"Two-way" radio breakthrough doubles Wi-Fi performance

bealtine

http://www.pcpro.co.uk/news/365275/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.”

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.

watty

Phone systems on wires have done this for years.

There is no free lunch. If you have twice the information, you actually have HALF the speed. (Shannon).
They are relying on totally cancelling a +18dBm Transmit signal at a receiver picking up a -70dBm signal or less. You are unlikely to get much better than 12dB to 20dB cancelling in the real world on Radio. You need about -90dB of cancellation, minimum.

1G ethernet transmits and receives simultaneously by using echo cancellation / hybrid techniques. Signal on a wire can have direction, thus it's possible to "talk" and "listen" at the same time in the same bandwidth (analogue phone does this). Also the characteristics of a cable are not affected by a hand, presence of nearby wall and the signal levels of received and transmitted signals are much closer together. But on a radio channel it's not possible.

Unlike WiFi, most Phone networks use a separate channel for Transmission and Reception at the handset or Mast anyway.

In the real world transmit signal cancellation on same channel as receiver is very poor. This has very little practical application and is a well known technique.

oscarBravo

It really is quite depressing reading about well-understood physical phenomena as if they were brand-new scientific breakthroughs.

jmcc

oscarBravo wrote: »

It really is quite depressing reading about well-understood physical phenomena as if they were brand-new scientific breakthroughs.

I'm almost expecting the Irish Times "technology" section to cover it in glowing terms. The problem with a lot of mainstream reportage, as has been pointed out elsewhere, is that most "technology" journalists don't have a clue about technology. The other aspect about such developments is the duplication/increase of hardware and the increase in power requirements.

Regards...jmcc

watty

Anyone could have done this in a lab 50 years ago.

I don't believe anyone can do it in the real world, at least not as presented.