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Communications Science

Twisted Radio Beams Could Untangle the Airwaves 183

Posted by ScuttleMonkey from the only-the-flying-spaghetti-monster-would-know-for-sure dept.
Urchin writes "The radio frequency spectrum available for wireless communication is becoming increasingly crowded thanks to new wireless technology. A solution to the shrinking space might be to put a spin on radio beams during their transmission, to produce a twisted beam, according to Swedish physicists. In theory, huge amounts of data could be sent in the pitch of the twist, which is distinct from the amplitude and frequency of radio waves — the features used at the moment to send information."
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Twisted Radio Beams Could Untangle the Airwaves More

Twisted Radio Beams Could Untangle the Airwaves

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  • damn (Score:5, Funny)

    by geekoid ( 135745 ) <{moc.oohay} {ta} {dnaltropnidad}> on Friday February 13, 2009 @05:04PM (#26850071) Homepage Journal

    Damn, this is so obvious now. I should have thought this up years ago.

    • Re:damn (Score:5, Interesting)

      by Anonymous Coward on Friday February 13, 2009 @05:10PM (#26850173)

      Am I missing something?

      These guys are proposing polarizing wireless transmissions. Polarization gets affected by ALL kinds of boundary irregularities, such as nearby cars light poles, traffic signal loops and, in buildings, conducting objects like nails, hinges, pipes, etc.

      This seems so noisy as to be useless.

      • Re:damn (Score:5, Informative)

        by Anonymous Coward on Friday February 13, 2009 @05:19PM (#26850267)

        The article suggests the technique only works really for point-to-point transmission. Regular amplitude/phase modulation (QAM) is still the best generally I'd imagine.

      • It's not about polarization (Score:5, Informative)

        by Doug Merritt ( 3550 ) <doug@noSPaM.remarque.org> on Friday February 13, 2009 @06:34PM (#26851011) Homepage Journal

        Am I missing something? These guys are proposing polarizing wireless transmissions.

        Yes, you are, and no, they aren't.

        This is about modulating the orbital angular momentum of photons, a property that wasn't even discovered until 1992.

        Each photon can have an integer quantity of orbital angular momentum (0, 1, 2, 3...) without obvious limit (or in the opposite direction, -1, -2, -3...). In principle, and increasingly in experiment, it is possible to encode information by modulating the orbital angular momentum carried. This provides and entirely separate channel with its own bandwidth in addition to traditionally understood modulation. They're right to be excited about it; it has the potential of being just as big in scope as was the invention of radio.

        See http://www.physics.gla.ac.uk/Optics/play/photonOAM/ [gla.ac.uk]

        • Re: (Score:2)

          by kmac06 ( 608921 )
          Mod parent up. This is about orbital angular momentum, not spin, or what you would typically think of as polarization.

        • Re:It's not about polarization (Score:4, Interesting)

          by johncadengo ( 940343 ) on Friday February 13, 2009 @08:00PM (#26851905) Homepage

          This provides and entirely separate channel with its own bandwidth in addition to traditionally understood modulation. They're right to be excited about it; it has the potential of being just as big in scope as was the invention of radio.

          Isn't one of the hugest factors in the Fermi Paradox [wikipedia.org] the "Great Silence" aka that if life in the universe is so abundant why don't we hear their radio transmissions?

          Now, how many other "channels" out there do you think exist that we simply have no grasp or knowledge of?

          Does this open up a new potential medium for listening [seti.org]?

          • That's not a wise civilisation which broadcasts messages to the universe using a very advanced technology. I hope that if one day we were to set up a permanent beacon marking our presence we would use only the most basic transmission method, to aim for the highest audience.

            If a civilisation only wanted to 'contact' other similarly advanced worlds then I suppose it could still hold true. But I like to think that every sentient being out there is just as curious and fascinated about the possibility as we ar

          • Re: (Score:2)

            by SEE ( 7681 )

            Isn't one of the hugest factors in the Fermi Paradox the "Great Silence" aka that if life in the universe is so abundant why don't we hear their radio transmissions?

            Well, you know, except that the actual Fermi Paradox is about why we haven't seen their spaceships or probes. It's Hart's variant that asks about radio transmissions. Even after you explain away Hart, Fermi's is still there.

          • Isn't one of the hugest factors in the Fermi Paradox [wikipedia.org] the "Great Silence" aka that if life in the universe is so abundant why don't we hear their radio transmissions?

            You'd be surprised how little RF escapes from our planet. Low frequencies are used because they bounce off the ionosphere, high frequencies because they can be focused into fairly narrow beams to hit specific targets (like satellites). Also, you don't have to go very far before your signal fades below the noise floor.

            • Re: (Score:2)

              by NateTech ( 50881 )

              More people should read up on the distance-squared rule and learn that double the power on RF is only 3dB of gain... then go re-read how far away and how little power the deep space probes used (albeit with relatively high-gain antennas pointed directly at Earth) and how the Deep Space Network works.

              When you start having to change the local environment and do cryogenic cooling of your entire receiving antenna system so you can raise the S/N ratio by lowering molecular noise in the receiver itself, because

        • Thanks for the heads up, I was about to dismiss this as fluff. Instead it is something 10-20+ years off, but much more interesting.

        • I don't actually believe that photons can have angular momentum. photons carry +/-1 angular momentum. You can't excite an atom to a j+2 state with a single photon.

          light fields can induce a torque on macroscopic object but this is through the accumulation of single photon absorptions delivering then J+1 angular momentum.

          As near as I can tell all instances of so-called orbital angular momentum are just structured light fields. this one is no exception.

          You can deliver info via the structured light field but

      • These guys are proposing polarizing wireless transmissions. Polarization gets affected by ALL kinds of boundary irregularities, such as nearby cars light poles, traffic signal loops and, in buildings, conducting objects like nails, hinges, pipes, etc.

        Good point, but I'm thinking that if the environment (and its influence on the polarisation) change slowly compared to the speed with which the transmitter modulate the polarisation, it might work anyway. What do you say?

      • Re:damn (Score:4, Informative)

        by johanwanderer ( 1078391 ) on Friday February 13, 2009 @06:54PM (#26851277)
        This is slightly different than simple polarization, see here: http://www.newscientist.com/article/mg18224515.000 [newscientist.com] -- full article requires log-in. Or here: http://www.physics.gla.ac.uk/Optics/play/photonOAM/ [gla.ac.uk] The point here is that a "pulse" can now encode more than just an "on/off" state. Instead, a pulse now encodes a "twistiness" level of states (can be 1, 2, 3, or up to 250 as in the NS article.) So, a 2GHz signal can now carries, let's say, 2x8 = 16 Gb/s. The trouble, it seems, is to construct a receiver capable of correctly identifying the pulses.

      • Re: (Score:3, Interesting)

        by mikael ( 484 )

        Yes, you did miss something. The authors are not talking about the planar or circular polarization of individual photons. They are describing how it is possible to combine photons together such that a light beam itself has orbital angular momentum. When such a beam of light hits a small particle, the combined arrival of the photons forces the particle to start rotating. The smallest light beam need only consist of two entangled photons.

        Maybe they will figure out how to combine several such light beams toget

      • Re: (Score:3, Funny)

        by Ihmhi ( 1206036 )

        Wait, so... basically, some Trekkie scientist in Sweden said "Hey, what if we messed with the polarity?" and it actually worked?

        • It aint trekkie unless it's CleverNickname insisting they have to reverse the polarity of the main deflector dish ;)

          Well, it's not to some of us, I guess.

    • Re: (Score:2)

      by blueZ3 ( 744446 )

      Shampoo invented this idea a long time ago

  • Oh, Great (Score:2, Funny)

    by Banichi ( 1255242 )

    Now we have "Spinnaz" for telecommunication geeks.

    • Re: (Score:3, Funny)

      by fbjon ( 692006 )
      Only problem is, packets received through a twisted link come with the evil bit set.

  • Two questions (Score:5, Interesting)

    by jandrese ( 485 ) <kensama@vt.edu> on Friday February 13, 2009 @05:10PM (#26850169) Homepage Journal
    1. How practical is this technology? Could you mass produce cheap low power receivers to put in every car/computer/etc...? How complex is the transmit circuitry?
    2. How resistant is this to atmospheric and other interference? In theory it should be pretty resistant, but in practice who knows.

    Needing multiple antennas to get this done sounds like a rather big limitation to me.

    • Re: (Score:3, Insightful)

      by PotatoFarmer ( 1250696 )
      3. Is there any way to extract this information from transmissions we've recorded in the past? Would be interesting if turns out that SETI has been pulling down alien sitcoms for years without knowing it.

      • Re: (Score:3, Interesting)

        by lobiusmoop ( 305328 )

        Interesting implications for other fringe-science fields, such as ESP and the paranormal. What kind of information has been being transmitted/received through the ether that we've never previously had the knowledge/tech to receive and interpret?

        • Re: (Score:2, Insightful)

          by Dekker3D ( 989692 )

          if you look at it like that, we'll never be able to disprove the paranormal since we'll never be able to claim that we've found all possible ways to receive and interpret data. it's one of the reasons why i think it's silly to even try disproving such things.

          • Re: (Score:2)

            by dodobh ( 65811 )

            You can't disprove the paranormal. You can merely point out that there is no evidence for it with our current knowledge.

            It is for those who claim the paranormal exists to come up with suitable experimental proof. Extraordinary claims need extraordinary evidence.

    • Re: (Score:2, Informative)

      by badboy_tw2002 ( 524611 )

      1. Its completely practical considering the first ever case of these types of waves ever being sent was just published and the first ever example was done on a 48 antenna space array, not to mention they don't have a receiver. Given that most technology moves immediately from research to mass production in the space of a week, I'd say $20-30.

      2. Again, seeing as the first ever examples of this were just transmitted with no receiver there's been a lot of time for field study. Or are you saying you're one of

      • Re: (Score:2)

        by hurfy ( 735314 )

        The no receiver part was interesting. Can we assume you need something similar to the sending array to receive? My car is going look funny if i add 47 more antennas, especially if i have to complete a particular design :)

        In other news...

        I have successfully sent a psychic beam transmission...noone can receive it and i haven't made a translator yet, so even if you do, you won't understand it...don't sweat the details....trust me...

        • Re: (Score:2, Funny)

          by __aasqbs9791 ( 1402899 )

          Then who sent me the message to, "Kill the family"? Or was that, "Bill loves Emily"? Reception isn't too good some days.

          • Maybe it was BOTH "Kill the family" and "Bill loves Emily" - and the message's quantum supposition function collapsed under observation to actually be "Bill is Emily" (and Bill's cat, being so hurt at her owner being exposed publicly as a freak, went into a box and fired the gun)

  • Obligatory (Score:4, Funny)

    by Bovius ( 1243040 ) on Friday February 13, 2009 @05:10PM (#26850175)

    Do a barrel roll!

    Sorry, couldn't resist.

  • As Dr. Egon Spengler once said (Score:4, Funny)

    by auric_dude ( 610172 ) on Friday February 13, 2009 @05:15PM (#26850235)
    Don't cross the streams.

  • No (Score:3, Informative)

    by rcw-home ( 122017 ) on Friday February 13, 2009 @05:22PM (#26850295)
    The article appears to be referring to right or left circular polarization [wikipedia.org], as opposed to horizontal or vertical polarization. A horizontally-oriented dipole transmitting near a vertically-oriented dipole will be heard much more faintly - 20db+ quieter [air-stream.org.au]. Similarly, a left-polarized antenna won't interfere with a right-polarized antenna. But a circularly-polarized antenna will still interfere with a horizontally or vertically polarized antenna - it'll only be 3db weaker [nitehawk.com].

    • Re:No (Score:5, Informative)

      by Doug Merritt ( 3550 ) <doug@noSPaM.remarque.org> on Friday February 13, 2009 @06:40PM (#26851123) Homepage Journal
      Nope, this absolutely is not about polarization.

      This is about modulating the orbital angular momentum of photons, a property that wasn't even discovered until 1992.

      Each photon can have an integer quantity of orbital angular momentum (0, 1, 2, 3...) without obvious limit (or in the opposite direction, -1, -2, -3...). In principle, and increasingly in experiment, it is possible to encode information by modulating the orbital angular momentum carried. This provides and entirely separate channel with its own bandwidth in addition to traditionally understood modulation. They're right to be excited about it; it has the potential of being just as big in scope as was the invention of radio.

      See http://www.physics.gla.ac.uk/Optics/play/photonOAM/ [gla.ac.uk]

      • Thanks. That link is much clearer than the original article, and describes a (relatively) simple experiment to reproduce the results.

        Now go update the Wikipedia article on photons [wikipedia.org]: "A photon [...] is described by exactly three continuous parameters: the components of its wave vector, which determine its wavelength Î and its direction of propagation."

    • Re: (Score:2, Funny)

      by Mr. Conrad ( 1461097 )
      I read a while back that both Fox and MSNBC were interested in polarization. Only Fox wanted to twist their signals to the right while MSNBC seemed more interested in twisting theirs to the left.

  • does satellite internet already do this? (Score:3, Interesting)

    by steak ( 145650 ) on Friday February 13, 2009 @05:26PM (#26850339) Homepage Journal

    I install wildblue satellite internet and we have two type of transceivers right hand and left hand polarization. after rtfa I am curious if this is the same thing or something different?

    • Re: (Score:3, Interesting)

      by scerruti ( 1233214 )
      I don't know about wildblue, but when I was working with satellite about 10 years ago DirecTV was circularly polarized DirecPC was not.

  • FM is polarized as it is for a reason (Score:3, Informative)

    by Anonymous Coward on Friday February 13, 2009 @05:33PM (#26850419)

    There is a reason that FM is polarized in the direction it is: any other direction is relative.

    FM is vertically polarized because that means that a car needs only have a vertical antenna to catch the signal, if they polarize it horizontally then the antenna on the car needs to rotate every time the car turns.

    At least this is what I was told in my RF/microwave design class.

  • Twisted Radio Waves (Score:3, Informative)

    by komische_amerikaner ( 1365847 ) on Friday February 13, 2009 @05:36PM (#26850443)

    AFAIK (yes, I did RTFA), this is tantamount to adding another method of data transmission using more of the envelope. You still have the frequency being used and still have a portion of the carrier plus sideband transmitted, no matter what type or method of transmission is used. This may be used to embed something similar to a sub-carrier, or a unique identifier. More directivity and narrower beamwidth during point-to-point transmissions will do wonders to keep the RF floor down.

  • Not New, Not News (Score:2, Informative)

    by DynaSoar ( 714234 )

    The "In Soviet Russia" joke has already been inserted, so I'll go on to the next step:

    The technique described is independent of amplitude and frequency in that it is based on polarization. Circular (clockwise and counter clockwise) polarization was used in Soviet and early post-CCCP Russian satellite communications. I had an article from ~25 years ago that showed how to alter a US type vertical/horizontal polarization low noise amplifier on a satellite receiving dish to pick up clock/counter signals. (The t

  • Is spinning radio waves anything like spinning bullets [xkcd.com]? Because that would be totally awesome.

  • Polarization has been known since about 1200AD when the Vikings used calcite crystals to navigate by. It also pops right out of Maxwell's equations.

    It's been used to make directional radio antennas since about 1925.

    It's been used to dynamically steer and polarize signals ever since phased-array radars came in use, circa 1965.

    And no, you can't transmit huge amounts of information that way. Circular polarization is just a vector sum of two quadrature vectors. There's nothing you can do with a sum that is m

    • NOT 140 years late (Score:4, Insightful)

      by Doug Merritt ( 3550 ) <doug@noSPaM.remarque.org> on Friday February 13, 2009 @06:48PM (#26851217) Homepage Journal
      Nope, that's not what they're doing; it's not polarization. They're using physics that wasn't even discovered until 1992.

      See http://www.physics.gla.ac.uk/Optics/play/photonOAM/ [gla.ac.uk]

      • As far as I can tell, they're phase-modulating the polarization. Very clever but not new on the transmitting end. If their fancy interferometer phase-sensitive receiver can be made to work well they may have something, but I think in the end Shannon's limits still apply.

        Signal theory has been extremely extensively studied, so it's unlikely someone not familiar with the field, like these optics guys, have found a loophole.

        • Re:NOT 140 years late (Score:4, Informative)

          by Doug Merritt ( 3550 ) <doug@noSPaM.remarque.org> on Friday February 13, 2009 @08:11PM (#26851987) Homepage Journal
          As far as you can tell? Why don't you just go look at the link I provided?

          It won't take but a second for you to stop guessing that it's about polarization once you see their clear explanation that it's different.

          • I looked at it. It looks like they're using an interferometer to gauge degrees of polarization.
            It's a little hard to follow, as they're trying to describe signals in optic-speak, which does not jibe too well. Nothing all that special, and they do note a major drawback-- due to the quantum nature of polarization, you don't get a definitive answer, just a probabilistic one. That shows up as random noise out of the detector, and there's where Shannon steps in.

            • "I looked at it. It looks like they're using an interferometer to gauge degrees of polarization."

              Well, you're contradicting them. Look at the left side of the page; there's an animation of polarized light.

              Look at the right side of the page; there's an animation of light with orbital angular momentum.

              Look at the text in between the right and the left, explaining how polarization is different than OAM, and that what they are doing is the latter, not the former.

              Now pretend they're lying, is that your pl

    • Re: (Score:2)

      by geekoid ( 135745 )

      If only this was polarization. SO the question is:
      Did you not RTFM, or were to just too stupid to UTFA

      *Understand.

  • Perhaps it's just the journalists messing this up, but the article suggests that these guys think that only amplitude and frequency are used in digital communication. However, every modern digital communication standard uses the phase as well, which is equivalent to a twist.

    Wikipedia has a reasonably easy-to-follow explanation [wikipedia.org] of how this works.

    • This NOT already done (Score:5, Informative)

      by Doug Merritt ( 3550 ) <doug@noSPaM.remarque.org> on Friday February 13, 2009 @06:49PM (#26851237) Homepage Journal
      Nope, that's not what they're doing; this particular "twist" is absolutely not identical to previously well-understood phase modulation.

      They're using physics that wasn't even discovered until 1992.

      See http://www.physics.gla.ac.uk/Optics/play/photonOAM/ [gla.ac.uk]

      • I think it's hilarious you finally got modded "Funny" for this, but really, thank you for swooping in and correcting everybody. With something new and interesting like this, the slashdot standard of not RTFA combined with the slashdot standard of jumping to conclusions and spouting off incorrect information as fact really does a disservice to everyone. So, thanks for trying to set everyone straight :)

        • Thanks. :-)

          Usually I and others will just make a correction once, and shrug off repetition of nonsense (although I must admit a lot of it was unusually erudite nonsense), but I got peeved this time.

          It's been a pet topic, ever since I heard a little tidbit about it years ago I've been waiting for the other shoe to drop, and it finally did (a bit, anyway), but what I thought was some of the coolest news of the century was swamped by noise. Argh!

  • This is not about technology. With new encoding schemes and whatnot, there is enough space to accomodate most uses. The problem is one of economics. First, entrenched infrastructure. It costs money to upgrade, as this whole "digital TV" transition proves (arguments about corruption aside). Also, in this country at least airwaves are sold off to the highest bidder, not necessarily the "Best interest" use of that spectrum. So we have technology from the 1940s working side-by-side with stuff that became out of

    • Re: (Score:2)

      by geekoid ( 135745 )

      heh, only for a few more years, then the airwaves will start to clear up as piping you entertainment from the internet to the 'TV' becomes mainstream.

  • Orbital Angular Momentum versus Polarization (Score:4, Informative)

    by TheSync ( 5291 ) on Friday February 13, 2009 @09:08PM (#26852397) Journal

    This article [aip.org] has a good explanation of the difference between Orbital Angular Momentum and Polarization of EM waves.

    If you look at the cross section of a "normal" polarized EM beam, the electric field amplitude and direction at every point of the cross section are in the same phase - although that direction may be up, down, or rotate over time depending on the polarization.

    In an EM beam with orbital angular momentum, the electric field amplitude at different points on the cross section are in different phases - although it is my understanding they are usually all in the same polarization.

  • The problem with a circularly polarized signal is that it is not orthogonal to any linearly polarized one. In other words, while two linearly cross-polarized signals won't interfere with one another, any linearly polarized signal will interfere with all circularly polarized ones. So, this technique won't help to avoid interference on the airwaves.

  • Yes, but can it get us to alternate universes [washington.edu]?

    (For the humorless, the novel "Twistor" describes an effect sort of like this and is a damned good "hard" science fiction book.)

  • From Vernor Vinge's "Fire Upon the Deep":

    "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 principles."

    Don't suppose anyone else thought of this passage, which takes place when Pham's team is trying to jump-start the low-tech Tine civilization?

  • The concept of phase modes has been known for quite a while.
    In the mid-thirties, Henri Chireix published [1] and patented [2] the application of phase
    modes in antenna arrays. Since then, the concept has been widely used in
    connection with circular arrays (e.g. [3]), multi-arm spiral antennas (e.g. [4]), radio
    navigation systems (e.g. [5]), etc. The literature within the area is substantial, with
    many papers published in various journals and conference proceedings.

    Prior art search is an extinct art, indeed...

    [1

    • "Prior art search is an extinct art, indeed"

      Apparently, so is the art of RTFA. And reading even the other comments.

  • I find this concept really interesting and confusing at the same time. Consider that within plasma laboratories, we can observe certain fundamental morphologies that naturally result from the existence of charge density. Plasmas naturally form double layers, which tend to protect a plasma's charge. The double layer leads to the formation of plasma filaments. We see within the laboratory that plasma filaments tend to exhibit long-range attraction and short-range repulsion with one another. This causes t

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