Two-way Radio Breakthrough To Double Wi-Fi Speeds 244
An anonymous reader writes "Scientists at Stanford University have built a radio that can transmit and receive at the same time on the same frequency. The breakthrough could lead to a twofold increase in performance for home wireless networks and end that annoying habit of pilots finishing every sentence with 'over.'" But you can still do it if you like. I'm not judging.
he! (Score:5, Funny)
First post, Over.
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Roger that. Over.
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Tower: Flight 2-0-9'er cleared for vector 324.
Roger Murdock: We have clearance, Clarence.
Clarence Oveur: Roger, Roger. What's our vector, Victor?
Tower: Tower's radio clearance, over!
Clarence Oveur: That's Clarence Oveur. Over.
Tower: Over.
Clarence Oveur: Roger.
Roger Murdock: Huh?
Tower: Roger, over!
Roger Murdock: What?
Clarence Oveur: Huh?
Victor Basta: Who?
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We have clearance, Clarence.
Roger, Roger. What's our vector, Victor?
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Looks like I picked the wrong week to quit sniffing glue!
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Nah. I was born in '86, and it's one of my favorite movies!
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You do realize everyone under 30 ain't got a clue of what you are talking about.
Pretty sure people under 30 still sniff glue. :-)
Innovative (Score:5, Informative)
Doing this On the same frequency is remarkable. but the gains they are claiming can be had right now by using TWO frequencies. Transmit on channel 1 receive on channel 12.. the other end does the opposite. the thing is, 90% of Ethernet traffic is not bi directional. it's packetized so their claims of DOUBLE will not be realized. when you set up a network connection from half duplex to full duplex you do not see a double in speed, just a double in capacity.
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Doing this On the same frequency is remarkable. but the gains they are claiming can be had right now by using TWO frequencies. Transmit on channel 1 receive on channel 12.. t
This might be problem if you want mesh network with many (n>2) nodes. They (mostly) want to hear each other.
Anyhow, with 100 dB (10 000 000 000) times stronger transmit signal I somehow doubt if geometry of antennas can be accurate
enough to keep it working with changing temperature, humidity etc. over MHz of bandwith.
Maybe with heavy DSP processing and continuos monitoring?
Compensating for scattering of own signal, and all reflections from surounding objects?
On top of it, we normally use MIMO: so you hav
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For example, they claim they will do it by using two transmitters. This of course requires more hardware only to generate destructive interference at the receiver and improve the SNR. However, these two transmitters will generate most likely deep nulls at certain distances from them. The question is, does this really solve the problem, or anyone moving at certain speed is under the risk of hitting all the nulls and not listening to anyth
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So if I send twice as much in the same amount of time it seems to me that that equals a doubling of speed or use of less resources in the case of sending and receiving on one frequency instead of tying up two frequencies. In the case of fiber optics where different colors are used to pump data that would enable twice the delivery totals for one cable in the same amount of time. Sounds good to me.
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Uh, this technology lets you SEND and RECEIVE on the same frequency at the same time. So, if the bandwidth of the link is 1Mbps, you can now send and receive 1Mbps at the same time. You can't send 2Mbps over the link, or receive as much.
So, other than your ACK packets getting out faster, this isn't going to speed up downloads much.
As far as fiber optic and different colors on the same cable goes - color is just another way of saying frequency. Using two colors at the same time is just another way of sayi
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when you set up a network connection from half duplex to full duplex you do not see a double in speed, just a double in capacity.
So a car analogy would be if you took a one way road and doubled the lane count with opposite flowing lanes, the cars don't move twice as fast, but twice as many.
Did you really need to be explained to anyone?
How about if we stacked bidirectional lanes on top of each other so one lane represented both directions, and double capacity in the same square footage? Oooohh, I see what I did, deeeeeeeensittttyyyyy.
Doing this On the same frequency is remarkable. but the gains they are claiming can be had right now by using TWO frequencies.
Then they could move twice as much again with TWO full duplex frequencies!!11
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While it's true that an end-node host will mostly do one-way transactions like downloading or uploading, intermediate systems (switches) use full duplex to much advantage.
Some wireless equipment is used in this same way; bridges, mesh, etc.
The other issue is latency. That's not at all important, is it.
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It's true that FDMA can potentially also roughly double the capacity, as well as something more sophisticated like CDMA, but I wonder about its inherent tradeoffs compared to this "full-duplex" system. For practical FDMA systems, the frequency spacing between channels must either be close (implying a lossy duplexing RF circuit) or the spacing must be large relative to the channel bandwidth (so that efficient resonant antennas may be designed). In the first case, there is more loss due to the RF circuitry, w
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"Doing this On the same frequency is remarkable."
Not really, Quadrature Amplitude Modulation has been around for a long time, its usually done with both signals going in the same direction, doing it with signals going in opposite directions is an improvement, but its not that great a leap.
I wonder why nobody thought of it before, now with al lthe patents they get it might become mainstream in 20 years.
http://en.wikipedia.org/wiki/QAM [wikipedia.org]
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Doing this On the same frequency is remarkable. but the gains they are claiming can be had right now by using TWO frequencies. Transmit on channel 1 receive on channel 12.. the other end does the opposite.
That only works when the conversation contains exactly 2 nodes. Node A transmits at freq 1 and receives at freq 2, whereas node B transmits at freq 2 and receives at freq 1. That CANNOT extended to a third node... hence, aviation conversations all use one frequency and everyone must take turns.
With this new breakthrough, everyone can be on the same frequency AND can be talking and listening at the same time.
None of this applies to ethernet because ethernet hubs/switches are built so as to separate every
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Re:Innovative (Score:5, Informative)
Well, dial-up modems don't matter much at this time (save for some corner cases), but I'll take it on anyway . . .
The phone line does, actually, have 112kb/s of bandwidth, but it is divided by the telephone network to go in opposite directions. 56k in, 56k out. At the trunk level, they actually travel over separate wire pairs (i.e. if you were to get a DS0 or a T-1 or higher, you have a transmit pair and a receive pair).
As for the notion that modems do this trick already, it is completely true. There are two main differences between a modem and a radio, though. First is that the modem can reasonably expect that, under normal conditions, the signal level of what it is receiving from the other end will not change much, and that its required transmit power will not change at all. Second is that the signalling going on in a modem is all at particularly low frequencies (4kHz and down) versus those going on via wireless which will be between one and 10 orders of magnitude higher in frequency, which is a tad more difficult to operate on.
Let me take that last point and expand on it a little. It is completely reasonable to take a modulated signal of a few kHz up to maybe a few tens of MHz, sample it digitally, push it through a DSP, slap some math on it, and get some sort of accurate filtering to take place. In dealing with higher frequencies, this is far more difficult, and achieving this, I believe, is the breakthrough.
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A phone connection has a limit of 64kbps. That's the bandwidth allocated for a single phone connection on a digital network. The only way to get a higher data throughput is via some sort of compression.
Ummm... no. (Score:3)
Sorry to break it to you, but your grandma didn't have a magic modem. On a plus side, she probably wasn't a witch either.
http://en.wikipedia.org/wiki/56_kbit/s [wikipedia.org]
A 56 kbit/s line is a digital connection capable of carrying 56 kilobits per second (kbit/s), or 56,000 bit/s, the data rate of a classical single channel digital telephone line in North America. In many urban areas, which have seen wide deployment of faster, cheaper technologies, 56 kbit/s lines are generally considered to be an obsolete technology.
The figure of 56 kbit/s is derived from its implementation using the same digital infrastructure used since the 1960s for digital telephony in the PSTN, which uses a PCM sampling rate of 8,000 Hz used with 8-bit sample encoding to encode analogue signals into a digital stream of 64,000 bit/s.
However, in the T-carrier systems used in the U.S. and Canada, a technique called bit-robbing uses, in every sixth frame, the least significant bit in the time slot associated with the voice channel for Channel Associated Signaling (CAS). This effectively renders the lowest bit of the 8 speech bits unusable for data transmission, and so a 56 kbit/s line used only 7 of the 8 data bits in each sample period to send data, thus giving a data rate of 8000 Hz × 7 bits = 56 kbit/s.
See also here:
http://en.wikipedia.org/wiki/56_kbit/s_modem#Speed [wikipedia.org]
Like 10 years ago, there was a period of a few weeks where, by some random bug or glitch somewhere, my grandmother's computer (with 56k modem) would regularly connect to her dial-up service at 118.2kbps. She, of course, never noticed it. I don't think anyone else did, either. I noticed it when my parents and I went over to visit, and I asked to use the computer because I was bored.
Let me guess... Windows 98?
That was a common bug back then. Probably something to do with all that 16-bit and 32-bit code [microsoft.com] just thrown on the pile there.
You were probably connecting way bellow even 56k, it's just that you couldn't really notice it.
Also, it could simply be that her PC was
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Some modems would report the link speed as 115000bps. This was the speed the computer talked to the modem at, not the speed at which the modem talked to the other computer. Some modems would only report 115000bps if the connection had certain data compression functions enabled.
The effective rate for transmitting data on a 56Kbps link could exceed 115Kbps when compression was used, but if the modem used a standard serial interface then 115000bps is the maximum rate it could support.
Non-compressed data would
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>>>Phone modem speeds weren't limited to 56kbps by technology
>>>...was arbitrarily limited by the FCC
Completely and totally false. Digital phone lines have 8000 samples per second at 7 bits. That yields 56000 bits per second maximum. (Analog lines are limited to 33800 bps/3429 baud.) So it's a technological limitation.
The FCC imposed a *power limit* due to reports of crosstalk between lines. The power limit reduces the max speed to 53,300.
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Phones are "full duplex" because there are 2 wires involved. One wire coming in to the receiver and going up to the earpiece, and one wire going out from the mouthpiece. (Yes, telco engineers, I know it's not quite that simple, but for purposes of this conversation, it is)
To put it another way, you don't fill the bathtub by reversing the flow of the drain.
To translate that to wireless, you'd need two frequencies for full duplex. Full duplex over one frequency would be like full duplex over one wire instead
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> Phones are "full duplex" because there are 2 wires involved. One wire coming in to the receiver and going up to the earpiece, and one wire going out from the mouthpiece. (Yes, telco engineers, I know it's not quite that simple, but for purposes of this conversation, it is)
Utter screaming gibberish.
The phone IS actually full duplex. The Receive and Transmit signals travel on the same wires at the same time (in opposite directions), thanks to a gadget called a Hybrid.
And believe it or not, the same thing
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Sorry, but it works nothing like you describe.
It is true that there is only one pair of wires involved. Phones (Plain Old Telephone Services P.O.T.S) achieve full duplex with a simple analog circuit called a hybrid. Until the 1980's most phones had no active electronics in them. The hybrid was a specialized transformer which by arrangement of the coils' polarities, the much stronger sending signal is subtracted from the receiving signal in the handset. The subtraction is purposely designed not to be per
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Phones are "full duplex" because there are 2 wires involved. One wire coming in to the receiver and going up to the earpiece, and one wire going out from the mouthpiece.
No, phones are full duplex because they were designed that way. Doing it using two wires is trivial. You simply make a loop that includes the earpiece of both phones and the mics from both phones and a battery. When you talk, your voice comes out both earpieces. That's called "sidetone". You hear what you are saying so you know the circuit is working. If you don't hear yourself, the phone sounds "dead". The same current that drives your earpiece drives the other end. And vice versa.
And doing it with "one
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Did you miss the part where I said it was simplified? Yes, I know all about the 4 wire phone system and how it works, but I didn't see the need to write a dissertation on it just to get people to see why full duplex over one frequency is *not* comparable to full duplex over the telephone.
Re:Innovative (Score:5, Informative)
GPS and CDMA use something completely different. Spread spectrum techniques like GPS and CDMA take a signal with (for example) 1MHz bandwidth and spread that data over a 100MHz bandwidth. Now up to 100 people employing this technique can transmit over that 100MHz bandwidth simultaneously, but there is no gain in throughput because it's the same in the end as those 100 users transmitting in a 1MHz bandwidth with user 1 at 1.000GHz, user 2 at 1.001GHz, and so on. The benefit of spread spectrum is that it's hard to segregate each radio into such a small bandwidth without interfering with adjacent users. It could not be used for full duplex single frequency radio because the transmitted signal would still swamp out the received signal, unless it were combined with isolation/nulling techniques like these Stanford guys are using.
The research page for the work in this article is here: http://sing.stanford.edu/fullduplex/ [stanford.edu]
They are using multiple techniques to selectively null out the transmit signal at the receiver. Their main novelty is spatial nulling of the antenna. Two antennas transmitting the same signal will have points in space where the signals destructively interfere and cancel. If they are spaced by an odd number of half wavelengths then this includes the entire line between the two antennas, so this is where the receive antenna is placed. Then they use existing analog and digital techniques to further cancel out the component of the transmitter which appear at the receiver.
Although the techniques for this are well known the trick is getting it to actually work effectively, because you need to achieve very high isolation from your own transmitter to receiver in order to avoid the transmitter effectively jamming the receiver. Their antenna nulling is apparently what gave them that extra isolation they needed.
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And therein is something perplexing, as multipathing ought to make this especially weird. Receiver discrimination would have to be unusually high; first it has to null out its own transmission (hoping that it doesn't null out it's own reception) and S/N has to be really high. Add in a bounce from something moving, or use any kind of slow slewing factor and this boat doesn't float.
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Reflections/multipath will reduce the actual isolation achieved by their antenna nulling technique, but they will still achieve some improvement in isolation as no reflections are 100% and there is two-way path loss involved. As long as they get enough isolation with the antenna nulling to keep the receiver front-end from saturating then they might be able to compensate for the multipath in the digital domain, depending on the processing power available. It would be pretty simple for it to do a self-calib
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In thinking about it further, root-hertz noise and other conditions would have to be optimal. Phase distortions, whether slew-induced/reflective or simple TD would probably be corrected like any other HDX transmission. And ultimately, it really opens up a lot of freq bands.
"Over"? (Score:2)
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I haven't flown anything in 10 years, and "Over" was considered quaint even then...
I was under the impression that "Over" helped in that it let the other person know when your transmission was...y'know complete, not just so the other guy knew when to start talking.
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The click when you release the mic switch, and the fact that you've shut up, seem to work well enough. :)
It might well be different out in Shanwick country on HF (sadly, I've never had the chance to get out there as pilot), but certainly on VHF I've never heard it from anyone but a couple of old-timers.
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How do you differentiate between the click as the mic switch is released and the pilot shuts up because he's finished his message, and the click because he's had a heart attack and died, or the click because the transmission ended because he hit the ground?
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Re:"Over"? (Score:5, Informative)
Because in any case, the pilot has finished his/her message when you hear the mic click. Surely you don't think the conversation is going to continue?
More importantly, the pilot and controller speak to each other in very precisely defined and very concise language. It's pretty obvious when one of them is done yakking, the mic click is a convenience, like the "over" used to be before all radios had mic clicks.
A typical initial approach might go something like this:
"Bangor approach, Cessna five-two-five-Lima-Charlie, 12 miles west, descending 5000 with information Sierra, full stop."
This tells the controller that:
1. You are intending to make an announcement to the controller at Bangor Center in charge of approaches (in case you fucked up your frequency, they can correct you quickly and get you on the right frequency).
2. You are a Cessna, US-registered, with tail number N525LC.
3. You are 12 miles to the west of the airport, at 5000 feet, and descending.
4. You have listened to their weather/conditions report recently, which is their update "S" (Sierra), and the letter is updated whenever the information is updated (usually once an hour). That means you already know the wind speed, altimeter settings, and preferred runway, and have adjusted all of your instrumentation and expectations appropriately.
5. You are requesting approach vectors for the currently-active runway (which you already know) and you intend to land there (full stop, as opposed to a touch-and-go or a practice approach but not a landing).
The controller will respond with something like this:
"Cessna Five-Lima-Charlie, Information Sierra current, enter 45 left downwind for runway one-eight-zero, report midfield"
This means:
1. The controller has acknowledged your presence, confirmed that you have the latest weather, and picked an abbreviation for your tail number that does not conflict with any other aircraft currently operating in his airspace. That will be your designation for the duration of your talk with this controller.
2. The controller wants you to enter the pattern at a 45-degree angle on the upwind side of the runway and call you again when you are properly established in a left downwind and abeam the middle of the runway.
3. There is no known traffic on that side of the field that will conflict with your entry, because the controller didn't mention any.
The conversation will proceed, with both the pilot and controller keeping radio use to the absolute minimum necessary to communicate what they need to say. If the frequency is really quiet, they might exchange a few jokes or snide remarks, but "over" is usually in the domain of CB radio, old timers who used to deal with really crappy radios, and bad movies.
Interruptions to what a pilot or controller is saying are obvious because of the way the language is constructed. This is done on purpose. If you say "Bangor approach, Cessna three-five..." then stop talking, you're going to hear a controller say something like "Unknown Cessna starting in three-five, please repeat, message not received." in just a very small handful of seconds.
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>pilot and controller speak to each other in very precisely defined and very concise language
Nice example, thanks!
>CB radio, old timers who used to deal with really crappy radios, and bad movies.
Saying "over" is necessary when operating SSB on HF, you don't hear the mic clicks and sometimes not sure if person on other end has finished talking. Coast Guard uses "over" when operating on VHF marine channels which I assume for boat drivers steering outside or with a noisy engine or wind.
Bad movie
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HAM radio (in the "real" sense, where the H shands for HF) uses Over quite heavily, as the signal you're picking up is often coming from thousands of miles away and isn't really any higher than the ambient noise level. Even if there is a mic click, it's entirely possible that the other side can't hear it clearly. The communication is also usually much more conversational, and may include pauses while one party keeps the mic keyed briefly (or releases it but expect to pick it up again imminently).
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ATC in the Southern Calfornia region appears to rely on patterns more than a click or silence, as they start talking the instant I've finished calling my tail number and a split second before I've released the mic switch. Then again, it does get pretty busy here: I've had to make six calls to SoCal Departure before I was acknowledged, and when I was, I was told to switch to another frequency because I'd al
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No it doesn't, I hope you don't fly anymore you're making a careless mistake about something that should have been taught to you before you took the ground exam.
The purpose of an End of Transmission marker is so that everyone listening has confirmation that they received ALL of your transmission as intended. So if for some reason my transmission is cut off and it seems like just silence you as a listener know it was cut off because you didn't h
Re:"Over"? (Score:5, Insightful)
It seems that in your rush to prove your superiority and brand me an idiot you missed the smiley, despite quoting it, possibly because it came after the End of Sentence marker and you'd stopped reading :P (There, did you get that one?) For the record, I haven't logged any flight time since summer 2000, so I'll grant you that my R/T is a little rusty, but I did know and use proper phraseology. I had to, or I'd get ritually humiliated by my colleagues in Air Traffic... Working at a commercial flight training centre, especially in one with "AREA OF INTENSE AERONAUTICAL ACTIVITY" plastered across it on the half-mill chart, you simply don't get away with sloppy R/T.
I love people who throw phrases like "idiots like you" around. Have to say I didn't especially enjoy sharing a cockpit with them, though, no matter how superior they thought they were. They tended to be precisely the sort of egotistical pillock that everyone but them knew was going to up in a smoking hole somewhere, and two I know of from flying elsewhere did just that. (Well, one in a smoking hole and one in a long line of aircraft parts across a mountain, since we're being pedantic.) A third disappeared behind the trees before recovering from his ill-advised attempt at aerobatics, I don't know how he survived.
I've flown as passenger and pilot with all sorts, from the late Mr. Cool to the chap who disabled the Bismarck (I saw the logbook entry) and a very quiet unassuming gentleman who turned out to have more types in his logbook than most of the instructors had hours. And I'll tell you this much: I'd far rather fly with the under-confident guy who's a bit mixed up on the R/T than the one who knows it all and thinks everyone else is an idiot. As my instructor said: The under-confident can learn, but the over-confident will. One way or another.
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Nope. You end the transmission with your tail number. It does double the work. Show's that your done and conveys information to the person receiving the transmission.
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Even longer than that. I was a stuent pilot in 1981, and even then the convention was long obsolete.
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I still fly, and almost never hear this.
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Correct. I last flew about two years ago. We don't say "over". Ever. You sound like a trucker on a CB and you're only going to piss off the tower and the other pilots on the freq because you're wasting airtime, and sound like you don't know what you're doing. ATC comms can get super busy, and lives are (literally) at stake. If you listen to even a Class C approach frequency, it will sound like a nearly uninterrupted stream during busy times of the day. There isn't time for extraneous nonsense when Cess
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This directly contradicts with what I was taught and how the Class C I frequent operates. In the example below the Pilot should end with four seven whiskey. If not how does the tower know the correct plane is responding?
T: Four seven whiskey, turn right on alpha three and contact ground point eight
P: Right on alpha three, ground point eight. good day
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CB Radio (Score:2)
Wow (Score:2)
Nice job. Though the problem off cross-talking has been solved for a long time using TDMA or CDMA.
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From the fine article, "Current phone networks allow users to talk and listen simultaneously but, the scientists said, they use a work-around that is expensive and requires careful planning."
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Afaict on mobile phone networks TDMA and/or CDMA are used to seperate different users while FDMA is used to seperate uplink from downlink.
Yaaawn (Score:2)
It's called a duplexer [wikipedia.org].
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A typical duplexer uses two frequencies in the same band that are usually close to each other. This is definitely an advance on that idea.
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Roger, Over (Score:5, Funny)
Captain Oveur: Roger!
Roger Murdock: Huh?
Tower voice: L.A. departure frequency, 123 point 9'er.
Captain Oveur: Roger!
Roger Murdock: Huh?
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?
Captain Oveur: Huh?
Victor Basta: Who?
Actual information (Score:5, Informative)
How this actually works :
The Challenge in Achieving Full-Duplex
The problem that has historically prevented full-duplex is that, when a node transmits, its own signal is millions of times stronger than other signals it might hear: the node is trying to hear a whisper while shouting. The challenge is canceling the node's own transmitted signal (shout) from what it receives (whisper). Existing approaches, such as digital cancellation and noise cancellation circtuis, can cancel some of the transmitted signal, reducing its strength, but not enough to make a node able to receive.
Antenna Cancellation
Our design uses two transmit antennas one receive antenna per node. The transmit antennas send the same data and the receive antenna is placed such that there is destructive interference from the two transmit antennas, thus reducing self-interference. Offsetting the two transmit signals by half of the wavelength causes them to cancel each other, creating a null position where the transmitted signal is much, much weaker.
Combining antenna cancellation with cancellation through a noise cancellation circuit gives ~50dB reduction in self-interference before the RF signal is demodulated and sampled to the digital domain. Digital cancellation removes the residual interference.
For more information :
http://sing.stanford.edu/fullduplex/ [stanford.edu]
The actual paper (PDF) :
http://sing.stanford.edu/pubs/mobicom10-duplex.pdf [stanford.edu]
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Have they tested this in non-laboratory conditions? The idea of transmitters being placed such that they perfectly cancel each other out sounds great, but what happens when you add in nearby objects that reflect RF?
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And have you seen that their first active component in the receive path is an intersil qhx220 that is a noise cancelling LNA. The IIP3 of this LNA is about -21dBm at 2.4GHz, so the P1dB will be about 10dB under that, and OFDM signals typically needing 5dB backoff from the P1Bb to get in the PER specs of 802.11x. So lets assume they are transmitting 15dBm from their transmit antennas (typical for a portable WiFi device) to avoid your LNA going non-linear you want to the cancellation of the transmit signals a
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It also limits the frequency range you can use, although depending on how good the digital concelation is this might still work for a relatively tight band. Oh, and there will be interference patterns beyond just the third antenna. If the receiver is in the wrong place, it will get the same massive cancelation.
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Thank you for the links. I was hoping someone would post them.
The PDF is pretty good. The idea is brilliant in its simplicity and damn, it works. Good for these folks, this is remarkable work.
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rock in water... (Score:2)
The transmitted signal is much, much weaker in the area of destructive interfierance.
Think of a pool of still water. If you throw a rock into it, you see waves propagate out from the impact.
If you throw two rocks in (or to be more accurate, 180 degrees out of phase, so one rock in and one rock out) at the exact same time, each rock will create the same waves as the single rock, but in one very tiny area directly between the two rocks the waves will cancel eachother out and the water will remain perfectly st
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Except that from my days working with ADCs and coherent demodulation I know that 1deg of phase error between the two transmit signals will reduce the isolation between the two transmitted signal to 40dB. That 1deg of phase difference is 0.3mm at 2.4GHz
The authors say they need 50dB of isolation, whereas as my guess they need more like 60dB for a reasonable transmit power. There is a need to precisely place three antennas probably about 10cm apart with a positioning error of a very very small fraction of a m
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I guess it would help with spectrum conservation or something, but I just don't see how that would help in practice - after all, this method requires three antennas! With that, you could be broadcasting and receiving (though not at the same time) on three different channels all at once [wikipedia.org]!
Actually, now that I think about it, this could work well from a security perspective. Imagine you've got two stations, A and B, transmitting data at the same time using this method. Now someone stucks an antenna somewhere in
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Offsetting the two transmit signals by half of the wavelength...
Wait, does is this over-the-air "same frequency", which would imply that they are merely trading off bandwidth to achieve full-duplex?
Two transmitters (transceivers) on the "same" frequency normally implies two transmitters / transceivers using the same frequency and the same bandwidth (and modulation), otherwise you are merely doubling the signal bandwidth used as this seems to suggest.
I can imagine that it could mean that is merely an offset (or delay) used for filtering, not over the air, but this is not
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*KSSCHK* (Score:5, Funny)
I end all my sentences with *ksschk* so it sounds like I'm in space.
FYI - Pilots don't use "over." (Score:2)
Pilots don't use over. Pilots end a transmission with their tail number.
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Yes generally calls to ATC are Who, Where, What. In no example you give does the pilot use over.
That burst of static you just heard. Is it the end of a transmission, a failed radio, interference, or the pilot being stepped on by another pilot?
What the military does is irrelevant because the author specifically target pilots.
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[THIS IS MEANT TO BE IN ITALICS]In reality, there's a bit of white noise (don't know what causes it, might be artificial),[THIS IS MEANT TO BE THE END OF ITALICS]
Radios have a noise gate that is sensitive to signal level. In the absence of signal, it mutes the speaker. Radios in aircraft use AM for various reasons related to what happens if two people talk at the same time (you can hear both, unlike FM), and AM has generally quieter "no signal" background noise than FM which has that loud rushing noise yo
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I believe AM was meant as a designator of modulation style, rather than referring to a frequency band.
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Nice!
There is another way (Score:3)
It's called time domain multiplexing. If you chop the transmitter on and off at a rate much faster than the data rate you can hear bits in between your chopped up transmissions. Sorta like fast break-in amateur CW where you can hear between the dots and dashes. This would require synching the two stations chop rate. Since the 'chopping' is done above the nyquist sample rate, no data is lost, and you get true full duplex speed.
Limitations (Score:5, Informative)
The signals will only perfectly cancel when they are separated by a distance that is exactly one half the wavelength. Assuming you separate the two transmit antennas by this distance at the carrier frequency, then there will be a limitation on the available bandwidth. This is because the further you get away from center frequency, and away from the ideal antenna spacing, the less destructive interference you will have (and the more your transmit signal will leak into your receive signal). So you will double your capacity for only narrowband channels.
The pdf gives actual numbers. I just wanted to point out that there is a limitation on bandwidth.
You might also think, "If I know what I'm transmitting, why can't I just subtract it from what I receive?" This has to do with the dynamic range of the receiver, which is a function of the number of bits in your analog to digital converter. You must attenuate your received signal so that you don't saturate your converter. Have you ever turned the volume up so loud that you begin to hear distortion? It's the same thing.
So you are receiving this loud unwanted transmit signal, and this soft receive signal. You must lower the volume so that you are not distorting the highest signal. This lowers the volume on the desired signal as well. You can lower it so much that your analog to digital converter is not able to differentiate between a 1 and a 0 anymore.
I think if you could have an A2D with enough bits that you didn't care if you received the transmitted signal, then you could just carefully subtract out the unwanted transmit signal. Maybe I should patent that? Meh. I'm probably wrong.
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You're correct in identifying dynamic range as one of the major issues here. An A2D with an extremely high number of bits would help, as you could recognize both the faint and large signals simultaneously, and with prior knowledge of the large transmitted signal it could be removed from the data.
But there is another issue, which is the dynamic range of the RF hardware itself. Their experiments were conducted at 0dBm (1mW) transmit power, but that is not at all realistic if you want to get decent range, a
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Lock-in amps are very nice for very specific tasks, like trying to measure very faint signals which would ordinarily be swamped by noise, but they don't fit in to communication systems. The principal of a lock-in amplifier relies on correlating an unknown signal with a known modulating signal over
when will we see this technology? (Score:2)
The researchers have not detailed when the technology might appear in hardware, but said they had applied for a patent and ...
So....never?
General Honoré (Score:2)
Circular polarization (Score:2)
Theoretically there are still other ways to double data flow while keeping the same frequency. Using circular polarization one sender can emit clockwise rotating waves, the other sender the opposite. Linear polarization can be destroyed by wave reflections on obstacles, but afaik circular polarization is rather immune.
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My grandfather was an anternna engineer contracting work for various US agencies (Air Force, Navy, NASA, and some others) for decades. They're well aware of using circular polarization for stuff like this. However, it's not practical to do on the kind of scale discussed here, where you're looking for something that can be put in a cell phone without significantly enlarging the case.
Not to be a nit pick (Score:2)
Seriously, pilots almost never say over. I'm not exactly sure when this stopped, but I never used over at the end of my transmissions.
Usually pilots start every request with who they're calling and their callsign, either full or short (on the West coast of the US you can usually get away with just your make and last three characters after your initial transmission to a controller. If they are getting instructions or information from a controller they usually end their acknowledgement with their callsign. Ex
Ummmm ... (Score:2)
Ummm, yeah. Except for with voice, you can't have fully bi-directional communication.
It's not possible to listen to the other guy while you're talking. So, pilots and anybody who needs to have any actual radio discipline will still need to say "over".
Otherwise it would sound like a typical con-call when everybody is trying to talk at once.
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It's not possible to listen to the other guy while you're talking. So, pilots and anybody who needs to have any actual radio discipline will still need to say "over".
Point taken about guys. But women seem to do it all the time. Whether any actual communications go on I can't say.
Now excuse me while I prepare the sofa in the den as a place to sleep for the next few days.
It's a clever twist (Score:2)
Obligatory (Score:2)
Family Guy [youtube.com].
Bi-directional modem transfers (Score:2)
Hey does anyone remember the old file transfer protocol you could use on some BBS systems during the 1990s?
I can't remember the name of it anymore, but you would essentially get double speed while sending and receiving two files at the same time. It seemed impossible but timing the transfers always showed that it worked as promised.
Ramble ramble ramble (Score:2)
https://slashdot.org/submission/1472690/Full-Duplex-Could-Double-Existing-Wireless-Speeds [slashdot.org]
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You went full duplex, man. Never go full duplex.
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Technically, sending and receiving a CW signal at the same frequency communicates zero information, so naturally there should be some measurable difference (whether in phase or something else) between a transmitted signal and a received signal for information to flow. Therefore, while your point is technically valid, it is practically ignorable, since no communication system can use it (and don't start talking about combining TDMA with a CW signal, as the implied Fourier analysis here assumes a periodic seq
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All the WoW players out there will know what it is like when a bunch of people are all trying to talk over Ventrilo/Teamspeak.
Some of us stick to FPSes.. you insensitive clod..
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That was my understanding. In unusual cases like when interference or distance is heavily mangling communication more verbose phrasing and procedure may be used to facilitate communication. Even then "Over" is not a standard part of aviation voice procedure, but merely an import from the voice procedure of other radio communication bands.