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AnonTechie writes:
According to an article from The Register, a team from Stanford University has patented technology that could halve the bandwidth that a mobile provider needs.
Operating under the name Kumu Networks, they are showcasing tech which they claim would exactly double throughput. Radio equipment (such as mobile phones) would be able to send and receive on the same frequency through a process similar to noise-cancelling headphones; by knowing what a base station is transmitting it can cancel out the information from the very faint signal it receives.
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Radio Tech Could Halve Bandwidth Needs
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(Score: 2, Informative) by tftp on Thursday February 27 2014, @11:16PM
It's easy only until you look closer. Then you discover that the antenna mismatch results in a frequency-dependent and environment-dependent phase shift. Also you notice that the electrical length between all components becomes critical - and that is temperature-dependent. Even a "simple" 180 degree phase shift has to be done with a transformer or a balun that is not ideal. However a tiny disbalance in the feedback path will cause not only a failure to receive, but perhaps a damage to the LNA (often they can't take more than 1 mW.) It's all doable... but it's much harder to do in a cell phone, when you have a whopping $0.50 in parts costs to spend on everything that it takes.
This whole approach has roots that go into early telephony. Every landline telephone that uses a SINGLE copper pair has a hybrid circuit [wikipedia.org] that separates, as well as it can, the incoming and the outgoing voice. Traditional hybrids [wikipedia.org] use exactly the scheme that you described. It's easy to do in 300-3400 Hz, compared to 1-2 GHz.
I will make no claims with regard to {T,C}DMA and their spectral efficiency.
(Score: 1) by adolf on Friday February 28 2014, @01:41AM
In terms of phasing and attenuation, I'm pretty sure I mentioned that already. As I've said before, that's the easy part.
Getting things synchronized and keeping there is also easy. You act as if the concept of a PLL hasn't been around since forever.
Regarding telephones: Yes, that's a similar problem. It's also a solved problem using rudimentary parts, whereas we have ridiculously-fast DSPs these days. *shrug* (And in other news, AMPS is dead, and cell phones have been much fancier than an FM transceiver for just a little while now...)
Regarding cost: Sheesh. With an attitude like that, it'll be a wonder if this color television thing ever takes off -- the sets are just so expensive.
Needing a transformer to rotate phase? Puh-leeze.
And if you don't want to comment about TDMA and spectral efficiency, why did you bring up TDMA in a discussion about spectral efficiency?
Aaand. Yep, that's enough for me on this thread.
Cheers.
I'm wasting my days as I've wasted my nights and I've wasted my youth