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New Full Duplex Radio Chip Transmits and Receives Wireless Signals At Once ( 33

Wave723 writes: A new chip by Columbia University researchers uses a circulator made of silicon transistors to reroute signals and avoid interference from a transmitter and receiver that share the same antenna. This technology instantly doubles data capacity and could eventually be built into smartphones and tablets. The chip enables them to work around the principle of Lorentz Reciprocity, in which electromagnetic waves are thought to always travel along the same path both forward and backward. Traditionally, electronic devices required two antennas -- a transmitter and receiver -- that took turns or operated on different frequencies in order to exchange signals.
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New Full Duplex Radio Chip Transmits and Receives Wireless Signals At Once

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  • good miniaturation (Score:5, Informative)

    by Anonymous Coward on Saturday April 16, 2016 @09:10AM (#51921041)

    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.

    • by MattskEE ( 925706 ) on Saturday April 16, 2016 @03:47PM (#51923319)

      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.

      • by Agripa ( 139780 ) on Saturday April 16, 2016 @10:42PM (#51924847)

        Active circulators with an arbitrary number of ports have been known of for decades but they have to operate within the noise, power, and linearity of their active devices. When used to separate a transmitter and receiver on the same frequency, their limited isolation will cause major problems on the receive side. Their big advantage is that they can operate over wide bandwidths which makes them very useful for test instrumentation.

        This design was published in 1991 and would be useless in this application. I ran across it when it was included in one of my microwave engineering books.

        I suspect the refinement they came up with involves a second adaptable stage to cancel feedthrough and near end echo but in order to do this, the output of the final amplifier has to be sampled to include its high levels of noise and even if it all works perfectly, all of the noise contributed in those circuits will get added to the receiver. I looked at doing something similar by sampling an earlier stage but just the noise contributed by the final amplifier was enough to overload the receiver. You can see this effect when powering up a SSB transmitter with no modulation which promptly raises the noise level for the entire band.

  • Whoa! (Score:2, Funny)

    Instantly doubles data capacity? I DID notice my phone seemed faster this morning! Good job Columbia!
  • Pretty cool. Not the first active circulator, but nonetheless pretty cool. I wonder how much isolation they are getting? []
  • by Anonymous Coward

    That is the news here. Normally circulators are made of ferrite... amirite?

  • Listening while talking is a major issue for all shared communications links including wireless. Cable TV Internet and *PON based systems all have the problem that they can blind the receiver while transmitting resulting in talking over another speaker resulting in resending packets.

  • by HuskyDog ( 143220 ) on Saturday April 16, 2016 @02:36PM (#51922959) Homepage
    The gist of what is clever here is the canceller which removes the transmitted signal from the receiver. Circulators have been around for donkey's years (not just in military systems) but they are bulky (especially at lower frequencies such as those for mobile comms). The are often used to allow a single antenna to operate at both transmit and receive either alternately (e.g. radar) or on different frequencies (e.g. satcom). Making a solid state one is clever, but this isn't the first one.

    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.
    • 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.

      • Yea, but this guy will absolutely get stomped upon in any mobile-phone scenario. It's just not feasible in the architecture. I get that the researchers put that tag line in there because it'll result in getting published far and wide, but it's totally useless for mobiles.

        If you stopped separating uplink and downlink bands and instead tried to make them the same with this handy device, then yea your own phone won't drown out the cell tower's incoming signal on the same frequency. But the phone next to
      • No true!

        I fear that you have entirely failed to grasp the point I was making. It is true that the transmit signal is many orders of magnitude stronger than the receive signal, but one cannot fix that entirely with the circulator, no matter how good it is. Time for circulator and antenna 101!

        I typical ferrite circulator has three ports (let's call them A, B and C). Energy put into port A comes out of B, energy into B and out C and in C to out A. You get the idea. Now, as with everything in life, c
        • As long as the antenna isn't far from that circulator, reflection from the antenna is just seen as an impedance mismatch. Match the receiver/transmitter/antenna impedances to the circulator (or compensate for the resultant errors) and theoretically the transmitted signal can be cancelled completely at the receiver. The problem is that the transmitted signal can easily be 120 dB greater than the received signal, meaning that the correction applied has to be better than 1 PPM.

          Generally, that's not possible be

  • by Mateorabi ( 108522 ) on Saturday April 16, 2016 @02:39PM (#51922981) Homepage
    Geeze, what happened to those 0.1" jumpers? Looks like they melted. Did someone accidentally the soldering iron on them?

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