September 09, 2011, 3:43 PM — Upgrading your cell phone to get the best networking speed available is expensive.
Upgrading your cell-phone towers to get a faster connection is a lot more expensive.
You could double the amount of data one cell phone can send and receive if you could convince it to listen to a radio signal at the same time it was broadcasting. Because cell phone radio links work just like walkie-talkies, though, they can only talk and listen simultaneously if they're doing it on different frequencies – cutting in half the number of devices a cell tower can support.
Full duplex connections – which allow each node on a network to both send data and receive it at the same time, are no small trick, especially via radio.
Even wired Ethernet networks make full duplex work only by sending data along one of a pair of twisted wires while receiving it on the other.
Researchers at Rice University think they've solved the problem of full-duplex cell phone networks by using selective hearing – a trick teenage humans have used to advantage for centuries.
In 2010 Ashutosh Sabharwal, a Rice University professor of electrical and computer engineering published a paper showing it was theoretically possible to create a full duplex connection using a single frequency by making each end of one connection deaf to its own voice, allowing it to hear the other.
Rice Univ. on full duplexing cell nets
Each device on a radio-frequency connection has one node that broadcasts its signal to the other device, and a second that receives responses. When a device broadcasts, its receiver is overwhelmed by the signal, so it can't hear anything else even when it should be able to do so.
Sabharwal and other members of the team – Melissa Duarte and Chris Dick, Achaleshwar Sahai and Gaurav Patel, also from Rice – solved that by creating a second outgoing signal that was the mirror image of the first – cancelling it out, but only in a very local area: right around the device's receiver.
Since two opposite waves cancel each other out, the receiving node ends up sitting in silence while its opposite number broadcasts its data. That allows it to hear a signal from the device on the other end of the connection and process it just as if its own broadcast node were not talking at the same time, according to Sabharwal.
Rice Univ./ Ashutosh Sabharwal