguide [] to me.

You might also be interested in this ham's work which exploits the Aharonov-Bohm Effect [] :

Robert Zimmerman, NP4B/VE3RKZ, describes five years of research at McMaster University in “Transmission and Reception of Longitudinally-Polarized Momentum Waves.” James Clerk Maxwell’s famous equations of electromagnetic radiation predict an alternative form of radiation, which Zimmerman refers to as vector potential radiation. He was involved in research that results in a demonstration of the communications potential of what was previously considered to be only a theoretical curiosity.

Google around a bit for 'vector potential waves'. Here's one tantalizing snippet [] . According to Zimmerman and others, metallic antennas are useless to receive these waves - Zimmerman uses plasma in the form of a fluorescent bulb!

Shannon says (-1)

Anonymous Coward | more than 2 years ago | (#39219823)


Shannon-Hartley still in effect. (4, Insightful)

neyla (2455118) | more than 2 years ago | (#39219829)

This might help, but it doesn't expel Shannon-Hartley. They don't get "inifinite channels" in finite bandwith. Not unless each channel has infinitely low capacity, anyway.

Re:Shannon-Hartley still in effect. (1, Funny)

mehrotra.akash (1539473) | more than 2 years ago | (#39219887)

Does an infinite no. of channels with infinitely low capacity give infinite effective bandwidth?

Re:Shannon-Hartley still in effect. (1)

gmaslov (1983830) | more than 2 years ago | (#39219959)

"Infinitely low" is zero. So no.

Re:Shannon-Hartley still in effect. (0)

Anonymous Coward | more than 2 years ago | (#39220217)

what is 0 * infinity?

Re:Shannon-Hartley still in effect. (1)

PlatyPaul (690601) | more than 2 years ago | (#39220263)


Re:Shannon-Hartley still in effect. (2)

MadKeithV (102058) | more than 2 years ago | (#39220281)


Re:Shannon-Hartley still in effect. (1)

gmaslov (1983830) | more than 2 years ago | (#39221213)

Good question. "Infinity" is not a real number, so the usual understanding of the multiplication operator (which takes two real numbers and produces a real number) does not apply. You can try to extend the real numbers by adding two objects called positive and negative infinity, defined in terms of the limit of an unbounded sequence. So positive infinity is something greater than any finite number (and negative infinity), and vice-versa. Then things like dividing something by infinity, or adding infinity to something, follow naturally from limit operations, and have the values that you'd expect.

Unfortunately there's still no help for "0 * infinity" and other so-called indeterminate forms. This kind of infinity is defined as the limit of any unbounded sequence, but unlike the defined forms like "1 / infinity = 0", the value of "0 * infinity" will depend on the details of the particular sequence. Consider: "x / infinity = 0" is true for any constant, finite x; substituting it into "0 * infinity" gives "(x / infinity) * infinity". The infinities cancel (since we can let them represent the same unbounded sequence), leaving "0 * infinity = x", for any x that you like.

So my preferred answer to the question "What is 0 * infinity" is: mu. It can take on any value, but only because you've thrown away the information about what unbounded sequence, exactly, is represented by this infinity. It means you need to go back and analyze the original problem more carefully. In the context of this particular problem, the question is if a finite bandwidth, divided into an infinite number number of infinitely small channels, gives you infinite bandwidth. Stated precisely this way it's almost obvious. If N is the number of channels and B is the total bandwidth, then the bandwidth of each channel is "B/N". What happens to the total of the channels' bandwidths as N approaches infinity? Well, N goes to infinity and B/N goes to zero, which is where the question "0 * infinity" comes from. But if we keep the information about the original sequences, "N * (B/N)" is just B, and nothing else.

Re:Shannon-Hartley still in effect. (0)

Anonymous Coward | more than 2 years ago | (#39220349)

But a zero watt transmitter does have 100% protection from interference.

Re:Shannon-Hartley still in effect. (1)

Baloroth (2370816) | more than 2 years ago | (#39220225)

Depends on what the limit of the product of the no. of channels by the capacity of the channel becomes as they approach infinity. Calculus, basically: one thing can approach zero and another can approach infinity, but their product can approach a finite number in between. It all depends on how they approach zero and infinity. Could also mean the bandwidth is effectively infinite, or effectively zero, in the extreme case, although the latter would be unexpected, to say the least.

Re:Shannon-Hartley still in effect. (0)

Anonymous Coward | more than 2 years ago | (#39219921)

I think the idea is that the channels are orthogonal. Just like with normal polarization, you can have two waves with different polarization, each follows S-H theorem, but the total information is more than S-H allows for one particular channel. The idea is that these channels do not interfere with each other, as if they were physically separate, instead of sharing the same medium.

Re:Shannon-Hartley still in effect. (1)

Bengie (1121981) | more than 2 years ago | (#39220367)

CDMA does the same thing. DOCSIS3.0 allows channel bonding to the same physical channel, but different virtual channel. Each physical 40mb channel is broken up into 127 CDMA codes, each with 40mb. Watching a cable modem channel bond 8 virtual channels to the same 6 MHz physical channel and sustain 320mb/s is quite cool.

It was called "black magic" when it first came out.

Re:Shannon-Hartley still in effect. (1)

Anonymous Coward | more than 2 years ago | (#39220577)

They're not beating Shannon here... the SNR is high enough to push the data through.

Consider a 56kbps modem over a 3kHz bw telephone channel. that's better than 18bps/Hz.

Re:Shannon-Hartley still in effect. (1)

bandy (99800) | more than 2 years ago | (#39221099)

You get 56k out of it because of compression. Actual physical bandwidth is limited to about 34kbps of actual data transfer.

Re:Shannon-Hartley still in effect. (3, Funny)

Idbar (1034346) | more than 2 years ago | (#39219937)

I think AT&T is fine with that. ;-)

Re:Shannon-Hartley still in effect. (2)

tibit (1762298) | more than 2 years ago | (#39220215)

Shannon's theory applies to an abstract concept of a channel. It says nothing about how you map such an abstract channel to a physical realization of it. So, you cannot make a leap from an abstract channel and abstract bandwidth to a physical realization using some means of transmission without saying how those concepts map to underlying physical reality. Do that first, otherwise your statement makes no sense.

Signal Power (2)

pavon (30274) | more than 2 years ago | (#39220261)

This might help, but it doesn't expel Shannon-Hartley. They don't get "inifinite channels" in finite bandwith. Not unless each channel has infinitely low capacity, anyway.

The other limiting factor in Shannon-Hartley is signal power. Transmitting with infinite power does allow you to have infinite channel capacity, and transmitting over an infinite number of channels each with finite power over does just that. That said, I am sure that practical limitations in hardware design will place a limit on how close the orbital angular momentum spacing can be and still be able to discriminate the channels.

Re:Signal Power (1)

pavon (30274) | more than 2 years ago | (#39220373)

Oh and I should add; the reason we don't solve the current spectrum congestion problem by just boosting signal power is because one channel's signal is another channel's noise unless filters can be designed to separate them. So without improvements in filters having everyone boost their signal power will just mean that everyone's noise floor increases as well and the whole thing is a wash as far as channel capacity goes (except now we are wasting more power).

I would imagine that transmitting 10 channel with different orbital angular momentums within a specific bandwidth would have the same effect on adjacent channels as a single channel with 10 times the power in that same bandwidth.

Re:Shannon-Hartley still in effect. (0)

Anonymous Coward | more than 2 years ago | (#39220659)

Don't get so fixated on Shannon-Hartley. There ways to get around it. You could separate the channels spatially. I could have 1000 lasers of the same frequency carrying different signals at high bandwidth, as long as they aren't pointed at the same spot it's trivial to not have interference between them

If you have a single receiver/antennas, separating the different signals is difficult. If you have more of them you can do fancier stuff. Already cheap wifi devices do that MIMO stuff.

There's also tech like: []
In theory you can use this sort of stuff to track and talk to multiple devices.

Re:Shannon-Hartley still in effect. (1)

YoopDaDum (1998474) | more than 2 years ago | (#39221961)

It doesn't invalidate Shannon, as an AC says below and as I understand it, it creates new orthogonal channels. Think MIMO spatial multiplexing.

But as the first poster said, and IIUC from how it's done, it shouldn't be robust to multipath. If true this would limit a possibly application to microwave trunking, but wouldn't help WiFi of your smartphone.

Terrestrial Microwave Links. (2)

neBelcnU (663059) | more than 2 years ago | (#39219905)

"It's potentially a boon for congested spectrum problems, although at the moment I suspect it would only work for directional links."

Wouldn't that mean a huge boon for telcos and state gov'ts that still use terrestrial microwave links? Could a state network take advantage of this, and sell off the unused portion? Speaking for IL and MN, both have microwave line-of-sight to all their toll booths, truck depots and weigh stations.

There are inevitably issues to this, but if this first appears in LoS, wouldn't these networks (telco+local gov't) be able to use it?

Re:Terrestrial Microwave Links. (1)

mooingyak (720677) | more than 2 years ago | (#39219965)

I was thinking of the DVD player in my minivan. It's one of those devices that broadcasts on at some FM frequency and I have to tune the car radio to it. It's pretty much unusable any time I pass through NYC, which, since I live on Long Island, is basically any road trip long enough to bother with putting a DVD on.

Re:Terrestrial Microwave Links. (0)

Anonymous Coward | more than 2 years ago | (#39220055)

Setting aside that you seem to say you'd rather invest in $100 antennas for both your car and your DVD player, instead of a $5 cable...

Do you have any idea just how big VHF broadcast waves are? About 3 m. Nothing you can fit in your minivan will produce a Gaussian beam, let alone more complex modes such as Laguerre-Gaussian [] (which I'm pretty sure is what TFA is about, though I didn't read it).

Re:Terrestrial Microwave Links. (1)

mooingyak (720677) | more than 2 years ago | (#39220113)

Ah. That's unfortunate then.

As for the cable, that would have been vastly preferable, and is also what I had believed would be installed. Of course, after the fact they tell me that there's no way to do that with the player I have.

Think of it as a phased array (2, Informative)

Anonymous Coward | more than 2 years ago | (#39219925)

I think that what's happening is no different from what you could achieve with a 802.11/n MIMO system. Think of their twisted antenna as a ring of patch antennas.

Essentially, the trade-off they are making is that they broaden the beam by warping their antenna, so they have a lower-gain antenna with a wider beam. Consequently, you need more power in each of the two orbital angular momentum states to transmit the data, consequently Shannon-Hartley is preserved.

Another way of looking at it is that their dish makes a broader beam because it is twisted. If you wanted to keep the beam width (and thus the gain) of the antenna the same as an unmodified dish, you'd need a bigger dish. Alternatively, instead of a bigger dish, you could use two unmodified dishes sending two separate beams.

So, I don't think they have accomplished anything except that they've (a) produced a nifty new antenna design that might occasionally be useful but isn't a great advance, and (b) shown some interesting math. And, they've also managed to confuse themselves and let themselves believe that they did something wonderful.

Re:Think of it as a phased array (1)

s122604 (1018036) | more than 2 years ago | (#39220591)

I'm not sure if that is completely correct
802.11/n MIMO uses a crude form of adaptive beamforming, where you screw with phasing to make intentional nulls in your antennas' receive/transmit pattern (this is also used in EW to null out jammers)

This doesn't seem like the same thing, although I'd be lying if I said I completely understood the article

Re:Think of it as a phased array (0)

Anonymous Coward | more than 2 years ago | (#39221569)

Absolutely correct! See this paper on that exact topic ...

Huh? Is this polarization? (0)

Anonymous Coward | more than 2 years ago | (#39219985)

If they're talking about polarization, this has been done for centuries now. Radio stations and satellites have been sending different signals on horizontally and vertically polarized modes for a very long time.

This is not new.

And you can't generalize it to N different channels, where N is much more than 2, as the polarizations are only separate if you pick them to be at right angles, and even then there's a few db of feedthrough.

Re:Huh? Is this polarization? (2)

jo_ham (604554) | more than 2 years ago | (#39220047)

If you do something totally crazy and actually RTFA you'll note that they address this very question.

It is distinct from polarisation, which the FA talks about considerably, including an analogy for the layman.

Topological charge (0)

Anonymous Coward | more than 2 years ago | (#39220027)

The idea is similar to what has been coming up in electron microscopy. The use of a topological charge on the beam. If you can detect it, you can encode N beam with different N charges on the same frequency.

BULLSH!T (3, Interesting)

AB3A (192265) | more than 2 years ago | (#39220037)

Any time someone starts talking of infinite channel capacity, you know they're going to be full of crap. Shannon's limit is a Mathematical principle. There is no such thing as "infinite" bandwidth/channel capacity.

What they're actually discussing is the spatial equivalent of spread spectrum. In other words, they have their own custom reflector with its own unique shape that can be reversed so that a coherent signal with minimal inter-symbol interference would be present. It is not a bad idea, except that you would need a line of sight path with very little exposure to the first Fresnel zones. Reflections would be a bitch to deal with.

Also note this method reduced point source noise, but it doesn't eliminate it. Likewise, a spread spectrum signal is still detectable as increased noise in a narrow-band radio.


Anonymous Coward | more than 2 years ago | (#39220235)

Admittedly, this isn't "infinite channel capacity", it's "an infinite number of finite-capacity channels". Not that I get why; it sounds like it should just increase the number of independent channels available within a frequency range by some finite factor.


tibit (1762298) | more than 2 years ago | (#39220249)

They are talking about a physical channel, not an abstract channel. Shannon's limit as you've properly said is a mathematical concept. You have to map it to a physical reality in a particular way. It may well be that such a mapping has some hitherto unused possibilities, and that's precisely what the authors are saying.


ozydingo (922211) | more than 2 years ago | (#39220311)

*In principle* is a key modifier, so let's think this through. Doesn't the EMR spectrum *in principle* have infinite capacity if we could use arbitrarily high frequencies to transmit information? I suppose there may be some modern-physics-predicted upper limit to what frequencies of radiation can exist, just as I suppose there may be a limit also to the orbital angular momentum states, but that's not what's at issue with violation of Shannon's limit. Shannon's limit applies to one-dimensional signal. I'm sure for a given bandwidth and a given resolvable orbital angular momentum state, Shannon's limit still applies. But if we have a theoretically unbound number of accessible, resolvable, states to use in each frequency bandwidth, just as there are a theoretically unbound number of finite-frequency bands in the entire EMR spectrum, would it not be appropriate to state that *in principle* the technology would allow for infinite capacity?


Prune (557140) | more than 2 years ago | (#39221789)

Infinite frequency is impossible even in principle because it implies infinite energy per photon (-> infinite mass -> black hole with event horizon at infinity), so, NO. This was such an obvious point that I'm surprised you put your foot in your mouth with that comment like this.


ozydingo (922211) | more than 2 years ago | (#39222173)

I believe you missed my point. I admitted that there's likely some reason for an upper limit (and no, IANAP), that's not what at issue with violation of Shannon's limit as per OP, which is what I was addressing. Even still, doesn't your argument about infinite energy still leave us unbounded? It does not provide a strict upper limit to what frequencies we can manipulate, and therefore, still infinite in principle. In practice, obviously, we can't expect to keep upping the energy without bound, I don't and didn't argue against that obvious point.

An aside; seriously, why is everyone so fucking combative in internet posts?


Anonymous Coward | more than 2 years ago | (#39220341)

But the Shannon's limit you refer to really channel capacity, this technique -- according to the authors -- is essentially putting you additional channels in the same frequency space. So no violation. See MIMO.

Re:BULLSH!T (5, Interesting)

Angst Badger (8636) | more than 2 years ago | (#39220411)

Shannon's limit is a Mathematical principle.

Unfortunately, most people have next to no understanding of mathematics beyond some rote memorization from school. This is just another example of people confusing analog signals with magic. To be fair, the actual researchers involved probably understand this quite well, but the scientifically uneducated class from which science and technology journalists are drawn is another matter.

The non-mathematical version, for those interested, is that yes, analog signals are continuous and so can occupy an infinite number of states. The reason you can't get infinite bandwidth out of that is because both the transmitters and receivers have limited precision, and because there is always noise, which is another manifestation of the Second Law. For example, there are an infinite number of real numbers between 0 and 1. If you could actually use all of that space, you could encode any amount of information in an arbitrarily short signal. (Well, there's a limit to that, too, for which see Georg Cantor.) In practice, you can't use all of that space, because your instruments might distinguish quite well between 0.001 and 0.002, but they can't reliably tell the difference between 0.001 and 0.0005. On top of that, there is noise, which is also a big topic, but you can think of it as a random fluctuation in the signal. If the ambient noise varies between 0.0 and 0.0005 in the same example, you can't even reliably tell the difference between 0.001 and 0.002.

What the parent is getting at is that laws of physics, being derived from observations of nature with limited precision, might occasionally be overturned by better observations. Fundamental mathematical principles, on the other hand, are much more reliable. There might be a difference between rest mass and inertial mass that we could exploit for thrustless propulsion. It's extremely unlikely, but it can't be ruled out. But there is zero possibility that 2 + 2 will ever equal anything other than four. Shannon's limit and, for that matter, the Nyquist sampling theorem are a little more complex than a simple integer sum, but the actual math for both would fit on an index card with plenty of room to spare to blather on about "infinite" analog signals. We use digital signals most of the time these days because it makes the hardware easier to design, but neither digital nor analog can be used to make an end run around the Second Law.

What the researchers in TFA claim to have figured out is another way to use part of the signal outside of the frequency domain to stuff data into. It's a really ingenious approach that might be quite useful if it pans out in actual practice, but it's not magic, and it's not infinite.


Prune (557140) | more than 2 years ago | (#39221823)

Infinite bandwidth would also violate the Bekenstein bound and holographic principle. But hey, people will still think they can encode arbitrary precision real numbers in physical objects with finite extent, as futile as that dream is.


Anonymous Coward | more than 2 years ago | (#39220471)

Even the summary says that it isn't infinite bandwidth in a channel, but hypothetically infinite channels in a spectrum. Reality will probably reduce 'infinte' to '4' or so if it even progresses.

Since you didn't even read the summary, I'll give you the teal deer.

"Italians found another way to shape an EM signal, in addition to classic polarization, phase changing, etc."


tizan (925212) | more than 2 years ago | (#39220889)

Indeed it is bullshit.
They are talking of using a different basis to send the energy ...e.g Sine waves is a commonly used mathematical basis.
So they are using different functions here and they are saying they will be able pack more energy in ...they have not shown that at all
and the fact they are talking "infinite" capacity...tells me there is more "you know what" that real proof here.


Anonymous Coward | more than 2 years ago | (#39221953)

Mathematical principles only apply to the world through models. When the assumptions of the model change, so do the mathematical principles. So saying that something is a mathematical principle and therefore certainly true about the world is a poor argument: the math may be right, but the model may not be, and then the math does not matter. So saying that Shannon's limit is a mathematical principle with "mathematical" capitalized with bold and italics is a misunderstanding about the way in which math applies to the world. Math applies to the world through models, and the models usually turn out to be wrong. Sometimes the models are wrong yet still Good Enough (TM) that we can still use them in certain circumstances (like Newton's laws). The point is that you seem to believe that a mathematical proof somehow applies to the world directly, so that we can transfer our confidence in the math directly into confidence in statements about the world. That's just not how things work. It's all about the models. That doesn't mean that infinite bandwidth is possible, but if it is impossible, we can only know that through constructing a model, and that model itself cannot be mathematically proven without reference to yet other models that themselves cannot be mathematically proven. We can verify the models through experiment, but then you will have to agree that we are no longer dealing with an infallible mathematical principle - it is possibly infallible as mathematics, but it is never infallible in terms of how it applies to the world.

Color me skeptical (0)

Anonymous Coward | more than 2 years ago | (#39220039)

OK, as someone with a Ph.D. in engineering electromagnetics, I'm skeptical. I'm aware that physicists have a nomenclature different from engineers and I'll have to go and read some of the cited papers to make sense of "orbital angular momentum" in my frame of reference, but anyone who refers to the noise level as "electrosmog background" in a scientific paper rather than using signal-to-noise ratio raises my suspicion. I also couldn't find the level of peer review the article has received. The journal homepage mentions a review policy [] , but I couldn't find the minimum number of reviews required for publication (for IEEE, e.g., this is usually at least two, plus more if the reviewers disagree).

It'll be interesting to see how this one plays out.

Re:Color me skeptical (1)

Muad'Dave (255648) | more than 2 years ago | (#39220351)

Google around a bit for "Vector potential waves" - a (presumably PhD level) professor and his wife are doing work on this very subject at McMaster U. in Canada. this is the basis for it [] . This really messes with the classical interpretation of the double slit experiment - add a solenoid and all bets are off!

A Modern Physics Letters B Paper [] on the subject at hand.

I read about it first in the Amateur Radio publication QEX.

Re:Color me skeptical (1)

0111 1110 (518466) | more than 2 years ago | (#39221851)

The guy from McMaster appears to be claiming that you can transmit information via some kind of longitudinal electrical 'wave' with virtually no power in the transmitter. That is very strange. It seems to defy basic logic and cause and effect and the TAINSTAFL principle. Yes, you still have some level of conservation of energy because the receiver uses the additional power, but it just doesn't seem possible. A macro scale analogy would be something like shooting a bullet from a gun without requiring any energy from the gun. It would be the target that supplies the energy. All I can say is the guy had better be very sure that he is not using transverse EM waves without realizing it. His controls better be very reliable because that is quite an extraordinary claim.

*Orbital* angular momentum (3, Insightful)

Urban Garlic (447282) | more than 2 years ago | (#39220049)

I RT first part of the FA (no, not actually new here...), and an important point is that the paper is talking about *orbital* angular momentum of the light beam. The circular polarization states correspond to *spin* angular momentum of the photons, orbital angular momentum is a different thing with its own phase space.

Infinite channels still seems unlikely, it has to be true that detectors for orbitally-tuned light beams won't be perfect, and will detect "nearby" orbitally-tuned beams as well, and it's likely that some parts of the space of orbital angular momentum will be more difficult to generate than others, so I remain skeptical of the claim.

But, the mechanism is not a trivial one. I note with some surprise that TFS actually correctly notes that it's orbital angular momentum they're talking about.

Re:*Orbital* angular momentum (1)

mprinkey (1434) | more than 2 years ago | (#39221111)

I think the key take-away is that there is another physical signal dimension to exploit--frequency, directionality, polarization, and now orbital angular momentum. They have demonstrated that they can distinguish between two channels on the same frequency using orbital angular momentum as the differentiator. So, OAM mode can be added to the tool kit. If they can distinguish among a few dozen modes and still allow beam forming, this could provide a huge benefit for cellular and other wireless networks. If they can distinguish among hundreds or thousands of modes, it could be truly transformative. It has been a long time since my EM class, but I wonder if similar mode discrimination could be applied to waveguides.

A solid answer to why SETI hears nothing (1)

ShooterNeo (555040) | more than 2 years ago | (#39220201)

Each and every advance in RF technology, the final signal becomes more and more chaotic. The entropy rises and rises as we cram more and more data into the available frequencies.

Also, the broadcasts have to become more directional and they use less energy.

Anyways, it's pretty easy to extrapolate on this trend. What will the RF emissions from earth look like in 1000 years, when we've developed radio technology to the physical limits? I suspect that those signals will be completely indistinguishable from noise from the reference of an observer located at another star.

Re:A solid answer to why SETI hears nothing (1)

felipekk (1007591) | more than 2 years ago | (#39220301)

But 1000 years from now, observers in a planet 1000 light-years away will be receiving our current transmissions, in their very "old and inefficient" modulations.

Health Concerns (0)

fluffythedestroyer (2586259) | more than 2 years ago | (#39220279)

This wikipedia page about Wireless electronic devices and health [] states that EMF are influencing the environment (but not people). But with this twist, I wonder if it will have any additional effect...or any effect. I personnaly feel concern on this subject. I try to limit my use on emf devices around me; to my knowledge of course.

NOTHING NEW - PROVEN (3, Informative)

OveE (2587057) | more than 2 years ago | (#39220409)

The claims made by Thidé et al. about finding an entirely new mechanism that can improve wireless communication, as reported by BBC in "'Twisted' waves could boost capacity of wi-fi and TV" (, have been proven incorrect in the following peer reviewed journal paper: "O. Edfors, A. J. Johansson: Is orbital angular momentum (OAM) based radio communication an unexploited area? IEEE Transactions on Antennas and Propagation, Vol. 60, No. 2, pp. 1126-1131, 2012." Existing and well known techniques produce the same 'twisted' radio waves. These 'twisted' waves bring nothing conceptually new in the area of wireless communications and cannot boost capacity further. The claims have been appearing repeatedly in media over the last few years, while consensus among experts in the area of wireless communications is that they are incorrect.


Anonymous Coward | more than 2 years ago | (#39220469)

The manuscript version of the paper mentioned above can be downloaded here:

Spectrum not overcrowded, mismanged (4, Interesting)

colsandurz45 (1314477) | more than 2 years ago | (#39220421)

I did my MS thesis on wideband spectrum sensing (just about everything under 2.2 GHz). Turns out the spectrum isn't actually overcrowded, it's underutilized, especially over 500 MHz. Look at some papers by the Shared Spectrum Company This is common misperception and it's the result of FCC policies (that they're working on changing). The underlying problem is that institutions that have spectrum allocated for them now actually need it, just not most of time.

A Fire Upon the Deep - Vernor Vinge (2)

Guppy (12314) | more than 2 years ago | (#39220513)

"...There are simple tricks that are almost never noticed till a very high technology is attained. For instance, quantum torsion antennas can be built from silver and cobalt steel arrays, if the geometry is correct. Unfortunately, finding the proper geometry involves lots of theory and the ability to solve some large partial differential equations. There are many Slow Zoners who never discover the principle."

What about use on fiber and coax? (1)

Eravnrekaree (467752) | more than 2 years ago | (#39220757)

Sounds like this might be useful for coaxial or fiber optic cable as well, perhaps vastly increasing the capacity of that? It might be able to be put to use in a much more quick way on that medium. Then you dont have to worry about the electromagnetic waves breaking strands of DNA in your body since its confined to the cable, given the very well justified concerns that EMF waves from cell phones could damage the body, which is an entirely reasonable concern since DNA in the body is actually rather delicate and is held together by EMF fields, which can be disrupted by an external EMF source.

Infinite bandwidth fiber optic connections would be a nice breakthrough. And it would end all of this ISP throttling nonsense.

This may work for a dish... (0)

Anonymous Coward | more than 2 years ago | (#39220909)

...but tv's and radios aka 'pop' aren't directional. Propagating a wave function in such a way would 'still' fall foul of superposition at some point in its 'orbit' unless the stream is highly directional from source to destination, as in TFA. I can foresee that not knowing the GPS of the source, and pointing directly at it, will render the destination fairly useless.

Re:This may work for a dish... (0)

Anonymous Coward | more than 2 years ago | (#39221089)

Correction: even 'if' the stream is highly directional...

Re:This may work for a dish... (0)

Anonymous Coward | more than 2 years ago | (#39221661)

correlating this effect will require serious amounts of discrimination and still a garble load of SNR.

The same as MIMO (3, Informative)

Jott42 (702470) | more than 2 years ago | (#39221103)

This is actually a subset of MIMO, which is already widely used in WiFi and other wireless networks. Thus it will, regrettably, not give access to any additional bandwidth. The details on the equivalence is in a paper from IEEE Transactions on Antennas and Propagation, titled "Is orbital angular momentum (OAM) based radio communication an unexploited area?" []

Re:The same as MIMO (2)

goodmanj (234846) | more than 2 years ago | (#39221717)

Yes. It's easy to get lost in the weeds when talking about rotational systems, especially when light is involved. Here's an analogue for what I think is going on:

Suppose I had a rectangular grid of directional transmitting antennas, and a rectangular grid of directional receivers. If I point one antenna array at the other, I can send data between each pair. With enough antennas and receivers, I can send arbitrarily large amounts of data using a fixed bandwidth. But there are problems: if I don't have really good directional antennas (which must be large), signals from one Tx-Rx pair will bleed onto nearby channels. If I mis-align the antennas, or have stray reflections, same problem. And eventually, I can't afford that many antennas.

This "twisted wave" thing is exactly the same concept, wrapped round in a spiral. It too will require large, expensive antennas with many components to distinguish each beam pattern. It too will have potential crosstalk problems if the antennas aren't large enough. It too will have to deal with crosstalk when the antennas are misaligned, or signals are reflected en route.

A lay perspective (2)

MajroMax (112652) | more than 2 years ago | (#39221343)

I am a scientist, but not an E&M specialist. Take this with a grain of salt.

I've read through the New Journal of Physics article. The ``radio vorticity'' means that the phase of the signal goes through a 180 flip across the beam centre, and the zero-point of this phase shift rotates as you move along the beam. The receiving antennas in the experiment were a pair of yagis, used to create a radio interferometer. The math and experimental results behind this appaer sound, but there are a few limitations:

  • This is a highly directional effect. Not only would multipath interference destroy the crap out of this signal, but they also needed pairs of antennas on opposite sides of the beam centre to discriminate between mode-0 and mode-1 rotations. Directionally-wide beams will have more interference, and building the interferometer will be more difficult with less than a 180 separation.
  • The transmitting antenna was very specialized. The transmitter itself not so much, but the antenna was a parabolic antenna ``mechanically modified'' -- they sliced through the top of it to turn the atenna into one loop of a parabolic spiral. If you have access to the article online, take a look at the picture, it's kind of neat.
  • ``In principle an infinite number of channels'' my ass. They're building an interferometer, so they need at least one antenna per mode they wish to discriminate between, and when they used antenna-separation to do the phase filtering for them they saw some significant interference form secondary lobes for intervals where the match wasn't perfect. This was okay for the two-channel experiment (mode 0 and 1), but the receiving antenna design would really start messing with higher channels, where those secondary lobes start seriously interfering themselves.
  • As written, the receiving antenna design is highly sensitive. The phase cancellation used required some pretty precise antenna positioning, since they needed a displacement of one half-wavelength in the beam direction for proper interference (to discriminate the mode 1 angular momentum). Trying this in a production environment is going to be pretty tricky -- perhaps they could get somewhere with electronic phase delay.

So for controlled channels -- perhaps even microwave links -- I'm optimistic about engineers being able to build something useful out of this. But the basic math isn't going to generalize to omnidirectional links, and it certainly isn't going to deal well with strong multipath interference. Simply being able to discriminate between modes requires straddling the beam centre, so this absolutely isn't going to work for general consumption.

Also, I don't think that practical antenna design will ever allow more than three or four channels of angular momentum outside of a lab setting. Even that may potentially be a huge win for fixed microwave links, though.

Oh Crap (0)

Anonymous Coward | more than 2 years ago | (#39221575)

A lay perspective, but, I am a scientist.

I'm a hairy butt monkey's uncle.

Not new (1)

Anonymous Coward | more than 2 years ago | (#39221397)

The reference paper wishes that it was describing a fundamentally newmultiplexing technique. However, it is not. They are instead using the well-known technique of antenna cancellation to exploit spatial diversity to create additional orthogonal channels. This is fine, but it requires that your antenna be larger than a quarter wavelength (so that it can have nulls) and in fact much larger still so that the nulls in your radiation pattern do not steer all of your transmitted power 90 degrees away from your receiver. This is why their antenna is 80 cm in diameter at the 2.4 GHz WiFi band. The large antenna is basically a phased array.

There is nothing "quantum" about what they have done, only classical wave optics.

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