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"Twisted" OAM Beams Carry 2.5 Terabits Per Second 142

Posted by samzenpus
from the greased-lightning dept.
MrSeb writes "American and Israeli researchers have used twisted, vortex beams to transmit data at 2.5 terabits per second. As far as I can discern, this is the fastest wireless network ever created — by some margin. These twisted signals use orbital angular momentum (OAM) to cram much more data into a single stream, without using more spectrum. In current state-of-the-art transmission protocols (WiFi, LTE, COFDM), we only modulate the spin angular momentum (SAM) of radio waves, not the OAM. If you picture the Earth, SAM is our planet spinning on its axis, while OAM is our movement around the Sun. Basically, the breakthrough here is that researchers have created a wireless network protocol that uses both OAM and SAM. In this case, Alan Willner and fellow researchers from the University of Southern California, NASA's Jet Propulsion Laboratory, and Tel Aviv University, twisted together eight ~300Gbps visible light data streams using OAM. For the networking nerds, Willner's OAM link has a spectral efficiency of 95.7 bits per hertz; LTE maxes out at 16.32 bits/Hz; 802.11n is 2.4 bits/Hz. Digital TV (DVB-T) is just 0.55 bits/Hz. In short, this might just be exactly what our congested wireless spectrum needs."
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"Twisted" OAM Beams Carry 2.5 Terabits Per Second

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  • by Jonathan_S (25407) on Monday June 25, 2012 @08:48AM (#40438027)

    This is very cool, but the current super high bandwidth demonstration is being done with optical light over very short (1 meter) distances.

    The article did point to an article from a couple months ago about the first ever OAM transmission; which was done with radio waves. But the antennas used look very directional and there was no mention of bandwidth.

    Optical might be useful to further increase the speed of fibers, and highly directional radio might help for satellite broadcast or to compete with microwave relay towers. But requiring highly directional antennas, on both ends, isn't good for mobile wireless.

    Hopefully we'll see another story soon where someone figures out how to detect and transmit OAM encoded radio waves from non-directional antennas.

  • Re:Holy Crap! (Score:5, Insightful)

    by sycodon (149926) on Monday June 25, 2012 @09:05AM (#40438207)

    I wouldn't get too excited.

    Network technology has been steadily advancing, yet in the U.S. Internet access speeds and costs have remained stagnant.

  • by Anonymous Coward on Monday June 25, 2012 @09:13AM (#40438285)

    Two reasons:
    * This is applicable to point-to-point links, not broadcast.
    * This involves a structured beam multiple wavelengths in diameter -- infeasibly large at 1-10 GHz frequencies.

    So what is it good for? Free-space optical comms! It could also be applied to sub-THz frequencies for increased range, but not to wavelengths as long as are commonly used today. Applications include backhaul for GSM towers and satellite-to-satellite comms.

    It's worth noting, however, that free-space optical comms are not particularly bandwidth-constrained, so the incredible spectral efficiency (TFA says 95.7 bits [sic] per hertz) is not as important as it might seem -- you have literally hundreds of terahertz available in the optical window, so when you need more capacity, you can simply add another wavelength to the beam instead of adding orbital structure to the beam.

    I'm not hating on this research -- it's ridiculously cool stuff, and far enough from my field I'd be foolish to think I know better -- but I do remain unclear whether this will end up with any definite advantage over existing techniques.

  • by dentin (2175) on Monday June 25, 2012 @02:24PM (#40442677) Homepage

    Yes, it does limit the number of channels, because the channels are not perfectly orthogonal due to the presence of noise. No single channel coding scheme can bypass Shannon; neither can any combination of elegant channel coding algorithms. Shannon is not a physical 'limit' to be worked around; it is a theoretical limit, and it does not care one whit about the properties of the channel or the modulations used.

    If you transmit bits in the presence of noise, Shannon applies.

    -dentin

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