Tuesday, November 4, 2014

DARPA's Terahertz Breakthrough Could Help Ease Spectrum Crunch

Administrators at Defense Advanced Research Projects Agency celebrated their first Guinness World Record last week for sponsoring the creation of the world’s fastest solid-state amplifier integrated circuit. At a ceremony in Arlington, VA, the Guinness representative joked it was the geekiest record ever.
The amplifier, which was developed by Northrup Grumman, can operate at 1 THz frequencies—about a trillion cycles per second—significantly faster than the existing record of 850 GHz that was set in 2012. It opens the door to the creation of terahertz radio, which could transmit exponentially greater amounts of data than today’s radios. Possible applications include covert satellite communications or the transfer of large amounts of data at close proximities. It also could be used for more detailed imaging and sensing. Think radar on steroids.
What we won’t see is terahertz-based telecommunications networks on earth or PCs running at terahertz speeds any time soon. In terms of communications, the sub-millimeter waves that make up the terahertz spectrum don’t travel well through the earth’s atmosphere. While terahertz computers are a theoretical possibility, today’s computers run on digital chips. DARPA’s breakthrough is an analogue chip that amplifies an analogue signal. In comparison, the world’s fastest desktop CPU, Intel’s 8-core Haswell-E has a maximum clock speed of 3.5GHz.
Still, Dev Palmer, the manager of DARPA’s Terahertz Electronics Program, said the nano-sized transistors that were developed for the amplifier could be instrumental in building next generation telecommunications networks known as 5G. Researchers are exploring how 5G networks could take advantage of little used spectrum in the 30 to 300 GHz range. This is known as millimeter wave communications in reference to the wavelengths of these frequencies. The 5G vision includes replacing the so-called last-mile fiber connection with wireless broadband and low-interference, highly dense small cells. This would help alleviate that so-called spectrum crunch in which ever-increasing amounts of wireless data is squeezed into the limited set of frequencies currently controlled by mobile carriers.
“One of the things about driving the transistor speed up into the terahertz region is that if you get rid of all the problems that prevent a transistor from operating at those high frequencies, as a side benefit you can run it back down at slower frequencies and get much better performance out of the transistor in terms of noise, which determines the sensitivity of the receiver, and also in terms of power efficiency, which affects the battery life of a handset,” Palmer said.
“While you have a pretty well-established chipset for 3G and 4G networks, when the communications industry moves into 5G, they are talking about taking a giant leap up in operating frequency,” ” Palmer explained. “If you take slower transistors and try to make them run faster, they don’t work very well. But if you take a faster transistor and back off (run it slower) it actually runs a lot better. So there is a potential application for millimeter wave communications.”

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