back to article Boffins set to reveal state of play on fully duplex comms - on the same FREQ

A conference at Bristol university is set to reveal the current state of the art on Full Duplex technology, which allows for transmitting and receiving signals on the same frequency at the same time. The idea that a radio can simultaneously shout and listen has been regarded as both old, established technology and a bonkers …

  1. Paul Kinsler

    orbital angular momentum proposals ...

    Since these typically generate a bit of debate here on the Reg, the interested reader might also look at this recent paper:

    Orbital angular momentum modes do not increase the channel capacity in communication links

    Mauritz Andersson, Eilert Berglind and Gunnar Björk

    http://dx.doi.org/10.1088/1367-2630/17/4/043040

    The orbital momentum of optical or radio waves can be used as a degree of freedom to transmit information. However, mainly for technical reasons, this degree of freedom has not been widely used in communication channels. The question is if this degree of freedom opens up a new, hitherto unused 'communication window'supporting 'an infinite number of channels in a given, fixed bandwidth' in free space communication as has been claimed? We answer this question in the negative by showing that on the fundamental level, the mode density, and thus room for mode multiplexing, is the same for this degree of freedom as for sets of modes lacking angular momentum. In addition we show that modes with angular momentum are unsuitable for broadcasting applications due to excessive crosstalk or a poor signal-to-noise ratio.

    1. This post has been deleted by its author

    2. Charles 9

      Re: orbital angular momentum proposals ...

      I've read about the OAM business but had been sitting on the fence looking for more concrete proof. Seems this report will provide the basis for a counter-example to slam the door on OAM. All I'm saying at this point is, "Let's see the proof, sonny."

    3. Anonymous Coward
      Anonymous Coward

      Re: orbital angular momentum proposals ...

      Thank you for that link.

      Once upon a time, I "invented" (imagined?) a new comms channel using a wee bit of RHCP/LHCP delta signal hidden on a linear polarization satellite link, or vice versa if you like. After sleeping on it, I realized that the cross talk noise probably ate as much of Shannon's limit as the 'new' channel opened up. It might be useful as a niche channel for hiding things, but it's not likely increasing the overall bandwidth.

      OAM seems to be exactly the same thing. It eats bandwidth in the SNR axis. I think.

  2. Anonymous Coward
    Anonymous Coward

    This concept is not new.

    It's popular in satellite comms, where space on transponders is VERY expensive. It's not a new concept, though with 5G standards there some new implementations.

    It's called paired carrier multiple access, it's been patented by ViaSat since around 2000, and real products have been available on the market for almost as long.

    1. Bob H

      Re: This concept is not new.

      Comtech has their Double Talk technology:

      http://www.comtechefdata.com/technologies/doubletalk

      I'm always disappointed when someone says something is impossible when its already been done.

    2. JP19

      Re: This concept is not new.

      That concept is not duplex and not transmitting and receiving on the same frequency. It is transmitting twice on the same frequency and a receiver can cancel out one of the signals if it knows what it is.

      The problem (which is pretty much impossible) is cancelling out a transmit signal which is 100's of millions of times more powerful than a signal at the same frequency you are trying to receive.

      1. Anonymous Coward
        Anonymous Coward

        Re: This concept is not new.

        @JP19 "...100's of millions of times more powerful..."

        Yes. 80dB is a fair assessment for some applications.

        But the ViaSat system (the AC's example) operates at the L-band IF, so the two signals are both at relatively the same amplitude, both arriving from the satellite above. Of course the local sample is of arbitrary amplitude since it's a local xmit sample; but don't let that confuse anyone. The known signal to be cancelled is received from orbit, same as the unknown other signal desired. Both are of the same approximate amplitude.

        Conceptually it's quite a simple concept. Just delay roughly, seek out the precise time delay and amplitude, and invert-add for cancellation. Might be some complications with precise transformation functions for precise cancellation.

    3. Anonymous Coward
      Anonymous Coward

      Re: This concept is not new.

      Older than that.

      Telephone sends the two parties' voice signals each way on a single twisted pair since Time Immemorial. There's a special box of tricks in the old 'whack a puma' sized telephones.

      If that's not good enough for you, long distance telephone lines have had 'echo cancellation' also since Time Immemorial.

      1. Anonymous Coward
        Anonymous Coward

        Re: This concept is not new.

        "...the old 'whack a puma' sized telephones."

        Special prize for anyone recognizing this 'whack a puma' reference.

      2. Anonymous Coward
        Anonymous Coward

        Re: This concept is not new.

        Telephone doesn't care much about crosstalk IIRC. That's why you can hear your own voice on the receiver even as you talk through the mouthpiece. Telephone only works because conversation tends to go back and forth, creating an implicit time-division multiplex (TDM). But when BOTH of you talk at the same time, the result generally is neither of you understands what the other's saying. That's what the claim is about: basically the wireless data version of two people talking simultaneously on the same phone line yet each able to clearly hear what the other is saying. Almost seems to go against physics: Shannon's limit and all, get it?

        1. Anonymous Coward
          Anonymous Coward

          Re: This concept is not new.

          AC: "Telephone doesn't care much about crosstalk IIRC. That's why you can hear your own voice on the receiver even as you talk through the mouthpiece."

          Nope. That own-voice you hear is called "sidetone" and it's intentional (typically about -10dB) and is locally generated. It's required due to basic human factors (people won't speak correctly without it).

          Separate topic from the cross talk in the shared medium of a single pair of twisted wires.

          The box of tricks in the telephone takes care of all of it. But the sidetone is intentional.

          1. Charles 9

            Re: This concept is not new.

            Sidetone is most definitely not intentional and in fact has been a natural artifact of the telephone system from its inception...because of the single pair of communication lines involved. Two lines limits you to one conversation line due to the limits of electricity. Put it this way: without sidetone, you couldn't properly record a telephone conversation using an acoustic coupler.

            There are two things which are intentional concerning sidetone. One is the attenuation of sidetone in traditional phones. This was because raw sidetone (at least since the introduction of the Edison carbon microphone) was too loud and made people speak too softly. The other is the introduction of sidetone in cell phones (which normally don't feature this because they can normally separate the two parties of the conversation) because otherwise people thought the signal was too soft and started to talk too loudly.

  3. Stevie

    Bah!

    I'm afraid the jury is out on whether this technology is old, new, innovative or been done before until it has been properly explained in something other than impenetrable science technoblither by Stephen Fry.

  4. roger stillick
    Alien

    See the Cambridge Site ad for July 2015 Conference...

    Sponsered by Rhode and Schwartz, and 2 others... Mentioned Plessy doing this in the 1970's with VHF radio repeaters similar to WECO E-6 voice cable repeaters in the 1960's... Negative Impedance Balanced Bridge networks that end up acting as bi-directional quasi analog amplifiers (or the definition of a Duplexer)... add some noise cancelling gear/alogrythms and you get what these folks are talking about... i think... can signup at the Cambridge site for symposium notes this July... until then, Anyone's Guess as to what is really going on, or ask Dr. Bose what he thinks= it's his patent...

    Please Note= TMC corp was making IF shift noise limiters for HF SSB in the same 1970's that Plessy made their AN/PRC-25 manpack radios w/audio speech VOGAD processor...(noise reduction eq.)...RS.

    1. roger stillick
      Alien

      Re: See the Cambridge Site ad for July 2015 Conference... Pt. 2

      Need to mention "echo-supressers" or TR switches that turn a 2 way telephone conversation into a 1 way at a time conversation... preventing standing wave reflections of your own voice (generated by every digital switch your conversation passes thru) being heard as echos of your own voice as you talk...

      Basically the preson talking mutes the other end, when the other talks, your end is muted... if both ends talk at the same time, both ends are muted... so, you really need to stop n listen if you want to find out what the far end is saying...

      Please note= echo suppressers are Not part of any Duplexer scheme...RS.

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