Columbia University engineers in the Columbia high-Speed and Mm-wave IC (CoSMIC) Lab have created a receiver integrated circuit (IC) intended for full-duplex wireless – an exciting new wireless communication paradigm where the transmitter and the receiver operate at the same time and at the same frequency. Since frequency and temporal resources are used to the fullest extent possible, full duplex wireless potentially doubles network capacity in the physical layer, while offering many other benefits at the network layer. The challenge associated with full-duplex wireless is the high transmitter self-interference, or echo, at the receiver input. This self-interference can be as high as a billion times more powerful than the desired signal to be received. This research builds on work on an integrated circulator that allows the transmitter and the receiver to share the same antenna, while providing isolation between the two

IC CIRCULATOR: Breakthrough integrated chip circulator for full duplex communication
https://www.youtube.com/watch?v=tIlj4RPbt8o

However, some of your transmit signal will always end up in the receiver for three reasons; (a) the circulator isn’t perfect, (b) the antenna doesn’t have a perfect match so some of the transmit energy sent to it bounces back again and (c) energy can reflect back from the immediate environment. Cancelling schemes exist, and invariably consist of some mechanism for sampling the transmitted signal and feeding just the right amount back into the receiver exactly out of phase. In theory this works, but in most practical circumstances the extremely high level of cancellation needed requires a completely unachievable precision.

For added pain, the solution tends to be very narrow band and the cancellor’s settings have to be continually updated as the transmit interference changes (particularly in a mobile environment due to (c)).

If they have managed to make this work in a practical and useful way then it will be very impressive, but I would need to see some real world experiments to be convinced of its practicality.

Re:The canceller is the clever bit (Score:4, Informative)
by Ungrounded Lightning ( 62228 ) on Saturday April 16, 2016 @03:14PM (#51923143) Journal

However, some of your transmit signal will always end up in the receiver for three reasons; (a) the circulator isn’t perfect, (b) the antenna doesn’t have a perfect match so some of the transmit energy sent to it bounces back again and (c) energy can reflect back from the immediate environment.

Combined with the many orders of magnitude strength difference between the transmitted and received signals in a typical communications application, even a miniscule imperfection in the circulator’s cancellation of transmit power at the received signal port can result in the transmit signal swamping the received signal. So the circulator must be EXTREMELY GOOD to be useful in the described way.

Source: https://hardware.slashdot.org/story/16/04/16/047225/new-full-duplex-radio-chip-transmits-and-receives-wireless-signals-at-once

What you describe is not full duplex. Two radios working together, taking turns (one transmitting, then one receiving, etc.) is the very definition of half duplex. And one radio in constant operation is simplex of course. Full duplex is always a situation where two radios are used in constant operation. One sending, one transmitting.

Full duplex using two radios on different frequencies is old school. Just a matter of a good combination of filters and enough frequency separation.

Full duplex using two radios on the SAME frequency, using directional signals is difficult but not undo-able. As long as you can prevent your receiver being blown up by your own transmission signal (and hope an unexpected reflective object in your signal path doesn’t undo all your careful physical transmitter-receiver antenna separation).

Full duplex using two radios (both in continuous operation, one transmitting, one receiving, as defined at the top of my post) on exactly the SAME frequency while using a SINGLE (omni-directional) antenna is a true nightmare. And apparently these guys did just that with technology that promises it to be available in hand-held appliances.

RTFA, they used a combination of a circulator on silicon (which is the most innovative part. The circulator used in the project described by the article should kill most of the transmitted signal otherwise picked up directly by the receiver) and echo cancellation (which they developed earlier and is used to subtract any transmitter signal left which should mostly be echoes from objects that reflect the transmitted signal at distance and possibly internal echo from a sub-optimal antenna) on the received signal at the receiver end, so they can then try amplifying what’s left. Which should be the (weak) signals that are transmitted towards the antenna by another transceiver.

Exciting stuff
73, PG8W

Source: https://hardware.slashdot.org/story/16/04/16/047225/new-full-duplex-radio-chip-transmits-and-receives-wireless-signals-at-once

Circulators are used all of the place (radar, satcom), so nothing new. But one small and efficient enough to potentially work in a cellphone? Neat stuff. They come with their own set of tradeoffs, so it might not be worth it in the end for smartphone use, but will find use somewhere

It’s kind of new, since this is an active circulator instead of the old passive ones.

Passive ones work great except they cannot be effectively miniaturized at the low frequencies used for current cell phone communication because size is proportional to the wavelength. Active circulators, based on non-reciprocal amplifiers and appropriate phase shifted combiner/divider networks, have existed for a long time. But there’s been a lot of recent attention and work to bring them to a point where they’re actually useful and efficient in communication applications.

Engineers develop the first on-chip RF circulator that doubles WiFi speeds with a single antenna; could transform telecommunications

Last year, Columbia Engineering researchers were the first to invent a technology–full-duplex radio integrated circuits (ICs)–that can be implemented in nanoscale CMOS to enable simultaneous transmission and reception at the same frequency in a wireless radio.

This is the first time researchers have integrated a non-reciprocal circulator and a full-duplex radio on a nanoscale silicon chip. The circulator research is published online April 15 in Nature Communications (DOI is 10.1038/NCOMMS11217) and the paper detailing the single-chip full-duplex radio with the circulator and additional echo cancellation was presented at the 2016 IEEE International Solid-State Circuits Conference on February 2.

“This technology could revolutionize the field of telecommunications,” says Krishnaswamy, director of the Columbia High-Speed and Mm-wave IC (CoSMIC) Lab. “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.”

You can play tricks with antennas and diplexers to help improve isolation. Like I said, this has all been demonstrated before, but the trick has been getting it into a low-power chip. Also, to fully get the advantages of full-duplex operation, it’s best to have both sides of the link operating full-duplex.

Source: comment at http://spectrum.ieee.org/tech-talk/telecom/wireless/new-full-duplex-radio-chip-transmits-and-receives-wireless-signals-at-once

Other issue on the article is question how well this work in practice.