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.