'Twisted' Waves Could Boost Capacity of Wireless Spectrum

Multipath by rullywowr · 2012-03-02 01:54 · Score: 5, Insightful

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 by Forty+Two+Tenfold · 2012-03-02 02:33 · Score: 4, Funny

Leeloo Dallas multipath!

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Re:Multipath by tibit · 2012-03-02 02:45 · Score: 2

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.

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Re:Multipath by ArsenneLupin · 2012-03-02 02:57 · Score: 1

oh yeah, first!
Mod parent Insightful!
Re:Multipath by Sponge+Bath · 2012-03-02 03:31 · Score: 2

Milla Jovovich with a lisp... very sexy.
Re:Multipath by camperslo · 2012-03-02 03:37 · Score: 1

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.
http://www.engineeringradio.us/blog/2012/01/the-never-ending-hd-radio-debacle-continues-to-not-end/
Re:Multipath by Mister+Transistor · 2012-03-02 03:39 · Score: 1

Less Thermal Tape, Please...

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Re:Multipath by rullywowr · 2012-03-02 05:04 · Score: 1

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 by YoopDaDum · 2012-03-02 05:32 · Score: 4, Insightful

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.
Re:Multipath by tibit · 2012-03-02 08:13 · Score: 3, Informative

Hah, CDMA should be plenty robust to multipath, you can use more than one adaptive correlator per channel, and each correlator gives you the relative multipath phase as a diagnostic output, too. Ideally you'd want more than one antenna to make the adaptive scheme more robust, but it'll work with just one. What's more, you can always record the high-bandwidth datastream from the digital radio I/Q inputs for offline data recovery: whatever processing you do online is limited by the maximum latency allowed in your decoder, offline has no such problem. To integrate "offline" with other recording equipment, you can simply have two outputs: a realtime output that goes to the program mixing console, and a more delayed offline output that goes to the multitrack "source" recorder for a studio mix (where you can easily shift things around, time-wise).
Admittedly satellite links have stable channel properties, but the error correction codes that they use are as close to optimal for given datarate-to-bandwidth as is feasible, and that's not very common in non-cellular consumer point-to-point gear. I agree that terrestrial channels are more challenging when it comes to varying channel properties.
A wireless mike is a very specific application. It shouldn't ever need a receiver, so the only way to deal with potentially strong narrowband interference is to use CDMA and as wide of a transmit bandwidth as possible -- using frequency division (one channel per mike) is not robust enough, usually. All of the "brains" need to be in the base station, the transmitter circuitry can be hardwired in a relatively simple FPGA that takes input from an audio codec, a couple jumper settings (node ID / code selection) and pushes it via a DAC to the filter/upconverter/final amp. All the encoding etc. is done completely digitally and can be probably modeled in a few pages of Verilog.

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Re:Multipath by TheInternetGuy · 2012-03-02 19:47 · Score: 1

Here on Slashdot you risk a revoked geek card if you don't capitalize at least the first character of Lisp. Plus, I always imagined Milla to more of a Simula or Smalltalk kind of gal.

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Not really new by scsirob · 2012-03-02 01:59 · Score: 2, Interesting

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: http://www.astronwireless.com/topic-archives-antennas-polarization.asp and http://en.wikipedia.org/wiki/Antenna_(radio)

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Re:Not really new by nedlohs · 2012-03-02 02:02 · Score: 1

Surely the "without using polarization" part means it isn't that?
Re:Not really new by virgil_disgr4ce · 2012-03-02 02:13 · Score: 4, Insightful

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

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Re:Not really new by camperslo · 2012-03-02 02:54 · Score: 1

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 by squidflakes · 2012-03-02 03:30 · Score: 1

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.
Re:Not really new by darenw · 2012-03-02 09:29 · Score: 1

Orbital angular momentum of a wave is unrelated to its polarization. It's like the difference between an electron's spin and its orbiting about a nucleus. Or, for an astronomy analogy, confusing polarization with the wavefront's angular momentum is like confusing days with years. Of course we're dealing with a broad wave spread throughout space in one case vs. a compact hard body in the other. But same distinction - a built-in symmetry in the naure of an object or field vs. a symmetry due to how it's arranged or moving in space.
Re:Not really new by ctrl-alt-canc · 2012-03-02 12:11 · Score: 1
Please RTFA:
- this is something new, so by definition this cannot have anything to share with ham radio.
- TFA talks about angular momentum of the EM field. This has nothing to do with polarization, but with another property of the EM field. Since they are emitting waves with an angular momentum, they cannot be plane wave (it can be shown, see for example here for details) that plane waves have the angular momentum of the field equal to zero).
- From the paper it is unclear how do they realize a field with an angular moment different from zero, I guess they used a technique similar to those described in this paper.
Re:Not really new by camperslo · 2012-03-02 13:56 · Score: 1

With a QAM signal, the ability to have one signal cancel allows for a second, but no more. And QAM really isn't doing anything extraordinary. With AM FM or phase modulation, the sidebands produced are mirror images, redundant. So the signal took twice the needed bandwidth to start with. Even analog t.v. from more than 60 years ago managed to filter off most of the lower sideband at the transmitter. They could have done more, but allowed for slop in simple receivers.
I've studied the links, and it's complete BS. They're getting a weak effect that is fragile and frequency dependent. It only could be demoed using narrow bandwidth, with the help of FM capture effect, and using extra power because of almost completely cancelling the desired signal while nulling the other. It took a laser to even find the spot to use. There is no way it could handle more than two signals, and in the real world it couldn't even be used for that.
Massive amounts of technical nonsense fool people who figure they just don't know enough to understand. Celebrities, ceremony, a gunshot, and "ordinary people" fit right in. The last time I read of a breakthrough tested in that setting it was a perpetual energy machine.
Using right hand and left hand circular would work for more efficiently, not require critical alignment, and tolerate path variations. Even simple cross polarizing would work far better.
Re:Not really new by __aaltlg1547 · 2012-03-03 03:15 · Score: 1

Reading a bullshit article about a bullshit demonstration won't improve anybody's understanding. The apparatus they show doesn't impart any novel characteristic to EM waves. It's a kind of polarizer and there is nothing new about using linear or circular polarization to transmit independent signals in the same bandwidth.
They can't use this method to increase the number of signals that can be transmitted in the same bandwidth over conventional methods because they are actually using conventional methods but describing what they're doing in a way that is unconventional and misleading. That's either because they are frauds or because theyre incompetent.

infinite number of signals by nopainogain · 2012-03-02 02:05 · Score: 0

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 by Anonymous Coward · 2012-03-02 02:24 · Score: 0

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 by Anonymous Coward · 2012-03-02 02:08 · Score: 0

n/t

Interesting but not convincing. Circ Polarization? by Muad'Dave · 2012-03-02 02:09 · Score: 1

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.

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Shannon-Hartley still in effect. by neyla · 2012-03-02 02:10 · Score: 4, Insightful

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. by mehrotra.akash · 2012-03-02 02:16 · Score: 1, Funny

Does an infinite no. of channels with infinitely low capacity give infinite effective bandwidth?
Re:Shannon-Hartley still in effect. by Anonymous Coward · 2012-03-02 02:23 · Score: 0

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. by Idbar · 2012-03-02 02:25 · Score: 3, Funny

I think AT&T is fine with that. ;-)
Re:Shannon-Hartley still in effect. by gmaslov · 2012-03-02 02:29 · Score: 1

"Infinitely low" is zero. So no.
Re:Shannon-Hartley still in effect. by tibit · 2012-03-02 03:07 · Score: 2

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.

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Re:Shannon-Hartley still in effect. by Anonymous Coward · 2012-03-02 03:07 · Score: 0

what is 0 * infinity?
Re:Shannon-Hartley still in effect. by Baloroth · 2012-03-02 03:08 · Score: 1

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.

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Re:Shannon-Hartley still in effect. by PlatyPaul · 2012-03-02 03:13 · Score: 1

Undefined.

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Re:Shannon-Hartley still in effect. by MadKeithV · 2012-03-02 03:16 · Score: 2

42.
Re:Shannon-Hartley still in effect. by Anonymous Coward · 2012-03-02 03:23 · Score: 0

But a zero watt transmitter does have 100% protection from interference.
Re:Shannon-Hartley still in effect. by Bengie · 2012-03-02 03:26 · Score: 1

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. by Anonymous Coward · 2012-03-02 03:49 · Score: 1

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. by Anonymous Coward · 2012-03-02 03:57 · Score: 0

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: http://en.wikipedia.org/wiki/Active_Electronically_Scanned_Array
In theory you can use this sort of stuff to track and talk to multiple devices.
Re:Shannon-Hartley still in effect. by bandy · 2012-03-02 04:31 · Score: 1

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

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Re:Shannon-Hartley still in effect. by gmaslov · 2012-03-02 04:40 · Score: 1

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. by YoopDaDum · 2012-03-02 05:44 · Score: 1

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.
Re:Shannon-Hartley still in effect. by YoopDaDum · 2012-03-02 05:59 · Score: 4, Interesting

CDMA is different than this. CDMA is just a multiplexing mechanism, splitting a single channel capacity between users. Here the scheme adds new independent channels.

And CDMA has been removed from DOCSIS 3.0. It had been added in DOCSIS 2.0, then people eventually realized it was a dumb idea over cable, and then removed it. The company that had pushed it went bankrupt, but not before its share peaked and some people made a lot of money selling at the right time...
What you mention (channel bonding) is also called carrier aggregation in HSPA and LTE (LTE advanced, not the current one). It's just adding the capacity of different physical channels and treating them as one logical pipe. Very similar to Ethernet bonding, although it's more complex when you get to the details. But it has nothing to do with CDMA.

CDMA is the most hyped multiplexing technology. It's been hyped to death, so much some people think it's some form of magic. But it's not, and it's our past now. CDMA key point was that it was the first mechanism that enabled deploying cellular over a single frequency, which maximized at the time cellular capacity. This was very useful in cellular system, but it's a non issue in cable (there's no cell, duh). So CDMA over cable is a marketing/hype driven monstrosity that should never have happened (CDMA may by useful for a contention channel though). And even in cellular there are better schemes which have become practical now. All 4G system are based on OFDMA for example, with just the contention channel using some form of code multiplexing to be more robust to collisions.
Even HSPA, which is still CDMA based, went back to something closer to TDM in spirit than CDMA: there are still codes, but they're usually allocated to a single user over a short duration, and multiplexing is mostly TDM. Instead of having multiple user at the same time using different codes, which is the essence of CDMA. The HSPA way to send with more density over a shorter period of time instead of spreading the signal is more power efficient.
Re:Shannon-Hartley still in effect. by Anonymous Coward · 2012-03-02 05:59 · Score: 0

Having zero infinities is the same as having zero of anything else.
Re:Shannon-Hartley still in effect. by Anonymous Coward · 2012-03-02 06:02 · Score: 0

The entire concept of the Shannon-Hartley limit is that, with a given bandwidth at a frequency, you can only modify the carrier waveform in a limited way before exceeding the bandwidth. Try encoding a 30MHz signal on a 20MHz carrier. Same thing. For an extreme example, if you have 100 million channels all changing states once per second, you can't encode that on a 100Hz signal, twisted waves or not. Infinite *usable* channels is a silly thing to say.
Re:Shannon-Hartley still in effect. by flaming+error · 2012-03-02 06:22 · Score: 1

No, I'd say we'd have an infinite number of zeros.
Re:Shannon-Hartley still in effect. by JoshRosenbaum · 2012-03-02 06:25 · Score: 2

You get 56k out of it because of compression. Actual physical bandwidth is limited to about 34kbps of actual data transfer.
I'm no expert, but I did go to Wikipedia and it appears to indicate that your statement is false and 56k is indeed the base speed. http://en.wikipedia.org/wiki/56_kbit/s
However, with upload speed you appear to be more correct. (33.6 for V.90 and 48 for V.92)
http://en.wikipedia.org/wiki/56_kbit/s_modem
Modem compression (v.44 for example) can provide much faster rates than 56k. For highly compressible text, Wikipedia suggests topping out at 3:1 (~150kbit/s) rates.
http://en.wikipedia.org/wiki/V.44#Error_control_and_data_compression
If you feel my understanding on these Wikipedia articles is off, I'm definitely interested in hearing more.
Re:Shannon-Hartley still in effect. by flaming+error · 2012-03-02 06:44 · Score: 1

That's a syntax error - data type mismatch
0 is a number, infinity is an idea.
Re:Shannon-Hartley still in effect. by fritsd · 2012-03-02 07:59 · Score: 1

Maybe you'd need an infinite number of carefully placed small spiky antennas to get infinite channels.
Seems like they are doing something like the interferometry of the extremely boring-looking LOFAR radiotelescope.
Amirite?

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Re:Shannon-Hartley still in effect. by neyla · 2012-03-05 19:08 · Score: 1

Better antennas is equivalent to a lower noise-floor, so yes, better antennas do genuinely allow you to transmit more data, especially if they are directional since that then also raises the effective transmit-power. (what matters is the power/noise ratio)

Re:Interesting but not convincing. Circ Polarizati by Anonymous Coward · 2012-03-02 02:17 · Score: 0

Maybe this helps. I'm still trying to grasp the concept.
http://en.wikipedia.org/wiki/Light_orbital_angular_momentum

Re:Interesting but not convincing. Circ Polarizati by buchner.johannes · 2012-03-02 02:17 · Score: 1

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: https://en.wikipedia.org/wiki/Light_orbital_angular_momentum

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Terrestrial Microwave Links. by neBelcnU · 2012-03-02 02:20 · Score: 2

"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. by mooingyak · 2012-03-02 02:31 · Score: 1

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.

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Re:Terrestrial Microwave Links. by Anonymous Coward · 2012-03-02 02:45 · Score: 0

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. by mooingyak · 2012-03-02 02:56 · Score: 1

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.

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Think of it as a phased array by Anonymous Coward · 2012-03-02 02:23 · Score: 2, Informative

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 by s122604 · 2012-03-02 03:50 · Score: 1

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 by Anonymous Coward · 2012-03-02 05:10 · Score: 0

Absolutely correct! See this paper on that exact topic ... http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=2062936&fileOId=2339120
Re:Think of it as a phased array by goodmanj · 2012-03-02 06:53 · Score: 1

Yep. In layman's terms, imagine a row of many dish antennas sending data to an identical row of dish receivers. You can send a lot more data than just one dish, right? But think about the problems: as you try to make the dishes smaller, the signal beams spread out and overlap multiple antennas, causing interference and crosstalk. Same happens if the dishes aren't aligned exactly right, or the signals bounce off walls on the way.
Wrap the whole thing around in a circle and apply a little math hocus pocus, and you've got the "Twisted wave" antenna. Same advantage, same problems.

not really by __aaltlg1547 · 2012-03-02 02:33 · Score: 1

Em waves don't HAVE orbital angular momentum.

Re:not really by NicknameAvailable · 2012-03-02 02:39 · Score: 2

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 by jo_ham · 2012-03-02 02:41 · Score: 3, Informative

Photons do.
Photons are part of the EM spectrum.
Re:not really by Chris+Burke · 2012-03-02 05:38 · Score: 1

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

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Re:not really by __aaltlg1547 · 2012-03-02 10:11 · Score: 1

Photons do.
Photons are part of the EM spectrum.
Polarization comprises photon angular momentum.
And there's nothing "orbital" about their apparatus. It's a reflector that imparts polarization at the cost of directivity.

Huh? Is this polarization? by Anonymous Coward · 2012-03-02 02:34 · Score: 0

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.

Topological charge by Anonymous Coward · 2012-03-02 02:41 · Score: 0

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.

So what are they orbiting then? by Viol8 · 2012-03-02 02:42 · Score: 1

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

Re:So what are they orbiting then? by Anonymous Coward · 2012-03-02 02:47 · Score: 3, Informative

Around the propagation direction of the beam. Read this:
https://en.wikipedia.org/wiki/Light_orbital_angular_momentum
Re:So what are they orbiting then? by Baloroth · 2012-03-02 02:59 · Score: 3, Informative

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

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Re:So what are they orbiting then? by tibit · 2012-03-02 03:02 · Score: 4, Informative

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.

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Re:So what are they orbiting then? by X0563511 · 2012-03-02 03:26 · Score: 1

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

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Re:So what are they orbiting then? by Anonymous Coward · 2012-03-02 03:31 · Score: 0

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? by Anonymous Coward · 2012-03-02 04:25 · Score: 0

What's all this? I stopped reading after Q.E.D.
Re:So what are they orbiting then? by Chris+Burke · 2012-03-02 06:04 · Score: 1

What's all this? I stopped reading after Q.E.D.
Har har!
Not that it's really apropos your post, but this seemed like a good chance to post this for anyone who's interested in what this Quantum Electrodynamics stuff is about.
It's a fantastic lecture series by Richard Feynman explaining QED in detail to non-physicists.

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The enemies of Democracy are
Re:So what are they orbiting then? by Anonymous Coward · 2012-03-06 02:36 · Score: 0

Laguree-Gaussian waves are a separate collection of solutions to the paraxial equation of wave propagation. The standard Gaussian solution has a peak intensity along the axis of travel, but these 'twisted' waves have peak intensities in annulae around the axis. The surfaces of constant phase spiral around the axis of travel, producing angular momentum. Also, these solutions exist separately for different polarizations (being solutions of the wave equation).
This is not a quantum effect! it is a purely classical effect and is merely a different set of solutions of the wave equation. Polarization has separate solutions of the wave equation for each polarization.

BULLSH!T by AB3A · 2012-03-02 02:43 · Score: 3, Interesting

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.

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Re:BULLSH!T by Anonymous Coward · 2012-03-02 03:11 · Score: 0

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.
Re:BULLSH!T by tibit · 2012-03-02 03:12 · Score: 1

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.

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Re:BULLSH!T by ozydingo · 2012-03-02 03:19 · Score: 1

*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?
Re:BULLSH!T by Anonymous Coward · 2012-03-02 03:22 · Score: 0

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 by Angst+Badger · 2012-03-02 03:31 · Score: 5, Interesting

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.

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Re:BULLSH!T by Anonymous Coward · 2012-03-02 03:39 · Score: 0

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."
Re:BULLSH!T by Prune · 2012-03-02 05:31 · Score: 1

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.

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Re:BULLSH!T by Prune · 2012-03-02 05:34 · Score: 1

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.

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Re:BULLSH!T by Anonymous Coward · 2012-03-02 05:43 · Score: 0

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.
Re:BULLSH!T by ozydingo · 2012-03-02 05:57 · Score: 1

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?
Re:BULLSH!T by Anonymous Coward · 2012-03-02 07:36 · Score: 0

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.
Indeed. And that domain is spatial (orbital angular momentum modes, hermite modes, as well as other transversal modes correspond to spatial variations of beam intensity across the beam). So, in essence, it is like running several beams side by side. Of course this allows to pass around more information, but not an infinite amount (on the planet Earth, that is ;-).
K.L.M.
Re:BULLSH!T by darenw · 2012-03-02 09:50 · Score: 1

Specifically, we're dealing with the arrangment of the wave in space, the phase relations of different portions of the wavefront. The additional channel capacity comes from having (in principle) unlimited transverse space for the wavefront to occupy.
It's sort of as if several straight narrow beams of radiation (e.g laser beams) were side by side. One beam is limited in information content as usual, but it's parallel buddy can carry independent information. Have as many parallel beams as you like. Now this isn't really practical, but by adding different linear combinations of beams, you can create orthogonal states with well-defined rotational (about the axis of propagation) properties.
Example: just add all the parallel beams in-phase. This is one big fat beam with zero angular momentum.
Another example: add all the beams on the left side of the bunch and subtract all the ones on the right side (putting it crudely) to get a fat beam that changes sign when rotated 180 deg about its axis. It has a partner, top half minus bottom half, so they are like sine and cosine. Add and subtract these two with complex coefficients, to be 90 degrees out of phase, for +1 and -1 states of angular momentum.
With N parallel beams, you can define N different "twisted beam" states. The hope is that these states, or at least a good fraction of them, survive the usual impediments to propagation - scattering, multipath interference etc - without mixing together. That's how we would carry "unlimited" capacity, although it's really limited by the size of the receiving array in terms of wavelength, necessary to distinguish these twisted beam states.
Re:BULLSH!T by Prune · 2012-03-02 18:52 · Score: 1

You're wrong again: there is an upper bound placed on us by cosmological considerations: the accelerating expansion of the universe means that our Hubble volume will forever only contain a finite amount of mass-energy (eventually everything outside the gravitationally bound local group of galaxies will be carried away from us by expansion at speed greater than the speed of light, making it forever out of reach). So where the hell are you going to get the arbitrary amount of energy you need to make an arbitrary frequency signal?

As for why people are combative: it's because we get upset when someone posts misinformation and we know we are likely too late in responding with a correction to bring the misled readers of the original post back to the path of righteousness.

--
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Re:BULLSH!T by ozydingo · 2012-03-03 04:02 · Score: 1

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.
I'm glad you can sort-of derive that upper limit. Good for you. You know far more physics than I.

Maybe you and I just have different interpretations of what "in principle" means in this context. I'm only referring to the point at hand, which was violation of a the mathematical principle. How we realize the application of that mathematical principle in the physical world is subject to whatever limitations due to our choice of medium. That the medium of EMR has the limitations you point out is wonderful, but is irrelevant to the principle of shannon's limit.

I simply wanted to point out how that mathematical principle was not violated. Is that not clear from my statements? If you think my statements imply in any way that I think there's a potential practical realization of infinite channel capacity, I have clearly failed to convey my meaning.
Re:BULLSH!T by Anonymous Coward · 2012-03-03 07:09 · Score: 0

But there is zero possibility that 2 + 2 will ever equal anything other than four.
2 + 2 = 1 (mod 3)

Color me skeptical by Anonymous Coward · 2012-03-02 02:43 · Score: 0

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 by Muad'Dave · 2012-03-02 03:24 · Score: 1

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.

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Re:Color me skeptical by 0111+1110 · 2012-03-02 05:36 · Score: 1

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.

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Re:Color me skeptical by Muad'Dave · 2012-03-02 06:41 · Score: 1

I agree that it's completely counter-intuitive and bizarre to boot, but if he's correct then there's a whole world of communications out there we're missing. The A-B effect is strange enough on its own.
Maybe teaching the E and B version instead of the A potential version of Maxwell's Equations has limited our thinking. The A-B effect seems to indicate that the A potential is real and not just a mathematical invention.
If you have access to a QEX archive (perhaps a local ham radio operator) the article is a pretty interesting read. It's light on math (thank heaven) but tries to explain what he's doing, with photos and details of the experimental setup. He's taken precautions against receiving 'plane' (plane waves - it a joke, son!) old EM waves.
Supposedly some experimenters are getting results using optical fibers to receive these waves.

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Re:Huh? Is this polarization? by jo_ham · 2012-03-02 02:44 · Score: 2

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.

*Orbital* angular momentum by Urban+Garlic · 2012-03-02 02:44 · Score: 3, Insightful

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.

--
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Re:*Orbital* angular momentum by mprinkey · 2012-03-02 04:32 · Score: 1

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.
Re:*Orbital* angular momentum by Anonymous Coward · 2012-03-02 19:03 · Score: 0

If you could change orbital to (within a 5 degree angle), then you could turn a standard signal into 360/5 = 72 channels on one frequency. Not really magic, but 72 times as much data. Ok, getting past noise limitations and other problems maybe only 70 or 60 channels. But 60 times as much data for the same bandwidth is not a bad improvement.

Multiple transmitters on same freq is a reality by Viol8 · 2012-03-02 02:48 · Score: 1

http://en.wikipedia.org/wiki/Single-frequency_network

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 by rullywowr · 2012-03-02 05:12 · Score: 2

http://en.wikipedia.org/wiki/Single-frequency_network
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 by YoopDaDum · 2012-03-02 05:35 · Score: 1

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:Multiple transmitters on same freq is a reality by Viol8 · 2012-03-02 07:58 · Score: 1

Well yes, obviously digital has to be converted to an analog format at some point , but in this case its the type of data being transmitted that matters. Besides which, digital transmission rarely uses AM and uses FM in a far more complicated way that analog radio. There is also phase modulation.
Re:Multiple transmitters on same freq is a reality by Trinn · 2012-03-03 05:48 · Score: 1

...ever heard of a photon? :-P
Re:Multiple transmitters on same freq is a reality by camperslo · 2012-03-03 09:53 · Score: 1

Actually, when it doesn't involve hearing a bunch of stations at once, the effect of signal combining from multiple paths off the ionosphere can be something of an audio adventure called selective fading. Although I suspect little is written about it, as one of the more unusual parts of the pop culture of a.m. radio I think it deserves a small place in history. (It still happens, No doubt some experienced it when listening to legends such as Wolfman Jack broadcast from outside the U.S. (Unfortunately the stations he was on sometimes had some heavy distortion that certain high power transmitters were prone to) The spectrum modifying aspect of selective fading is emulated by hardware or software flangers as used by musicians. It often gives a very unusual character to (a.m.) shortwave broadcasts, and sometimes a.m. medium wave broadcasts that are hear via skywave or combined ground wave and skywave. If near a powerful directional a.m. but listening closer to a null than a major lobe in the directional pattern, the higher energy power from the antenna system in other directions may come back as unusually strong skywave even at relatively short distances. Since many of the west coast directional a.m.s have to protect inland stations from interference, many are throwing most of the signal out over the ocean at night. In the heyday of A.M. radio then KDAY 1580 KHz Santa Monica (Los Angeles) was well known for intense selective fading effects in many areas relatively close by. I heard that the signal was often more stable in Hawaii at night than in southern California. The selective fades were actually fun to hear, and many imagined that if t.v. signals ever came back from space they would sound that way. (they actually would not, the sound being f.m.) Flanging can be heard in music such as The Letter remake by The Arbors (moldy oldie) and sometimes in sci-fi as a fluctuating long distance communication sound effect, as heard in Silent Running (1971). I think the effect may have actually been more popular in music long ago due to more people hearing it on a.m. radio and finding it captivating. It is a rarely mentioned part of pop culture.
Due to the different path length measured in wavelengths (how far a signal of a specific frequency travels during one complete cycle) resulting in phase differences, the various components of a stations signal spectrum across a channel will see differing many combinations of aiding and cancelling, and those will be constantly changing since the ionosphere does. Although most of the time the ionization density is not high enough to be visible, the unseen reflecting regions have the same changing properties seen when viewing the Aurora Borealis. Except for when the carrier frequency is suppressed too much causing common receivers to distort, the rest of the effect is like a flanger.

Italian translated to english by reporters by Casandro · 2012-03-02 03:00 · Score: 1

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.

A solid answer to why SETI hears nothing by ShooterNeo · 2012-03-02 03:06 · Score: 1

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 by felipekk · 2012-03-02 03:19 · Score: 1

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.
Re:A solid answer to why SETI hears nothing by Anonymous Coward · 2012-03-02 07:34 · Score: 0

SETI aren't looking for a coherent signal that we can decode: they're looking for signals who's power is significantly above background, and are located in a fixed bandwidth range I.e. "strong narrow band signals". No one actually expects to decode anything that SETI might pick up.
Re:A solid answer to why SETI hears nothing by Anonymous Coward · 2012-03-02 07:56 · Score: 0

And will either be so primitive they can't receive them, or so advanced they don't think to look for anything as primitive as AM.
And that's only slightly tongue-in-cheek -- even now, how many radio operators would recognize the output of an old spark-gap transmitter splattering across broad swaths of HF as a comms transmission rather than interference from some industrial process, if it weren't for the familiar Morse encoding?
Re:A solid answer to why SETI hears nothing by psydeshow · 2012-03-02 08:08 · Score: 1

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.
Unfortunately, those observers will be busy working on how to make usable tools out of bronze and so our signals will pass right by. By the time they develop radio technology 3000 years later, we will either have blown ourselves into oblivion or be communicating using far more advanced technology as the parent comment suggested.
Re:A solid answer to why SETI hears nothing by felipekk · 2012-03-02 08:35 · Score: 1

And what exactly makes you think they will be less advanced than us? I mean it could possibly be, I'm just curious if there's a reason or not. Because what I first thought was that anyone else would likely be more advanced than us.
Re:A solid answer to why SETI hears nothing by psydeshow · 2012-03-02 09:03 · Score: 1

Oh I don't. Just pointing out how narrow the window is given the vastness of space and time.
Will the SETI project continue for another 3000 years? What if we're using quantum entanglement to communicate at faster than light speeds, would we even notice if a weak electromagnetic signal wandered into the neighborhood? Completely different communications gear, probably not.
Re:A solid answer to why SETI hears nothing by sjames · 2012-03-02 11:17 · Score: 1

If their technology is sufficiently advanced. Otherwise by the time they develop good enough receivers, our signals will look like noise.
It doesn't preclude detection, but it does considerably reduce the odds.

Re:Interesting but not convincing. Circ Polarizati by Muad'Dave · 2012-03-02 03:06 · Score: 1

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!

--
Tiller's Rule: Never use a word in written form that you've only heard and never read. You will end up looking foolish.

Signal Power by pavon · 2012-03-02 03:13 · Score: 2

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 by pavon · 2012-03-02 03:27 · Score: 1

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.

Health Concerns by fluffythedestroyer · 2012-03-02 03:16 · Score: 0

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 by OveE · 2012-03-02 03:31 · Score: 3, Informative

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" (http://www.bbc.co.uk/news/science-environment-17221490), 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.

Re:NOTHING NEW - PROVEN by Anonymous Coward · 2012-03-02 03:39 · Score: 1

The manuscript version of the paper mentioned above can be downloaded here:
http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=2062936&fileOId=2339120

Spectrum not overcrowded, mismanged by colsandurz45 · 2012-03-02 03:32 · Score: 4, Interesting

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 www.sharedspectrum.com/. 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 by Guppy · 2012-03-02 03:42 · Score: 2

"...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? by Eravnrekaree · 2012-03-02 04:04 · Score: 1

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.

BULLSH!T by tizan · 2012-03-02 04:14 · Score: 1

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.

This may work for a dish... by Anonymous Coward · 2012-03-02 04:15 · Score: 0

...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... by Anonymous Coward · 2012-03-02 04:30 · Score: 0

Correction: even 'if' the stream is highly directional...
Re:This may work for a dish... by Anonymous Coward · 2012-03-02 05:21 · Score: 0

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

The same as MIMO by Jott42 · 2012-03-02 04:31 · Score: 3, Informative

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?" http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=2062936&fileOId=2339120

Re:The same as MIMO by goodmanj · 2012-03-02 05:25 · Score: 2

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 by MajroMax · 2012-03-02 04:51 · Score: 2

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.

--
"Evil company X is threatening to restrict our rights! Let's all get together to stop--OOOH! SHINEY!!!" -- AC

Not new by Anonymous Coward · 2012-03-02 04:55 · Score: 1

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.

Re:Not new by darenw · 2012-03-02 13:16 · Score: 1

I want "Antenna Cancellation to Exploit Spatial Diversity" on a coffee mug and/or t-shirt.

Oh Crap by Anonymous Coward · 2012-03-02 05:10 · Score: 0

A lay perspective, but, I am a scientist.

I'm a hairy butt monkey's uncle.

Research paper for the OP twisted OAM by Anonymous Coward · 2012-03-02 06:15 · Score: 0

http://arxiv.org/ftp/arxiv/papers/1107/1107.2348.pdf

It's not the same.

More by Anonymous Coward · 2012-03-02 06:36 · Score: 0

http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=2062936&fileOId=2339120

http://www.aim.uu.se/Publications/Preprints/ThideEtAl:PRL:2007.pdf

The Wrong Bounce by glorybe · 2012-03-02 06:43 · Score: 1

What happens to such signals when they reflect from a building or other structure? Do the bounced signals maintain their relationship when bounced or does some kind of conflict and noise result in the reflections? It sounds suspicious to me as in too good to be true..

In other news by Anonymous Coward · 2012-03-02 07:05 · Score: 0

HAM is not an acronym, and should not be capitalized.

MOD UP by Anonymous Coward · 2012-03-02 07:56 · Score: 0

IANAP but pp seems informative.

PS had to laugh at ref 2 Emmy Noether 1918 :-) Pity I don't understand much 1918-level physics :-(

Block diagram of the apparatus. by CurryCamel · 2012-03-02 09:13 · Score: 1

As a lay M.Sc., EE, radio tech., I'd have appreciated a simple block diagram of the apparatus to explain "for the rest of us" what exactly they were doing (and how it differs from e.g. plain old MIMO). Not images of Yagi antennas.

That is the problem with revolutionary ideas. People tend to call "BS" when they don't understand. And I didn't.

Re:Block diagram of the apparatus. by Anonymous Coward · 2012-03-02 09:34 · Score: 0

The problem is that it is not different from MIMO. See the following paper: "Is orbital angular momentum (OAM) based radio communication an unexploited area?" http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=2062936&fileOId=2339120

incoherent radio by AdamWill · 2012-03-02 10:02 · Score: 1

"physicists have shown that it is possible to use two beams of incoherent radio waves"

Finally! A use for Rush Limbaugh!

Dupe! by scumfuker · 2012-03-02 14:35 · Score: 1

http://tech.slashdot.org/story/09/02/13/2039222/twisted-radio-beams-could-untangle-the-airwaves Well, at least it was more than a couple hours apart!

Orbital Angular Momentum by ka9dgx · 2012-03-02 18:20 · Score: 1

It turns out that if you can use circularly polarized light to manipulate nanoscopic objects, and make them spin.

I wonder what would happen if you built a 2 Ghz transmitter system which fed an antenna with a spin on the order of 10? Would it cause something like the Norway Spiral by spinning the air that happened to absorb part of the signal?

Google "Orbital Angular Momentum" and you'll find all sorts of stuff that almost seems like magic, or science fiction, that actually could work.

I finally grok this! by ka9dgx · 2012-03-03 04:25 · Score: 1

It took a few hours contemplation for me to finally get my mind wrapped around this one, here's my explanation.

Imagine you have an AC motor, with 2 poles. If driven with 60 hz power, it will spin at 3600 rpm (60 rotations per second).
The same 60 hz power can be fed into a 4 pole AC motor which will spin at 1800 rpm (30 rotations per second)
Generalizing, The same 60 hz power can be used for a 2n pole motor to get a spin of (7200 /.n) rotations per second.

If you were to hold a magnet in the center of any of these motors it would vibrate at 60 hz. - This is analogous to a normal antenna trying to pick on one of these signals, it would pick up the carrier frequency regardless of the spin.

It is only when you let the magnet spin that you can measure speed at which the field rotates - This is why it takes multiple antenna to discriminate between signals.

Now the real fun is when you imposed BOTH a 2 pole and a 4 pole signal in the same space... if you put a rotor in and let it spin, you might get either 3600 or 1800 rpm... hard to guess.... but if you spun it up to just under 3600 rpm, it would pull forward to 3600 rpm, with the same effect if you spun it at 1800 rpm. There would be a lot of energy lost in cross coupling of the winding coils, though.

If we went a bit further, and considered a motor which had a way to simultaneously be powered in 2, 4, 6, 8, and 10 pole modes, you'd be able to measure the voltage fed into each of them by rotating the motor up to the appropriate speed and measuring the torque on the rotor... you'd get 5 different numbers, each linearly related to the amount of excitation for that set of windings.

You lose the utility of a motor, but you get the ability to convey 5 different signal levels with 1 frequency. Cool stuff!

helix antennas anyone ? by Anonymous Coward · 2012-03-06 23:05 · Score: 0

whats the difference between this and helix antennas ?

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