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Two-way Radio Breakthrough To Double Wi-Fi Speeds
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.
First post, Over.
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.
Do not look at laser with remaining good eye.
full duplex?
I haven't flown anything in 10 years, and "Over" was considered quaint even then...
We say over or have a tone to signify when we are done speaking. There may be more than one person listening and its a cue for the next person not only that you are done talking, but your message came through. If you are listening and don't hear "over" or "beep" you say "come again" or "missed that last bit" or whatever jargon that the bands you are using requires. I'm not a pilot so all I know is terms i've used on CB over the years.
https://slashdot.org/submission/1472690/Full-Duplex-Could-Double-Existing-Wireless-Speeds
vos nescitis quicquam, nec cogitatis quia expedit nobis ut unus moriatur homo pro populo et non tota gens pereat.
Nice job. Though the problem off cross-talking has been solved for a long time using TDMA or CDMA.
As a pilot I can tell you that I hear "over" only about once a year, and only when someone is repeating themselves trying to see if the other party can hear them. Also this technology would take literally decades to work into all aircraft. Aircraft last for decades themselves, and people are not that fast to upgrade.Aviation is about what is proven to work, not the latest and great bleeding edge technology.
Pilots end a transmission with their plane's tail number, not "over."
With provided carrier waves instead of plain sin(), it always has been easier for split send receive. Simple split sin() is how UNIX micro-seconds work independently. Less hardware reads to the atomic timers meant faster methods for instructions per cycle. Same applies to ethernet.
It's called a duplexer.
Take the cheese to sickbay, the doctor should see it as soon as possible - B'Elanna Torres, "Learning Curve"
Roger Murdock: Flight 2-0-9'er, you are cleared for take-off.
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?
A bad analogy is like a leaky screwdriver.
Radio users say "over" because due to propogation, radio noise, and the lack of body language such etiqutte is needed for efficient communication. On the phone with only two people you can get away without such "annoyances" by simply having longer pauses then would be typical in face to face communication but this doesn't scale to larger groups. 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.
This new technique is welcome because those of us interested in ameteur radio really don't want to see the hobby die because the entire radio spectrum is taken up by people downloading porn and updating Facebook over Wi-Fi.
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/
The actual paper (PDF) :
http://sing.stanford.edu/pubs/mobicom10-duplex.pdf
I end all my sentences with *ksschk* so it sounds like I'm in space.
How is this new? Isn't it the same echo cancellation ADSL modems (and older) have been using for decades? Which textbooks say you can't do this?
Technically none of the signals we use these days are using a single frequency. The frequency is modulated so that it gives more bandwidth for transmitting data.
An exact frequency would require a continuous wave of radio energy and that has very little data transmission capabilities. You can not transmit and receive two continuous wave signals on the exact same frequency, there would be no way to tell them apart. Well, in theory you could use phase shifting but in practice that is impossible to do and keep them separate because as the radio signal travels it bounces around causing the phase to change. So basically it's physically impossible to transmit and receive two exact frequency signals.
That's not what they're doing here though, they're taking regular modulated signals and running filters to pick out each signal. So they grab the true received signal by filtering out the one they are transmitting. They operating around a similar center frequency but it's not the exact same frequency.
Pilots don't use over. Pilots end a transmission with their tail number.
I find being offended by me offensive.
Can some explain how this is different from CDMA?
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.
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.
The researchers have not detailed when the technology might appear in hardware, but said they had applied for a patent and ...
So....never?
I do wish someone would explain to Ret. General Honoré that when doing television interviews, ending sentences with "over" is not really necessary.
Sometimes the light at the end of the tunnel is the headlight of an oncoming train.
Transmitting and receiving at the same time absolutely nothing unusual.
Means of achieving this is usually a circulator, plus possibly a bi-static antenna setup (TX and RX antennas separate and isolated; there's a IEEE paper somewhere about an "Isolation Antenna" that has 70dB+ of isolation between its ports), and in some times even active cancellation of the leakage signal (by feeding a sample of it, with the correct phase and amplitude so it cancels out).
It has been used in RFID systems for many years already.
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.
it seems like this would only benefit protocols that load evenly between send and receive. maybe skype?
but if you're watching a movie on netflix or surfing the web or probably a lot of other things, you'll be doing so much more receiving than sending that it's not really worth it to have another antenna.
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 still.
In that very small area is where they put the reciever antenna. The transmition signal is very weak, so all of the other signals can still be heard. Once you are outside of the destructive interfierance area, the waves propagate as usual and you have roughly the same range and amplitude as you would with a single antenna.
-Rick
"Most people in the U.S. wouldn't know they live in a tyrannical state if it walked up and grabbed their junk." - MyFirs
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
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
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 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 reporting the port speed, not the actual speed it connected at.
Even XP will gladly report to you the speed of your NIC or your hub/switch/router instead of your actual internet connection speed.
Mit der Dummheit kämpfen Götter selbst vergebens
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. Examples:
(Cessna 182) N12345: "Seattle Center, Cessna one two three four five, with you, level four thousand"
Seattle Center: "Cessna one two three four five, radar contact, local altimeter two niner niner two"
N12345: "two niner niner two, Cessna three four five"
Seattle Center: "Delta six seven eight, descend and maintain flight level two two zero"
(737) Delta 678: "Down to two two zero, Delta six seven eight"
The real question is: Can this be used to eliminate that terrible noise that happens when two users try to transmit on the same frequency at the same time?
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.
Lost at C:>. Found at C.
"It's like two people shouting messages to each other at the same time," said Levis. "If both people are shouting at the same time, neither of them will hear the other."
Clearly, Levis has never been to Spain.
Why did it take more than 100 years for someone to think of it? If this is the first discovery of this idea, then that makes me despair for the intelligence of the human race ...
The actual claim of doubling capacity is way overblown for most deployments. The only time you will get double capacity is when you only have two radios and they are only trying to talk to each other. So, for a home network that might be the case.
However, in the far more common cases of lots of radios competing for medium access with each transmitting towards a very small subset of the nodes in range, you will not get doubling of capacity. What you can get is a significantly better media access control (MAC) layer by improving the channel access control mechanism.
This new mechanism will allow a transmitter to detect if its signal is colliding with another transmitter's signal. Currently, when a radio transmits it can only hear itself and will continue transmitting even if another radio was transmitting at the same time, which usually garbles both signals for all receivers. With this new mechanism, a transmitter will be able to stop very quickly if it hears another radio simultaneously transmitting.
This would allow radios to, for example, use CSMA/CD rather than just plain CSMA.
This technique sounds like they are feeding an 180 degree out of phase transmit signal back into the receiver so it cancels out it's own transmission, leaving only the other transmitters signal. Or am I oversimplifying?
This technique is called echo cancellation and has been used in dialup modems for many years.
I do not understand how this article got written this way. This article describes a form of SDMA, spatial domain multiple access. Back in the late 90's there was a startup called ArrayComm that created a working cellular station with a 12 antenna SDMA system. Their demo had two callers on the same channel and timeslot (it was a TDMA cell system) walking right next to each other and even sticking their phones into the opposing cells antenna array without dropping the call.
The reason it never went anywhere was not because it did not work, but because CDMA got there first, works well enough, and does not cost as much to deploy. As wireless density increases, we keep seeing antenna diversity schemes pop up (MIMO), but usually they are two antenna systems. Maybe someday we will need to deploy SDMA systems that use large numbers of antennas, but it will be at least 20 years after it was done the first time.
The idea sounds great. But when you think realistically, you will know there is always a tradeoff. If you look at the paper and ideas by ignoring all the marketing messages, you can spot the fundamental flaw. Basically, the idea is to place the Rx antennas between two Tx antennas so that the signals from two Tx antennas are out of phases at the Rx antenna positions. Yes, it works for the purpose that you want the Rx antenna receives no signal from Tx antennas. However, this also changes the antenna beam pattern which will reduce the coverage for the reception of the signal by half. The placement of 2 Tx antennas is the same as have a Uniform Linear Array (ULA) with 2 antennas with some inter-element distances. For example, if you place the antennas with lambda/2 away (where lambda is the wavelength), you will receive very weak signal at the broadside angle. In the other word, you trade the reception quality at broadside angle for the null-out effect at your Rx antenna. Actually, you have two degrees of freedom here to choose any position/angles you want to have the weakest signals (null-out effect). 1) by changing the phase difference between two Tx antennas. For example, making them 180 degree out of phase, the null will happen at the middle between two antennas. In this case, you trade your reception along the direction perpendicular to your antenna array with the so-call single duplex. 2) by changing the inter-distance between two antennas. For example, you can make the distance with lambda*3/4 away to create the 180 degree out of phase. The drawback is the same. You trade the reception at certain area with this null-out at certain position. People can argue, you can increase the inter-distance more, so that more grating lobes can be observed. Because there is multiple paths, eventually, the whole space can be covered. Yes, you are right. But how far away two antennas should be separated? It definitely depends on the environment. You can make it adaptive. So a dedicated engineer needs stand at the access point to change the antenna separations per request. And if you place the antennas so far away, is that really practical to have such systems? I don't want to say the technique posted in the Stanford news is well-known to some other communities. The method has been used in other communities for case-by-case basis as mentioned in some other comments as they realize this method does not apply the the communication with whole space coverage. I totally love the idea that they tried hard to help the wireless communications area a better world. But I would like to say, before one claims his work is a breakthrough, please think why you are the only one who can think of this ideas. I think Stanford has many well-renowned professors who are more capable of pointing out to the authors that why it is not used in other areas.
This one is cool because it seems it can be retro-fitted to an existing transmitter, it works by creating local interference tending to cancel the forward transmission so that the station's receiver is unaffected by it.
I'd be interested to know what it does to the radiation pattern of the transmitting antenna and how sensitive it is to the way in which the antenna is mounted. I'm sure it works great on a flat plate.
Nullius in verba
Family Guy.
I'm a pilot. I've never added that to a radio call. - $0.02
And this Prof. Philip Levis character just managed to say absolutely nothing of substance throughout the entire article.
Doesn't even sounds like Levis is on the research team of interest, but merely the first warm body wearing pocket protector that the reporter managed to snag in the CS building.
BTW, I'm not a pilot, but I say "over" repeatedly at clubs to impress chicks.
Wasting my breath I know, but....
Single Frequency Duplex radios were demonstrated decades ago.
It's just a matter of using an adaptive equaliser to exactly cancel the Transmit signal at the Receiver.
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.
Cwm, fjord-bank glyphs vext quiz
Suddenly the only form of radio communication that exists is aeronautical?
Check out a band plan some time. There are loads of other services on the air. Amateur radio uses 'over' heavily in some modes, as do several other services.
A breakthrough of CDMA proportions.
I stopped reading after "Uniform Linear Array." I am simply too tired at the moment to rewrite what you posted with appropriate whitespace/paragraphs so that I might be able to actually parse it.
I think that you are right and that your idea makes sense, based on the little that I did read of your post. However, there were about 375 more words after that point which I [ITALICS*]couldn't stand to read[/ITALICS*].
It looks like you've made a tried to make a good contribution, #1997052**, but I really think you need to look into formatting if you want people to read what you've got to say -- either here, or elsewhere. It does not matter how good your ideas are if it hurts people to read them: Folks simply won't bother.
*: AFAICT, the I tag is still broken since the redesign. Rob? Bueller? Anyone? Anyone?
**: #1997052? Really? I feel old.
Kid-proof tablet..
http://www.youtube.com/watch?v=KJCfUm21BsI
over.
http://www.youtube.com/watch?v=KJCfUm21BsI
that the usual "Roger"ing will also go the way of the Dodo? In the cockpit, that is.
LOL OMG They discovered throughput! Nothing that hasn't been done with cables, and Better.
Sorry for the formatting. I tried to format my message with some paragraphs but didn't know why Slashdot undid all my formatting. Here is my comments again, hope it's not too late.
----
The idea sounds great. But when you think realistically, you will know there is always a tradeoff. If you look at the paper and ideas by ignoring all the marketing messages, you can spot the fundamental flaw.
Basically, the idea is to place the Rx antennas between two Tx antennas so that the signals from two Tx antennas are out of phases at the Rx antenna positions. Yes, it works for the purpose that you want the Rx antenna receives no signal from Tx antennas. However, this also changes the antenna beam pattern which will reduce the coverage for the reception of the signal by half. The placement of 2 Tx antennas is the same as have a Uniform Linear Array (ULA) with 2 antennas with some inter-element distances. For example, if you place the antennas with lambda/2 away (where lambda is the wavelength), you will receive very weak signal at the broadside angle. In the other word, you trade the reception quality at broadside angle for the null-out effect at your Rx antenna.
Actually, you have two degrees of freedom here to choose any position/angles you want to have the weakest signals (null-out effect). 1) by changing the phase difference between two Tx antennas. For example, making them 180 degree out of phase, the null will happen at the middle between two antennas. In this case, you trade your reception along the direction perpendicular to your antenna array with the so-call single duplex. 2) by changing the inter-distance between two antennas. For example, you can make the distance with lambda*3/4 away to create the 180 degree out of phase. The drawback is the same. You trade the reception at certain area with this null-out at certain position.
People can argue, you can increase the inter-distance more, so that more grating lobes can be observed. Because there are multiple paths, eventually, the whole space can be covered. Yes, you are right. But how far away two antennas should be separated? It definitely depends on the environment. You can make it adaptive. So a dedicated engineer needs stand at the access point to change the antenna separations per request. And if you place the antennas so far away, is that really practical to have such systems?
I don't want to say the technique posted in the Stanford news is well-known to some other communities. The method has been used in other communities for case-by-case basis as mentioned in some other comments as they realize this method does not apply the the communication with whole space coverage.
I totally love the idea that they tried hard to help the wireless communications area a better world. But I would like to say, before one claims his work is a breakthrough, please think why you are the only one who can think of this ideas. I think Stanford has many well-renowned professors who are more capable of pointing out to the authors that why it is not used in other areas.