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Stanford Wireless Breakthrough

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Re: Stanford Wireless Breakthrough

#21

Post by VladRussian »

nimrody wrote: post #3

Some more information here: http://sing.stanford.edu/fullduplex/ The problem with full duplex wireless comm. on the same frequency is that the transmitted signal is much stronger than the received signal. Therefore, echo cancelling is usually impractical. Not sure how these guys overcame the difficulties with transmitter nonlinearities and other unknown impairments. EDIT: they claim to do partial cancellation by plac…

it may be practical in the office setup where 6+ antenna phased arrays Wi-Fi switches are "cost-practical". With phased array you have much more geometrical flexibility - you may "narrow beam" transmission to a client while better adjusting the transmitter's null onto the receiver's physical location to the current conditions, reflections, etc...

Re: Stanford Wireless Breakthrough

#22

Post by VladRussian »

powertower wrote: post #20

Can't each transmitter/radio add some type of a 2-nd order frequency onto the transmitting signal (imagine a sin-wave, except it's line is not smooth, the line has its own "frequency") and detect that to filter the incoming signal?

what you proposing is equivalent to increasing the frequency of the channel. If both do the same "2-nd" order frequency - we're back to the same "1-frequency" channel problem. If different - that's outside of the "1-frequency" channel problem.

Re: Stanford Wireless Breakthrough

#23

Post by powertower »

VladRussian wrote: post #22
powertower wrote: post #20

Can't each transmitter/radio add some type of a 2-nd order frequency onto the transmitting signal (imagine a sin-wave, except it's line is not smooth, the line has its own "frequency") and detect that to filter the incoming signal?

what you proposing is equivalent to increasing the frequency of the channel. If both do the same "2-nd" order frequency - we're back to the same "1-frequency" channel problem. If different - that's outside of the "1-frequency" channel problem.

Each radio would have a unique 2-nd order frequency for it's own filtering use, as a "tag" of it's signal. The primary frequency is known and used for the transmition, and the 2-nd order one is piggybacked on it. I'm not saying there are 2 transmiting frequencies.

Re: Stanford Wireless Breakthrough

#24

Post by coolgeek »

"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."

That's going up on the wall above my monitor.

Re: Stanford Wireless Breakthrough

#25

Post by 83457 »

hristov wrote: post #19
regularfry wrote: post #10

Earlier quoted context omitted.

...which, assuming you're sending and receiving equal amounts, doubles the amount you can send in a given time period. http://en.wikipedia.org/wiki/Duplex_(telecommunications)

I don't think that is the case. Suppose a given channel (e.g. a frequency) has a maximum information per second it can carry X, this system will not allow 2X information to be carried. It will allow the information carrying capacity of the channel to be split, such that each side can carry a maximum amount of information A and B respectively such that A+B<=X.

"this system will not allow 2X information to be carried"

I believe that is the entire point of the article. To allow double the capacity between two devices. The original capacity would be the amount of data that could be sent by a single device. However if both devices can send at the same time that is double capacity.

Re: Stanford Wireless Breakthrough

#26

Post by derobert »

JoeAltmaier wrote: post #4

The claim that this doubles the amount of information you can send is nonsense. It simply allows you to send and receive simultaneously.

The way "full-duplex" fixed wireless gear often works is by splitting the spectrum in two halves (plus a sometimes small guard band: frequency division). Each end uses one half for TX. Alternatively, you use the full band but switch off which end is transmitting (time division). So it really does double (or even a little more, if eliminating a guard band) the amount each side can send.

Re: Stanford Wireless Breakthrough

#27

Post by reemrevnivek »

VladRussian wrote: post #21
nimrody wrote: post #3

Some more information here: http://sing.stanford.edu/fullduplex/ The problem with full duplex wireless comm. on the same frequency is that the transmitted signal is much stronger than the received signal. Therefore, echo cancelling is usually impractical. Not sure how these guys overcame the difficulties with transmitter nonlinearities and other unknown impairments. EDIT: they claim to do partial cancellation by plac…

it may be practical in the office setup where 6+ antenna phased arrays Wi-Fi switches are "cost-practical". With phased array you have much more geometrical flexibility - you may "narrow beam" transmission to a client while better adjusting the transmitter's null onto the receiver's physical location to the current conditions, reflections, etc...

No, I think that the parent post was referring to the transmitters on the radio device. The transmitting and receiving antennas are different, and they place the receiving antenna in a null of the transmitters.

This is easy and practical because they're in a location which is fixed by the PCB/housing. There's no phased array required.

Re: Stanford Wireless Breakthrough

#28

Post by thisrod »

powertower wrote: post #23
VladRussian wrote: post #22

Earlier quoted context omitted.

what you proposing is equivalent to increasing the frequency of the channel. If both do the same "2-nd" order frequency - we're back to the same "1-frequency" channel problem. If different - that's outside of the "1-frequency" channel problem.

Each radio would have a unique 2-nd order frequency for it's own filtering use, as a "tag" of it's signal. The primary frequency is known and used for the transmition, and the 2-nd order one is piggybacked on it. I'm not saying there are 2 transmiting frequencies.

> I'm not saying there are 2 transmiting frequencies.

200 years ago, people might have believed you. Then Fourier showed that your statements contradict each other. He said a lot of other interesting things - Bracewell's book is a good introduction.

Re: Stanford Wireless Breakthrough

#29

Post by harshpotatoes »

JoeAltmaier wrote: post #4

The claim that this doubles the amount of information you can send is nonsense. It simply allows you to send and receive simultaneously.

If I'm understanding correctly this does double the amount of information sent in a chunk of time. Example: You send 1Mbit over a sec. Then you pause for 1 sec to receive 1Mbit. Effectively, you've only sent 1Mbit over 2 seconds. Now, due to being in full duplex mode, you can send 1Mbit over 1 sec while simultaneously receiving 1Mbit over 1 sec. Thus, allowing you to send 2Mbit over 2 seconds. 1Mbit/sec is double .5Mbit/sec.
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