After four years of not-so-gentle disbelief and mockery, Bo Thide of the Swedish Institute for Space Physics and a team in Italy have finally proven that it is possible to transmit multiple radio channels simultaneously on the exact same wireless frequency. In theory, according to Thide, we could potentially transmit an “infinite number” of TV, radio, WiFi and cellular channels at the same time on the same frequency, blowing up our very crowded wireless spectrum.
Thide’s approach is quite simple. Basically, electromagnetic waves can have both spin angular momentum and orbital angular momentum (OAM). If you imagine the Earth-Sun system, the rotational moment is the Earth rotating on its axis (producing the day-night cycle), and the orbital moment is the Earth rotating around the Sun (producing the seasons). In standard wireless communications – radio, television, WiFi – we only modulate the angular momentum of rotation of the waves. For years, Thide had speculated that orbital angular momentum could also be added to wireless signals, creating a spiraling signal resembling fusilli pasta; or, in Thide’s words, a “radio vortex”.
Now, in an experiment in Venice, Thide and his Italian colleagues transmitted two signals at the same time, on the same frequency, over a distance of 442 meters (1,450 feet). In the photo on the right, the antenna used by the team. No, your eyes aren’t deceiving you: To create these radio swirls, simply cut out a standard parabolic reflector and twist it slightly. If you imagine a corkscrew of radio signals streaming from the outer edge of the antenna, that is indeed what is happening. On the receive side, there are two “normal” TV antennas (Yagi-Uda) spaced at the same angle as the transmitter cutoff. These antennas “decode” the vortex, and voila: two radio signals transmitted on the same frequency.
It’s hard to put into words just how significant Thide’s discovery could be. If the vortex preserves other aspects of wireless communications, such as multiplexing, then in the short term we could envision a wireless spectrum that can carry 10 or 20 times more data. In the long term, as our understanding of orbital angular momentum grows, our wireless spectrum could effectively be infinite. To be honest, this is such a twist for wireless communications that the full repercussions are not yet known.
Along with radio and television, and now cellular networks, wireless spectrum is one of humanity’s most valuable resources. It’s because the airwaves are so congested that companies like Verizon or Vodafone are paying billions of dollars for just a few megahertz. If Thide’s discovery comes to fruition, not only would wireless spectrum lose most of its value, but the issues and conflicts surrounding LightSquared, international roaming, LTE deployment, wireless white space, and digital TV would simply cease to be.
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