Last year, researchers from the University of Columbia invented a full-duplex radio IC (integrated circuit) for super-fast WiFi reception and transmission using two antennae. Now, the same team have developed their system to function on a single antenna, which delivers the same wireless speeds but at half the size, marking the first time that anyone has integrated a non-reciprocal circulator and a full-duplex radio on a nanoscale silicon chip. The team’s work is showcased in a new Nature paper entitled “Magnetic-free non-reciprocity based on staggered commutation”.
“This technology could revolutionize the field of telecommunications,” Harish Krishnaswamy, Electrical Engineering Associate Professor at Columbia University’s School of Engineering and director of the Columbia High-Speed and Mm-wave IC (CoSMIC) Lab, said in a press release. “Our circulator is the first to be put on a silicon chip, and we get literally orders of magnitude better performance than prior work. Full-duplex communications, where the transmitter and the receiver operate at the same time and at the same frequency, has become a critical research area and now we’ve shown that WiFi capacity can be doubled on a nanoscale silicon chip with a single antenna. This has enormous implications for devices like smartphones and tablets.”
The technology has been years in the making, with the researchers struggling to “break” what is known as Lorentz Reciprocity, which restricts to electromagnetic waves travel in two directions.
“Reciprocal circuits and systems are quite restrictive because you can’t control the signal freely,” PhD student Negar Reiskarimian, lead author of the Nature Communications paper and developer of the circulator, added. “We wanted to create a simple and efficient way, using conventional materials, to break Lorentz Reciprocity and build a low-cost nanoscale circulator that would fit on a chip. This could open up the door to all kinds of exciting new applications.”
In order to break Lorentz Reciprocity, the team eschewed the usual use of magnetic materials – which are effective but either are expensive or are incompatible with silicon chip technology – in favour of a new design of miniature circulator that is able to rotate signals around the capacitors, via switches, to lose reciprocity.
“Being able to put the circulator on the same chip as the rest of the radio has the potential to significantly reduce the size of the system, enhance its performance, and introduce new functionalities critical to full duplex,” PhD student Jin Zhou, responsible for integrating the circulator with the full-duplex receiver, said.
The researchers are currently working on improving the system in anticipation of any potential implementation in, say, smartphones and computers.
“What really excites me about this research is that we were able to make a contribution at a theoretically fundamental level, which led to the publication in Nature Communications, and also able to demonstrate a practical RF circulator integrated with a full-duplex receiver that exhibited a factor of nearly a billion in echo cancellation, making it the first practical full-duplex receiver chip and which led to the publication in the 2016 IEEE ISSCC,” Krishnaswamy said. “It is rare for a single piece of research, or even a research group, to bridge fundamental theoretical contributions with implementations of practical relevance. It is extremely rewarding to supervise graduate students who were able to do that!”
