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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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I'm not a robot like you. I don't like having disks crammed into me... unless they're Oreos, and then only in the mouth.
-- Fry
(Score: 3, Interesting) by tftp on Thursday February 27 2014, @10:01PM
It will be very computationally intensive to recognize all the reflections - there will be more than one, all superimposed.
But that's at least is theoretically possible. What is less possible is to subtract your own signal (at +33 dBm) from an incoming signal that is at, say, -100 dBm. You need at least 130 dB of dynamic range. Traditional RF systems use analog components (circulators, filters, separate antennas) to suppress unwanted signals and to bring them into the range that the receiver can handle. A directional coupler is one such possibility... but it is not going to be good enough because the TX signal reflects from the antenna, and sometimes those are very strong reflections (if you are holding it wrong.)
The easiest way to implement full duplex today is by packetizing data that comes in and out, and use only a fraction of time to receive and transmit those packets. Then you don't have to receive while you are transmitting.
(Score: 1) by adolf on Thursday February 27 2014, @10:50PM
Eh? That's the easy part:
If A is our locally-transmitted and very strong signal, and B is a combination of whatever is coming into the RX antenna, then:
Transmit signal A. Invert it (rotate phase 180 degrees...give or take), attenuate it as appropriate, and mix it with the input to the receiver (B). We A minus B equals C, which is everything but the local transmitter.
Done.
Meanwhile, TDMA isn't full-duplex. It's just two or more transmitters taking turns. Normally, they take turns very quickly, but they're still not talking at the same time. Meanwhile, the spectral efficiency of TDMA is approximately the same as simplex: Nothing is gained.
I'm wasting my days as I've wasted my nights and I've wasted my youth
(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