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The Myth of Radio Spectrum Interference
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.
I had a old radio that would make noises based on what my processor was doing...
Hard processing on the CPU, made the most interference.
Wise men speak because they have something to say, Fools because they have to say something!!!!
Given adaquate equipment, anyone could transmit thier webcam to EVERYONE with a tv. Sounds like that would make for some interesting tv.
I know a physicist who claims that pi is in fact rational. He claims that the only reason we don't realize it yet is because of the current limitations of our circle measuring devices.
Kan jeg få en pils, vær så snill?
Let's stretch Salon's death row for as long as possible, that makes them produce good stuff!
Sleep Deprivation? Hell, I haven't slept in days, bring it on.
400 Person LAN for Charity: Zion LAN 2005
It is just a bunch of meaningless words slapped together with phrases that make it sound intelligent. This guy looks like a CS grad or (oh horrors) a digital designer. I would really love to see his credentials. He has no clue about communication theory. My profs would flunk him.
Interference is a fact of life. Sure, the technology can improve and allow us to do the same things with less of the spectrum, and other things like spread-spectrum can come along and lessen the interference problem, but spectrum is still a limited resource.
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.
Slashdot gets worse every day... Pipedot: News for nerds, without the corporate slant
From the article:
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!"
If Reed is right, nearly a century of government policy on how to best administer the airwaves needs to be reconfigured, from the bottom up.
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
The flying hamster of DOOM rains coconuts on your pitiful city.
This article is complete bunk. Yes, its true that radio frequencies are like colors. So imagine this scenario: you are receiving signals from someone who is using 'green'. They are flashing a huge green light, and you can pick up the pulses they are sending by being bathed in the green light. Now someone else comes along and also starts flashing a huge green light. You can't read the signal any more, because there are now two huge green lights bathing you with their signals. How can you tell which pulse is coming from which light? You can't! That's interference.
All is Number -Pythagoras.
by reducing the impact of interference.
You get less for your monet with digital, but at least you know what your getting.
thank God the internet isn't a human right.
Perhaps, I'm not the most knowledgeable guy on RF interface, but I went to The University of Texas at Austin, got my degree in electrical engineering (studying electromagnetics), worked at Ericsson designed cellular systems and RF planning, worked at a company making "smart antennas" for cellular systems. From my experience, I had a hard time understanding what he was talking about. "Spectrum is more like the colors of the rainbow"? Of course it is, that's how the radio spectrum works. But then he goes off on, "There's no scarcity of spectrum any more than there's a scarcity of the color green." Which makes little sense to me.
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.
Insert simplistic political, ideological, or personal proselytization here.
Lessig: ...Coase's arguments reflected the state of the art at the time. Property was the best way to allocate spectrum in 1959. But it's the wrong answer today. Not because property does no good -- in fact, it does a great deal of good. This should not be taken to imply that administrative allocations are inevitably worse -- a market has costs, and if those costs exceed the value, then markets result in misallocation. Coase's insight -- most prescient -- is that spectrum is not in its nature rivalrous. It's not a thing at all. Colors, sounds correspond to frequency.
I woulda rated this one (Score: 5, Funny)
I mean, yeah, there is an infinite number of spectrum "buckets" if you get better and better tuned equipment. So what? We don't have perfect equipment. Maybe we could manage to split down the bands more finely but there are still a finite number.
As for "photons don't interfere with each other" - this is bullshit. Photons act like waves and waves interfere with each other.
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.
So he compares radio waves to that of visible light -- a good analogy, but it doesn't mean his argument holds up. This article jumps around a bit, from the beginning to where he mentions quantum mechanics, to adopting frequency-hopping algorithms. I just don't get the bit in the beginning. If you've got two stations allowed to broadcast, say, Forest Green, in the air at the same time, then how can an optical receiver (say, my eye) discern between the two? In the broadcast world, you're going to have multiple receivers trying to 'tune in' to multiple sources. Broadcasting at the same freq. and the same time will alias the signals.
It just means that he failed out of engineering school and is good at BS.
Large radio broadcasters love to claim this when there is a threat of a new station being added in their market. Not because there is a possibility of interference if the frequencies are close - they're scared of competition.
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.
Sit back and relax as Windows 98 installs on your computer.
David Reed is not being completely honest, he is being overly optimistic, IMHO, and hasn't demostrated with actual experiments his claims.
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.
Heres part of the real problem. In order to communicate over radio waves, you must use a well defined bandwidth for your transmission and reception. As we scale up the number of simultaneous connections over a range of frequencies, each individual connection must be allocated a central frequency and an ever decreasing bandwidth. As the bandwidth gets smaller and smaller, we are decreasing the uncertainty in photon energy. If we keep decreasing the bandwidth, then we get to a point where we have a nontrivial uncertainty in time. This uncertainty in time makes it so that we cannot properly measure the time variation of our signal. Thus, there is a point when our bandwidth is so small that we cannot recieve a reasonable signal. This is interference in transmission itself. If you can figure out how to filter this out, you'll win a nobel prize.
If i wasnt so sleep deprived, i could give some approximations with numbers and stuff.
Kan jeg få en pils, vær så snill?
...just took place earlier this month. There's a lot of good information here. An audio/video archive of the conference will be available on the 17th for those who didn't catch the webcast.
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
...yellow, purple and orange?
An Italian radio wave dressed up.
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, and the guy is clearly a nut. Perhaps the editors should read their own articles?
Al.The Daily ACK - Eclectic posts by yet another hacker
He argues that interference is a symptom of inadequate equipment
As my chemistry teacher once said to me, 'A poor craftsman blames his tools'
"I only speak the truth"
Karma: null(Mostly affected by an unassigned variable)
Given that visible light is part of the radio spectrum, wouldn't it be possible to broadcast light in the same way as a radio transmitter broadcasts?
Or for that matter, would it be possible to use some sort of LED setup to broadcast non-light signals such as TV or radio? Based on what little I know about LEDs, if this were possible, FM-type broadcasts would be significantly more difficult than AM-style broadcasts.
He also thinks that everyone is going to start using $200 ADC/DAC subsystems in your $2 garage door opener or $20 walkman.
I don't think any "economy of scale" will scale far enough to drop high performance DAC prices from >$50 to $0.50.
The political and other non-technical aspects of this are covered in The Future Of Ideas by Lawrence Lessig. Good read.
Developers: We can use your help.
I think by "meme" he means "me! me! look at me!"
Fact: All radio, visible light, cosmic rays, infrared, x-rays all the good Electromagnetic radiation exhibits interference. Do a search for the double slit experiment if you don't believe light acts the same way. If you let light through a pinhole as he suggests, and then sent it through two more pinholes so there were essentially two sources of coherent light spaced apart, you'd get interference. And, this still happens if you're only letting a photon through at a time. Basic quantum theory people....
If I shout across a crowded room, the other people talking could, in a manner of speaking, be called interferrence. However, its not a failure of the sound waves projecting from my mouth, its a failure of the ears on the person across the room. If you had one of those satelite dish looking microphones you could hear me better.
Manipulate the moderator system! Mod someone as "overrated" today.
Prof. Frink: "A-hem, um, ahem! Excuse me!....Pi is exactly 3!!"
Audience: "HUH?!? WHAT?!?"
Prof. Frink: "Sorry I had to do that, but now that I have your attention..."
Sometimes I doubt your commitment to Sparkle Motion.
And the daily crop of "bash John Ashcroft" stories haven't even been posted yet!
Reed's article is based on the observation that Maxwell's Equations are linear (for most materials) and that, therefore the waves pass through each other without modification (again, unless you're in pretty exotic environments --- early universe, etc.) The problem with interference arises because of imperfect spectral content and non ideal antenna response for both transmitters and receivers. 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.
... the reason that it works is that your eyes have very fine angular sensitivity (high quality antennas) compared to your ears.
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.
Just a reminder, if you enjoyed reading this Salon article (or any of the dozens of others that /. has posted), you should consider becoming a Salon member!
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.
The radio spectrum isn't a finite resource. How much can you increase frequency? You can infinitely increase it. What is limited is usable frequency. Usable frequency is limited not just by technology, but also by the physics of the environment. I have always said that trying to implement 802.11b like what has been done with cellular tech cannot be done because of it's frequency. 802.11b uses 2.4 GHz band of frequency. The physics of the problem makes 2.4 GHz not suited for long haul. 2.4 GHz can go through buildings but can only go around 50 feet. You could extend that by using a beam or a better omnidirectional antenna, but your definitely not going to go miles in most current instalations. Now HF frequencies can go thousands of miles with current equipment. I am sure BOTH RF frequency bands can and do go thousands of miles and maybe even light years, but current technology limits that. If the signal is so low in strength that current recievers can't detect it, then it's not useful. It's finite. Theoretically, if you can develop a reciver that can recieve the very very low strength signal, then you could....possibly say that a RF wave can be infinite.....but conditions have to be perfect. No walls and a total vacuum. On the other hand, interference that we currently have comes from going for that extra buck. If one were to build proper recievers and transmitters, they would be very expensive, but they would not be susceptible to interference. Cheap devices absolutly breed interference.
Gorkman
The big different between RF and optical receives is that RF receivers (radios) are usually fairly omnidirectional, whereas optical receivers (eyes) are usually pretty directional. In part, this derives from the physics of the things - longer waves go turn more round obstacles, and tend to broadcast wide angle if their wavelength is similar in size to their aerial.
/. a few months ago. These could very well lock onto the signal from a particular direction, and ignore signals on the same frequencey from a different direction.
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.
Consciousness is an illusion caused by an excess of self consciousness.
As long as the equipment we use daily remains "inadequate" enough to not distinguish finely enough the different transmissions we see, my aural pleasure will always be shat-upon by Pirate broadcasts.
There's many Pirate radio stations breaodcasting all over our FM bands and it leaves me with no way to listen to a radio programmes that I am interested in.
Not that I'm against Pirate radio, I just think that if they opened up the spectrum more, then cramming 100+ stations into a very narrow band would be unecessary.
Smokey, this is not 'Nam, this is bowling. There are rules.
So how about an easy to use open source TV transmitter? I mean when HD hits there will be tons of TV we could do some low power broadcasting to.
You say things that offend me and I can deal with it. Can you?
He's probably talking about multiuser detection, which is an idea that has been around for about 20 years. The idea is that instead of observing only the signal that you're interested in, you also observe every other transmitted signal. If the other signals are digital, you can reconstruct those signals electronically and subtract the resulting interference. Unfortunately it is a hideously complicated problem in practice, and is not terribly robust, so no major wireless standard incorporates it (not even any of the 3G standards).
Toronto-area transit rider? Rate your ride.
with improved transceivers we could open the spectrum up to high-quality broadcasts by anyone
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.
If he is right, then cheap radios are a myth.
People who disagree with you are not automatically evil, greedy, or stupid.
There are many concepts that, if tweaked to the current technology, could be greatly improved. However, keeping old technology also has it's merits: Firstly, it's proven technology so all quicks are known or resolved; New technology undoubtedly has more problems. Even the threat that new technology has more problems, people will not use it. Also, changing to a new kind of technology require huge investments. New technology has to be pretty profitable if it is to overcome the investments made in the old one.
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...
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
Anything I post is strictly my own thoughts and doesn't necessarily have anything to do with the opinions of IBM.
Like ever go up to traffic lights on a 2 or 3 or more lane road?
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.
The message on the other side of this sig is false.
Of course a poor crafstman blames his tools; a poor craftsman can't afford good tools!
The subject of the interview mixes his metaphors pretty badly. He seems to have (or at least to express) little idea that his color analogy only describes the baseband: it's got to _do_ something to encode information. And then all the familiar noise analogies apply.
I'm usually a pretty satisfied Salon reader, but they sure dropped the ball on this one.
- - - Patent applied for and deliver us from evil
Is it an accident that two consecutive Slashdot stories (this one and the "Croquet" one) are about David P. Reed's projects/ideas?
His example of a camera obscura is a filter that allows the organization of the light (the image) to be perceived. Without this filter, the photons do interfere with each other, or you'd still see the image! Filters limit bandwidth. His argument that we could all enjoy unlimited bandwidth falls apart. The many additional logic errors in Mr. Reed's musings are left as an exercise for the reader ... ;)
.. if someone else has to do the work. That's the 'hook' or motivation for the author, make it look like all the spectrum problems can be solved by wishful thinking, without going into the details of the solution. Cheap journalism at it's worst. How much will such devices cost? What sort of power consumption do SDR's have? Will I be able to get 16 hours use out of a $30 SDR walkie-talkie using 4 AA alkaline batteries? All the refinements made in radio design over the last 100 years have been motivated by cost and capability. During this time the FCC has tried to encourage innovation, without degrading existing systems. They are very interested in SDRs but also must consider current users of the radio spectrum and their needs. They aren't likely to obsolete several billions of dollars worth of existing equipment on a whim, there must be proven rewards to the public first.
Based on my poor knowledge of quantum physics I can say that Reed might have a point. This is what I think it means: An electron can only interfere with ITSELF. In the famous double split experiment when one electron passes through both holes it will interfere with itself. However, if two electrons are emmited, one from each hole, they will not interfere with each other. In that sense photons are fundamentally different than waves on the surface of a lake. However I would not know how and if it is possible to make use of this fact to build an antena that distinguishes which photon is which. That is not at all clear from the article.
The surface of the planet is becoming entirely the wrong place for radio telescopes.
My Karma: ran over your Dogma
StrawberryFrog
If the spectrum is truly capable of holding a limitless number of broadcasts without interference then doesn't this mean that any subset of the spectrum is also truly capable of holding a limitless number of broadcasts?
In my mind this spread-spectrum technology is good, but it will not open it up to limitless broadcasts it will only reduce the amount of bandwidth required...
Am I missing something?
Note to self. Not to bosses. Note to consumers: Quality hardware matters. Quality hardware matters.Quality hardware matters. Quality hardware matters.Quality hardware matters. Quality hardware matters.Quality hardware matters. Quality hardware matters.Quality hardware matters. Quality hardware matters. Until electronics is based upon something other than the laws of phyisics, premium hardware will make a difference. Given that most people--and this is fine, they're consumers and busy with other things--buy electronics based on a price: colour ratio,they will tend to buy junk. What's not okay is that they're surprized. The thing that's maddening is that most of the sound electronics that is marked 'hi-fi' actually isn't. Grrrr.
---- The above post was generated by the Turing Institute. Maybe.
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).
In the article he gives an analogy of using the light through a pinpoint of a camera to show why there is no interference. That made me think of the Young's double slit experiment (which shows light interference) and makes me wonder how this is to be explained if there is no interference. Doing a quick search on google, I found a list of light interference experiments and I don't see how any of these could be explained off, and so all of this should work just like radio interference.
This guy isn't quite a crackpot. Before you skip this comment you should know that I do have a Masters in Electrical Engineering where I specialized in methods to reduce RF interference.
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.
Karma: Abstruse (Mostly as a result of using words nobody understands)
Comment removed based on user account deletion
One of Reed's points (though the Salon article doesn't mention it) is that radio receivers don't need to be omnidirectional.
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.
He seems to be talking about a technique called spread spectrum.
There are 2 (common) ways to "spread" a signal's spectrum, Frequency Hopping (directly mentioned) and Direct Sequence. Non of this is new, and if you have an 802.11 card, then you are using a spread specturm radio already.
The wider the signal is spread, the more "gain" the reciever has and the less energy the signal has at any one frequency. This makes sense, it's like spreading a glass of water on the floor.
Trouble is, just like a glass of water spread on the floor (so to speak), this raises the noise floor for other signals. You can't just go on doing this willy nilly. The oher problem is these signals look a lot _like_ noise, so it's hard to monitor, if you happen to be a government wanting to do those things (like, oh, the USA).
When people first take a look at Spread Spectrum, there is a natural reaction that they have found the magic bullet! It ain't so.
As most people already said, radio waves DO interfere with one another, no matter how good your equiptment is. However, that may not be what he's talking about.
What if, instead of parceling out frequency X for TV, frequency Y for radio, and so on, we took all the frequencies and gave them to wifi, making one huge high-bandwidth network. Then, using good old ip, if you want to watch TV just connect to a television server and stream it.
I think this is what he meant with the statement that, "If you want to maximize the utility of a network, their paper maintained, you should move as many services as feasible out of the network itself." By using all the frequency to create a pure communication network, we then have plenty of bandwidth and flexibility to implement whatever service we want.
Jw
He is basically proposing the entire spectrum be unlicensed like visable light, and the spectrum used by WiFi devices and cordless phones. So we already have bandwidth with which we can see this theory in practice.
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.
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.
"It take 9 months to bear a child, no matter how many women you assign to the job."
The essential claim of "unlimited spectrum" that this fool is waving around is really, just barely sensible enough to fool someone who hasn't studied information theory. Take any finite dimensional span, like a foot-long ruler. You have, in theory, an infinite number of possible subdivisions of that 12-inch length--you can have arbitrarily many divisions, if you make them all small enough.
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.
Damn you, Bill Clinton.
Life is like surrealism: if you have to have it explained to you, you can't afford it.
With proper antenna design, you don't need to move the antenna to change the direction that it points.
What you need is an antenna with multiple elements, and electric circuits that can combine the signals from the elements in arbitrary combinations.
With SDR techniques, it's even easier: just digitize the signals from the elements and combine them with your signal processing software.
Changing the combinations you use is a lot faster than moving hardware. Your software could also include techniques for tracking particular stations.
Could we do this for US$20 today? Probably not. But if we can do it for US$500 today -- and I think we could -- then we could probably do it for US$20 with 5 years or so...
yeah...your "green light" analogy is totally shattering the knowledge of a former MIT professor.
my suggestion: put that theory/analogy back in the oven. read a couple of books on RF and EMF, and then come back here with something different.
While the article brings up spread spectrum the concept of non-interference is not spread spectrum. If you put two highly directional transmitters at one side of an X and two recievers at the other two sides, the two signals won't interfere at those receivers locations but if a receiver was placed at the center of the X the two signals will. If you can wall off the direction of one of the signals from recieving then the other signal will be clear at the center.
Modest doubt is called the beacon of the wise. - William Shakespeare
To carry a signal you have to modulate either the frequency (FM) or the amplitude(AM) in either case you DO use up part of the spectrum. It doesn't matter how you encode the information, eventually you end up occupying a range of frequencies.
You can share a defined channel so long as you accept a reduced data throughput as you have to allow for collisions (ie interference) this is what frequency hopping does, but it relies on the channels not being 100% utilised by one signal.
Eventually you have to deal with the inherent photon noise in the receiver. This puts a theoretical limit on the ability of a receiver to detect and extract an RF signal. Some radio telescopes are pretty close to the limit now, but run at liquid helium temperatures.
It's certainly possible to make better use of the existing spectrum if you could upgrade all RF equipment - but that's just a dream.
I suspect the Salon article doesn't do justice to the original work; I also suspect the original work is just a re-statement of well known information theory principles such as error correction.
It's the sorry nature of consumer electronics that makes RFI [radio frequency interference] noticeable. With proper filtering and front-end design, it shouldn't be noticed or be a problem.
More to the point, though, is if consumer electronics were properly built to FCC standards, they would suffer fewer problems.
All it takes is a few ferrite beads, bypass capacitors here and there, and most of the problems go away. Anybody involved in electronics should learn the basics of blocking RFI.
The right one is sending the address you expect to receive. Then you can expect the data to follow to be the data you expected to receive reasonably enough.
The duality of light (or electomagnetic radiation for that matter), is something mister Reed is forgetting. This results in the bad example of the camera obscura.
The dualty means that light and radiowaves can be viewed as being rays as well as being particles, depending on the situation. Reed only looks at the particles, or photons. However, with the camera obscura you need to view light as being rays. (because the size of the pinhole is much bigger than the wavelenght of the light, or even the size of a single photon).
Mr.Reed also doesn't present any proof of his theory or even an experiment that can verify that theory, now that's bad science!
I personally have seen photons interfering: just let a beam of light (from a laser) pass through a very fine grating (bar spacing smaller than 700nm) and you will get the same interference pattern that you get when you have waves in water passing through a row of bars.
Furthermore, people have been using interference microscopes, where you split a beam of light, one half passes through the object (and is changed) and the other half travels the same distance without hitting anything. When these two beams are "re-united" there will be interference which gives you information about the object.
Beware of Programmers who carry screwdrivers. -- Leonard Brandwein
all ground-to-ground radio transmitters are polarized in the same direction in order to reflect off the ionosphere
My 802.11b is polarized to bounce off the ionosphere? With its range, that seems like a waste to me.
aspect of this article are total bunk. However, I do think we should rethink our spectrum.
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.
Blogging because I can...
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
The Mongrel Dogs Who Teach
So...he's talking about using the spectrum more efficiently.
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).
Mod me down and I will become more powerful than you can possibly imagine!
If we were starting our broadcasting systems today, he'd be right. There are many better ways to do it today.
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.
nuclear iraq bioweapon encryption cocaine korea terrorist
I had always suspected that pi would be rational, if not in denary (decimal), then in another base.
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
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 !
>|<*:=
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.
Ya can't change the laws of physics captain!
'Nuf said...anonymous Ham
I think maybe what he's really trying to say is that the elements that make up the colour are not interfering with each other..
I don't know too much about bandwidth at the actual transmission/radio level, but from what I gather from the article, he's saying that if a bunch of people are transmitting green, and another person also transmits green, the signal is still whole and ininterrupted.
What he's saying is that our equipment needs a way to distinguish between each of the transmissions that are all within the green colour. TCP/IP is already doing this by using packet headers.
Just my take on it anyway
And it wouldn't be particularly amusing if a fleet of aliens swooped out of space and gave us a major fine for littering the astronomically important parts of the radio spectrum :-)
Cheers,
Toby Haynes
Anything I post is strictly my own thoughts and doesn't necessarily have anything to do with the opinions of IBM.
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?
Fiat Lux.
Well, pi is really rational for some fractionnal bases. I don't know really how that works, but there was an article in the "Scientific American" in 1995, with a method to iteratively computing pi decimals.
:
But in integer bases it has been proven to be irrational as another post said.
I don't think pi, e or i are able to produces bases
bases are designed to procure a way to write numbers. Base n uses n digits, it's a convention to choose symbols for them. But how would you represent a number with, well, 2.1 digits ?
You may obtain an infinite number of symbols...
I don't know what all of these silly posts everyone is putting up are about. It seems like half of the people don't know what they're talking about. If you don't know what you're talking about, post an article with that in mind, don't spout garbage.... (like me) Truth of the matter is, when i read the article i immediately thought of ways that i could write a program to deal with multiple transmissions on the same frequency. Now let me just say, I'm no expert on radio, or photons, or anything. I know a bit about radio tranmission and how it works, but here's my idea: Why can't this be done just like TCP works?! Each transmission is given a specific identifying number, sort of like the tcp sequence number - but not randomly generated. The radio holds a buffer, reads in all transmissions at a certain rate calculated based on the total number of tranmissions active, and outputs whatever number tranmission the user of the radio specifies. Example: if there are 3 transmissions, the radio buffer reads at 3 times the rate a normal radio program should be output. say we call these transmissions A, B, and C. if the user is listening to A, then A, which was received at a rate 3 times that of a normal radio program, will be transformed and slowed from its original state in the buffer to be presented as a radio program at a normal rate. The read rate of the buffer corresponds to the amount of data coming in from the broadcaster. I don't know how many transmissions could be handled this way, and I'm SURE there's a better way, but my purpose is not to tell this guy how to make his "smart" radio, i just want to point out that this guy's idea is not complete garbage, and me, with no experience in the field, can already formulate some ideas about how it might be possible. I don't know whether there really is interference, or at what point it actually occurs, but i'm pretty sure we can pack a few more stations on to each frequency this way, if nothing else. Am i right or am i right? Right right right? *TWHACK* -Groundhog Day
I'm currently 18 months through a PhD revolving around the assignment of frequencies in a frequency hopping spread spectrum network (more details here) so I know a bit about this stuff. And that article is not fantastically insightful.
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.
You win again, gravity!
Without addressing any other elements in the article, I'd like to point out that describing frequencies as "colors" is a terrible idea.
Color is a phenomenon of human visual perception. Specifically, color is a function of the power spectral distribution of incident light. Is yellow synonymous with 500nm? No. We may see light at 500nm as yellow, but we also see a mix of 650nm and 400nm as yellow too. This is the basis behind computer monitors-- even with only the ability to generating 3 different wavelengths (with different intensities), humans will perceive a very large number of colors.
There are many other ways of showing that color and frequency are not the same thing. Look at an artist's color wheel. We perceive a continuous circle of color. It's circular. But if color was a frequency, there would be a discontinuity as we wrap around from long wavelengths to short wavelengths.
Radios do not "perceive" color. They are interested in frequencies. Best not to confuse the two.
-Ed
e.g. a major chain of petrol stations trademarked the use of green for their station forecourts, and won against a smaller station, even though the offending station was using a different pantone colour.
I work for a wireless ISP (802.11b), we run into all sorts of fun stuff.. 2.4 Ghz phones, old microwaves that people decide is good to place next to their radio.. Finally got a Spectrum Analyzer so that we could see what we were dealing with. Fun, but expensive toy..
But yeah, there's plenty of interference.. at least in northeast washington state...
- This isn't the sig you're looking for. Move along, move along..
I just thought the DJs and playlists just sucked, with too many commercials thrown in. Hopefully, the stations around here will get this new equipment soon.
--
"Outlook not so good." That magic 8-ball knows everything! I'll ask about Exchange Server next.
diffraction effects which, loosely speaking, are due to the photons interfering with each other
That statement is patently false. The diffraction grating and pinhole effects you describe are from the interaction of the wave/particles with the edges of the grating material. Photons/waves do not interfere with one another.
Reed is very wrong on other counts, but not on the one you suggest.
Typical quote from a UWB supporter: "Let's abolish the FCC and let everything go UWB and unlicensed. All that will happen to existing services is the noise floor comes up a little."
So... let's take a technology like instrument landing systems, which by the way, need to work everywhere on planet earth. Let's say in the good ol'US of A we let UWB go ahead in spectrum reserved for ILS. So, when is noise margin the worst for ILS? When you are close to the ground during a rain storm. Gee... that's just when I want ILS to go wonky. Of course, the UWB nuts want every airplane everywhere in the world to upgrade to a UWB version of ILS. Yeah, right. Multiply by 100's of specialized radio services.
The UWB guys are not "enlightened", they are walking, talking, flame-baiting trolls.
Being an Electronics Engineering student, I can make sense of what he is saying, but there are a few problems:
Yes, you can "tune in" to more frequencies with better equipment, but that equipment would be very expensive to do what he is talking about. The main way that waves interfere with each other is because of the way waves, well, "wave". Lets say you are receiving a signal at 100Mhz. That means the wavelength is 1/100 Meters or 10cm. That means that the peak of every wave is 10cm apart. Now, if someone down the street starts broadcasting at 200Mhz, the wavelength of their signal is 5cm which means it has a peak every 5cm. The problem is that means it also has a peak every 10cm that your receiver can easily pick up and confuse for the signal it's looking for. That's where the difference in radio quality comes in. If you have a better radio, it can tell the difference between the signals.
Yes, everyone could go buy the most expensive equipment out there, or technology advances could make it cheep for everyone to use and the FCC could start dividing up the bands into micro slices. Then you have 10, 100, 1000 times the radio signals going through the air bombarding every plant, animal, rock with electromagnetic radiation. That reminds me of the disease in Johnny Mnemonic, NAS. Where people started loosing control of their muscles because all of the "interference" in the air.
So, I don't think there is anything wrong with his theory, infact, I thought it was common sense. The question is: do we really *want* to do something like this?
Yeah, right.
Doktor Doktor Jochum Bloch, chief naval architect for the Austrian Navy, has announced that it is a myth that ships sink: "With the proper application of inherently bouyant designs, limitations on the load, and the use of double-hulled and compartmentalized designs, it is quite possible to build a ship that cannot sink." Herr Bloch added that the ships on the bottom of the seas are simply representative samples of poor design. "Putting too much stuff into ships and not spending enough money to keep them afloat." Herr Bloch is now turning his attention to "airplanes that cannot crash."
I tuned out as soon as I saw the subhead "Unlimited bandwidth for everyone." It's one of those words that trips my BS detector. It's one thing to say our present usage is suboptimal. It's quite another to start throwing around words like "unlimited."
We'll never run out of nuclear energy, because breeders create more fuel than they consume... the hydrogen economy is limitless, because the amount of hydrogen atoms in the ocean is inexhaustible... there's no shortage of petroleum because rising prices CAUSE new supplies to be discovered WITHOUT LIMIT...
Yeah, and the Dow is going to reach 36,000. And Moore's Law will hold indefinitely.
And the buffalo are inexhaustible.
"How to Do Nothing," kids activities, back in print!
What a freaking genius.
He discovered Q.
Send him a hardcopy of a JPG of a Nobel Prize and can we get on with our lives?
I am no expert here, so take what I say with a grain of salt, or a shot of JD whichever you prefer. As outlined by others here, if two transmissions (A and B) are received on the same frequency a conventional receiver is listening on, the perceived signal to the receiver is the sum of both transmissions (A+B). When listening to radio, this sounds like two stations superimposed on each other, because it is. I believe conventional radio receivers simply monitor the current induced on a piece of metal (antenna) by the electromagnetic waves passing by. Through some nice circuitry you can 'tune' into a certain frequency and route that to an amplifier and speaker. This method inherently limits Reeds statements as the antenna is in fact measuring the modulating magnetic field at that point in space, a natural effect of the photon/wave passing by. There is no way to distinguish between two signals beyond this point(antenna) as this value is a scalar, a simple measurement, like temperature at a certain point in space. However, if we could develop another way to read these signals, some sort of photon detector (I think there is work being done on these), we could significantly increase the number of signals we could distinguish on a single frequency. If our signal is thought of as a finite series of photons with a given energy level and distribution (I am not so sure it can be), then could we not separate multiple signals/streams through timing. We expect the photons to be a certain time frame apart, photons outside of the expected timeframe are either part of another stream or have been reflected or altered in such away they are no longer relevant to the current stream.
This sounds all fine, however assumes that photon interference does not occur and thus does not explain all those interference experiments I did in physics labs involving single slits, double slits, thin films etc. Although, I have read about the statistics properties of these effects in such that the same effect (double slit interference pattern) can be observed if a single photon is sent through once a second. If the photons are not actually interfering with each other, is there an effect of having two 'streams' overlapping? Those more knowledgeable of quantum mechanics would likely have greater insight into this, and I would be glad to hear it.
It's BECAUSE waves DO interfere that we can hetrodyne two DIFFERENT frequencies to get a third. Without this fact the superhetrodyne receiver would be impossible. Two waves slightly different in frequency interfere and so do two at the SAME frequency. This effect is know as capture, an FM receiver will lock onto a stronger signal as if the weaker one WASN'T even THERE. When two signals are almost the same stength the receiver will jump from one to the other as its AFC circuit tries to lock on. Go listen to the FM band when the sun spots are hot and see how local stations disapear and are replaced by DX. Then go dig up some old QST magazines from the 30's and read up Ross Hull's articles on DX propagation. Reed probably couldn't even pass a Novice class FCC ham test.
Seriously, if RF interference was a myth, then so are holograms, interferometry, radio spectrometry and anything else which depends on RF interference to work.
It also contradicts all of Shannon's work on signals and information theory. Not to mention all observations of analog signals, analog to digital conversion, etc.
Then, there's this small matter of there being no evidence to back the alternative. Nobody, to the best of my knowledge, has demonstrated a 100% interference-free lossless signalling system using any part of the electromagnetic spectrum. Nor is there any indication of anyone doing so soon.
So, lots of theory/observations saying RFI exists, versus none that says it doesn't. Y'know, that's kind of conclusive.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
Thank you for pointing that out. I fucking hate that word. I can't wait until something replaces "meme" as the nerd word of the moment.
That would be a hell of a power bill to transmit a signal to other TVs and Radios. There aren't that many pirate band TV and radio stations. The sheer cost would prevent people from putting random crap like webcams on the waves. Most likely just radical political groups would throw their money into a system like this.
The antennas that are needed would be rather expensive, although you could probably broadcast to your neighbors. Perhaps a Neighborhood Broadcast, about something that would actually apply. This then becomes like local radio and Public Television (on a slightly smaller scale)
'We have stupid radios not because we haven't figured out how to make them smart but because there's been little reason to make them smart.'
(From the article, did you read it?)
Right, the receiver is VERY cheap to make, so at the cost of some bandwidth (meaning the width of the signal in the frequency domain, not bit rate/bit transmission), everyone can listen. If we start making smart radios, not everyone could afford one, and things like old cars wouldn't get upgraded, etc. The user base wouldn't be large enough to support the technology, and it will flop. There is still little reason to make them smart.
My point is, that of course you can make something run on only one frequency, and there should be enough of the Frequency Spectrum to go around, but the hardware complications of the receivers, let alone the transmitters make it a little more complicated and more expensive than consumers would want than he made it seem in the article.
Finally, I'm just talking about the stupidity of changing regular radio, as entrenched as the system is.
New technologies like bluetooth already use frequency hopping in the ISM band, and that is what is probably meant. The author blurred the lines a bit there.
Here's a thought from reading his article.
Instead of directly specifying a particular frequency as the "channel number" for a given broadcaster, use frequency hopping. To determine the frequencies, use a PRNG (pseudo-random number generator). Since a PRNG is completely deterministic, the channel number could be specified as the seed of the PRNG. Different seeds would give you a different sequence of frequencies. If two broadcasts happened to interfere at a given moment, with the next hop they probably would move on to different frequencies.
When you tune into a radio station, you pick a particular frequency. However, the broadcaster can't broadcast anything without a band of frequencies around that carrier. That is, when you modulate the carrier, you use frequencies nearby the carrier, not just the carrier frequency. No one can use these frequencies without interfering with your broadcast. Thus, the radio spectrum is divided into bins that provide the necessary bandwidth to broadcast audio quality signals. If you're doing wireless digital, the bandwidth you need is roughly 1 bit/Hz.
Vote for Pedro
Opening the spectrum up to high-quality broadcasts by anyone doesn't seem that attractive an idea to me. Guess you haven't seen Contact yet? I don't want no Nazi broadcast or prime number tones when trying to tune into my favorite radio station.
Rodgers wrote a follow up article about 10 years ago updating his 1971 thesis. Unlike this Salon article, Rodgers properly explains the physics and actual applications of "wide and quiet" broadcasting (a.k.a. wideband, widecasting). Alas, I cannot find it on the web (work connection too slow). Can someone else who knows what I'm talking about provide a link?
The bitter lessons of a veteran coder: http://bitterprogrammer.blogspot.com
Then, given how important astronomy has been and still is to the development of science and technology, on the fundamental level, I hope /.ers see that cutting off astronomy from the most important sources of radiation is a Bad Thing[tm], and that alltough deregulating the spectrum may be a good thing, astronomers should be heard.
Also, for more about the dark sky problem, check out the International Dark Sky Association.
Employee of Inrupt, Project Release Manager and Community Manager for Solid
Wasn't it just a few days ago that I read an article addressing how to detect junk science?
The magic of SDR is not the ability to discern between two adjacent or overlapping signals, but to use one piece of hardware to recover a multitude of modulation schemes.
:)
Instead of using separate hardware to recover AM, broadcast FM, broadcast TV (AM video, FM audio), etc., a SDR can be programmed to recover them all. (maybe not all at once
David Weinberg tells a good story and it does see into an important future, but neither he, nor Reed, nor Blossom can program "any way" they want. Close inspection of the conveniently linked source code shows that it does not, as promised, decode two broadcasts over a single frequency. From the source:
Actually, if you are using an embedded processor with no floating point co-processor, it's sometimes very handy to use a rational approximation of pi.
I would say that the spectrum is open to any one that wants to use it rightly. It is very easy to get a ham ticket. And this way it will alow the airs to stay clean (in content) in this I refernce CB is a very dirty (content wise) band.
I feel that CB shows why we can not just open up the freqs up to just any one with out haveing the be able to get one with out the threat of repecutions if you don't follow the rules of the air, ie keep it clean, no explitives on the air, there is other things to.
Also there are safty issues, RF can have a negative effect on the human body, but if used proporly the effect can be minimized or even numified.
For all of these reasons I do support the need for a licence to get on the air for comercial or amature rasons.
Put two of these on the same frequency, close enough, and you have inteference at the receiver. PERIOD.
Your 25 years as a ham are limiting your perspective. Ultrawideband doesn't work on specific frequencies, it's very short bursts on a very wide band. Bandwidth is vastly higher than with narrowband, though not unlimited.
What Reed doesn't talk about is that interference is a receiving
problem, not a transmission problem. You also have to remember that
radio broadcasting predates the internet by almost 100 years. His main
focus seems to be to get needed spectrum for the expansion of the
internet into the wireless world. In the early days, the only way to
prevent interference was to separate the spectrum into pieces and assign
each user a specific piece. Up until the 1970's, there was no frequency
sharing between active users. This begin to change in the late 1970's
with the introduction of spread spectrum techniques. This is the
bandwagon that Reed seems to be jumping onto. However, there are
theoretical limits on how many users can share the same piece of
spectrum even using spread spectrum techniques - thus you still need a
spectrum policeman to decide who gets what.
Anyone with even a rudimentary grasp of radio knowledge would see this as old patently obvious news. .. "Radio Spectrum" are just like different colors in the visible spectrum - this is high school physics.
Of course the radio waves themselves don't interfere.
Of course various frequencies of the
The author makes out like this is some new concept
that's been hidden away like the 400 mile per gallon carburator locked away in the Indiana Jones
warehouse.
The meat of the technical argument is to get everyone to switch over to Ultra Wide Band techniques. This is also old news, and may be
a good idea, but is hardly original.
I like radios because they are simple and tough.
:)
In a war time scenario you can depend on low-tech radios to get a message across to the masses.
When the machines declare war on mankind and the EMP weapons kill off the new smart radios, you'll be trading bags of gold and water for your grandpas old fashioned radios.
The processor in your Palm Pilot is completely different than the DSPs found in many digital radios, etc. The Palm Pilot is a general-purpose CPU, which means it requires much more hardware to do what a dedicated DSP designed around signal processing does. (DSPs are often HEAVILY pipelined to maximize throughput because decisions rarely have to be made so branch mispredictions are a non-issue. If you thought the P4 had a deep pipeline, check out some DSPs...) Also, many "software" radios aren't really software - More appropriately a lot of them are "reconfigurable hardware" - Essentially using FPGAs to implement custom dedicated logic. (Once the domain of ASICs, but for small runs FPGAs are much cheaper, and for anything where you might expect to change the logic around later FPGAs are a must.) An FPGA can do things that a 2.4 GHz P4 could barely dream about, while costing not much more than the CPU in your Palm Pilot, simply because it's dedicated to the task.
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.
retrorocket.o not found, launch anyway?
The FCC will never open the spectrum to everyone. Doing so would put them out of a job. They are not about to sign their jobs away for advancing anything regardless of how much better it will make society.
Dirk
The problem is background noise. According to communications theory, the amount of information you can push through a channel is proportional to the frequency bandwidth and the signal to noise ratio. There are modulation schemes (Quadrature amplitude modulation, for example) which are designed to squeeze more information through a given bandwidth by taking advantage of a good signal to noise ratio.
Spread spectrum technololgy (which includes things like code division multiplexing and frequency hopping) follow these same rules, but with a wider bandwidth than a tradition radio or TV signal.
So I think this guys point is this - looking at the usable frequency spectrum (100 KHz to 100 GHz), and the noise distribution from background noise across this very wide band, are we putting as much information through as we can?
No, because we've divided up the frequency space solely based on frequency bandwidth, while ignoring the signal to noise ratio, which is inefficient. It's inefficient because everything must be designed around a worst-case background noise, without the ability to adjust when noise is less than this designed for worst case. It is also inefficent because some transmissions are not continuous, and when they are quiet, that portion of the usable spectrum is wasted.
The details of negotiated use of spectrum, spread spectrum usage, and other points are just expounding on the fundamental point - we have one big communications channel of radiated RF, and we are not coming close to using the full capacity of it because we are forcing a certain architecture on it by way of government regulation.
It's not wasting time, I'm educating myself.
Reed's analysis, badly presented in Salon, deals with networks of wireless nodes that not only use frequency diversity (e.g. spread spectrum), but also use multiple antennas for spatial diversity (e.g. phase arrayed antennas) and the nodes cooperate not only for relaying (e.g. mesh network) but also for detecting and eliminating interference.
All of these elements increase the efficiency of radio spectrum use.
Optimal Operation of Wireless Networks
Combined Space Time Diversity and Interference Cancellation for MIMO Networks
Information Theory at the Extremes
Linear Multiuser Receivers: Effective Interference, Effective Bandwidth and User Capacity
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.
Basically, the history of radio is the history of our practical ability to coordinate multiple stations. In the beginning, radio signals were generated by spark gaps; the resulting impluse occupied the entire longwave spectrum, propagating by groundwave. Separation was accomplished by time, and stations scheduled their transmissions by the clock. This held sway until the invention of the triode vacuum tube by DeForest, which enabled coherent, narrowband transmission of information, and thus coordiation by wavelength. The government then got involved as a third party coordination body.
As more stations went on the air, technological development was aimed at expanding the useable spectrum beyond longwave -- first medium wave (300 kHz to 3MHz) then shortwave (3-30MHz) then VHF (30-300MHz).
WWII advanced the pace of development in UHF (300-900 MHz) and microwaves (above 900 MHz). With those developments came the ability to use polar and spatial diversity. But the latter really took off with the development of microprocessor controlled radios, which enabled spatial diversity by cell -- cellular radio.
However, even with all of the spectrum that these techniques have enabled, the fact remains that, owing to propagation differences, some parts of the spectrum are inherently more valuable than others, a scarcity that leads to economic realities that agencies like the ITU and FCC have been exploiting for decades.
Quietly, however, which these developments were taking place in wavelength coordination, our ability to coordinate transmissions in time has caught up -- first with spread spectrum (not that funny frequency hopping junk) and now individual pulse trains for Ultra Wide Band. UWB in particular holds the promise of ending the economics of scarcity found in wireless. Aside from a thousandfold increase in spectral efficiency, it also maps well to the bursty nature of information -- you don't need a channel all the time, but thanks to coordination by wavelength, you sit on it anyway.
Needless to say, when you challenge the economics of the status quo, you're not going to be too popular in certain political circles.
...-.-
"Why?"
"You are factually correct, but your answer is of no use whatsoever."
He's right, in that there need be no interference. But we live in the real world, and the overriding concern in the real world, after "does it work?" is "how much does it cost?"
Ask yourself why interference between consumer devices exploded suddenly in the 70's. Why cell phone hands-free kits send loud pulses into stereos, wired phones, computer speakers, etc. Why cordless phones can trash TV reception.
It's because we live in the real world, where TV's, stereos, and all manner of consumer goods used to be built with metal housings or at least metallized components combined with metal. Then manufacturers and industry groups protested that the cost was just too high and that other countries with less stringent regulation were passing us by. So it was all deregulated.
Did you know that the TV/DVD/Camcorder/Wireless phone/etc/etc/etc came with a contract that said it was going to have interference problems, and you agreed to it? Yup, all that stuff is licensed under Part 15 of FCC rules, which clearly state "this device must not cause interference with other devices, and must accept interference from other devices." Deregulation was great for cheap and plentiful electronic widgets, but it came at a price.
...to 7 ways [for journalists and judges] to tell voodoo science from the real thing.
Towards the Singularity.
The trouble is in the receivers. But the trouble is not the colour stuff. The trouble is most consumer receivers don't distinguish signals by location or direction.
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.
Apparently the author of the article hasn't seen the television reception in my apartment....
I'm out of my mind right now, but feel free to leave a message.....
David Reed is not one of the people I would deride with the anonymous "a technologist."
Douglas Calvert
I think you have no idea what you're talking about...
For one, I'd like you to point me to this "next generation" standard you're talking about. The current next-gen standards for cellular technologies are CDMA2000 and UMTS (which uses a modulation scheme called W-CDMA)
These are all channel-based, although they do allow for multiple users on the same channel. (Maybe this is what you're referring to? But the carriers are still at 1.9 GHz (CDMA2000 PCS) and 2.1 GHz (UMTS)), with a symbol rate of well over 1 MHz. (3.84 MHz in the case of UMTS, somewhere just above 1 MHz for CDMA2000 1x).
So yes, the next generation cellular technologies still use "channels" - But they allow multiple users to share each channel. (Note: This number is not infinite, there is a finite limit on the number of individual signals present.)
The channel spacing for such systems is also quite close - UMTS channels are 3.84 MHz wide with a 5 MHz spacing. That spacing is already at the limits of what modern power amplifier technology can achieve at the transmit side. (Nonlinearities in amplifiers will cause channel power to "spill over" into adjacent channels, and even with modern techniques for correcting nonlinearities, there's still a limit on just how sharp that dropoff can be.)
Modern cellular technologies are already very close to the limits of information theory as it is. CDMA2000 doesn't even really improve spectum efficiency that much over cdmaOne, it just improves the management of available bandwidth. (Mainly the support of packet-based data rather than circuit-switched.)
retrorocket.o not found, launch anyway?
Did he think of that all by himself?!? Perhaps he can solve the mysteries of the donut!
Well.. maybe. Or Maybe not. But Definitely not sort of.
I never realized Slashdot had so many radio experts. I guess everyone is an expert nowadays with Google at their side.
Oh. great I can see it now, radio software crashes right in the middle of my favorite program. No thanks I'll stick with my crystal set.
"Technology.....the knack of so arranging the world that we don't have to experience it." Max Firsch
Take two polerized lasers in a vacume. Cross their paths. You will not see any photons bounce, aka no light. Moron.
Send this guy on over to my shop. I'll start by putting him in my 911 center. Then he can either convince my bosses of what he says or he can help me fight the interference that is driving me nuts.
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.
. Quit playing Monopoly with Bill. Switch to one of many non-Microsoft products today.
How innovative is this? It's just the ethernet concept sent over radio frequencies instead of over a wire... Geesh!
While he may be correct in saying that radio signals, in and of themselves, don't "interfere" with each other he's neglecting to mention a critical point.
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.
73 de KC7GR
Bruce Lane, KC7GR,
Blue Feather Technologies
Is this a problem with the FM signal, or with the basic design of receivers??
Both. But receivers are mostly responsible.
Big transmitters do not produce perfect signals. The transmitters often produce side bands (offset frequencies) that are much lower in power. There are specific standards stateing how much noise is acceptable.
The standards are set so that most recievers should have no trouble discriminateing the correct signal. But cheap recievers are everywhere. Some of the problems are poor design. Others are from useing cheap parts. In some cases a really good reciever with high quality parts will find all the low power side channels and apear to be of poor quality. But the high quality reciever will be able to pick off each signal perfectly.
Ofcourse the cost of the reciever does not indicate quality. My supposed to be good quality Sony reciever could not recieve two low power stations. The signal would be swamped by one of the large high power stations. The low power stations would not be heard at all. The reciever would tune to the high power stations instead. My, at the time, 10 year old cheap JVC "boom box" on the other hand could recieve both stations although with a bit of noise. In this case the JVC's old anolog reciever was superior. The Sony (proudly) used an all digital reciever.
This article makes a lot of sense to me, and I don't know shit about the technology we use. It made me think of an analogy of how limited our technology is in relation to the UNlimited potential of light.
If you take the fact that if every single creature on the planet were to look up at the sun at the exact same time, for any amount of time, the sun won't become dimmer or less warm in anyway. However, if our current technology were factored into the equation, it would take about 1/8 the world population to collapse the star and suck the planet into the resulting black hole.
Can anyone recommend good 2-way converters,
digital-to-analog as well as analog-to-digital?
I mean those fast enough to work with signals
like those used by the GNU Radio project.
Thanks for any recommendations. I want a
software radio transceiver that can cover
as many VHF/UHF/Microwave bands as possible,
for Amateur Radio experimentation.
I realize that this is late in the discussion and by no means am I knowledgable
in RF theory, but what effect would this have on jamming radio transmissions?
SealBeater
-- Its survival of the fittest...and we got the fucking guns!!!
Have you reported this? Part of what the FCC is there for is to fix this sort of problem.
In the United States. But grandparent is in the UK. What's the British counterpart to the American FCC?
Will I retire or break 10K?
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.
Have you ever actually played the telephone game? It's too easy for a message to get corrupted by accident. Though error-correction solves this in practice, that doesn't eliminate the possibility of a malicious conspiracy of men in the middle from f*ing with the network.
Will I retire or break 10K?
the difference between 24.567 and 24.5668 MHz
Which would provide a bandwidth of only 0.0002 MHz, or 200 Hz. Under theoretical best conditions, this can carry only 400 words per second, and noise sources such as thermal noise and leakage from other stations limit the signal-to-noise ratio, which determines the theoretical best word length.
right now, it's impossible. In the future, you could (but why would ya want to?)
Precisely. Such narrowband transmissions are theoretically possible but hardly practical.
Will I retire or break 10K?
The two light beams in the Michaelson-Morley experiment do not affect one another. It is the superposition of the two beams that causes the interference patterns. Thus, when you add the effect of one beam to the effect of the other beam, you are left with a mysterious pattern that is dark in some areas and brighter in others. This would not happen if they somehow magically affected each other.
The radical sect of Islam would either see you dead or "reverted" to Islam.
was that there is infinate spectrum. This is true because there are an infinate number of frequencies (as in points on a line) between any two different frequencies. The problem arises when you want to put INFORMATION (as in modulation) on the frequency in question. All known modulation types (eg. AM/FM/PM/PSK etc.) cause changes in the (measurable) frequency of the carrier. There will always be some amount of interference if two modulated carriers have bandwidths which overlap. Those effects can be minimized in hundreds of ways, but never eliminated.
This is the danger of Slashdot over most other web boards.
All boards have crackpots, but on Slashdot that "crackpot" could not only be right, but be a Ph.D. in the field that he's commenting in!
If that is so, then why do I lose my wireless network connection when I press the talk button on my Siemens 2.4GHz phone?
Humans speak at frequencies somewhere between 90 Hz (Barry White) and 1100 Hz (Barry White after getting kicked in the balls). Try having a converstion with either of these people near an operating pneumatic jackhammer. If there is no such thing as interference, then you should be able to hear the conversation just fine.
This guy is nuts.
-ted
I think this makes sense. For example, lets say you have dual band stations. Here they are:
Station 1 transmitting at 1 mhz and 2 mhz.
Station 2 transmitting at 2 mhz and 3 mhz.
Station 3 transmitting at 3 mhz and 4 mhz.
Well at this point we're using four bands for three stations, which doesn't help much. But what if we also add
Station 4 transmitting at 1 and 3
Station 5 transmitting at 1 and 4
Station 6 transmitting at 2 and 4
Now you've got six stations transmitting on four bands. I imagine the logic to pull a clean signal out of two frequencies wouldn't be that hard assuming the interference was completely different.
Obviously we have more than four frequencies, and I think there's a cumulative effect here. Plus you can probably do greater overlapping if you use three frequecies per station rather than two. I don't know - I'm no engineer and I suck at math... (not to mention I'm at work!) Does anyone have the smarts/time to come up with a formula for this?
Assuming I'm not missing something terribly obvious (a risk for sure) it sounds like we really are wasting our radio bandwidth terribly by using such simplistic receivers.
Thoughts?
If suddenly every hundredth of a hertz were opened up to broadcasting, I wonder if supporting radio via advertisements would be a viable business model any more. I mean, you may never even find a particular radio station again. Who is going to pay for 10 people to hear their ad?
Shannon showed that the proper way to control RF spectrum is to regulate *power* not *bandwidth*. Trade off bandwidth for a higher S/N ratio and you can allow multiple communicatoins channels *on the same frequency*. This is the key to direct sequence spread spectrum, where proper orthogonal PN-codes are delt out to allow multiple calls on the same channel.
Many things are impossible in general theory but with increasing knowledge of your problem domain these theoretical limits can be overcome.
In this case for example (see www.aip.org/enews/physnews/2003/split/621-1.html) by adding the direction a signal is coming from you can not only eliminate certain interference, but in fact boost your bandwidth in some useful cases.
One way to think about it is to imagine all transmitters sending very narrow beams exactly to the receiver. Woah, what interference?
No doubt Heizenberg's is the ultimate limit on this.
I've seen a lot of comments in this thread about how his ideas are impractical or just plain wrong. To me, this is missing the point. The point I got from the (admittedly bad) Salon article is that Interference is what the spectrum policy is based on. interference isn't a property of the radio signals. It's defined by the FCC based on the equipment (from the time of the Titanic) which while it has been updated some, it's holding things up. FCC makes policy based on technology->companies make products based on the policy->loop infinite (yes some updates along the way, but much slower than the tech we are developing). Add that to the structure of the policies designed to support powerful broadcasters in one direction, and it's really outdated and scary.
As a geek, I want to see cool gadgets. where is the motivation for companies to sell cooler gadgets if the FCC policies give no motivation to build 'em? the policies keep 'em building equipment that does the same old thing based on the concept of interference as a boundry to spectrum.
Yes all harmonics are made, theoretically, but you failed to mention that the strength of each succeeding harmonic as you go away becomes considerably less.
I am sure the FCC carefully considers this when giving out bandwidth. With badly designed filters, this can very well be a problem. However, as the article indicates, there will always be "interference" if transmitter and receiver are not both selective enough.
I guess you forgot about this Slashdot article.
All the bandwidth of all the current crop of wireless devices [2.4 & 5 Ghz] adds up to only 1 maybe 2 standard TV channels! The FCC allocates 84 TV channels! [+ audio on another channel!] Between the Phones, bluetooth, wi-fi you have dozens of usable channels with 100's+ of Mbits combine of thru-put all in the space of several standard TV channels. Also, the TV & FM radio have "prime" real estate. Radios on those frequencies are an order of maginitude easier and cheaper to build and control than your cell phone or wi-fi.
Current broadcast is like using a firehose to water your houseplants! The collateral RF they use up thru brute force is even several times larger than the actual allocated bandwidth! You compare it to a conversation, well they have a giant amplifier turned up to drown everyone else out! They monopolize the entire waveleangth. You'll notice that in the new scheme of things with digital TV, 50 of the channels [they are reducing the number] are crammed into the bandwidth of about a half-dozen current TV channels.
There is a real option open to get the FCC to provide more "Areas" for spread-spectrum instead of specific "channels" when the TV channels give up their space in the next 10 years. That would lead to 100X+ more bandwith for everyone--even if they only allocated a portion of the recovered space!
The article would be more interesting if it wasn't for the fact that the guy who wrote it is an idiot. I don't understand how 10 or more paragraghs are necessary for justifying the "band-color" analogy.
Ive taken some telecommunications classes, where we talk about modulation techniques, signal multiplexing, receiver architecture and transmitter architecture. This whole thing with him comparing the radio spectum to color, while it is a valid comparison, has nothing to do with his actual argument. Even the part where he mentions that photons pass through eachother, and you can project an image through a pin hole. Well thats great, but the light is coming from different directions and from multiple sources. Unless his argument was that we should make directional antenna, and point them at the transmitter, I dont see how this is valid.
The only idea that sounded reasonable was where he mentions a "technique" for seperating signals in the same frequency band. When you click on the link for a demonstration however it gives you some c++ code. As far as I know, this can only be done in very specific cases. I want to read a paper on it, not sort through some source code. I seriously doubt that it is possible for any X arbitrary signals. My guess is that the "demonstration" is an example of multiplexing the signal in time, or two different modulation techniques that are very easy to dicern from eachother.
I am not opposed to his ideas, but they are presented with very little technical data. He spends a lot of time talking in circles about things which appear to have no impact on his arguments. As a final note I would like to add that the frequency spectrum is regulated in such a way as to reduce transmitter and receiver cost. A simple AM receiver consists of nothing more than a rectifier and a first order low pass filter. Opening up the spectrum the way he suggests closes many doors to people who simply cannot afford the new technology.
GENERATION 25: The first time you see this, copy it into your sig on any forum and add 1 to the generation. Social exper
jammers dont exist, either.
:)
I also guess that everytime I'm between two radio stations and my radio can't decide which to lock on to (FM recievers lock onto the strongest signal, AM plays both at once) I must be hallucinating.
By his definition of "interference" I suppose he's right: photons don't crash into each other, but that is an utterly useless definition and he needs to take an EE class, but he would probably fail - they're much harder than CS classes
This article was all over the place, and he basically admits he has no answer other than the FCC is wrong. So what is he proposing? Nothing? Spread spectrum? Frequency hopping? CDMA? I like his idea of bursting an entire DVD in a second with a "very wide band" transmittion. THAT won jam anything, mostly because it doens't exist.
Each direction I can look is a channel of its own, and I can look in a lot of directions even in a 2D plane.
I am walking, living proof. My son will ask me to move or run me out if I stand in certain parts of his bedroom. All I have to do is stand (no electronic equipment of any sort) and the signal will break up. If I move two feet to the right or left, it stops.
I have always done this and I affect both AM and FM signals.
Besides, how many times have you seen a vacuum cleaner interfere with your television reception?
David Reed carefully says that the final architecture should not be prejudged. However, I think I see the general direction of his thinking. He sees many more, but lower power transmitters. Presumably, the receiver will say what it wants to receive and a suitable nearby transmitter will send it. The transmitter may, in turn need to receive it from another node. By restricting the power (and distance) of the signals (and being able to dynamically choose a frequency) and by having the relay transmitters be highly directional, I think the available bandwidth is indeed close to infinite.
Sounds like there are MANY confused people out there. (Or I don't know what I am talking about, so help me)
Radio waves are long wave light that exhibit quantum effects on a large scale because they have a long wavelength. For radio at 100Mhz, the wavelength is 3 Meters. For light its ~0.4e-6 Meters. The quantum effects scale with the wavelength. Diffraction of light at microscopic scales is EXACTLY the same phenomenon as diffraction of radio waves at larger scales which have to do with loss of information concerning postion and momentum of the photon. Its a quantum effect. Quantum mechanics NEVER actually describes particles. Everything is a wave/field. Radio waves are really an example of quantum wave effects on large scales.
The photon can be best thought of as a thing that appears randomly within the electromagnetic field wich appears with a rapidness proportional to the intensity of the field. Quantum mechanics describes the nature of the field and thus where we most likely will observe particles. No one understands exactly why the fields manifest themselves as particles (and vice versa).
I'll admit to being an "armchair physicist". Posting this troubles me. Either I am total wrong or 90% of the people posting don't understand this basic physics.
Am I wrong? And why?
Compression helps only because the typical "message" contains a tremendous amount of redundant information (especially true of video and top-40 radio).
Recommended reference: "An Introduction to Communication Theory" by John Pierce, especially chapters II-V and VIII.
800kbits per second. To get this, your radio stations have to be about 800 kHz apart
You don't need 800 kHz of bandwidth to transmit 800 kbps. By increasing the number of levels of amplitude modulation, you can trade more bits per second for noise tolerance. For instance, v.90 modulation sends up to 53 Kbps on a 4 KHz channel.
And you don't need 800 kbps for CD quality either; you can get that from Ogg Vorbis audio coding at 192 kbps or so, which should be relatively easy to squeeze into about 70 Hz of bandwidth.
Will I retire or break 10K?
If one ever goes to RIT (Rochester Inst. of Tech, in Rochester, NY), the first thing he/she will notice is the bland color of orange-red that is all of its buildings.
guess what, they have the right on that color too. Nobody may use that color without getting into legal trouble.
which is kinda funny because - well - that's like if I draw a color-cube, I am bound to hit the stupid color, eh?
Don't tread on me.
Anyway I don't see what VisiCalc has to do with bandwidth. This guy needs to slow down a little bit and think before he talks. Spread spectrum != unlimited bandwidth. Yes it results in more efficient bandwidth utilization but it is still finite. You cannot avoid the fact that transmitting data consumes bandwidth, and the faster your data rate, the more bandwidth your signal consumes. Sure you can spread it out but it still uses bandwidth and the more people who share your band the less bandwidth is available to each user.
And, shit, it's not like spread spectrum isn't already hugely popular. Cell phones, cordless phones, high-end commercial 2 way radios, and yes even HAM RADIO OPERATORS are all using spread spectrum. 802.11 is spread spectrum. Yeah it's cool but put 100 people on a single 802.11 channel and I think you'll realize just how limited that bandwidth really is. The nice thing about spread spectrum is that it's graceful under load. As more people are sharing the "channel", it doesn't break, it just slows down. It's not "unlimited".
-73, de n1ywb
www.n1ywb.com
Problem is that radio waves aren't just used to listen to the radio they are used for all kinds of stuff.
/etc/services? Why can't all my daemons run on the same port?"
.... and where would we store that list of service identifiers!? (and who would maintain it?)
Basically he's saying why can't all radio devices IN THE WORLD happily co-exist using the same frequency - that's like saying "why do I need this list of common port numbers in
As far as I can see the answer is the same for the PC and the radio world, technically they could, but you would not really be improving anything, just complicating things - when someone connected to your groovy-phat-all-encompasing-port-service (port 1 I presume?) they would have to specify which service they want (and/or what service they are offering in the case of radio) and ooh how would that be done? prolly with a number!
So the port model is sensible for an OS and equally in radio frequencies it is sensible to allocate separate bands for separate uses (and it always will be) - Besides don't some radio devices already use *exactly* the same frequency? For example remote-locking-car-keys they just broadcast a particular "key" encrypted on a set frequency don't they? This is one of few practical uses for devices on the same frequency though because there is no constant stream of data to be interrupted by other devices.
are you saying science is more important than tv?
At optical weavelengths, we *want* a directional, even a focussed, image
Speak for yourself, son. That's why I drink Old English 800.
I thought this was already well known and accepted. Light == electromagnetic waves == radio waves == cosmic waves. Fiber optics have an enormous bandwidth because it's using light instead of photons, they could similarly use microwaves instead of light.
Of course, separating the separate broadcasts are the issue, but the more sensitive the equipment, the less of a problem this seems. I have a radio that has a "fine-tune" dial, so that I can probably go down to 92.305 FM if I wanted to, and it would be almost identical to 92.3 FM, This is sloppiness on the transmitter, if they were 92.3 then you would have a very small window, and then you can pack more stations in the same window, without opening up the demodulator can of worms.
I'd be happy to see this put into practice, but I don't see many big-name companies backing something to lower their market share, even if it's totally unfair.
Wer mit Ungeheuern kämpft, mag zusehn, dass er nicht dabei zum Ungeheuer wird. --Nietzsche
Die TeX-Artikel [..] aber doch inzwischen wohl nicht mehr an den
Fingern zweier Hände abzählbar (außer vielleicht von Informatikern,
die bekanntlich mit den Fingern bis 1023 zählen können.
-- Anselm Lingnau
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