Twisted Radio Beams Could Untangle the Airwaves 183
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."
Two questions (Score:5, Interesting)
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:damn (Score:5, Interesting)
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.
in this house we obey shannon's theorem (Score:1, Interesting)
It's not obvious to me what all the excitement is about.
"Huge" amounts of data as compared to what exactly ?
Whatever they are doing, it can't get past Shannon's theorem as a limit on the amount of information available for a given bandwidth.
This looks to me like it probably simply reduces to MIMO :
http://en.wikipedia.org/wiki/Multiple-input_multiple-output [wikipedia.org]
Either way the capacity is limited to N * the capacity for one antenna (remember Shannon's law applies per channel).
So back to, what does this do exactly ?
does satellite internet already do this? (Score:3, Interesting)
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:does satellite internet already do this? (Score:3, Interesting)
only 140 years late (Score:2, Interesting)
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 more information efficient than a single vector.
FM is circularly polarized, not vertically! (Score:4, Interesting)
Actually, broadcast FM is nearly always circularly polarized using a multi-bay antenna with a bunch of 3/4 circle center-fed elements, each with one end pointing up and the other down.
If you weren't aware of this, go look atop an FM tower with binoculars some day.
Good luck finding the published theory on these antennas, since they're all proprietary designs!
Re:Two questions (Score:3, Interesting)
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:It's not about polarization (Score:4, Interesting)
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]?
Re:damn (Score:3, Interesting)
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 together such that it is possible to push and pull particles towards and away from the light source as well as translate them sideways and make them rotate.