Pasta-shaped radio waves beamed across Venice

Mar 02, 2012

A group of Italian and Swedish researchers appears to have solved the problem of radio congestion by cleverly twisting radio waves into the shape of fusilli pasta, allowing a potentially infinite number of channels to be broadcast and received.

Furthermore, the researchers have demonstrated this in real-life conditions by beaming two twisted across the waters of Venice.

Their results have been reported today, Friday 2 March, in the Institute of Physics and German Physical Society's and are accompanied by a video abstract that gives an excellent insight into the authors' work.

As the world continues to adapt in the digital age, the introduction of new mobile smartphones, wireless internet and digital TVs means the number of radio frequency bands available to broadcast information gets smaller and smaller.

"You just have to try sending a text message at midnight on New Year's Eve to realise how congested the bands are," said lead author Dr Fabrizio Tamburini. The researchers, from the University of Padova, Italy, and the Angstrom Laboratory, Sweden, devised a solution to this by manipulating waves so that they can hold more than one channel of information.

A wave can twist about its axis a certain number of times in either a clockwise or anti-clockwise direction, meaning there are several configurations that it can adopt.

"In a three-dimensional perspective, this phase twist looks like a fusillli-pasta-shaped beam. Each of these twisted beams can be independently generated, propagated and detected even in the very same frequency band, behaving as independent communication channels," Tamburini continued.

To demonstrate this, the researchers transmitted two twisted radio waves, in the 2.4 GHz band, over a distance of 442 metres from a lighthouse on San Georgio Island to a satellite dish on a balcony of Palazzo Ducale on the mainland of , where it was able to pick up the two separate channels.

"Within reasonable economic boundaries, one can think about using five orbital angular momentum states, from -5 (counter-clockwise) up to 5 (clockwise), including untwisted waves. In this instance, we can have 11 channels in one frequency band.

"It is possible to use multiplexing, like in digital TV, on each of these to implement even more channels on the same states, which means one could obtain 55 channels in the same frequency band," said Tamburini.

In addition to increasing the quantity of information being passed around our planet, this new discovery could also help lend an insight into objects far out in our galaxy. Black holes, for example, are constantly rotating and as waves pass them, they are forced to twist in line with the black hole.

According to Tamburini, analysing the incoming waves from the supermassive black hole at the centre of the Milky Way, Sagittarius A, could help astronomers obtain crucial information about the rotation of this "million-solar mass monster."

Explore further: How the hummingbird achieves its aerobatic feats

More information: "Encoding many channels on the same frequency through radio vorticity: first experimental test" Tamburini F et al 2012 New J. Phys. 14 033001 - iopscience.iop.org/1367-2630/14/3/033001/article

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SteveMerrick
1.7 / 5 (6) Mar 02, 2012
What happened to electromagnetic radiation propagating in straight lines? ... Twisted radio waves. ... Is this a joke article? [Sincere question.]
kochevnik
1.4 / 5 (11) Mar 02, 2012
EM waves propagate in a helical shape, faster than the speed of light c. Only the apparent motion, linearly drawn along the helix, is apparently constrained at c unless traveling in a waveguide.

All matter travels in a helix. If you traced out the Earth it is being pulled in a helix around the sun, which in turn is traveling in a helix around the Milky Way.
Bowler_4007
1.8 / 5 (5) Mar 02, 2012
the shape of EM waves is known as a sinusoidal wave

in http://www.physic...254.html masudr says
"An EM wave is a three dimensional object since it exists in three dimensions (or 4D if we consider special relativity).

It is an electric field vector and a magnetic field vector which oscillate about 0 sinusoidally at a fixed time period. That time period determines frequency.

Photons do not spiral because that would require a force towards the center of the spiralling (all circular motion requires a force towards the centre of the circle). Basically the photon moves in a straight line (or is likely to on macroscopic systems) because there is nothing to stop it. Macroscopically, photons do not spiral, although there is a small probability that they do."
antialias_physorg
5 / 5 (13) Mar 02, 2012
What happened to electromagnetic radiation propagating in straight lines?

It still propagates in a straight line. The electric and magnetic fields (which osciallate at the frequency of the photon) are at right angles to the direction of propagation of the photon (and at right angles to each other). If the E an M components are 90 degrees out of phase you get linearly polarized photons.

But if you have the phase different from 90 degrees then you get a circular polarized wave (or even elliptical if the amplitudes are not the same)

Here's a good animated GIF of this
http://en.wikiped...on_state

What these clever guys did was filter according to the speed of the circular component.
So, with the same frequency (and amplitude) you can transmit several signals that only differ by the speed of circulation and separate them again at the target location.

Pretty neat.
Kinedryl
1 / 5 (1) Mar 02, 2012
you can transmit several signals that only differ by the speed of circulation and separate them again at the target location
Such way of modulation will indeed come with its own price, because most of existing antennae are utilizing some form of polarization already for improving signal/noise ratio (even your pocket radio doesn't play well for every orientation) and it would require to increase the strength of signal (and the level of electromagnetic smog) for the sake of transfer reliability.
antialias_physorg
5 / 5 (4) Mar 02, 2012
The point of this is for transmission between known endpoints which need to handle many channels at once (i.e. the backbones of high speed nets). For the end user QAM is still more than enough.

But I'm pretty sure one could even overcome that shortcoming by changing the antenna design. Metamaterials would be well suited for creating different exit points dependent on circulation speed. Then you'd just need to add a regular antenna to each exit point.
Wolf358
not rated yet Mar 02, 2012
Ummmmm... isn't this just left- and right-handed circular polarization? Oh, wait... i get it. Cool!
hb_
2 / 5 (4) Mar 02, 2012
What is the point? Their technology will only work with fixed end-points, and there you can use fiber-optic communication with essentialy limitless bandwidth.

Ít does nothing to help releive the real congestion that occurs when mobile units try to communicate with the base stations. Or am I missing something here?
hjbasutu
not rated yet Mar 02, 2012
I have to revise my Physics
antialias_physorg
5 / 5 (7) Mar 02, 2012
What is the point? Their technology will only work with fixed end-points, and there you can use fiber-optic communication with essentialy limitless bandwidth.

Have you seen someone put up a fibre optic cable to a sattelite? No? Me neither.

Ít does nothing to help releive the real congestion that occurs when mobile units try to communicate with the base stations.

Depending on the antenna used. If a mobile phone can use this type of modulation and the base stations can use this type of modulation between each other then the amount of information carried by the entire network can be vastly increased.
Kinedryl
1 / 5 (2) Mar 02, 2012
HAARP antenna is already utilizing the switching mode of polarization. It's a field of antennae, which work as a single one in phase, the orientation of which can be changed dynamically.
hb_
3 / 5 (2) Mar 02, 2012
@antialias_physorg
OK, the technology could be useful in space. Still, linking landlines together should enable much higher capacities. Also, point-to-point laser comunication in space also holds the promise for much larger capacites. But this is a different discussion.

As for the cell phones, I thought that you needed the correct orientation of the receiving antena with respect to the incomming wave. This would pretty much make it impossible for use in a cellphone, right?

Cellphones are used in buildings and subways, where the waves are bounces of surfaces before being recieved. Would this not also make it very impractical for use in mobile units?
ab3a
not rated yet Mar 02, 2012
This is not polarization. This is a customized spatial reflector that causes what looks like inter-symbol interference to a point source. However, with a special reflector that undoes this spatial twist, one can recover the signal, while causing point source signals to appear to have inter-symbol interference --just as you would get with any imperfect reflector.

My concern with this method is that one would need to maintain strict line of sight and that one would need to stay far away from the first Fresnel zone --or distortion of the signal would result.

Note that their first attempt was over water from high above the ground. I have doubts about how useful this trick may be, though it is an interesting trick nevertheless.
antialias_physorg
3.7 / 5 (3) Mar 02, 2012
OK, the technology could be useful in space. Still, linking landlines together should enable much higher capacities.

Landlines are oftentimes expensive.radiowaves can go a long way (and you can bonuce them off the ionosphere if you really want to)

In the financing sector (computer trading of stocks) they're already switching to direct line of sight because it gives you a timing advantage over landlines and sattelites(!)

thought that you needed the correct orientation of the receiving antena with respect to the incomming wave. This would pretty much make it impossible for use in a cellphone, right?

It would require a new antenna geometry. But actually now that I think about it this should work at any angle. What the antenna would 'see' at an oblique angle is an elliptical circulation. But the timing aspect of the circulation would still be the same. And since you're decoding only the relative modulation of the QAM signal (not absolute) it should still work.
Bruce42
not rated yet Mar 02, 2012
Why is this not just "circular polarization" that has been used since the 1960s? All known/proven technology. OK maybe some advantange to varing the "pitch", but that is usually optimised to a given frequency, so variants will be less effecient.

Google Images "circular polarized antenna" for examples.
Skultch
not rated yet Mar 02, 2012
OK, the technology could be useful in space. Still, linking landlines together should enable much higher capacities.


Also, mountains. It is prohibitively expensive to dig trenches in the mountains. They don't call them "Rocky" for nothin'. :) In many locations, the wireless backhaul solutions are more cost effective per Mbps. Simply replacing them with this new tech will be HUGE for mountain and rural areas.

In the financing sector (computer trading of stocks) they're already switching to direct line of sight because it gives you a timing advantage over landlines and sattelites(!)


Really? I guess if the landline has to go through multiple routing hops that would have better latency, but I would have thought these businesses would have some sort of multi-gigabit Metro-Ethernet connection at sub-1ms latencys in a colo facility or something. I personally know of a 2gig lines that can achieve that, and I'm pretty sure 10gig-plus lines are doable, as well.
kochevnik
1 / 5 (1) Mar 02, 2012
Macroscopically, photons do not spiral, although there is a small probability that they do."
There is no photon between measurements. Only the electric and magnetic field propagating in a helix. Straight lines are not fundamental in nature. Only in your head.
Yevgen
not rated yet Mar 02, 2012
To polarize two signals differently, we need 2 antennas and twice the transmission power.
What if we just make transmission power twice larger with 2 normal antennas? That will allow to increase the signal/noise ratio and therefore increase the bandwith according to Shennon's theorem, achieving the same result.
Considering this, it looks like we don't win anything in overall bandwidth by making the slits/twists in the antennas.
wealthychef
not rated yet Mar 02, 2012
"Within reasonable economic boundaries, one can think about using five ..." is this a translation problem? I hate to sound stupid, but are we talking about dollars and cents economics here, or something else?
Dan Quixot_eacute_
5 / 5 (2) Mar 02, 2012
(Longtime RF/Antennas guy here...) While our industry's developed and deployed a bag of tricks that has taken us up to, and occasionally over, the Shannon limit, I don't know anyone who's proposed this cute little trick. Now, all they've _demonstrated_, is separately modulated and dedecoded signals in a single physical channel, when one has static polarization and the other is circularly polarized. In itself, this isn't different than transmitting separate data streams in orthogonal polarizations along the same path (well known prior art). But let me distill for you what they *propose*: separate co-channels based on distinct polarization _rates_. Decoding would be similar to higher-order QAM in that you'd need deeper A/D converters and more SNR on your I&Q channels. And it would be similar to spinning Doppler correlation phasors we do for CDMA & GPS. It might be a wash, but there might be some benefit to be had too. Like why we do OFDM in LTE rather than super-high-order QAM.
Bog_Mire
1 / 5 (5) Mar 02, 2012
da spaghetti ghod will now be heard and all pastafarians will have a direct line to their ghod. Wasn't a guy called Macaroni big on radio waves? Well, he would be like their Jesus. Repent, oh infidels, and embrace the one true Ghod, on frequency 99.3FM!!!!
PoponDex
not rated yet Mar 02, 2012
isnt this a pretty big deal ?

Cellular companies pay billions of dollars for rights to certain parts of the spectrum.
Dan Quixot_eacute_
5 / 5 (1) Mar 02, 2012
A co-worker looking at this with me notes that each logical RHCP/LHCP (right or left hand circularly polarized) spin rate "channel" would, in the digital domain at the receiving end, have to "ring up" (and "ring down"), similar to a a digital bandpass filter. Thus, this really is feeling increasingly like OFDM (orthogonal frequency division multiplexing), the more one thinks about it. We do OFDM rather than mega-high/super-fast QAM in 4G networks, in order for each OFDM channel itself to operate at a slower rate, to obtain decreased degradation from multipath fading and decreased ISI (inter-symbol interference). By itself, or in conjunction with, OFDM, this could permit improved aggregate data rates, with the same transmit power-SNR product. However, this would be exceptionally difficult to implement in the cell phone. We've already got 4-8 antennas in these things; becoming CP spin rate sensitive would require more and/or thicker (volumetric) antennas. This would be better for Laptops
Skultch
not rated yet Mar 02, 2012
What if we just make transmission power twice larger with 2 normal antennas? That will allow to increase the signal/noise ratio...


I'm not sure if this is the best answer but, there is an easily reached upper limit of SNR (with licensed freqs; not 2.4 or 5 MHz). You can't do better than perfect, which is actually not that hard these days (ok, not perfect, but close enough that other bottlenecks are more significant), especially with GPS-enabled stations, even if you've got some neighbors.

Maybe a better answer is that we don't make perfect antennaes with unlimited gain. At some point you HAVE to use amplifier gain, and that obviously amplifies the noise at the same time.

*If I'm off on my science, please forgive. I'm an ISP engineer/project manager, not a scientist.
pup
not rated yet Mar 03, 2012
regarding the Antenna mass ,the generic Fractal Antenna Systems of all the known generic classical designs are growing in retail as well as commercial outlets today....

so the question is it seems to me.. do we have any actual commercial process ready today to electro chemically (its cheaper) rather than atom by atom building these new required cylindrical/spiral nano wireless Antenna for mass production?

and more than that, does a real life commercial CAD/CAM system that can automate these real life generic Fractal products from design to prototype and then up to commercial scale ?

im not just thinking generic nano Fractal Antenna but also nano CPU, integrated many nano software radios and related nano versions of all the required parts for both short range 11n 1 gigabit through 10gigabit and nano range on chip/SOC ARM clusters for wireless bonded channels to move mass processing data for mass consumer consumption and long term profits etc.
ean
not rated yet Mar 03, 2012
The electric and magnetic fields (which osciallate at the frequency of the photon) are at right angles to the direction of propagation of the photon (and at right angles to each other). If the E an M components are 90 degrees out of phase you get linearly polarized photons.

But if you have the phase different from 90 degrees then you get a circular polarized wave (or even elliptical if the amplitudes are not the same)



Magnetic field is ignored when describing polarization, since it is proportional and perpendicular to electric field. The EF vector is divided into two perpendicular components x and y. And the amplitude and phase of these x and y components defines polarization state of the wave.
cyberstealth
5 / 5 (1) Mar 03, 2012
Per Ove Edfors and Anders J. Johansson article, "Is orbital angular momentum (OAM) based radio communication an unexploited area?"

In this paper they prove that radio vortices are a subset of MIMO. Specifically, they show that OAM radio communication, i.e. using radio vortices, is a sub-class of traditional MIMO communication with circular antenna arrays. So, if you have a set of antenna elements that can create radio vortices, the calculations inherent in a MIMO radio system will automatically create and use vortices to the extent they are useful.

Unfortunately they also proved vortices don't give us additional independent paths. To get spatial multiplexing gain, MIMO needs additional independent paths, a.k.a. multi-path. Multipath is easy to come by in an office environment (due to reflections from walls, ceiling, floor, filing cabinets, etc.). But in an outdoor point-to-point link with directional antennas there are no reflections.
Sonhouse
not rated yet Mar 03, 2012
Another problem I see is in a crowded RF environment, say between buildings of a city, it seems to me there would be problems with interference and diffraction, suppose these twisted beams diffract off some structure and then meet again at the receive antenna, I think that would cancel a lot of channels by simulating a twist already in use by another channel.

If this system works when proven independently, it might not be useful in an urban environment but maybe between space probes and say a lunar station. That is to say, where there would be no diffraction problems, completely point to point.
Vendicar_Decarian
0.3 / 5 (36) Mar 03, 2012
"Is this a joke article?" - Steve

Of course not. The radio waves are just being given a circular polarization rather than a transverse (left right) polarizaton.

http://upload.wik...lors.gif
Vendicar_Decarian
0.1 / 5 (35) Mar 03, 2012
Wrong.

"the shape of EM waves is known as a sinusoidal wave" - Bowler

EM waves have no easily described shape.

What you start with is two lobes of vacuum polarization. Lets call the positive polarization up and the negative polarization down. As time progresses these vacuum polarizations draw inward and begin to cancel, passing through each other and extending back out to the opposite polarization state where negative is up and positive down.

This oscillation occurs indefinitely with the frequency of the exchange determining the photon's energy.

Since charges are assumed not to change magnitude under relatavistic motion, the real change in their charge field that does occur is interpreted as being the result of a new force called magnetism.

The vacuum polarizations can also have a rotational component to their oscillation. This rotational component is a left/right oscillation. In addition there can be an in/out component to the oscillation.

Cont.
Vendicar_Decarian
not rated yet Mar 03, 2012
My understanding is that these oscillations all have to be of the same frequency (if not then you can't have a photon with a fixed frequency), but they may differ in phase.

The sine waves you see in textbooks represent the change in magnitude of the displaced charge and do not represent a physical shape any more than a sine wave represents the physical shape of a water wave.
Vendicar_Decarian
not rated yet Mar 03, 2012
"In itself, this isn't different than transmitting separate data streams in orthogonal polarizations along the same path (well known prior art)." - Dan

Exactly, and as every satellite dish owner should recognize.
Yogaman
not rated yet Mar 03, 2012
This method does not involve circular polarization, but Orbital Angular Momentum. For background, see:
http://www.physic...Away.pdf

But cyberstealth's link above refutes the communications gain asserted by this article. Thank you, cyberstealth.

Let's hope that the article's professor's antenna design is better than his bandwidth proposal.
Graeme
not rated yet Mar 04, 2012
An interesting idea, but does not actually increase transmission capacity in reality. The rotating transmission can be fabricated by two cross polarized antennas, that get a phase shift. For the higher rotation rates, the linear polarized antennas see a double for triple or even more times frequency, this is just cheating by using more bandwidth.
MRBlizzard
1 / 5 (1) Mar 05, 2012
What kind of radiance would we see astronomically for this light containing angular momentum. And similarly, what kind of radiance would we see astronomically high angular momentum photons. Would the background appear dark enough to clearly show ET contact signals?
Also, would combinations of angular momentum and circular polarizations provide low noise channels in order to provide clear signals? Or unnatural signals?
hb_
1 / 5 (1) Mar 05, 2012
@Skultch
Two things. Surely, an application to replace landlines in rural areas is a nieche application at most?

Second, in rural areas there are less radio emissions and the bandwidth is less occupied. Would it not be cheaper per gigabit per second using conventional point-to-point technologies? And is data congestion a problem in rural areas, or is it just expensive to build connections?
hb_
1 / 5 (1) Mar 05, 2012
@antialias_physorg

Please explain what you mean by your timing argument. I thought - without reading the original article, I confess - that the antenna selected the right orbital momentum by orientation. Correct? And in this case, you would have an amplitude that scales as something like cos(theta).

But, let us assume that you are right. Even if it is only a "timing" issue, you can still twist the cellphone so that the antena is perpendicular to both the electric and magnetic field. Then you have zero amplitude, right?

Finaly, let us assume that you still have some signal that you can extract by using timing information (still don't know how to do it..). You still have the problem that amplitude noise will be translated to jitter (timing noise). In the end, how much information you can pack into the bandwidth will be a question of signal to noise ratio. Right?
antialias_physorg
1 / 5 (1) Mar 05, 2012
If I understand themethod correctly then the speed of circulation is the deciing factor for the channel. So even if you get an eliptical signal (due to your antenna being at an angle to the transmission) the circulation speed stays the same. The information in your channel isn't encoded in the circulation - only the channel ID. What encodes the information is the phase and amplitude modulations of that signal (QAM).

Since the elliptical signal you're getting with a oblique antenna angle is symmetric it should be fairly easy to map this to a circular signal space and extract the information.

As far as I can see it is 'just' ordinary radio transmissions but with two (or many) circular polarized beams at once on the same carrier frequency.
Skultch
not rated yet Mar 05, 2012
@Skultch
Two things. Surely, an application to replace landlines in rural areas is a nieche application at most?

Second, in rural areas there are less radio emissions and the bandwidth is less occupied. Would it not be cheaper per gigabit per second using conventional point-to-point technologies? And is data congestion a problem in rural areas, or is it just expensive to build connections?


I was thinking this would be for rural areas that have no terrestrial connection yet; the current satellite internet customers. (full disclosure: I'm one of those) Scaling up a community's network fed by a wireless ISP will be much cheaper than launching an extra satellite. I'm a big believer in the idea that getting rural high-speed working will help bridge the cultural divide in the US.

There's a lot of different situations out there. Yes, in many areas the *spectrum* is not as used up, but many others have military interference to deal with (i.e. much of Wyoming).

Cont...
Skultch
not rated yet Mar 05, 2012
...cont

I'm not sure what you mean by "data congestion." I think you mean low spectrum availability and/or noise issues. Regardless, I don't think that is the issue in rural areas, usually. I think the real benefit for rural areas will be more indirect; more like this tech, when available, would drive down current prices on high end carrier-grade equipment. This might have a more direct implication like freeing up physical tower space. With this, we might be able to bring the same amount of bandwidth, with 1 link instead of 4 load-balanced links. That would also remove multiple points of failure (load-balancing and bonding are relatively less reliable for wireless links due to differing link qualities messing up the protocols).
Kinedryl
1 / 5 (1) Mar 05, 2012
isnt this a pretty big deal? Cellular companies pay billions of dollars for rights to certain parts of the spectrum.
They're using the phase shift multiplexing already in their radial antenna arrays known from BTW. The further optimization of it would require to make the radio signal directional and less accessible in such way.
hb_
1 / 5 (1) Mar 06, 2012
@Skultch

But the article implies that there is a cost penalty for using their helical scheme. So, if available bandwidth is not an issue, would it not be cheaper to use conventional technologies in rural areas?

Consider this. You set up a very expensive mutli-orbit technology to link to points in the rocky mountains. It works beautifully and uses only 10 MHz of bandwidth. Or, you could use 100 MHz of bandwidth for half the price with conventional technology. Now, as long as there is bandwidth available, would the second option not be better?
hb_
1 / 5 (1) Mar 06, 2012
@antialias_physorg

I think I get it now. What the authors call "orbital momentum" is simply the phase difference between the magnetic and the electrical field. At 90 degrees, the elipse is as close to a circle as you can get, and at zero degrees you have linearly polarized wave.

The question is, how effective is their antenna for separating waves with different phase differences between the electric and magnetic fields? Does it really give anyting in terms of data-rate and signal to noise?

And by the way, the argument of the antenna orientation still holds. You can orient it so that there is no induction (and hence no reception) by rotating it. Of course, having three perpendicular antenas should enable you to always have at least one that receives the signal.

But, I beleive that this would hardly make things easier. The signal to noise ratio is bound to be affected by the orientation of the antenna.
antialias_physorg
1 / 5 (1) Mar 06, 2012
[qDoes it really give anyting in terms of data-rate and signal to noise?
It's independent of these two. This method is just used to make separate channels available. There should be no crosstalk between various channels - as long as the circular frequencies are prime to each other. Otherwise you might get some occasional clicks. I'm just assuming this from how a fourier analysis of the circular frequencies would look.
But otherwise all channels should be as good as a 'normal' one (without circular polarization).

As for the antenna. My first guess would be that you could make it spherical. But since this type of multi-channel thing is not for mobiles but for fixed installations the optimal antenna position can be predetermined/fixed.
hb_
1 / 5 (1) Mar 06, 2012
@antialias_physorg

Now, I might have missunderstood the science - please correct me if this is so - but I am pretty sure that the magnetic field must have exactly the same frequency as the electric field.

It must also be directed at a 90 degree angle to the electrical field. This only leves the phase difference between the two fields. It also measns that the fourier analysis of the frequency would be identical to the non-polarized spherical wave (same frequency).

An antenna that can separate one "orbital momentum", i.e. phase shift between the electric and magnetic field, should be prone to interference from a neighbouring "orbital momentum". Think about it... I must admit that I do not understand how the antenna would work. Do you? If so, please explain it to me!

And, since there is bound to be interference, the signal-to-noise ratio becomes relevant once more.
antialias_physorg
1 / 5 (1) Mar 06, 2012
but I am pretty sure that the magnetic field must have exactly the same frequency as the electric field.

It must also be directed at a 90 degree angle to the electrical field.

Yep.

This only leves the phase difference between the two fields. It also measns that the fourier analysis of the frequency would be identical to the non-polarized spherical wave (same frequency).

I meant the fourier of the circulation speeds of the various channels used - not of the ferquency of the waves.

I must admit that I do not understand how the antenna would work.

The electronics behind it are probably akin to what you do in frequency channel encoding (you add/subtract the corresponding frequency). In this case you add/subtract a circular polarization to the incoming wave (just speculating here). As for the physical antenna. I think with metamaterials one could separate the waves according to phase difference. I'm not too hip to what these can do to make a definite pronouncement.
Skultch
not rated yet Mar 06, 2012
@Skultch

But the article implies that there is a cost penalty for using their helical scheme. So, if available bandwidth is not an issue, would it not be cheaper to use conventional technologies in rural areas?


I don't see that implication. I don't see how this tech wouldn't be subjected to normal supply/demand dynamics. If ISPs are buying this tech instead of the older, single band stuff, (for whichever market) then the price of that older stuff *must* go down. Will it still be made? Maybe. It might actually bring the prices down enough to *create* the rural market for the older tech.

Some rural areas are so far from a OC (optical carrier) line that there simply is no cost effective conventional tech to get them service. (by conventional I mean cable/DSL/T1/DS3) Who knows where this tech is going to come out price wise compared to current wireless point-to-point tech? I admit, I am a little overly optimistic on this.
Skultch
not rated yet Mar 06, 2012
Consider this. You set up a very expensive mutli-orbit technology to link to points in the rocky mountains. It works beautifully and uses only 10 MHz of bandwidth. Or, you could use 100 MHz of bandwidth for half the price with conventional technology. Now, as long as there is bandwidth available, would the second option not be better?


With bandwidth, you always have to consider scalablity costs, because it will always get used up. My company has doubled or tripled the bandwidth we provide every year for four years, and we are still falling behind demand. I'd much rather pay someone to climb a tower, or even build a new one, than have to pay for an extra satellite.

Also, and this is a highly technical opinion, satellite sucks donkey balls. ;) The latency is unacceptable for gaming or SSL connections. It has it's place, but IMO, that is a smaller niche.
hb_
1 / 5 (1) Mar 07, 2012
@Skultch

But conventional technology can work just fine with towers, right? And if the technology is not cheaper per gigabit*mile (or some other unit), then it will not help the rural areas.

The reason why there are not enough backbone capability in rural areas, is not that the bandwidth is occupied, but that the cost of building the point-to-point transmissions is expensive. Technologically, you can supply the entire yellowstone park with wi-fi, if you would like..

So, what you need is a technology that can do the same job (or better) for less money.
hb_
1 / 5 (1) Mar 07, 2012
@antialias_physorg

Ok, this time I think I get it. The technology is based on continuously rotating linearly (or circularly) poralized radio wave in time. As someone pointed out above, this could be done with two transmission antennas that are perpendicular to each other.

The receiving antenna could in principle also consists of two orthogonal antennas. At each instant, the signal in each antenna would be proportional to the momentaneous angle of the polarization to the antenna.

You could then use a conventional demultiplexer to get rid of the the carrier signal of each receiving antenna ("vertical", "sideways"). By adding "vertial" (V) to "sideways" (S) with a momentaneous weight that is time dependent (S*cos(omega*t) V*sin(omega*t)) you would have selected for circular rotation speed (omega = angular speed of the rotation).

Clearly, you would have massive interference from other linearly polarized waves. I fail to see how this would increase the information carrying capability.
antialias_physorg
not rated yet Mar 07, 2012
Clearly, you would have massive interference from other linearly polarized waves.

Only from those that are on the same frequency (that is: carrier frequency in this case - not circular polarization frequency. remmber that with this trick you can have many channels on one carrier frequeny).
If you do this the way it's done now - i.e. reserve certain frequencis for mobile phones - then there would be no interference.

It increases the information carrying capacity for the very same reason: you can now use one carrier frequency for many channels where before you could only use it for one.
hb_
1 / 5 (1) Mar 08, 2012
@antialias_physorg

Linearly polarized waves that have a component in the circular frequency after being demultiplexed with the carrier frequency will turn up as noise in your signal.

Of course, you may still recover the signal since you combine it with the signal from the perpendicular detector, but the noise is still there. The question is if you really gain anything.
antialias_physorg
1 / 5 (1) Mar 08, 2012
Linearly polarized waves that have a component in the circular frequency after being demultiplexed with the carrier frequency will turn up as noise in your signal.

Linear polarized signals would (or should) no longer be used on that frequency. That is not much of a drawback (taking one channel away from basically an infinite number of possible, concurrent channels)

even if you do it: The noise is at very specific (and known) intervals of the circular polarization. A very basic error corection scheme could take care of that. It would even not have to be applied over the entire signal but just at critical timeslots.

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