A wireless radio that can send and receive signals at the same time

A wireless radio that can send and receive signals at the same time

Summary: Stanford researchers have developed a new technology that allows wireless signals to be sent and received simultaneously on a single channel. Their research could help build faster, more efficient communication networks, at least doubling the speed of existing networks.

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Radio waves make the world go around.  They make communication and navigation satellites possible,  underpin modern aviation,  and allow you to access the Internet without wires.  One characteristic of radio technology is that traffic flows in only one direction at a time on a specific frequency. That's why pilots, police, and other walkie-talkie users frequently use "over" as they take turns speaking.

But now Stanford researchers have developed a way that allows wireless signals to be sent and received simultaneously on a single channel. Their research could help build faster, more efficient communication networks, at least doubling the speed of existing networks.

"Textbooks say you can't do it," said Philip Levis, assistant professor of computer science and of electrical engineering. "The new system completely reworks our assumptions about how wireless networks can be designed," he said in a university release.

Levis and his team made the discovery based on a seemingly simple idea. What if radios could do the same thing our brains do when we listen and talk simultaneously: screen out the sound of our own voice?

The main obstacle to two-way simultaneous conversation is that incoming signals are overwhelmed by the radio's own transmissions, making it impossible to talk and listen at the same time.

"When a radio is transmitting, its own transmission is millions, billions of times stronger than anything else it might hear [from another radio]," Levis said. "It's trying to hear a whisper while you yourself are shouting."

The researchers reasoned that if a radio receiver could filter out the signal from its own transmitter, weak incoming signals could be heard. "You can make it so you don't hear your own shout and you can hear someone else's whisper," Levis said.

Each radio knows exactly what it's transmitting, and therefore what its receiver should filter out. The process is analogous to noise-canceling headphones.

Up next for the team is to increase both the strength of the transmissions and the distances over which they work before the technology can be of any practical use in WiFi networks.

But even more promising are the system's implications for future networks. "Once hardware and software are built to take advantage of simultaneous two-way transmission,  there's no predicting the scope of the results," Levis said.

Watch the accompanying video to see the wireless set-up in action.

Topics: Mobility, Networking, Wi-Fi

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14 comments
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  • RE: A wireless radio that can send and receive signals at the same time

    Limited. Not that big of a deal, but it is an interesting concept.
    davidmpaul
    • I disagree.

      @davidmpaul
      Double the throughput for every spectrum of radio would mean that, specifically, wireless carriers can offer double the number of simultaneous calls for a given frequency. On the data side the impact will not be double since most data is from the internet to the phones but with spectrum going for billions of dollars, this really could be a big deal.

      TripleII
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    • RE: A wireless radio that can send and receive signals at the same time

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      meimeili
  • RE: A wireless radio that can send and receive signals at the same time

    I do this on a regular basis in wired communications systems. It's old hat on telephone and intercom systems :P But, it's cool they are figuring ways to extend the idea to wireless :)
    RyuDarragh
  • RE: A wireless radio that can send and receive signals at the same time

    How does one keep the two carriers on the same channel from hetrodyning and creating spurious interfereing cross-modulation products?
    Bruce.Whiteside@...
  • RE: A wireless radio that can send and receive signals at the same time

    Heck, cellphones that use CDMA have put dozens of signals on the same channel simultaneously for decades. Dynamic power control is needed to balance the relative signal strengths.
    Bruce.Whiteside@...
  • This is old hat tech from 50 years ago!

    As a ham operator since the 1960's this is routine. SSB (SingleSideband) has NO carrier, only voice that has been transformed by a diode mixing bridge, so there is no heterodyning or interference. Talking and receiving on the same frequency simultaneously is absolutely no problem, as long as you have your RF AGC set very fast on the receiver. The only interference you will note is difficulty on hearing some words from the other party while you talk. Jesus, you young kids think everything is FM or code-key modulation...
    dave@...
    • RE: A wireless radio that can send and receive signals at the same time

      @dave@...

      But the article really is talking about something different. What you describe works only if party A shuts up when party B talks. The article lets both talk at the same time and still hear each other. No wait for AGC necessary.

      That is why it says "two way simultaneous conversation".
      mejohnsn
    • Telecommunications -SSB or USB/LSB

      @dave@...
      Sounds like nothing more that USB on one side and LSB on the other. Same frequency just whether modulation is occruing on the lsb or usb. This to me would be to simplying multiplexing on the same frequest using the entire bandwide of the carrier and dividing the carrier in the middle. Hence (USB/LSB). Some frequency shift and there you have it. Transmit on the upper side, received on the lower side. This is not Navigational Science, more like rocket science. As you know rock science is simple, tube, add propelate, plug both ends, small opening in one end and light. The science is in the navigation.
      jfbyers@...
  • It would only between two radios

    The sending radio may be able to filter out his side of the signal but what about a third radio trying to receive that same signal. May only work for two point to point but never for broadcaseing or multiple radio sets on the same channel.
    fred@...
  • RE: A wireless radio that can send and receive signals at the same time

    I'm not seeing anything so radically new here. The idea has always been present: it was just that the filtering technology was too primitive, being mainly static bandpass filters, whether Butterworth or something similar. Being static and linear, the only way they could get that cutoff would have been by introducing intolerable ringing. And they still would not dynamically adapt to the output signal.

    Somehow, I doubt this new filtering technology will ever prove to be as cheap and practical as frequency multiplexing or, better yet, code multiplexing, both of which we already have.
    mejohnsn
  • RE: A wireless radio that can send and receive signals at the same time

    Sounds like the same way that most high speed modems worked on POTS so full duplex communication was possible. Reinvention of the wheel lives on.
    DNSB
    • RE: A wireless radio that can send and receive signals at the same time

      @DNSB
      No, POTS is like using different channels, not full duplex on the same channel. In POTS the signals are tranmitted at different frequencies.
      herrgott073
      • RE: A wireless radio that can send and receive signals at the same time

        @herrgott073

        In the early days of modems, you would have been right. The later high speed modem designs could use the full bandwidth of a POTS line. If you would like, I could get very boring about equalizer and echo cancellation training (phase 3 of the handshake), constellation shaping, etc. used to achieve this.
        DNSB