"Two-way" radio breakthrough doubles Wi-Fi performance
By Stewart Mitchell
Posted on 15 Feb 2011 at 12:54
Wi-Fi and mobile phone radio network speeds could double after scientists showed radio is able to send and receive over the same frequency at the same time.
The technology would overcome the problem best exemplified by pilots having to say “over” each time they take turns in talking over radio, but it could also be applied to wireless data networks, scientists at Stanford University said.
"Textbooks say you can't do it," said Philip Levis, assistant professor of computer science and electrical engineering at Stanford. "The new system completely reworks our assumptions about how wireless networks can be designed. Unlike radio before it has the unique ability that it can receive and transmit at the same time.”
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The technique mimics the way humans are able to screen out the sound of our own voices during a conversation.
"It's like two people shouting messages to each other at the same time," said Levis. "If both people are shouting at the same time, neither of them will hear the other."
"When a radio is transmitting, its own transmission is millions, even billions of times stronger than anything else it might hear [from another radio]," Levis said. "It's like trying to hear a whisper while you yourself are shouting."
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.”
The researchers claim this immediately makes radio equipment twice as fast as existing technology, and with further tweaking could lead to even faster and more efficient networks.
Current phone networks allow users to talk and listen simultaneously but, the scientists said, they use a work-around that is expensive and requires careful planning.
The researchers have not detailed when the technology might appear in hardware, but said they had applied for a patent and were working to commercialise it and improve signal strength to make it more suitable for Wi-Fi networks.
Two way radio what took so long?
Although it's being implemented in a different way, the principle is as old as the hills, or at least as old as the telephone. The telephone allows two way conversation over a single channel and achieves it by using negative feed back of the transmitter output to the receiver. How come it took so long to look for a method of doing it at RF frequencies?
By teddypig1 on 17 Feb 2011
Not so long really
The answer is hinted at in the article. In a telephone the receive and transmit are equal in signal strength, so cancellation as little as 50% can work though 90% is better and typical for a cheap pots phone. The best digital systems manage 99%, however the WI-Fi example needs 99.9999999% or a suppression of transmissions by between 1 and 100 billion.
Getting this level of cancellation is a very significant achievement and the real question is whether is can be made in volume.
By tonyyates on 17 Feb 2011
Motorola had a patent
Something very nearly the same as this was invented by Motorola in the 80's.
By chuber on 19 Feb 2011
Using this setup effectively prevents omnidirectional radiation and beamforming, I think. They gain full duplex on a single channel but lose other features found in modern radio systems.
By storm311 on 19 Feb 2011
I'm a pilot & I was never trained to say "over". Standard phraseology, yes, but "over", definately not.
Noise cancelling headsets have been around for some time & are continually being improved.
By Dairs on 21 Feb 2011
Two way radios continue to be improved upon year after year.
By Amanda on 10 Aug 2011
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