Researchers at Rice University have invented a way for mobile carriers to double the capacity of wireless networks without adding a single tower or base station. The trick is not listening to yourself as you talk.

Ashutosh Sabharwal, professor of electrical and computer engineering at Rice University, has been leading research into achieving full duplex communications in wireless. Early radio communications used half-duplex signaling: two people using the same frequency took turns talking to one another. Today’s wireless uses two frequencies to allow more natural, interactive conversations. The uplink from a mobile device uses one frequency while the downlink uses another, so information can stream in both directions simultaneously.

What Sabharwal and his team have developed is a way for mobile devices to use the same frequency and still achieve simultaneous up and down data flow. Further, the technology does not need any additional hardware in the mobile device – just software. It all stems from repurposing the antennas needed for MIMO and diversity.

The reason you cannot have simultaneous bidirectional data flow on a radio channel is that the signal you are transmitting dominates the signal you want to receive. In effect, the sound of your own voice shouting prevents you from hearing what someone across the room is whispering. What Sabharwal’s team has developed is a way to make you deaf to your own voice while still able to hear those whispers.

In signal processing terms, what duplex wireless technology does is to generate a local signal out of phase with the signal you are transmitting so that the two signals cancel at your receiving antenna. The local signal is structured such that the cancellation is only effective at the transmitting end. It does not compromise the transmitted signal at the receiving end. As far as your receiver is concerned, then, your transmitted signal has vanished from the ether and your receiver is free to hear what the other guy has to say.

Don’t look for this technology to appear in cellular communications any time soon. There is still much work needed to understand all the technology’s implications and tradeoffs as well as a whole lot of standards development needed to ensure reliable interoperation of equipment designed to use the technology. But the basic question of how to make wireless communications fully duplex has been answered. Now it’s just a matter of reducing it to practice.

Who knows? With all the added capacity that this technology will ultimately bring to wireless communications, perhaps service providers will not need to spend as much for building infrastructure as currently expected and the cost of service will decrease.

Stranger things have happened. Like learning how to listen to whispers while you’re shouting.