Stanford Wireless Breakthrough
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Stanford Wireless Breakthrough
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Re: Stanford Wireless Breakthrough
#2Not to belittle their announcement, but what textbook says you can't filter a signal? Or is the novelty in the degree to which they had to filter the outgoing signal?
Re: Stanford Wireless Breakthrough
#3Some 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 placing the receiver antenna at the null of the two transmitting antennas (getting 50 dB reduction in echo power). Whether this is practical in a commercial low cost radio remains to be seen.
Re: Stanford Wireless Breakthrough
#4The claim that this doubles the amount of information you can send is nonsense. It simply allows you to send and receive simultaneously.
Re: Stanford Wireless Breakthrough
#5Not to belittle their announcement, but what textbook says you can't filter a signal? Or is the novelty in the degree to which they had to filter the outgoing signal?
> ... but what textbook says you can't filter a signal ...
i don't think any textbooks makes that claim. from the article: ...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.
Re: Stanford Wireless Breakthrough
#6Not to belittle their announcement, but what textbook says you can't filter a signal? Or is the novelty in the degree to which they had to filter the outgoing signal?
The much larger signal (local TX) would always capture your RF chain, being that using standard selectivity techniques in the analog domain the unwanted looks exactly like the desired. Being so large, it also would generally saturate your receiver.
Re: Stanford Wireless Breakthrough
#7Not to belittle their announcement, but what textbook says you can't filter a signal? Or is the novelty in the degree to which they had to filter the outgoing signal?
They put the receiver in a "node" of destructive interference between two transmitting antennas. That way, the transmitting signal doesn't swamp the receiver.
Re: Stanford Wireless Breakthrough
#8Not to belittle their announcement, but what textbook says you can't filter a signal? Or is the novelty in the degree to which they had to filter the outgoing signal?
> ... but what textbook says you can't filter a signal ... i don't think any textbooks makes that claim. from the article: ...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.
I can certainly understand that. My confusion arose from the quote:
> "Textbooks say you can't do it," said Philip Levis, assistant professor of computer science and of electrical engineering.
Re: Stanford Wireless Breakthrough
#9Sounds very interesting but I wonder if the null of the transmitting antennas is stable in the presence of multipath reflections.
This scheme also works only if all nodes have full-duplex setups, which is impractical for small devices.
Re: Stanford Wireless Breakthrough
#10The claim that this doubles the amount of information you can send is nonsense. It simply allows you to send and receive simultaneously.
...which, assuming you're sending and receiving equal amounts, doubles the amount you can send in a given time period.