The Myth of Radio Spectrum Interference 603
Selanit writes "Just came across a fascinating article on Salon about a technologist who claims that there is no such thing as "interference" in the radio spectrum. He argues that interference is a symptom of inadequate equipment, not a fact of nature, and that with improved transceivers we could open the spectrum up to high-quality broadcasts by anyone. Reference is made to the GNU Radio Project. Neat stuff." We've posted other stories about this. I wonder if the "color" meme will catch on.
Interesting thing about radio signals (Score:2, Interesting)
Hard processing on the CPU, made the most interference.
Re:Interesting thing about radio signals (Score:2, Funny)
Re:Interesting thing about radio signals (Score:2)
I had a drum synth program (I must still have it somewhere on a tape) for my Sinclair ZX81 (I think you Merkans called it a Timex).
It worked by generating RF interference, that you needed to pick up and amplify using a transistor radio.
I'm not so sure (Score:5, Funny)
Sorry, Obligitory Simpsons Quote (Score:3, Funny)
Audience: "HUH?!? WHAT?!?"
Prof. Frink: "Sorry I had to do that, but now that I have your attention..."
Number system (Score:4, Funny)
Binary octal and hex don't appear to be too promising, but I now realize the answer:
Base pi
Heck, it might even work in base e or base i
Limited Quantities (Score:3, Informative)
The FCC is currently forcing the switch to digital communications all over, which is shrinking the required spectrum. I'm sure when other technologies mature, they will make use of those as well to further free-up the spectrum.
shrinking the required spectrum.... (Score:2)
You get less for your monet with digital, but at least you know what your getting.
Re:shrinking the required spectrum.... (Score:5, Informative)
A major part of communications theory is issues dealing with bit-error rates, and interference. It is a reality. Now we can move to things like "spread spectrum" but even this is no panacea. Fact - for a given bit errror rate, bandwidth, and communications path conditions - there are a finite number of spread spectrum transmitters than can coexist in the same band before the bit-error rate is exceeded!
How do I know? Well I've been a ham for 25 years giving me practical experience, and I'm a EE as well.
Re:Limited Quantities (Score:2, Insightful)
Patented Colours! (Score:4, Funny)
Pantone may own the standard numbers by which digital designers refer to colors, but only the FCC can give you an exclusive license to a color itself.
So I could patent the wavelength of a colour of my choosing, and claim royalties every time someone uses a colour that matches my wavelength? Now there's a way to get rich quick...
Except people wearing clothes using your colour could run away from you really quickly and cause red shift:
"See? It's not the same as your colour. It's very slightly more red. You can't sue me!"
Re:Patented Colours! (Score:2)
They then either claim violet shifting or just run into you. They might even hit you somwhere where it hurts...
Not going to happen (Score:4, Insightful)
Based on the power that Television companies hold, does anybody really think this is going to happen? We have a hard enough time with the record labels, now they want to go up against people like NBC?
Great idea. Unfortunatly, it would never happen without serious reform within the Gov itself.
Not that I don't like making waves, but one step at a time.
Just my humble opinion,
SirLantos
Re:Not going to happen (Score:3, Funny)
Not that I don't like making waves. . .
Ouch! No pun intended, I hope?
complete bunk (Score:4, Insightful)
Re:complete bunk (Score:2, Interesting)
With multiple antennae you can use signal processing to separate signals from different directions, just like we do with our ears when listening to people.
By your logic government should regulate people talking at certain places
Re:complete bunk (Score:3, Insightful)
Re:complete bunk (Score:2, Informative)
Re:complete bunk (Score:5, Interesting)
In your example, it's true that your eyes can't discern the difference between the signals and this is classically how we've viewed radio detectors. However, the information in the signals is not lost - you're ability to detect between them is altered, but the photons themselves are unaltered.
If you switch to a different type of sensor or encoding scheme - for example, utilize frequency hopping (aka spread spectrum) then you could easily broadcast the two signals over the same range of frequencies (colors).
Overall the article has a lot of merit in providing a different and, in my mind, compelling metaphor of bandwidth as colors as opposed to the classical bandwidth as land. As to his ideas of limitless bandwidth being true, the idea is beyond my ability to see how this is feasible, but that does not detract from his idea that we could actually be communicating a LOT more over the current spectrum than we are today.
Re:complete bunk (Score:5, Informative)
Clearly there is no such thing as limitless bandwidth; Shannon's theory tells us there is maximum amount of information that can be transmitted over any one channel, and simple physics tells us that there are a limited number of channels, no matter how you slice it.
Re:complete bunk (Score:3, Insightful)
There is a theoretical limit to how much information can be transmitted over any one channel of fixed width and signal to noise ration. How close are we to 100% of that theoretical limit?
Re:complete bunk (Score:4, Informative)
The answer is none; you can't change the signal at all, so you can't send information. Once you start changing the signal, (i.e. change the amplitude) you are actually adding in more frequencies - this is Fourier 101.
To send information, you have to use a band of frequencies. The wider the band, the more information per channel, but the fewer channels. So there is a limited amount of information that can be sent.
Re:complete bunk (Score:3, Interesting)
Sure, if you're using stone age equipment. Consider if instead you used two colors. One guy (who you are listening to) flashes green and yellow, another does green and orange. Yet a third person uses orange and yellow. You'll have a few errors when both people you're not interested in happen to flash at once, but for the most part, the signal will get through.
Now, imaging using dozens of colors, error correction, and a protocol so that you can ask anyone who's signal you can see to choose a different color or time division on that particular color.
Or we can stick to the current system where the government grants you the exclusive right to that shade of green ( and because you insist on using poor quality celluloid filters, several shades around it as well).
Re:complete bunk (Score:2)
Suppose, however, you have five colors: red, green, blue, magenta, and orange. You could license each to five different signallers.
However, suppose instead of a simple monochromatic flash, the guy was sending you a sequence of five colors, say green, magenta, blue, orange, red. Instead of five licensees, we can have 5! or 120. If a second guy is sending green, blue, red, orange, magenta, he may "talk over" the first guy's signal. However, if the communication is two way, I can send an ack or a nack. This means I can have greater capacity in my network but I have to retransmit sometimes.
In other words, this idea works well for interactive services, but not so well for broadcast servcies. A popular broadcast service is an extremely efficient use of bandwith. A popular AM radio station takes, what, 10KHz? FM, 200KHz? They can reach hundreds of thousands of users.
I think the ideas in the article argue more for freeing up additional bandwidth for technological innovation, like the 2.4 GHz band.
Re:complete bunk (Score:2)
Asuming you didn't already know which way to look exactly (think roaming)
You might be able to get that information from the messages they are sending, but then again if it were ten green lights you would have to read ten messages simultaniously. If you can do that imagin a hundred flashing green lights....
Jeroen
Partially..... (Score:4, Insightful)
Re:Partially..... (Score:2)
Re:Partially..... (Score:2)
Wha? (Score:4, Informative)
It's not that using a radio frequency somehow "depletes" a resource -- it means that if you put a green object in a green room with green lights, after a point you won't be able to see the object any more, kind of like how camouflage works. The problem is when you have a lot of signaling broadcasting in an area, the noise level can increase to the point that no single signal can be resolved. The classic example is how it's very difficult to understand a particular conversation in a noisy room. And that's why you have to generally parcel out radio spectrum and define limits on how it can be used (signal strength, bandwidth characteristics, noise levels, coverage patterns, etc)
That guy's nutty analogy makes me think he's a leftover of the dotcom era -- when eyeballs was more important than revenue and other silly things. Admittedly, I should read the whole article, but the first few paragraphs made me feel like I'm talking to a crazy guy on the bus.
Re:Wha? (Score:4, Interesting)
However, far from being revolutionary, his 'discovery' is a well known fact, which is already in wide use by now:
Also, his analogy breaks when you compare wavelengths: light having much shorter waves is much more directional (allowing for the pinhole camera phenomenon) whereas radio need much bigger spatial separation to avoid interference. While you can put several green objects into one room, and still distinguish them, you need much larger cells for RF.
Re:Wha? (Score:3, Informative)
Your point is also a good one, in that from an engineering point of view as the signals get closer together in the spectrum the ability to distinguish one signal from another is reduced.
However his answer to this is that the current method of spectrum allocation does a terrible job at utilizing the available spectrum partly because the transceviers we use for radio and television broadcast for example are relatively stupid and inefficient compared to what we could be doing, partly because of how the historical licensing stucture grew to be fixed ownership of particular frequencies and the space around them to allow dumb recievers to utilise them.
His idea is to try to promote the reduction of frequency requirements to the least restrictive set of rules to allow a reciever to recieve a broadcast from a broadcaster. One example given is through the use of smarter SDRs (software defined radios) to make more efficient use of the available spectrum.
Re: (Score:2)
Re:Wha? (Score:2, Informative)
CDMA systems showed us that it is possible to transmit two signals at the same time and the same frequency and distinguish them at the receiver; a task which at first might seem impossible. However, Shannon's theory still imposes limits on the maximum possible transmission rate.
What's new today is that by using multiple antennas it is actually possible to go beyond the limits Shannon established for point-to-point communication! This is not snake oil; it is well established, refereed research. In fact, it is already demonstrated technology [google.com]!
I still think it is a long, long way from these ideas to an unregulated spectrum.
Re:Wha? (Score:5, Informative)
Interference as we know it is the inability to derive meaning from information about the local radio environment. That's what happens when two people broadcast on the same frequency -- your receiver can't figure out which information to care about, because all it knows is "stuff on this frequency is important information" and we keep more than one person from broadcasting on more than one frequency by convention.
Where he seems to be going is treating the endpoints of radio communication more like endpoints in a network. Something analogous to modulation of a carrier frequency (in terms of complexity) is voltage modulation of wires in CAT5 cable. But network interfaces lay the notion of connections between two endpoints over something a good deal more abstract than that. They abstract the modulations into a binary stream, decode the binary into discrete data structures, interrogate the data structures to get meta-information about the data, demux the data (or defrag the packet, or reassemble the stream) based on the meta-information, and so on.
What he seems to be proposing is that radio receivers and transmitters do the same thing that network interfaces and protocol stacks do -- make the actual dance of bits considerably more complicated (to allow for things like error-correction when traditional "interference" is a problem, and to add more meta-information), then apply layered abstractions on top of it to get at the actual data.
Spread-spectrum communication does this already -- two SS messages can be sent to two SS receivers in the same range of frequency, because the two transmitters won't usually be broadcasting on the same frequency, and redundancy can be built into the transmission protocol so that when collisions occur, information isn't lost.
The article overpromises -- if I understand, this mode of communication is no better or worse than what we enjoy by using the OSI model to structure network communications. Even if the information space is "theoretically infinite" (which I doubt), we have to get increasingly more creative in how we utilize the space. In the networking world, however, we can talk at gigabit speeds over the same physical media that only supported 10mbps 10 years ago. We accept that wireless networking can find ways to squeeze increased "bandwidth" out of what is, in reality, a fixed width of spectrum allocated by the FCC.
What Reed seems to be agitating for is that the FCC and others get out of the way entirely, architecting a basic framework for the exchange of information and letting the transmitters/receivers figure out the rest of the details -- essentially the same thing he advocated for the Internet. I don't think it's a crackpot idea at all, though the style of the article masks that pretty well.
bOINGbOING transcript from the spectrum conference (Score:2, Informative)
Too optimistic, in my view (Score:4, Insightful)
Radio's basic signal function defined in software? Sure, "Maximize your bandwidth with our new RadioBooster!!!" (at the cost of your neighbors).
While this guy might have a point - the current FCC policies on RF spectrum might be a bit outdated, I would be careful with deregulation here.
Re:Too optimistic, in my view (Score:2)
Sure, "Maximize your bandwidth with our new RadioBooster!!!" (at the cost of your neighbors).
That's why he sees a continuing role for the FCC. It's just that they would ensure that devices obey the necessary protocol rules rather than their current role of making sure that only megacorps can get new allocations and only a few controllable broadcasters can reach an actual audience (gotta keep those naughty words off the air!)
This has been a known fact for a long time... (Score:4, Insightful)
Well made and tuned equipment can eliminate any chance of interference and allow for more radio stations within an area. However, organizations like NAB (www.nab,org) and now, the FCC stonewall any attempts to open up the airwaves. At one time, there was a proposal to allow low power broadcasters to operate, unlicensed, if they could prove they weren't interferring and accept the interference from other channels. It was approved but still puts the "little guy" at a disadvantage: http://www.fcc.gov/mb/audio/lpfm/.
If there ever was an "ol' boy network", it's broadcasting. If you want to broadcast legally, you're looking at dropping half a million in legal and license fees alone before you buy your first piece of equipment.
Re:This has been a known fact for a long time... (Score:5, Insightful)
Unfortunately, this is not true.
Suppose a city has two stations, one on 1600 kHz and one on 900 kHz. Let's add a station on 700 kHz, ok? Let's put him near the 1600 kHz station, since we don't want these damn antennas cluttering up the whole city. No problem with "well made equipment", right?
Now consider that near to both the 1600 and 700 antennas is a large, old, steel-framed building, containing tens of thousands of rivets and metal-to-metal joints. Some of these joints have some corrosion. Consider that there may be several such buildings. Why is this a problem?
Each joint is a potential non-linearity. Each joint is capable of taking the 1600 and 700 signal and creating the sum and difference signals and re-rediating them. The sum is 2300 kHz, outside the AM broadcast band. The difference is ... 900 kHz. The same frequency as an existing station.
Now consider if you live inside one of these buildings. You used to listen to the station on 900 kHz. Now you hear a wonderful mixed babbling of both the 1600 and 700 kHz stations -- and your radio has nothing to do with creating the problem.
Let's go one step further. These same non-linear conductors will cause sum and difference issues with single-frequency signals, too. The new station on 700 kHz will sum with itself and cause a signal on 1400 kHz. And it's even worse. The actual result will be signals on every multiple of 700 kHz well up into the shortwave bands. (If the non-linearity created a perfect square wave, you'd get only the odd harmonics, but these aren't perfect and you get even harmonics, too.)
Can't happen, you say? Yes, it can, and does. I've lived with this problem for the last 4 years from two nearby stations. It has finally gone away, since one of them moved their antenna location a mile further away, but before they did that, they made a lot of the spectrum useless here.
sorry he's not being honest (Score:4, Interesting)
Based on stories of 802.11b (Wi-Fi) and/or Bluetooth suffering from interference either from like-protocoled devices being operated by other parties, or cross-protocol interference which results in the one or both protocols not being effective in their data transmissions, and these are supposed to be advanced intelligent devices which don't suffer from interference due to their use of Spread Spectrum technology, and intelligent software controlled radios (which may or may not be software defined radio - SDR).
So unless he can demostrate experimental evidence, I'm a scepetic.
Re:sorry he's not being honest (Score:2)
The problem is that none of those devices are software updatable, and they don't have a minimal negotiation protocol in common. The biggest offender is cordless phones (that have no negotiation protocol other than do what you want until you can hear the base station). If they negotiated, they could coexist with little problem.
Consider how it would be if the phone spoke 802.11b and used 64Kbps over ethernet.
Re:sorry he's not being honest (Score:2)
Re:sorry he's not being honest (Score:2)
That's where the software upgradable part comes in. At least one of those networks is cheating the rules a bit. If their radios were upgradable, a simple firmware update would fix the problem.
Re:sorry he's not being honest (Score:3, Insightful)
I realise the sarcasm, but, Yes, they will do just that if the FCC tells them fix it or recall it NOW! (or more likely, it wouldn't have reached the market with the bug since it couldn't pass the protocol certification). Presumably, the FCC would transition from frequency to protocol compliance. The problem with 802.11b is one of extremes. That is, other bands are impossible to license, but the one they're in is TOTALLY unregulated except for maximum radiated power. It's too far in the other direction.
Of course, if that band wasn't available without licensing and allocation, there would be no digital cordless, Bluetooth, or WiFi at all. They'd all still be mired in allocation squabbles and attempts to dominate the market by dominating the spectrum.
Uncertainty Principle (Score:2, Insightful)
If i wasnt so sleep deprived, i could give some approximations with numbers and stuff.
The Stanford Spectrum Conference... (Score:5, Informative)
The idea that Spectrum doesn't need to be regulated is quite old, and it seems more and more likely to be valid. In any case, the idea that it needs to be controlled by government interests is less and less likely.
-R
The guy is a nut... (Score:2)
There's no scarcity of spectrum any more than there's a scarcity of the color green....
I can't believe Salon published the article, or that it got picked up by Slashdot. This is bogus science [chronicle.com], and the guy is clearly a nut. Perhaps the editors should read their own articles [slashdot.org]?
Al.Re:The guy is a nut... (Score:2)
I think that the point he is missing is that applications tend to expand to fill available bandwidth.
interesting, but a bit arrogant (Score:3, Insightful)
As my chemistry teacher once said to me, 'A poor craftsman blames his tools'
And the cost to "upgrade" is? (Score:2)
I don't think any "economy of scale" will scale far enough to drop high performance DAC prices from >$50 to $0.50.
Covered in a book (Score:2)
Reed is wrong (Score:5, Insightful)
For a variation on this theme, there's an interesting moment in a movie (Frankie and Johnnie?) where there's a terrific racket in a diner, impossible to understand anything, but a cook and a clerk are communicating easily --- by sign language. Consider also those occasional TV images of the Wall Street pit traders flinging gang signs at each other
Spectral purity and antenna quality limitations can be overcome --- by money. You can build higher quality receivers and transmitters, bigger antenna installations but it costs money and space in fairly unavoidable ways.
Reed is also wrong from a regulatory level. It's not just the FCC that you'd have to work with, but the ITU. Those pesky radio waves have this interesting habit of leaking over borders on the ground, and pretty much everywhere down here from satellites.
There are pretty good reasons to pick on modern broadcasting: crappy content, media concentration --- but "broadcasting" is not one of them. Those great big transmitters permit the use of very dumb receivers with poor sensitivy. The very simplicity and asymmetry of broadcast provides tremendous economic and technical appeal, and I'd be amazed if it ever went away.
Far more interesting is the glacial progress of DTV in broadcast.
Re:Reed is wrong (Score:4, Insightful)
Yes. In practice at microwave frequencies the radio waves are rapidly absorbed. This actually raises the potential capacity of the network, since it acts a bit like sound deadening in a building.
The problem with interference arises because of imperfect spectral content and non ideal antenna response for both transmitters and receivers.
Not just that though. It also happens because one or other of the users of a particular band is using too much power, or is using it too much. Think of the airwaves as a multidrop ethernet and you're probably more what Reed is talking about. You wouldn't try to use 1 ethernet cable for a whole country- but they seem to want to do that with radio- why are the transmitters so 'loud'?
Also, are you claiming that the interference is likely to be so bad that none of the frequencies available to you are free? Because that's what it would take. Don't forget that you don't have to see the source directly, you can route through other radio users; and they can be situated at different angles. Also, consider that if both sources are interfering at your location, there's a high probability that they are interfering at other locations as well; a protocol that changes one of them to a different frequency automatically would do very well.
Interference is like being at a party: There are a lot of people talking, and your ears hear in all directions, so you have to be near the person you're trying to talk to.
Good analogy. Trouble is, ears are unidirectional. But if we give everyone cat ears, the party gets much quieter; even though cat ears are imperfect. Also if someone in the middle of the party needs to talk to someone across the room- he can always whisper it to his neighbour, who can pass it along, rather than standing up and bellowing at the top of his voice.
Like the article? (Score:2)
I've joined, and it was well worth the money. Their articles on the state of the music industry, Payola, etc., were enough to deserve my cash.
He's also right in some ways..... (Score:3, Informative)
Color Wheel (Score:4, Insightful)
Back to the color thing:
Ever had a color wheel, a circle with pie shapped sections in various colors. You spin it and it all looks white. The higher the data rate at any frequency the more the signal is spread out over adjacent frequencies, so rather than being just green or blue it all looks white. Engineers call a signal with equal power across the whole spectrum "white noise". Usefull signals disappear into noise.
Ultra Wide Band (Score:3, Interesting)
Of course UWB is still in the laboratory, and these two think that the FCC should rewrite the laws now for a technology that may work well (i.e. not cause widespread interference), and may be cheap. Except we don't know yet!
Baloney (Score:2, Insightful)
Big difference betwqeen RF and optical receivers (Score:5, Interesting)
The way we use radio takes advantage of this - we don't have to aim the antenna for our car radio, and we prefer it that way so we can listen as we drive. This leads to a promiscuous sort of receiver, which is subject to interference. I think it is going a bit far to say thai is because of the legislative environment or technological background - it is because it is the way we *want* it to be.
At optical weavelengths, we *want* a directional, even a focussed, image - and our eyes produce it. In between, we tend to use directional transmissions with point-to-point microwave dishes.
However, the simple reflector style lens, depending upon newtoinian optics to fouca an image of the transmitter onto the receiver, is not the only way to receive a signal. People are already working on multi-aerial systems which take a "holographic" approach to reconstructing the signal. There was an article about one of them on
I think the frequencxy hopping bit is actually somewhat of a red herring. It doesn't generate new spectrum, it meakes better use of the spctrum we have. It gets rid of the wastage caused by blank safety space betwenn radio stations both in geographical space and in spectum space.
Directional radio (Score:2, Interesting)
It's possible -- especially with software defined radio techniques -- for a receiver to tune in a particular direction (in addition to frequency, perhaps). Presumably we would design the receiver so that it tracked the radio source, rather then having to fiddle with the dials everytime the receiver moves. But as long as the possible transmitters aren't all in a straight line, there's no reason that a receiver built today couldn't distinguish between many transmitters on the same frequency -- even with fancy coding techniques. (You do mention this in your post -- I'm just amplifying a bit.) You might fiddle with a "direction" knob to get the station you want, then turn on a "track" feature to keep that station tuned in as you drive your car around, or whatever...
This won't make the spectrum infinite, but would expand the usable spectrum substantially... Reed phrases his arguments in ways that border on pseudo-scientific, but there are real possibilities underneath his hype.
Open Source TV Transmitter (Score:2)
He's right (Score:5, Insightful)
While this is *techniclly* correct, On could also say that A knife could be built that can cut a loaf of bread into infinite pieces, if we could design it to cut sub-elementary particles. Why are we not making knives that can do this? Because the technology isn't there, and if it was it would probably be cost prohibitive.
Qwerty is a fact of life... Live with it. (Score:3, Insightful)
This principle is part of human nature: People get used to some kind of technology/ideas and stick to it. Even when these concepts stop to be meaningful. I refer to the Querty-effect: Old typewriters had little pins with letters on them which hit an ink-soaked ribbon and presses it onto the paper. To prevent these pins from hitting eachother (which happened a lot), the qwerty keyboard was invented. The most abundant letters in English were as far apart as possible to prevent collisions. But a computer doen's have pins, so why do we still use a qwerty keybaord?
But also think of buttons in programmes: You press buttons in real life, why show them on a screen and press them with a virtual hand (the mouse cursor)? There are many more examples; the radio/TV frequency story if Mr. Reed being one of them.
The problem usually isn't the technology, it's the ideas that need to be changed. But sometimes technology improvements do get through, e.g. the DVD is nothing than an up-to date CD. MP3-player replacing the old walkman. Telefones replacing the telegraph.
Things change, ideas change. Some want to accellerate it, some want to slow it down. In the end, things just change at the rate they do and, as harsh as it sounds, there's nothing you can do about it. It just takes a little time...
There are more sensitive radio receivers out there (Score:5, Interesting)
Radio Astronomers have a hard enough time keeping the important wavebands free of interference without the radio spectrum being unregulated. Lots of useful, hard science is being done by the radio telescopes around the world observing the machinations of galaxies out in the distant universe. One of the key problems is that these signals are amazingly faint. The standard unit used in radio measurements is the Jansky - thats 10^(-26) Joules per second per square metre - which should give you some indication as to how faint. Lift that coke can off the floor onto the table and you've just used up more energy than has been received from distant galaxies by ALL the radio telescopes on the surface of the planet.
Terestrial radio transmitters are so many orders of magnitude stronger than these signals that any sideband transmissions even 90db below peak transmission still totally swamps the surrounding spectrum. And very few transmitters are truely 'perfect'. It's not as though a transmitter broadcasting at frequency X with HWHM waveband Y can't be detected at X +/- 8 Y. Yes - better quality receivers allow you to separate out signals at close frequencies, but a very strong signal next to a very weak signal will drown out it's neighbours.
Cheers,
Toby haynes
He's right, just wrong focus. (Score:2)
I can tell those lights apart just fine.
What is difficult here is that radio waves are damn hard to pinpoint where they come from since they go in all directions.
But so does light doesn't it?
Man this gives me an idea.
Everything is easy... (Score:2, Interesting)
Hardware can't make a difference--it's digital (Score:2, Insightful)
"Just ask this scientician..." (Score:3, Interesting)
What I'm unclear about is what he proposes we use all these radios for. Is he talking about making cellular networks more open and inexpensive? Is he talking about making radio and TV licenses cheaper and easier to acquire? Is he talking about replacements for Bluetooth and 802.11b/a/g? I guess he's talking about all of the above and more. Having spectrum open to such a wide array of uses with "autonegotiation" will result in huge drops in throughput. The article suggests that autonegotiation is used in frequency hopping systems,
Um..the TX and RX aren't negotiating -- they're following a very strict prescribed pattern of frequencies to which they hop. Same is true in cell networks, 802.11, Bluetooth..doesn't matter if it's frequency hopping or direct sequence spread spectrum, everything is planned out.
Where I work we've been doing preliminary work on software-definable radios for a couple of years now. The two biggest problems we foresee are: (a) how to justify the cost to customers up front, and (b) how to justify (to our company) selling someone a radio they will (conceivably) never have to replace. We're struggling to make money through software upgrades, and we've already seen that it's really hard to displace an existing, working system with a new, better system (just look at UMTS adoption).
He's correct, on a technicality.... (Score:4, Informative)
The jist of the article is that RF waves do not "interfere" with each other. By this he means that two RF waves will not affect each other as they pass by each other in space. This is correct. The two waves will simply pass through each other. The problem is when you try to receive the signal.
When you receive a signal you get ALL the radio waves from the entire spectrum (not quite this simple, but it will do). Then the signal is amplified and the spectrum you don't want is filtered off. The problem is that if your antenna is receiving two RF waves in the same spectrum they will be superimposed.
What he's trying to say is that an intellegent receiver will be able to pick out one of these waves while rejecting the other. Much like when you pick out one conversation in a noisy room. Much easier said than done.
There are currently some schemes to do this, such as CDMA phones which work on a spread spectrum. Each of them transmit and receive on the same spectrum at the same time using what are called "codes" (Code Division Multiple Access). However there is still a capacity issue. When too many phones come into the same area, the noise floor comes up and nobody can receive information. To prevent this the cellular phone comany will limit the number of active cell phones in a given cell and drop any new calls over the limit.
There are more advanced methods, but as many people in this field know, the signal processing that your brain does to pick out only one conversation is mind blowing.
To sum up, he's technically correct. His use of the word "interference" is confusing to say the least. RF engineers talk about interference as the superposition of singnals as you receive them. He talks about interference as the interaction of signals in space.
802.11 offers some proof of what he says (Score:3, Insightful)
If transmissions carry identification about which source they are coming from, then why couldn't a reciever be able to descriminate the information?? That is all he is saying. Although, it would seem that we would still want to regulate the power output to some extent... so I would completely agree with him that spectrum should not be restricted by licensing, but power output from a point source should still be.
Someone hand this guy a physics book, stat! (Score:5, Informative)
There are some very commonplace phenomena, such as the colors on a soap bubble or oil slick, which are the manifestation of interference of light. There are more fundamental experiments that can be done with lasers or radio waves to demonstrate interference.
Actually, if you do the experiment, there is a specific pinhole size at which you get the best image. Make the pinhole any smaller and the image starts getting blurrier because of diffraction effects which, loosely speaking, are due to the photons interfering with each other.
From his misunderstandings of the nature of light so far, it's impossible for him to have any real understanding of the quantum nature of light. He wouldn't know Schrodinger's equation if it walked up to him and smacked him upside the head, seeing as how Schrodinger's equation is a wave equation and predicts all sorts of interference phenomena.
The most fundamental problem is that he admits the notion of frequency, which is intrinsicly tied to the wave nature of light and radio. If he admits the wave nature of light, then he also has to admit interference of light as a natural phenomenon and not as a detection artifact, at which point all of his theories crumble.
Re:Someone hand this guy a physics book, stat! (Score:3, Informative)
It would have been much better if Reed had used the term 'interact' rather than 'interfere'. All waves interfere, as you point out.
The important point is that photons do not interact with each other (well, they actually do but the cross-section is so small that it is of no practical relevance). So, you can shine a laser at something, and the photons in the laser beam are essentially unaffected by passing through whatever background light in between the source and whatever you shine the laser at. This is a distinct effect from 'interference'.
And yes, just because something is non-interacting doesn't mean it doesn't occupy space. But it does mean that (in principle) an infinite number of photons can occupy the same space at the same time. So he is being very sloppy with his quantum mechanics, but its very hard to be precise when explaining these things to a magazine.
You are being no less sloppy with your statement that diffraction effects are "due to photons interfering with each other". You can do the same experiment with a single photon, and still get difraction. You probably already knew this, but I'm just making the point that its hard to explain quantum mechanics without being sloppy!
Re:Someone hand this guy a physics book, stat! (Score:3, Funny)
I see somebody skipped out on their physics lab on "Michelson-Morley interferomoter" day. I wonder how he thinks we measured the speed of light...
Re:Someone hand this guy a physics book, stat! (Score:5, Informative)
The colors from a soap bubble are due to light interfering with light. Light is partially reflected from each surface of the soap film, and the reflected beams do interfere with each other and result in the colors that you see. That's about all the detail I want to go into describing it, but if I still don't believe me, it's probably described better and in more detail in either Hecht Optics, Born & Wolf Principles of Optics, or Lipson, Lipson & Tannhauser Optical Physics (in any of those books, look for the section on "multiple-beam interference").
It is true that when two beams of light cross paths in vacuum, if you were to observe them after they cross, you could not tell that they crossed. However, in the region in which they cross, they can interfere with each other. Again, any of the references I mentioned above will probably explain this much better than I can.
Even worse, once you physically manifest this signal by modulating it onto an electromagnetic carrier wave (like radio does), this communications spectrum is now superimposed on the physical spectrum of the electromagnetic wave. Now the signal is subject to the physical phenomenon of interference, which can further corrupt the signal if you don't allocate communications channels in the electromagnetic spectrum properly. And I think it's the allocation of commmunications channels which is what the article is trying to be about. However, that doesn't change the fact that Reed is dead wrong in the way he describes or interprets many of his physical examples, probably because he has a lot of background in computer science but not as much in physics.
Furthermore, Reed is wrong if he thinks that ultrawideband (UWB) or frequency hopping will increase the Shannon limit within a given range of the electromagnetic spectrum. Ultrawideband will interfere with other electromagnetic signals. It requires a lot of electromagnetic bandwidth, hence the name.
Frequency hopping can improve the efficiency of the spectrum allocation by moving communications channels to unused regions of the spectrum, but it does not create communication capacity where there is none. Furthermore, those channels have to be allocated in advance to prevent them from with other signals.
Reed is probably right that the electromagnetic spectrum is inefficiently utilized. But the many of the physical examples or explanations of physical phenomena that he presents are dead wrong, which was the point that I was trying to make in my original post.
Yes, Claude Shannon says "he's full of shit." (Score:3, Informative)
In short:
YOU CAN'T TRANSMIT AN ARBITRARILY LARGE AMOUNT OF DATA/SECOND ON A FINITE AMOUNT OF BANDWIDTH. No matter how good your equipment, or how clever your signaling patterns, you will never be able to increase your data rate above the amount determined by Shannon's equations.
The flaw in Reed's reasoning is that we're talking about subdivisions of frequency, and the amount of data that can be transmitted in a given wavelength band has an absolute upper limit. It's Shannon's rule about bandwidth. So yes, Reed can go around giving everybody a gnat's ball hair width of radio frequency to push their data, but each riny segment will only be able to transmit a piddle of bits per second.
This is like people who don't know Calculus, but who think they've disproved Special Relativity with a thought experiment. Anybody who's sat through a class on it, or read a book, will laugh and laugh, while everybody who hasn't had the benefit of learning will probably be suckered.
Re:Yes, Claude Shannon says "he's full of shit." (Score:4, Insightful)
You mean through an information channel of finite bandwidth.
However radio paths exist in a 3D environment, which can multiply the number of channels of finite bandwidth. Reed's point is really about mesh networks and using spatial diversity receivers to create more "pipes" (i.e. channels) through the air at the same frequency.
In his concepts, mesh networked receivers can even work together to untangle interfered signals. It doesn't lead to infinite information capacity, but it sure is higher than what most radio spectrum is used for today.
Reed really shouldn't say that there isn't interference...it is that interference as physicists know it is a useful and constructive tool (as in holograms), unless your radio architecture is stupid (i.e. uni-frequency, uni-source broadcast).
I think the technical (Score:4, Insightful)
High quality broadcasts for everyone is a pipe dream. Want to know how that works out? Check out our Citizens Band. Not pretty at all.
I am in the process of getting an amateur radio license again. HAMs do more with less spectrum than just about anybody. Doing this has made me rethink spectrum allocations and how they are wasted. The amateur bands have very reasonable band plans that allow for a number of uses and work well.
Our primary problem with spectrum use is the band planning, not the avaliable resource. (Which is limited no matter what this guy says.)
Commercial and military uses basically get what they ask for and they ask for everything they can.
Comes back to this really. We live in a competitive culture. We have given companies the same rights we have. They are better competetors than we are.
We lose.
Our fault.
What I found astounding... (Score:5, Informative)
There must be some other explanation, but it seems like Dr. Reed is making a freshman-physics terminology mistake. When a physicist says that two waves "interfere", he/she doesn't mean that one wave knocks out the other or that they undergo some linked dance. The linearity of Maxwell's equations indeed does show that each wave "passes through" the other without reducing or amplifying it.
Nonetheless, they interfere -- because "interference" is the interaction of the waves at a given point in space, where the amplitudes add algebraically. Consider a given location x at a given time t. If at that moment wave A has ampitude 5 and wave B has amplitude -2, then a receiver will measure a disturbance of amplitude 3. It doesn't -- and can't -- know that there are two waves, because there is only one signal. If the content in wave A is uncorrelated with the content in wave B (for example, two different radio stations playing different songs), then their addition will be essentially random -- and hence sound like noise (because it is noise).
Dr. Reed's proposal doesn't really speak to this. He wants smarter receivers that can track a signal and so distinguish wave A from wave B. The technology is not here, not cheap, and certainly not universal. The system we have was not foisted on us by some big government conspiracy and it's not maintained by the pressures of a cartel. It's here because interference is a fact and that "overcoming" it -- which is really more like shuffling past it -- is expensive and unproven.
And you would still have to deal with the transition from legacy to newfangled
He's right, but he's completely wrong (Score:5, Interesting)
However when radio and television began, there were no computers or even transistors, there were no phase-locked oscillators or QAM modulation, and there were only a handful of broadcasters.
Yes, some of the frequency hopping and CDMA type concepts have been around for a while, but only in the last 10 years available at a price that anyone but the government could afford.
Mr. Reed's ideas are insightful, but not very practical. Our entire telecommunications infrastructure relies on spectrum assignments. The technology does encounter interference. To simply point the finger at bad planning and blaming the decisionmakers from the 50s for not predicting the state of technology fifty years later is ludicrous.
Reasonable proposals to more forward with UWB that doesn't interfere with traditional infrastructures should be pushed. Eventually the old technologies will fade away like the telegraph.
But to simply rant that "It sucks. Cooler, better tech exists." doesn't do anything.
The myth of color spectrum interference (Score:3, Insightful)
You will need:
- A sheet of college-ruled paper
- A green marker
- A copy of Moby Dick
Open up the Moby Dick to the first page. Then, with the marker, start transcribing the text onto the sheet of paper -- "call me Ishmael" and all. When you run out of space, don't get more paper -- instead, just go back to the top of the sheet, and overwrite the text that's already there. When you are done with the entire Moby Dick, mail the sheet to Mr. Reed.Since there is no such thing as color spectrum interference, Mr. Reed should be able to read the entire Moby Dick just from the one sheet of paper.
This revolutionary discovery will surely eliminate waste, and save our rainforests... If only the paper-making companies didn't want to keep it under wraps !
he's partially right, but that's irrelevant (Score:4, Interesting)
Furthermore, allowing "substandard" receivers to exist is deliberate. We did this with the AM spectrum when FM came along, and we are doing it with other receiver technologies. AM can be received with a few cents worth of primitive electronic components and it is widely deployed, that's why we continue supporting it.
The division into bands also allows enforcement and specific power limits. Without that, people might broadcast over astronomical frequencies, or they might engage in RF shouting matches until they light up each other's fluorescent lightbulbs.
Basically, Reed's science is iffy, and his arguments are completely missing the point. Yes, we can open up spectrum (UWB is essentially trying to do just that), but let's not kid ourselves about the consequences, which will at the very least include the obsolescence of lots of radio equipment and probably a kind of arms race over the airwaves.
They've found a way - (Score:3, Interesting)
Too bad, but the physics of radio propagation does put a limit on the range of useful frequencies. If you want to do international broadcasting, you are pretty well limited to 3 - 30 MHz. If you want to do TV broadcasting with a single transmitter over a range of 100 miles, you are probably limited to 50 - 1000 MHz, and so on.
The problem is that governments, not knowing anything better to do, have carved up the spectrum into fixed allocations to various "services" - broadcasting, police & fire, military, amateur, etc. But if you listen with a wide coverage receiver, you will find most of the frequencies are empty most of the time. That is a real waste.
Theoretically, "software defined radio" lets you divide up frequency and time and modulation type in arbitrary dynamically programmable ways. The problem with that is that both ends have to agree on the algorithm and everybody has to agree to use the minimum power necessary. (Because there IS interference if you use too much power.) The price of flexibility is a huge burden of coordination. Of course, this is great for covert communications.
To paraphrase one of my profs, if you pave all of Delaware County, you don't need stop lights anymore.
-Martin
Sig of the day: What became of humble foreign policy?
Not a great article (Score:3, Interesting)
Interference, as it says, is not a law of nature. It's what happens when you are trying to listen to, say, a 1.1Mhz signal coming from over there and someone over here is also transmitting on 1.1Mhz. How can the radio receiver tell the difference between those signals? As the article hints, it's an engineering issue; but it's a non-trivial one. Radio engineers all over the world will not read this article and rejoice. Reclassifying the problem in some bizarre colour analogy has not magically solved it.
Now as for the politics of spectrum allocation and the potential improvements of a free spectrum policy: now that's a more interesting issue, but one the article doesn't address in any but the most superficial of ways.
Bah, I say to it.
Real citations (Score:3, Interesting)
All of these elements increase the efficiency of radio spectrum use.
Optimal Operation of Wireless Networks [comsoc.org]
Combined Space Time Diversity and Interference Cancellation for MIMO Networks [vt.edu]
Information Theory at the Extremes [cornell.edu]
Linear Multiuser Receivers: Effective Interference, Effective Bandwidth and User Capacity [nec.com]
Abstract: Multiuser receivers improve the performance of spread-spectrum and antenna-array systems by exploiting the structure of the multiaccess interference when demodulating the signals of a user.
He's right and wrong at the same time. (Score:3, Insightful)
If you don't distinguish signals spatially then they will interfere at the receiver.
Simple example: I send two electromagnetic signals, one out of phase with the other. If you only receive at a single point, at certain locations you will get zero signal.
Unless you start talking about quantum stuff I don't see how you're going to distinguish the signals if you're measuring them at only one point.
I Need This Guy NOW! (Score:3, Funny)
Sounds like this guy could use some experience in the real world anyway. Not that I disagree with him, just that I think the world he lives in is a perfect, wonderful, simple place that is not this world.
Reed is only partly correct... (Score:4, Informative)
It's also true that two radio signals, each of a different frequency, will, when mixed together, produce an entirely different set of signals based on the sum and difference of the two frequencies.
This is the same principle that superheterodyne circuits (the type used in just about any kind of modern RF receiver) are dependent on. Example: You want to receive a signal on a carrier frequency of 146.5200 MHz, and your receiver has a 10.700 MHz IF.
OK, so the local oscillator (LO) in your receiver needs to produce a frequency of its own that will mix with the incoming 146.5200, and produce 10.7MHz as a result. That 10.7 signal will then be demodulated and turned back into audio.
Assuming you use low-side injection, your receiver's LO would need to generate a frequency of 135.8200MHz (this, by the way, is why scanning receivers are not permitted in commercial aircraft. 135.8200 is in the aircraft comm band), which is merely 146.5200MHz minus 10.700MHz.
Anyway... What I'm driving at is this; Think of a mountain top transmitter site that's got a ton of broadcast, public safety, amateur, and other kinds of transmitters on top of it, many of which are producing hundreds, if not thousands, of watts worth of RF.
There's going to be signal mixing. Lots of it. That means tons of the very "interference" that Reed doesn't seem to think exists.
The techniques mentioned in the article, BTW, including software-defined radios, are nothing new. They've been around for decades, and ham radio folk are already experimenting with them. For one example of a purely software-controlled radio, take a look at this radio kit from TAPR. [tapr.org]
73 de KC7GR
Re:The article is crap (Score:5, Informative)
David Reed is many things, but crackpot is not one of them. He was a professor of computer science at MIT, then chief scientist at Software Arts during its VisiCalc days, and then the chief scientist at Lotus during its 1-2-3 days. But he is probably best known as a coauthor of the paper that got the Internet's architecture right: "End-to-End Arguments in System Design."
thank you for reading the article.
Re:The article is crap (Score:2)
Re:The article is crap (Score:3, Interesting)
The author of this paper is right! There is no interference in a spectrum (besides the modulation of the signal to broadcast, but that is an effect of no importance here). This is mathematically and physically true.
However I can understand that electrical engineers have problems with this, because they notice interference every day. This has however to do with the _implementation_ of the radio signals, not the theory.
A lot of comments here deal with issues which are quite off-topic, such as what antenna (omni or not, size) you use. This has nothing to do with the spectrum or interference, the direction is an extra design parameter for a system, which can be used to pick up a certain frequency, but there is no coherence with the interference topic; a a certain spectral component stays the same in the air, no matter what antenna you use.
However I don't find this artical inspiring, because it contains nothing new. Let the electrical engineers deal with the problems, they are more experienced with the implementation..
[Disclaimer: I have phys. degree]
Re:The article is crap (Score:3, Interesting)
- Two transmitters in two different places, but with an overlapping range, both broadcast on the same frequency.
- A receiver is halfway between the two transmitters and so within range of both.
- The receiver has two or more antennae, each antenna has some directionality. You do a lot of DSPing in software to distinguish the two signals even though they are both on the same frequency.
Re:The article is crap (Score:5, Interesting)
This is done by spreading your signal over a large spectrum with a pseudo random key. The number of possible keys is still limited (There has to be a certain difference between two keys for it two work) and thus you still have a maximum number of users although things like roaming are a lot easier since you are limited by keys overlapping and not range overlapping.
This is what is being done in CDMA cellphones, Wireless Lan, Bluetooth etc. It is nothing new, already happening and you still need regulation to make sure the spectrum doesn't get completly unusable.
Jeroen
Not entirely (Score:3, Informative)
More than that... (Score:5, Interesting)
But more than that, I think. Consider that the spectrum itself is not quantized. We quantize it with different radio stations, but this is not really absolutely necessary. If our recievers/transmitters where all spread spectrum, and they could all recieve/transmit at nearly any frequency we wanted, then there really wouldn't be much problem with interference. Sure, you might get signal degradation in one frequency band because someone else was using it, but you'd get less in another band that would make up for it.
To make sure that the spectrum doesn't become completely unusable wouldn't require government regulation of WHO uses it as much as it would require regulation on HOW they use it. If people used the spectrum the way that broadcasting companies do now, we would certainly have a problem.
But it is unlikely that anyone would be able to completely use all of the spectrum because of the unbelievable energy requirements that this would need.
In short, with the appropriate scheme, there really is enough bandwidth for everybody (that is, bandwidth would be limited by power, not by regulation).
Re:More than that... (Score:3, Informative)
You are still left with a limited piece of the spectrum and in this piece you are still going to run out of space (either in the frequency domain or in the code word domain). Shannon's law still applies for the signal/noise ration.
Jeroen
Re:The article is crap (Score:2, Interesting)
For example most cell phone systems work by dividing the spectrum into channels, each with an available bandwidth. If you think about it this means that you loose a lot of bandwidth before you've even started because you have to leave gaps between the channels to prevent interference. In addition when a channel isn't being used its bandwidth is being effectively wasted: it would be far more efficient to give all the bandwidth to the people who actually wanted to use it.
This is why many countries are adopting a standard for their next generation of cell phones that resembles ethernet in transmission. You use a low frequency wave of around 50HZ as this travels further and allows the cell sizes to be larger and instead of modulating it (as is done with traditional cell phone systems) you either turn it on to represent a 1 or off to represent a 0. Do this many millions of times a second and you have an efficient way of transferring data. Collisions can be detected by error checking techniques developed for wireless lan and so everybody can communicate whenever they nead to with the maximum bandwidth possible.
Multiuser Detection (Score:3, Interesting)
Re:Salon ads (Score:2)
The site is just showing you an example of interference in the world of colors ;-) It's not a physical phenomenon, it's just your brain (... the receiver...) that is too easily disturbed by the ad...
Re:The Economics of RF and 'smart radio' (Score:3, Interesting)
Um, no... (Score:5, Interesting)
Note that the GNU Radio project recently achieved ATSC (US digital TV) demodulation.
Using $1000+ worth of hardware
40x slower than realtime.
Compare that to the MyHD HDTV tuner card, which can do realtime demodulation, MPEG decoding, and display scaling for $300. Why? Because it's designed for the task. It's somewhat reconfigurable, but you can't take a Palm Pilot and turn it into a software-defined radio.