Radio breakthrough could double Wi-Fi performance

Scientists at Stanford University have made a breakthrough that could double the speed of Wi-Fi and other wireless networks. This boost comes courtesy of a new radio design capable of sending and receiving on one frequency at the same time. The act of broadcasting one signal would normally make a radio unable to “hear” incoming transmissions. However, assistant professor of computer science and electrical engineering Phil Levis explains to PC Pro that the incoming signal can be tuned to cancel out the outbound one.

According to the researchers, the breakthrough uses two transmitters in the hardware at each end of a conversation, with the two transmitters working in a similar way to noise-cancelling headphones.

“The two transmit signals interfere destructively at the receive antenna to create a dead signal that the receiver can’t ‘hear’,” said Levis. “So you create this null position where the receiver can’t hear that signal and so is able to receive packets from other areas.”

So, you only get double the performance if you want to send and receive at the same time. That’s still quite a breakthrough, but it won’t make transfers faster in any one direction.

The researchers behind the technology have applied for a patent and are working to improve signal strength for Wi-Fi applications. Although no timelines are provided, they’re already looking to get the radio tech implemented in real products. Thanks to Tested for the tip.

Comments closed
    • conlusio
    • 9 years ago

    Having read the article a few times now, this looks fairly interesting but its going to have some limitations.

    1) They tested this using 802.15.4, not 802.11. This solved a lot of problems, noteably the fact that they have problems nulling out large amounts of transmitted power (greater than 0dBm)

    2) The system has a hard time working with protocols that have a wide bandwidth (ie, 802.11). The test they demonstrated this technique used 2.48 GHz only. The larger the bandwidth, the digital cancelation circuit causes more and more problems with peak sidelobe signals.

    3) Scalability. If you’re looking at this for systems that operate in the 2.4 and 5 GHz bands, you’re probably going to be ok, so long as you avoid the issues above (power, and frequency agility). It definitely doesn’t scale down in frequency (think 700 MHz spectrum auctions) in any practical manner. The power issues alone make that a problem, unless you’re doing very short range work.

    Still, its a pretty cool technique, combining the known nulling between two transmitting antennas and a digital cancellation circuit, but making it commercially viable for something of reasonably high power is going to very difficult.

    • My Johnson
    • 9 years ago

    I’m a little surprised this wasn’t thought of a long time ago as signal cancellation is taught in basic college physics.

      • zaeric19
      • 9 years ago

      Agreed, destructive interference was taught in my high school physics class.

    • cygnus1
    • 9 years ago

    So they figured out how to do full duplex on one band, that’s cool but it sounds like it would need to be point to point and not shared between multiple nodes like wifi.

      • sluggo
      • 9 years ago

      No, it’ll work on wi-fi as well. Right now, the transmit antenna is screaming so loud during a send that the receive antenna can’t hear anything on the same frequency. All this new method does is add a second transmit antenna that screams out of phase with the primary, creating a null (presumably) at the receiving antenna. Since the transmit and receive antennas are (nearly) always co-located, this is not hard to do. The secondary antenna may not even a lot of power, since it can be very directional and doesn’t have to broadcast very far.

        • cygnus1
        • 9 years ago

        Ah, gotcha. So only the receive side of a device hears the 2nd out of phase transmitter and not other devices.

        Edit: Would it even really need to broadcast, or could it just be hardwired to the receive side?

          • sluggo
          • 9 years ago

          My assumption is that the phase-cancelling antenna is very highly directional and low-power so that it doesn’t create nulls other than right at the receiving antenna. Hard to do, but that’s why they’re smart, I guess.

          I thought about the “hardwired” phase cancellation as well. In principle it would work just like the acoustic cancellation in speakerphones and the like, but it may be that the antenna scheme is actually the simpler implementation. It’s a good question, and I’d love to know the real answer.

            • conlusio
            • 9 years ago

            sluggo,

            Actually they both appear to be omni-directional antennas. They’re either relying on multipath considerations to provide coverage away from the desired null, or crossing their fingers and hoping no one really notices.

            The technique will work with Wi-Fi in theory, the real issue is the higher power that is generated in Wi-Fi transmission, they can’t provide enough cancellation to really make it work.

        • zaeric19
        • 9 years ago

        They could also move the transmit antenna a little farther away from the receive antenna and put the secondary antenna that cancels out the signal extremely close to the receive antenna. Then because of the difference in distances the transmit antenna can have the signal strength really high and the secondary antenna really low, which will still cancel out the signal at the receive antenna without intfering with other devices.

          • NeelyCam
          • 9 years ago

          Neat trick, but matching? Adaptive phase and amplitude?

          Sounds kind of difficult to implement in practice, but neat idea nonetheless.

    • Sam125
    • 9 years ago

    Sounds like a technology with a very clear application if you understand the implications.

    • UberGerbil
    • 9 years ago

    Doesn’t sound particularly power-efficient, which is usually a consideration for at least one end of most WiFi conversations.

      • NeelyCam
      • 9 years ago

      Certainly limits the possible usage models. But could be used to connect to static, plugged-in objects such as AV equipment (TVs, bluray players…), desktops etc. Maybe even a laptop would be willing to burn some extra power to double the throughput.

        • cygnus1
        • 9 years ago

        Could also be shut off in a power saving mode

          • NeelyCam
          • 9 years ago

          An excellent point.

    • ew
    • 9 years ago

    It will still be marketed as being 10x faster then it actually is.

    • dpaus
    • 9 years ago

    Hmm, I doubt ‘double’ – at those speeds, there’s going to be some processing lag involved. I know how ‘efficient’ my noise-cancelling hedphones are, and they’re only dealing with up to 25 [i<][b<]KHz[/i<][/b<], not GHz...

      • Squeazle
      • 9 years ago

      …not to mention the wide tolerances that are already used by most wi-fi companies.

      • zaeric19
      • 9 years ago

      Whether it’s KHz or GHz doesn’t matter. What matters is that with noise cancelling heaphones they need to cancel out the audible range, ~20 Hz to ~20 KHz for most people. With Wi-Fi you are operating at a single frequency which will be much easier. Additionally noise cancelling headphones cancel out an analog signal with a mechanical speaker, there is going to be distortion it won’t be 100% correct, obviously. With this device you will be cancelling out a digital signal with only electrical components, no mechanical parts here, so it will be more precise and since it is digital you can have some small distortion and still get the signal 100% correct. On top of that there is the fact that with noise cancelling headphones outside noise can come from any direction, resulting in non-perfect cancellation by the speaker in the headphone. With this you know exactly where the signal you need to cancel out is coming from.

      Apples and oranges.

      Edit: Wifi actually uses a set of discrete frequencies, not a single frequency. This is still vastly easier to work with than an analog signal range that is 3 orders of magnitude from one end to the other.

        • NeelyCam
        • 9 years ago

        [quote<]With this you know exactly where the signal you need to cancel out is coming from.[/quote<] This. And you know exactly what the signal is - you don't need a 'mic' to figure it out.

        • Anomymous Gerbil
        • 9 years ago

        I think you sort of answered yourself with your edit, and I understand (and agree with) the thrust of your comment. However, I think I’m right in saying that RF is analogue (even if the signal being transmitted is digital), and the cancellation will be done in the analogue domain.

          • NeelyCam
          • 9 years ago

          The lines are very blurry, but if I had to vote, I’d go with your “RF is analogue” argument.

          • zaeric19
          • 9 years ago

          Any signal can be viewed as analog, even a pure digital signal can be viewed as an analog signal (fourier series). In that regard I agree; the antenna receives an analog signal but it is processed digitally. As long as the signal is cancelled out enough to the point that the receiver can tell if there is a 1 or a 0 present it should work. We hear things in analog so any distortion in the signal is moticable but with a digital system there can be some distortion but the data still gets through. With Wi-Fi you have a set number of frequencies that you are working with (usually 64 or less) compared to an infinite number with audio. The point I am trying to make: this is easier to do than noise cancelling, the technology exists so it was only a matter of time before someone thought to apply it to Wi-Fi and because the signal is processed digitally you don’t need to perfectly cancel out the transmitted signal for this to work.

      • My Johnson
      • 9 years ago

      No, there won’t be processing lag because that lag is predictive and and can be tuned for.

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