Bi-directional RF doubles cellular capacity
That is, either transmitting and receiving at the same time, but on different frequencies, or at different times on the same frequency. But that is a lie, according to researchers at Columbia University in New York City.
CoSMIC Lab full-duplex transceiver IC that can be implemented in nanoscale CMOS to enable simultaneous transmission and reception at the same frequency in a wireless radio. ISource: Jin Zhou and Harish Krishnaswamy/Columbia University.
Columbia researchers recently demonstrated a complementary metal oxide semiconductor (CMOS) chip called CoSMIC (Columbia high-Speed and Mm-wave IC) for doing full-duplex on the same frequency at the same time, thus doubling wireless communication’s speed. Electrical engineering professor Harish Krishnaswamy told EE Times:
Full duplex at the same frequency has been thought to be impossible until today because if you transmit and receive at the same time at the same frequency, the receiver will get drowned out by the interference from the transmitter, which can be one billion times more powerful than the signal that one is trying to receive. But we have devised an echo- or self-interference cancellation scheme that can do away with the transmitter’s interference with one part per billion accuracy, so that after cancellation, the received signal can be easily detected.
Without Krishnaswamy’s team’s circuitry, full-duplex would be like trying to hear someone whisper while someone next to them was shouting at the top of their lungs, according to Krishnaswamy, who performed the work with doctoral candidate Jin Zhou.
"But if you could somehow cancel or block out the screaming next to you, and note that you would need to cancel it near-perfectly, you could then hear the whisper," Krishnaswamy said. "And we have found a way to do this for electromagnetic wireless signals using a tiny silicon chip."
Diagram of traditional RF communication (left) versus two-way full-duplex on same frequency at the same time (right) thus doubling speed. Source: Columbia University.
What Krishnaswamy calls an "echo canceler or self-interference canceler"–CoSMIC–is installed at the receiver’s input port, silencing the louder transmission signal so that the quieter receiver signal can be heard.
The key innovation is that to cancel the transmitter self-interference with one part per billion accuracy, the chip needs to make a near-exact replica of the transmitter self-interference. This is hard to do especially because the transmitter self-interference or echo will distort and change as it reflects off objects in the nearby environment.
In principle, all RF communications are amenable to this technique, Krishnaswamy noted, adding that his team have devised a circuit that can do this with a single silicon chip. The researchers will begin by trying to double the speed of wireless signals–in particular WiFi and cellular communications for smartphones and tablets.
"Wireless communications is facing a need for 1000x data capacity increase with 5G–a significant challenge–and full duplex operation could play a very important role in achieving that goal," Krishnaswamy said.
Beyond RF, the technique could also be used to double the capacity of optical communications channels. "We have been thinking about optical, but for the immediate future, we have our hands full with wireless," Krishnaswamy added.
According to Krishnaswamy and Zhou, their CMOS chip had to be fabricated at the nanoscale to achieve its billion-to-on cancelation rate. To deliver the chip in a package that can be commercialized, the team is working with EE professor Gil Zussman’s group.
Funding for this work was provided by the Defense Advanced Research Project Agency (DARPA).
About the author:
— R. Colin Johnson, Advanced Technology Editor, EE Times
If you enjoyed this article, you will like the following ones: don't miss them by subscribing to :
