A DARPA-funded research team said recently it had developed a tiny component for silicon-based circuitry that could double the radio-frequency (RF) capacity for wireless communications—offering faster web-searching as well as the development of smaller, less expensive and more readily upgraded antenna arrays for radar, signals intelligence, and other applications.
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The work was led by Columbia University electrical engineers Harish Krishnaswamy and Negar Reiskarimian and funded under DARPA’s Arrays at Commercial Timescales (ACT) program, which is looking to develop wireless electronic components that can be integrated into larger, more advanced systems quickly. DARPA said ACT products aim to “shorten design cycles and in-field updates and push past the traditional barriers that lead to 10-year array development cycles, 20- to 30-year static life cycles and costly service-life extension programs.”
In this case the creation focuses on an electrical component known as a “circulator” typically used to control the direction of signal flow in a circuit.
“The defining feature of circulators is that RF signals, in the form of electronic waves in the circuitry, travel only in a forward direction with reverse propagation of the wave forbidden by the physics of the circuit. That’s what you need for minimizing on-chip interference and for keeping signals separated. Most materials can’t play this role because RF traffic can flow both ways through them; these materials exhibit what engineers refer to as reciprocal behavior,” DARPA stated.
“Traditionally, circulators have relied on external, ferrite-based magnets to force RF signals into a one-way course through downstream circuitry. Those magnets and ferrite materials have rendered the circulators bulky, expensive, and incompatible with the workhorse microcircuit technology, or CMOS, so it has been hard to miniaturize circulators for CMOS integrated circuits,” DARPA said.
In a nutshell the Columbia researchers got around these problems by enabling two-ay or full-duplex communications design that does away with the need for ferrites and magnets.
“This new circulator component could enable full-duplex systems that let you speak and listen all at once,” said William Chappell, director of DARPA’s Microsystems Technology Office in a statement. In radar applications, this capability could put an end to brief but potentially deadly blind moments since the system would not have to toggle between separate transmission and reception modes.
And by halving the frequency needs, full-duplex communication has the potential to double a network’s capacity for voice, data, and other forms of information. In powerful radar and other RF systems that require large arrays of transmitters and receivers, “a compact, efficient, high-performance circulator” makes it easier for RF engineers to make their systems smaller, Columbia researcher Krishnaswamy said.
ACT research is but one of the programs DARPA is currently working on to bolster eh wireless arena.
In March the defense research agency recently announced a $2 million Grand Challenge called the Spectrum Collaboration Challenge (SC2) whose primary goal is to infuse radios with “advanced machine-learning capabilities so they can collectively develop strategies that optimize use of the wireless spectrum in ways not possible with today’s intrinsically inefficient approach of pre-allocating exclusive access to designated frequencies.”
DARPA said the current practice of assigning fixed frequencies for various uses irrespective of actual, moment-to-moment demand is simply too inefficient to keep up with actual demand and threatens to undermine wireless reliability in the military as well as civilian applications, DARPA stated.
The challenge is expected to take advantage of recent significant progress in the fields of artificial intelligence and machine learning and also spur new developments in those research domains, with potential applications in other fields where collaborative decision-making is critical,” DARPA stated.
“DARPA Challenges have traditionally rewarded teams that dominate their competitors, but when it comes to making the most of the electromagnetic spectrum, the team that shares most intelligently is going to win,” said SC2 program manager Paul Tilghman of DARPA’s Microsystems Technology Office in a statement. “We want to radically accelerate the development of machine-learning technologies and strategies that will allow on-the-fly sharing of spectrum at machine timescales.”
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DARPA said it will build what it called the largest-of-its-kind wireless test bed – “the Colosseum” -- which will serve during and after the SC2 as a national asset for evaluating spectrum-sharing strategies, tactics, and algorithms for next-generation radio systems. The “Colosseum” will let researchers remotely conduct large-scale experiments with intelligent radio systems in realistic, user-defined RF environments, such as the wireless conditions of a busy city neighborhood or battle setting.
The actual SC2 will include three, year-long phases beginning in 2017 and finish in early 2020 with a live competition of finalists who have survived the two preliminary contests. The team whose radios collaborate most effectively with various types of other radios to dynamically optimize spectrum usage will win a grand prize of $2 million, DARPA stated.
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