Wireless breakthrough: one frequency, multiple signals, page 2

Originally posted by -PLB-
It looks interesting, but from what I understand of it, it only works in a fixed direction. So the antennas requires to be pointed exactly towards each others. Practical applications may be satellites and other long distance connections, but I don't see how it would work for any mobile device, as the direction the antennas are pointing to is constantly changing. I may be wrong though.

Yes, the setup as originally described does use specific spatial orientations in transmitter & receiver.

Calling it 'orbital' vs 'spin' angular momentum (referring to polarization) is a bit of a fluff.

At the frequencies and intensities involved, this is all 100% classical physics from Maxwell's equations. If you impart twist at space scales near or smaller than a wavelength they'd call it "spin" angular momentum vs "orbital" angular momentum. But it all relies on the fact that E&M has 3 propagating vector field (though no longitudinal component), and you can modify it spatially as well (which is what this group is doing). I think this is a continuous-space version of "MIMO", multiple-input-multiple-output transmitter/receiver which is already a developed technology.

In a practical sense the big problem is scrambling of all the spatial information after reflection & refraction. If you take a modulated FM signal, for instance, even though you have all sorts of spatial interference/reflection etc, you can still pick it up well. Why? Because interaction with the ground or trees or buildings won't change the carrier frequency or, especially, the modulations of that frequency. (You would need active transmitters to do that, known as electronic counter measures). That's why FM was the first high-quality radio system---you can both transmit the signal well and after inventing superheterodyne it's practical to demodulate with a few analog components.

The natural environment, on the other hand, will naturally scramble nearby spatial patterns.

I'll play product manager for free....so here goes...:

Market: The best application for this will be large-bandwidth satellites, where you have line-of-sight connectivity at high frequencies. The NSA & NRO contractors will be all over it---you might be able to get the benefits of MIMO in a large antenna just by clever physical design, without requiring the typical engineer's brute-force approach, a huge number of active components in an array all sucking down valuable and limited electrical power. You would need as many individual transmitters as signals {can't get around that}, but use passive physics instead of active array modulation to apply the spatial modulation.

Technological future: The current system applied two different spatial patterns with a classical symmetry. That might not be the ultimate---you could imagine multiple transmitters/recievers on some kind of 'fractal' or otherwise spatially complex antenna, and then a a very smart reciever (which is is possible now) which untangles the N independent spatial patterns that it detects with a complex geometry receiver. Advances in machine learning & signal processing in the last 15 years or so have greatly improved the capability of blind-source separation, something like ICA (independent component analysis) could possibly even be implemented in hardware at GHz speeds, with some major effort. One advantage of using adaptive learning methods is that you may be able to ameliorate the spatial scrambling effect from scattering. Scattering might change the geometrical relationships, but as long as there are N distinctly separable spatial patterns (as natural objects will not have the specific spatial complexity of the transmitter), you could likely recover them.

I'll coin this as "spatial-code-division-multiple-access" (S-CDMA) --- applying encoding/decoding analogous to the time-series codes, but in x,y,z instead of in t.

edit on 3-3-2012 by mbkennel because: (no reason given)