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?
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.
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.
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.
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.
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.
> 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.
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.
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.
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?
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.
I can see this being a great improvement in capacity, but wouldn't data from other 'vortices' leak data into the one you're listening to? Any integer multiple would add noise to every bit sent to station X, and lots and lots where isolated bits from other channels leak in (what would that be, divisible by the station's period?).
It 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.
jpablo -- the seasons are produced by the tilt of the earth axis because the earth rotates around the sun. (The earth's axis always points in the same direction relative to the distant stars, so the planet's tilt changes relative to the sun as the planet orbits it.)
Those two statements do not conflict. Seasons are the result of the Earth orbiting around the sun, just not the way most people think. Most people would say it's because we're getting closer or further from the sun, which is incorrect. What's really happening is that as we orbit around the sun the Earth's inclination (difference between our axis of rotation and our orbital plane) causes either the northern or southern hemisphere to face the sun more and thus get more sunlight. Thus, seasons are the result of both axial tilt and rotation around the sun.
The next time you feel the urge to pour disdain on an article because of a supposedly-incorrect statement, I suggest two things. First, make sure it's actually incorrect. Second, beware of http://rationalwiki.org/wiki/Skitts_Law especially wrt to typos.
[+] [-] femto|14 years ago|reply
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?
[+] [-] SiVal|14 years ago|reply
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.
[+] [-] jpdoctor|14 years ago|reply
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.
[+] [-] dvdkhlng|14 years ago|reply
[+] [-] Gravityloss|14 years ago|reply
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.
[+] [-] DanielBMarkham|14 years ago|reply
[+] [-] bh42222|14 years ago|reply
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/
[+] [-] ars|14 years ago|reply
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.
[+] [-] aquarin|14 years ago|reply
[+] [-] duaneb|14 years ago|reply
[+] [-] 4rgento|14 years ago|reply
I hope this helps.
[+] [-] JunkDNA|14 years ago|reply
[+] [-] Stwerp|14 years ago|reply
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.
[+] [-] joezydeco|14 years ago|reply
[+] [-] JoeAltmaier|14 years ago|reply
[+] [-] kruhft|14 years ago|reply
[+] [-] Groxx|14 years ago|reply
edit: thanks!
[+] [-] ec429|14 years ago|reply
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.
[+] [-] jcarreiro|14 years ago|reply
[+] [-] jcarreiro|14 years ago|reply
[+] [-] Gravityloss|14 years ago|reply
[+] [-] Gravityloss|14 years ago|reply
[deleted]
[+] [-] Groxx|14 years ago|reply
[+] [-] it|14 years ago|reply
http://en.wikipedia.org/wiki/Branch_point#Branch_cuts
[+] [-] ars|14 years ago|reply
[+] [-] mnl|14 years ago|reply
[+] [-] jakeonthemove|14 years ago|reply
[+] [-] ck2|14 years ago|reply
How is that possible if they move at the speed of light for any observer?
[+] [-] sp332|14 years ago|reply
[+] [-] henryaym|14 years ago|reply
[+] [-] dosenwurst|14 years ago|reply
http://en.wikipedia.org/wiki/Polarization_%28waves%29
[+] [-] ars|14 years ago|reply
This is apparently something new, not sure what though - it's not something I ever learned about with photons.
[+] [-] philwise|14 years ago|reply
http://www.qsl.net/dk7zb/Cross-Yagi/crossyagi.htm
[+] [-] donnawarellp|14 years ago|reply
[deleted]
[+] [-] Porter_423|14 years ago|reply
[+] [-] ktizo|14 years ago|reply
http://www.gla.ac.uk/schools/physics/research/groups/optics/...
[+] [-] unknown|14 years ago|reply
[deleted]
[+] [-] cs702|14 years ago|reply
The article is correct.
[+] [-] CPlatypus|14 years ago|reply
The next time you feel the urge to pour disdain on an article because of a supposedly-incorrect statement, I suggest two things. First, make sure it's actually incorrect. Second, beware of http://rationalwiki.org/wiki/Skitts_Law especially wrt to typos.