Feeds

Boffins biff over ‘twisted radio’

Is infinite capacity possible?

High performance access to file storage

Six months after an Italian/Swedish group set the comms world alight with a wireless technology of theoretically infinite capacity, debate over his work is becoming increasingly bitter.

To recap the original story: today’s wireless technologies use a handful of venerable modulation schemes to carry information (amplitude, frequency and phase). To pack more data on a carrier, you can increase its baseband frequency, use a wider wireless channel, or find some way to multiplex the wireless channels.

Frequency division multiplexing gets extra capacity by allowing stations to transmit simultaneously over multiple carriers; and spatial multiplexing (using multiple antennas – MIMO) does so by using the same carrier over different paths.

The “spin modulation” group – led by Fabrizio Tamburini of the University of Padua and Bo Thidé of the Swedish Institute of Space Physics and first demonstrated this year in Venice – proposed using a previously-unexploited characteristic of radio waves, their orbital angular momentum, or “spin”.

The theory, then, is this: if Bob and Alice both want to communicate on the same frequency, they can do so by applying different spin values to their signal, so long as the receiver can detect that spin. In the original test, that spin was imparted by a modified dish antenna.

Multiple-signal demonstration antenna

Did the spinning antenna create a MIMO channel?

Since there’s no limit to the number of spin states that can exist, this was heralded all over the world as “infinite capacity wireless”. There were, however, sceptics at the time, and more recently, that’s become what the BBC calls “’he says, she says’ with references”.

One issue is that the demonstration earlier this year only multiplexed two signals. According to this paper (lead author Michele Tamagnone of EPSL), the antenna configuration for the “spin modulation” test could be seen as creating a MIMO case – sending Bob and Alice’s signals over different paths created by the shape of the dish.

It’s important to note that Tamagnone’s group do not dispute whether multiplexing was observed in the “Venice experiment”, only that OAM isn’t needed to explain the results.

Tamburini and Thide disagree, here, reiterating their belief that OAM was observed in their experiments both at Venice and at Padua.

The other dissenting paper, (here) from Lazlo Kish and Robert Nevels of Texas A&M University’s department of electrical and computer engineering, doesn’t dispute whether the original experiments demonstrated OAM – but vigorously disputes the “infinite capacity” notion. These two authors argue that if a free-space system multiplexed more than two signals, OAM would violate the Second Law of Thermodynamics.

A final note from El Reg, so as those leaving comments don’t get drawn down a rabbit-burrow: multiple spins have been encoded onto optical waves and transmitted down fibres. The current – and presumably ongoing – furore is about whether the phenomenon can be used for free space radio transmissions. ®

High performance access to file storage

More from The Register

next story
Fancy joining Reg hack on quid-a-day challenge?
Recruiting now for charity starvation diet
Red-faced LOHAN team 'fesses up in blown SPEARS fuse fiasco
Standing in the corner, big pointy 'D' hats
KILLER SPONGES menacing California coastline
Surfers are safe, crustaceans less so
Opportunity selfie: Martian winds have given the spunky ol' rover a spring cleaning
Power levels up 70 per cent as the rover keeps on truckin'
Discovery time for 200m WONDER MATERIALS shaved from 4 MILLENNIA... to 4 years
Alloy, Alloy: Boffins in speed-classification breakthrough
Elon Musk's LEAKY THRUSTER gas stalls Space Station supply run
Helium seeps from Falcon 9 first stage, delays new legs for NASA robonaut
Top Secret US payload launched into space successfully
Clandestine NRO spacecraft sets off on its unknown mission
prev story

Whitepapers

Top three mobile application threats
Learn about three of the top mobile application security threats facing businesses today and recommendations on how to mitigate the risk.
Combat fraud and increase customer satisfaction
Based on their experience using HP ArcSight Enterprise Security Manager for IT security operations, Finansbank moved to HP ArcSight ESM for fraud management.
The benefits of software based PBX
Why you should break free from your proprietary PBX and how to leverage your existing server hardware.
Five 3D headsets to be won!
We were so impressed by the Durovis Dive headset we’ve asked the company to give some away to Reg readers.
SANS - Survey on application security programs
In this whitepaper learn about the state of application security programs and practices of 488 surveyed respondents, and discover how mature and effective these programs are.