Twisting radio beams to transmit ultra-high-speed data

Transmissions reach speeds of 32 gigabits per second
September 18, 2014

A graphic showing the intensity of the radio beams after twisting (credit: Alan Willner / USC Viterbi)

Building on previous research using twisted light to send data at unheard-of speeds, scientists at USC have developed a similar technique with radio waves, reaching high speeds without the problems with optical systems.

The researchers, led by electrical engineering professor Alan Willner of the USC Viterbi School of Engineering, reached data transmission rates of 32 gigabits per second across 2.5 meters of free space in a lab — “one of the fastest data transmission via radio waves that has been demonstrated,” Willner said.

(For reference, 32 gigabits per second is fast enough to transmit more than 10 hour-and-a-half-long HD movies in one second and is 30 times faster than LTE wireless.)

Faster data transmission rates have been achieved. Willner’s team two years ago used twisted light beams to transmit data at 2.56 terabits per second. “The advantage of radio is that it uses wider, more robust beams,” he said. “Wider beams are better able to cope with obstacles between the transmitter and the receiver, and radio is not as affected by atmospheric turbulence as optics.”

Willner is the corresponding author of an article about the research published in Nature Communications (open access) on Sept. 16. University of Glasgow and Tel Aviv University researchers were also involved in the research.

To achieve the high transmission rates, the team passed each beam — which carried its own independent stream of data at millimeter wavelength — through a “spiral phase plate” that twisted each radio beam into a unique and orthogonal DNA-like helical shape. A receiver at the other end of the room then untwisted and recovered the different data streams.

“This technology could have very important applications in ultra-high-speed links for the wireless ‘backhaul’ that connects base stations of next-generation cellular systems,” said Andy Molisch of USC Viterbi. Molisch, whose research focuses on wireless systems, co-designed and co-supervised the study with Willner. The technology could also have potential applications in places such as data centers where large bandwidth links between computer clusters are required, according to the paper.

Future research will focus on attempting to extend the transmission’s range and capabilities.

The work was supported by Intel Labs University Research Office and the DARPA InPho (Information in a Photon) Program.


Abstract of Nature Communications paper

One property of electromagnetic waves that has been recently explored is the ability to multiplex multiple beams, such that each beam has a unique helical phase front. The amount of phase front ‘twisting’ indicates the orbital angular momentum state number, and beams with different orbital angular momentum are orthogonal. Such orbital angular momentum based multiplexing can potentially increase the system capacity and spectral efficiency of millimetre-wave wireless communication links with a single aperture pair by transmitting multiple coaxial data streams. Here we demonstrate a 32-Gbit s−1 millimetre-wave link over 2.5 metres with a spectral efficiency of ~16 bit s−1 Hz−1 using four independent orbital–angular momentum beams on each of two polarizations. All eight orbital angular momentum channels are recovered with bit-error rates below 3.8 × 10−3. In addition, we demonstrate a millimetre-wave orbital angular momentum mode demultiplexer to demultiplex four orbital angular momentum channels with crosstalk less than −12.5 dB and show an 8-Gbit s−1 link containing two orbital angular momentum beams on each of two polarizations.