It's no secret that one of the biggest topics in the mobile broadband sector is spectrum. Mobile operators are not only looking to get more spectrum for LTE – particularly in the coveted 700-MHz band – but also to get more out of spectrum they already have, hence the growing interest in refarming the 1800-MHz bands for LTE by players like StarHub, Telstra, CSL and Indosat.
There’s a number of technological solutions on the horizon to milk as much spectral efficiency out of spectrum as possible, from small cells to advanced MIMO solutions. But a team of researchers in Europe have hit upon something a little more radical to boost capacity in a radio signal by – literally – giving it a twist.
Research led by Italian astrophysicist Fabrizio Tamburini and Swedish physicist Bo Thidé claims to have found a way to increase spectrum capacity by twisting radio waves. The “twisting” part stems from the application of orbital angular momentum (OAM), a century-old discovery which states that electromagnetic fields can transport not only energy and linear momentum but also angular momentum, to radio beams. OAM has already been applied to laser optics, but not to RF technology until recently.
As the abstract of the team’s research paper explains: “We have shown experimentally that it is possible to propagate and use the properties of twisted non-monochromatic incoherent radio waves to simultaneously transmit to infinity more radio channels on the same frequency band by encoding them in different orbital angular momentum states. This novel radio technique allows the implementation of, at least in principle, an infinite number of channels on one and the same frequency, even without using polarization or dense coding techniques.”
What that essentially means is that it's possible to leverage OAM to twist a radio wave into a vortex, which creates distinctly shaped sub-frequencies that can be used to transmit and receive data without interfering with one another.
Result: a potential 100x increase in bandwidth for wireless broadband (although Tamburini says that, in theory, an OAM vortex could generate sub-frequencies to infinity).