Researchers develop new wireless technology for faster, more efficient networks

Feb 14, 2011
Jung Il Choi left, and Mayank Jain, both electrical engineering graduate students, pose by their demonstration setup used to show that their idea for creating full duplex wireless communication does indeed work, despite what the textbooks say about it being impossible. The third graduate student on the team, Kannan Srinivasan, is not pictured. Credit: L.A. Cicero, Stanford News Service

"Wireless communication is a one-way street. Over." Radio traffic can flow in only one direction at a time on a specific frequency, hence the frequent use of "over" by pilots and air traffic controllers, walkie-talkie users and emergency personnel as they take turns speaking. But now, Stanford researchers have developed the first wireless radios that can send and receive signals at the same time.

This immediately makes them twice as fast as existing technology, and with further tweaking will likely lead to even faster and more efficient networks in the future.

"Textbooks say you can't do it," said Philip Levis, assistant professor of computer science and of . "The new system completely reworks our assumptions about how can be designed," he said.

allow users to talk and listen simultaneously, but they use a work-around that is expensive and requires careful planning, making the technique less feasible for other wireless networks, including Wi-Fi.

A trio of electrical engineering graduate students, Jung Il Choi, Mayank Jain and Kannan Srinivasan, began working on a new approach when they came up with 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?

In most wireless networks, each device has to take turns speaking or listening. "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."

It took the students several months to figure out how to build the new radio, with help from Levis and Sachin Katti, assistant professor of computer science and of electrical engineering.

Their main roadblock to two-way simultaneous conversation was this: Incoming signals are overwhelmed by the radio's own transmissions, making it impossible to talk and listen at the same time.

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A new technology that allows wireless signals to be sent and received simultaneously on a single channel has been developed by Stanford researchers. Their research could help build faster, more efficient communication networks, at least doubling the speed of existing networks. Credit: Jack Hubbard, Stanford News Service

"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."

But, the researchers realized, 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.

Their setup takes advantage of the fact that each radio knows exactly what it's transmitting, and hence what its receiver should filter out. The process is analogous to noise-canceling headphones.

When the researchers demonstrated their device last fall at MobiCom 2010, an international gathering of more than 500 of the world's top experts in mobile networking, they won the prize for best demonstration. Until then, people didn't believe sending and receiving signals simultaneously could be done, Jain said. Levis said a researcher even told the students their idea was "so simple and effective, it won't work," because something that obvious must have already been tried unsuccessfully.

But work it did, with major implications for future communications networks. The most obvious effect of sending and receiving signals simultaneously is that it instantly doubles the amount of information you can send, Levis said. That means much-improved home and office networks that are faster and less congested.

But Levis also sees the technology having larger impacts, such as overcoming a major problem with air traffic control communications. With current systems, if two aircraft try to call the control tower at the same time on the same frequency, neither will get through. Levis says these blocked transmissions have caused aircraft collisions, which the new system would help prevent.

The group has a provisional patent on the technology and is working to commercialize it. They are currently trying to increase both the strength of the transmissions and the distances over which they work. These improvements are necessary before the technology is practical for use in Wi-Fi 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.

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User comments : 16

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wealthychef
not rated yet Feb 14, 2011
Two definite questions here. First, how does the ability to listen while sending double the amount of data you can send? That must be a typo. Second, how does this solve the problem of two aircraft trying to send a message to the control tower at the same time? Since the tower does not know what either aircraft is sending, how can it cancel or filter the signal?
jjoensuu
3 / 5 (2) Feb 14, 2011
Two definite questions here. First, how does the ability to listen while sending double the amount of data you can send? That must be a typo.


yea I guess a journalistic mistake.

It will not automatically double human communications because humans always stop talking when listening. And it wont double home networking (such as e.g. wifi between laptop and router) because the home wifi does far more receiving (from router to laptop) than sending (from laptop to router).
Skultch
not rated yet Feb 14, 2011
Good job, but it won't change much. Use two radios, two antennae, one board, one cpu. Done. That's why no one did this before. MIMO
Eikka
3 / 5 (4) Feb 14, 2011
For point-to-point communication between two network nodes, this indeed doubles the bandwidth because the radios don't have to take turns.

This would increase bandwidth even in the case that the other radio is just listening, because in wireless networks, you have to send "OK, got it!" confirmations back for every data packet.

For n-node system, it wouldn't work so easily for the obvious reason that two radios would try to speak on top of each other and a third wouldn't be able to make sense of it. In that situation, the network nodes would still have to arrange turns when each pair is allowed to communicate.
Eikka
1 / 5 (1) Feb 14, 2011
because the home wifi does far more receiving (from router to laptop) than sending (from laptop to router).


In total amounts maybe, but it doesn't say anything about when the data is sent and recieved.

Try sending a big email while downloading something, like listening to a web radio, and the network speed will drop to half. Printing through a wireless network is usually a PITA because there's a lot of data to be sent and anything else going on in the network at the same time will slow it down significantly.
ab3a
1 / 5 (3) Feb 14, 2011
Oh dear. Have they never heard of a transponder, a repeater, a diplexer, a hybrid transformer, or even orthogonal codes for spread spectrum?

Please, this is like claiming you have reinvented the light bulb, and claiming credit from Edison.
MorituriMax
3 / 5 (4) Feb 14, 2011
Oh dear. Have they never heard of a transponder, a repeater, a diplexer, a hybrid transformer, or even orthogonal codes for spread spectrum?

Please, this is like claiming you have reinvented the light bulb, and claiming credit from Edison.

I'm sure they have, which is why they are filing the patent, and you are not. God, give smart people who do neat things some credit instead of trashing them.
gwrede
1 / 5 (2) Feb 14, 2011
First, how does the ability to listen while sending double the amount of data you can send? Second, how does this solve the problem of two aircraft trying to send a message to the control tower at the same time?
They should have said "up to doubles" and "per used channel". Second, the aircrafts would hear each other talking at the same time, like what happens at a dinner table. Then they,d agree who talks first.
trekgeek1
5 / 5 (1) Feb 14, 2011
I'm an EE, and I've never seen anything in any textbook that said it couldn't be done. I hate it when people say that the book said it couldn't be done, or that physics said it wasn't possible. It usually turns out that the theory said no such thing, but rather people just never saw all that was predicted and possible by the theory.
stealthc
3 / 5 (4) Feb 14, 2011
Now all we have to do, is increase the range of wifi, improve meshing capabilities, make this affordable on the consumer level, and we can give all these greedy cell providers the boot they have sorely deserved from us for so long. If we boost throughput to handle hdtv then we can give the cable companies the boot.

We should be using technology to get rid of these parasite monopolies that are in league with the government and with our educational institutions. We don't need their control.

This is simple technology and can be made with off-the-shelf parts. Of course it would be better to not have to use two radio chips for this but I suppose that'll have to wait till we develop a single chip to do this (because current chips have no operation built in to handle rx and tx at same time, so even if the antennas are there and hooked up it won't work unless dual radio configuration).
Kayreios
not rated yet Feb 14, 2011
I disagree that they will be able to acheive the granularity of cancellation required for the RX to maintain even a -85 dBm threshold. Processing power towards higher spectral efficiency is better leveraged with proven techniques, most of which are not in widespread use yet and can be easily implemented.
jscroft
1 / 5 (1) Feb 14, 2011
I dunno. I've been pushing electrons in one capacity or another for a pretty long time now, and this is kind of a forehead-slapper for me. SOMEBODY had to do it first! :)
antialias
5 / 5 (2) Feb 15, 2011
First, how does the ability to listen while sending double the amount of data you can send?

Because you don't have to stop sending while listening. If your send/receive rate was 50/50 before then you have just doubled the time you can send data in (and hence the amount)

I'm an EE, and I've never seen anything in any textbook that said it couldn't be done.

I am an EE, too and it is just obvious that it couldn't be done (without the trick they used). Think about how the electrons move in the antenna to produce a sent signal and a received signal. If you don't factor out the sent signal then you won't be able to filter the information of any received signal.

What they did (rather clever I think) was use the idea of noise-cancelling headphones on the cumulative antenna signal.
rgwalther
3 / 5 (2) Feb 15, 2011
Victor Basta: Request vector, over.
Captain Oveur: What?
Tower voice: Flight 2-0-9'er cleared for vector 324.
Roger Murdock: We have clearance, Clarence.
Captain Oveur: Roger, Roger. What's our vector, Victor?
Tower voice: Tower's radio clearance, over!
Captain Oveur: That's Clarence Oveur. Over.
Tower voice: Over.
Captain Oveur: Roger.
Roger Murdock: Huh?
Tower voice: Roger, over!
Roger Murdock: What
Skultch
1 / 5 (1) Feb 15, 2011
..., improve meshing capabilities, ....


Now THATS a tall order. MESH and WDS are inherently limited, in my experience. WDS is horrible, but I haven't used MESH much. AFAIK, in either way, every step beyond the node you lose half your bandwidth. Extra redundant links halves it again. Even with the advance in this article it's still better to use dual radios instead of MESH/WDS.

From my perspective as a WISP engineer, I think it is unclear how this will all play out. It is promising, though. There is some really cheap and reliable wireless hardware that has become available in the past year or so. (mostly Ubiquiti and Mikrotik)
Grallen
5 / 5 (1) Feb 15, 2011
It's done the same way parity is done on hard drives. You deduct the outgoing waveform from what it heard.
Only issue is it will still require higher sensitivity or higher power to accomplish more throughput. Still a good idea as it might one day save spectrum.

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