Whether it be over walkie talkies or Wi-Fi, wireless communication is a one way street, meaning radio traffic can flow in only one direction at a time on a specific frequency. To get around this limitation mobile phone networks use a workaround that is expensive and requires careful planning, making the technique not feasible for other wireless networks. Now researchers at Stanford University have created a full duplex radio that allows wireless signals to be sent and received simultaneously, thereby instantly doubling the speed of existing networks.
The problem the researchers had to overcome is that when a radio is transmitting and receiving at the same time, the incoming signals are drowned out by the radio’s own transmissions.
"When a radio is transmitting, its own transmission is millions, billions of times stronger than anything else it might hear [from another radio]," says Philip Levis, assistant professor of computer science and of electrical engineering at Stanford. "It's trying to hear a whisper while you yourself are shouting," he says.
To overcome this problem a trio of electrical engineering graduate students, Jung Il Choi, Mayank Jain and Kannan Srinivasan, hit upon the idea developing a radio receiver that could filter out the signal from its own transmitter so the weak incoming signals could be heard. Similar to the way in which noise-canceling headphones filter out ambient noise, each radio would know exactly what it is transmitting and therefore what it should filter out.
The idea seems so obvious that other researchers even told the students their idea wouldn’t work because something so obvious must have already been tried unsuccessfully. Luckily for the students, the naysayers were wrong and the team successfully developed the first full duplex radio device by designing a radio with two transmit antennas located either side of a single receiving antenna. When the signals from the two transmitting antennas meet at the receiving antenna, they effectively cancel each other out – not completely, but enough to allow the receiving antenna to pick up signals from other radios.
The most obvious advantage of the technology is that it instantly doubles the amount of information that can be transmitted, but it also has other benefits. With current air traffic control systems, when two aircraft try to call the control tower at the same time on the same frequency neither will get through. The new system would prevent such potentially disastrous scenarios.
Before the technology is practical for use in Wi-Fi networks the team will need to increase both the strength of the transmissions and the distance over which they work. They are currently working on this but are even more excited about the possibilities once hardware and software are built to take advantage of simultaneous two-way transmission.
The Stanford University students demonstrated their device last year at MobiCom 2010, where they took out first prize for best demonstration. The group has a provisional patent on the technology and is now working to commercialize it.
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