Full-duplex radio communication usually involves transmitters and receivers operating at different frequencies. Simultaneous transmission and reception on the same frequency is the Holy Grail for researchers, but has proved difficult to achieve. Those that have been built have proven complex and bulky, but to be commercially useful in the ever-shrinking world of communications technology, miniaturization is key. To this end, engineers at Columbia University (CU) claim to have created a world-first, full-duplex radio transceiver, all on one miniature integrated circuit.

Implemented at the nanoscale on a CMOS (Complementary Metal Oxide Semiconductor) integrated circuit (IC), the new device from the CU team enables simultaneous wireless radio transmission and reception at the same frequency. Dubbed CoSMIC – for Columbia high-Speed and Mm-wave IC – the team believes that its transceiver could help revolutionize mobile communications technology.

"This is a game-changer," said Associate Professor Harish Krishnaswamy of CU's Fu Foundation school of Engineering and Applied Science. "By leveraging our new technology, networks can effectively double the frequency spectrum resources available for devices like smartphones and tablets."

To achieve this reported full-duplex capability, the team needed first to cancel out the transmitter's echo on the frequency so that the minute "whisper" of the received signal could be heard. The team likens this to you trying to listen to someone else whispering a distance away whilst another person is standing next to you shouting. To hear that whisper, you must first cancel the sound of the person yelling.

"If everyone could do this, everyone could talk and listen at the same time, and conversations would take half the amount of time and resources as they take right now," said Jin Zhou, Associate Professor Krishnaswamy’s PhD student. "Transmitter echo or ‘self-interference’ cancellation has been a fundamental challenge, especially when performed in a tiny nanoscale IC, and we have found a way to solve that challenge."

The researchers are not actually the first to produce a full-duplex radio system, nor are they the first to use the analogy of the whisperer/shouter. Stanford University produced a system using ostensibly similar techniques, and explained its system using exactly the same premise as the Columbia team.

However, what Columbia is first at is the miniaturization of the full-duplex transceiver onto an integrated circuit. Other systems have been built using much larger, bulkier electronics and printed circuit boards. The CU system is the first to bring all of that down to the size that will easily fit inside a smartphone, a tablet, or any other modern communications device.

As such, the most pressing and useful application of this technology would be in helping to solve the increasing frequency spectrum crisis where wireless networks operating in the not-too-distant future will be unable to cope with the enormous increases in data transfer. This problem is exemplified by the fact that current protocols, such as 4G/LTE, currently bear the weight of 40 separate frequency bands, with almost no room for the inevitable expansion required. All this while the planned 5G network is set to grow data exchange capabilities a thousand-fold.

As a result, it is this increased demand for data transmission capacity that the team members see as the greatest advantage for full-duplex, device-mounted integrated circuits like theirs.

"Our work is the first to demonstrate an IC that can receive and transmit simultaneously,” said Associate Professor Krishnaswamy. "Doing this in an IC is critical if we are to have widespread impact and bring this functionality to handheld devices such as cellular handsets, mobile devices such as tablets for Wi-Fi, and in cellular and Wi-Fi base stations to support full duplex communications."

The next phase for this research will see Krishnaswamy and Zhou run tests on a range of full-duplex nodes to gauge what the real benefits are at the network level.

"We are working closely with Electrical Engineering Associate Professor Gil Zussman and his PhD student Jelena Marasevic, who are network theory experts here at Columbia Engineering," Krishnaswamy added. "It will be very exciting if we are indeed able to deliver the promised performance gains."

The results of this research were recently presented at the International Solid-State Circuits Conference (ISSCC) in San Francisco.