The Myth of Radio Spectrum Interference 603
Selanit writes "Just came across a fascinating article on Salon about a technologist who claims that there is no such thing as "interference" in the radio spectrum. He argues that interference is a symptom of inadequate equipment, not a fact of nature, and that with improved transceivers we could open the spectrum up to high-quality broadcasts by anyone. Reference is made to the GNU Radio Project. Neat stuff." We've posted other stories about this. I wonder if the "color" meme will catch on.
Interesting thing about radio signals (Score:2, Interesting)
Hard processing on the CPU, made the most interference.
sorry he's not being honest (Score:4, Interesting)
Based on stories of 802.11b (Wi-Fi) and/or Bluetooth suffering from interference either from like-protocoled devices being operated by other parties, or cross-protocol interference which results in the one or both protocols not being effective in their data transmissions, and these are supposed to be advanced intelligent devices which don't suffer from interference due to their use of Spread Spectrum technology, and intelligent software controlled radios (which may or may not be software defined radio - SDR).
So unless he can demostrate experimental evidence, I'm a scepetic.
Re:Anyone (Score:1, Interesting)
The last thing that I want are a bunch of gaotse pics on my tv, and trolls on my radio. The news is bad enough.
Re:The article is crap (Score:3, Interesting)
- Two transmitters in two different places, but with an overlapping range, both broadcast on the same frequency.
- A receiver is halfway between the two transmitters and so within range of both.
- The receiver has two or more antennae, each antenna has some directionality. You do a lot of DSPing in software to distinguish the two signals even though they are both on the same frequency.
Re:complete bunk (Score:2, Interesting)
With multiple antennae you can use signal processing to separate signals from different directions, just like we do with our ears when listening to people.
By your logic government should regulate people talking at certain places
Ultra Wide Band (Score:3, Interesting)
Of course UWB is still in the laboratory, and these two think that the FCC should rewrite the laws now for a technology that may work well (i.e. not cause widespread interference), and may be cheap. Except we don't know yet!
Big difference betwqeen RF and optical receivers (Score:5, Interesting)
The way we use radio takes advantage of this - we don't have to aim the antenna for our car radio, and we prefer it that way so we can listen as we drive. This leads to a promiscuous sort of receiver, which is subject to interference. I think it is going a bit far to say thai is because of the legislative environment or technological background - it is because it is the way we *want* it to be.
At optical weavelengths, we *want* a directional, even a focussed, image - and our eyes produce it. In between, we tend to use directional transmissions with point-to-point microwave dishes.
However, the simple reflector style lens, depending upon newtoinian optics to fouca an image of the transmitter onto the receiver, is not the only way to receive a signal. People are already working on multi-aerial systems which take a "holographic" approach to reconstructing the signal. There was an article about one of them on
I think the frequencxy hopping bit is actually somewhat of a red herring. It doesn't generate new spectrum, it meakes better use of the spctrum we have. It gets rid of the wastage caused by blank safety space betwenn radio stations both in geographical space and in spectum space.
Re:Wha? (Score:4, Interesting)
However, far from being revolutionary, his 'discovery' is a well known fact, which is already in wide use by now:
Also, his analogy breaks when you compare wavelengths: light having much shorter waves is much more directional (allowing for the pinhole camera phenomenon) whereas radio need much bigger spatial separation to avoid interference. While you can put several green objects into one room, and still distinguish them, you need much larger cells for RF.
Multiuser Detection (Score:3, Interesting)
Re:complete bunk (Score:5, Interesting)
In your example, it's true that your eyes can't discern the difference between the signals and this is classically how we've viewed radio detectors. However, the information in the signals is not lost - you're ability to detect between them is altered, but the photons themselves are unaltered.
If you switch to a different type of sensor or encoding scheme - for example, utilize frequency hopping (aka spread spectrum) then you could easily broadcast the two signals over the same range of frequencies (colors).
Overall the article has a lot of merit in providing a different and, in my mind, compelling metaphor of bandwidth as colors as opposed to the classical bandwidth as land. As to his ideas of limitless bandwidth being true, the idea is beyond my ability to see how this is feasible, but that does not detract from his idea that we could actually be communicating a LOT more over the current spectrum than we are today.
There are more sensitive radio receivers out there (Score:5, Interesting)
Radio Astronomers have a hard enough time keeping the important wavebands free of interference without the radio spectrum being unregulated. Lots of useful, hard science is being done by the radio telescopes around the world observing the machinations of galaxies out in the distant universe. One of the key problems is that these signals are amazingly faint. The standard unit used in radio measurements is the Jansky - thats 10^(-26) Joules per second per square metre - which should give you some indication as to how faint. Lift that coke can off the floor onto the table and you've just used up more energy than has been received from distant galaxies by ALL the radio telescopes on the surface of the planet.
Terestrial radio transmitters are so many orders of magnitude stronger than these signals that any sideband transmissions even 90db below peak transmission still totally swamps the surrounding spectrum. And very few transmitters are truely 'perfect'. It's not as though a transmitter broadcasting at frequency X with HWHM waveband Y can't be detected at X +/- 8 Y. Yes - better quality receivers allow you to separate out signals at close frequencies, but a very strong signal next to a very weak signal will drown out it's neighbours.
Cheers,
Toby haynes
Re:The article is crap (Score:5, Interesting)
This is done by spreading your signal over a large spectrum with a pseudo random key. The number of possible keys is still limited (There has to be a certain difference between two keys for it two work) and thus you still have a maximum number of users although things like roaming are a lot easier since you are limited by keys overlapping and not range overlapping.
This is what is being done in CDMA cellphones, Wireless Lan, Bluetooth etc. It is nothing new, already happening and you still need regulation to make sure the spectrum doesn't get completly unusable.
Jeroen
Re:complete bunk (Score:3, Interesting)
Sure, if you're using stone age equipment. Consider if instead you used two colors. One guy (who you are listening to) flashes green and yellow, another does green and orange. Yet a third person uses orange and yellow. You'll have a few errors when both people you're not interested in happen to flash at once, but for the most part, the signal will get through.
Now, imaging using dozens of colors, error correction, and a protocol so that you can ask anyone who's signal you can see to choose a different color or time division on that particular color.
Or we can stick to the current system where the government grants you the exclusive right to that shade of green ( and because you insist on using poor quality celluloid filters, several shades around it as well).
Re:Wha? (Score:1, Interesting)
Trying to talk in a crowded room is a really good example.
What we call "interference" is just a special case of "noise". Different technologies and models deal with noise differently. In this case we are talking about narrow band vs. spread spectrum.
Spread spectrum suffers from noise in terms of reduced bit rates and bit errors.
With many users trying to use the same bandwidth (spectrum, colors, I don't care what you call it.) the guy with the most powerful transmitter wins. Foghorn Leghorn can kill all other conversation in a room.
At low powers we already have a lot of unlicensed spread spectrum working happily together. (although I have heard that there are places where Bluetooth has caused problems and is banned.)
Coincidence? (Score:1, Interesting)
Everything is easy... (Score:2, Interesting)
Re:The article is crap (Score:2, Interesting)
For example most cell phone systems work by dividing the spectrum into channels, each with an available bandwidth. If you think about it this means that you loose a lot of bandwidth before you've even started because you have to leave gaps between the channels to prevent interference. In addition when a channel isn't being used its bandwidth is being effectively wasted: it would be far more efficient to give all the bandwidth to the people who actually wanted to use it.
This is why many countries are adopting a standard for their next generation of cell phones that resembles ethernet in transmission. You use a low frequency wave of around 50HZ as this travels further and allows the cell sizes to be larger and instead of modulating it (as is done with traditional cell phone systems) you either turn it on to represent a 1 or off to represent a 0. Do this many millions of times a second and you have an efficient way of transferring data. Collisions can be detected by error checking techniques developed for wireless lan and so everybody can communicate whenever they nead to with the maximum bandwidth possible.
"Just ask this scientician..." (Score:3, Interesting)
What I'm unclear about is what he proposes we use all these radios for. Is he talking about making cellular networks more open and inexpensive? Is he talking about making radio and TV licenses cheaper and easier to acquire? Is he talking about replacements for Bluetooth and 802.11b/a/g? I guess he's talking about all of the above and more. Having spectrum open to such a wide array of uses with "autonegotiation" will result in huge drops in throughput. The article suggests that autonegotiation is used in frequency hopping systems,
Um..the TX and RX aren't negotiating -- they're following a very strict prescribed pattern of frequencies to which they hop. Same is true in cell networks, 802.11, Bluetooth..doesn't matter if it's frequency hopping or direct sequence spread spectrum, everything is planned out.
Where I work we've been doing preliminary work on software-definable radios for a couple of years now. The two biggest problems we foresee are: (a) how to justify the cost to customers up front, and (b) how to justify (to our company) selling someone a radio they will (conceivably) never have to replace. We're struggling to make money through software upgrades, and we've already seen that it's really hard to displace an existing, working system with a new, better system (just look at UMTS adoption).
Directional radio (Score:2, Interesting)
It's possible -- especially with software defined radio techniques -- for a receiver to tune in a particular direction (in addition to frequency, perhaps). Presumably we would design the receiver so that it tracked the radio source, rather then having to fiddle with the dials everytime the receiver moves. But as long as the possible transmitters aren't all in a straight line, there's no reason that a receiver built today couldn't distinguish between many transmitters on the same frequency -- even with fancy coding techniques. (You do mention this in your post -- I'm just amplifying a bit.) You might fiddle with a "direction" knob to get the station you want, then turn on a "track" feature to keep that station tuned in as you drive your car around, or whatever...
This won't make the spectrum infinite, but would expand the usable spectrum substantially... Reed phrases his arguments in ways that border on pseudo-scientific, but there are real possibilities underneath his hype.
Re:The article is crap (Score:3, Interesting)
The author of this paper is right! There is no interference in a spectrum (besides the modulation of the signal to broadcast, but that is an effect of no importance here). This is mathematically and physically true.
However I can understand that electrical engineers have problems with this, because they notice interference every day. This has however to do with the _implementation_ of the radio signals, not the theory.
A lot of comments here deal with issues which are quite off-topic, such as what antenna (omni or not, size) you use. This has nothing to do with the spectrum or interference, the direction is an extra design parameter for a system, which can be used to pick up a certain frequency, but there is no coherence with the interference topic; a a certain spectral component stays the same in the air, no matter what antenna you use.
However I don't find this artical inspiring, because it contains nothing new. Let the electrical engineers deal with the problems, they are more experienced with the implementation..
[Disclaimer: I have phys. degree]
More than that... (Score:5, Interesting)
But more than that, I think. Consider that the spectrum itself is not quantized. We quantize it with different radio stations, but this is not really absolutely necessary. If our recievers/transmitters where all spread spectrum, and they could all recieve/transmit at nearly any frequency we wanted, then there really wouldn't be much problem with interference. Sure, you might get signal degradation in one frequency band because someone else was using it, but you'd get less in another band that would make up for it.
To make sure that the spectrum doesn't become completely unusable wouldn't require government regulation of WHO uses it as much as it would require regulation on HOW they use it. If people used the spectrum the way that broadcasting companies do now, we would certainly have a problem.
But it is unlikely that anyone would be able to completely use all of the spectrum because of the unbelievable energy requirements that this would need.
In short, with the appropriate scheme, there really is enough bandwidth for everybody (that is, bandwidth would be limited by power, not by regulation).
He's right, but he's completely wrong (Score:5, Interesting)
However when radio and television began, there were no computers or even transistors, there were no phase-locked oscillators or QAM modulation, and there were only a handful of broadcasters.
Yes, some of the frequency hopping and CDMA type concepts have been around for a while, but only in the last 10 years available at a price that anyone but the government could afford.
Mr. Reed's ideas are insightful, but not very practical. Our entire telecommunications infrastructure relies on spectrum assignments. The technology does encounter interference. To simply point the finger at bad planning and blaming the decisionmakers from the 50s for not predicting the state of technology fifty years later is ludicrous.
Reasonable proposals to more forward with UWB that doesn't interfere with traditional infrastructures should be pushed. Eventually the old technologies will fade away like the telegraph.
But to simply rant that "It sucks. Cooler, better tech exists." doesn't do anything.
he's partially right, but that's irrelevant (Score:4, Interesting)
Furthermore, allowing "substandard" receivers to exist is deliberate. We did this with the AM spectrum when FM came along, and we are doing it with other receiver technologies. AM can be received with a few cents worth of primitive electronic components and it is widely deployed, that's why we continue supporting it.
The division into bands also allows enforcement and specific power limits. Without that, people might broadcast over astronomical frequencies, or they might engage in RF shouting matches until they light up each other's fluorescent lightbulbs.
Basically, Reed's science is iffy, and his arguments are completely missing the point. Yes, we can open up spectrum (UWB is essentially trying to do just that), but let's not kid ourselves about the consequences, which will at the very least include the obsolescence of lots of radio equipment and probably a kind of arms race over the airwaves.
They've found a way - (Score:3, Interesting)
Too bad, but the physics of radio propagation does put a limit on the range of useful frequencies. If you want to do international broadcasting, you are pretty well limited to 3 - 30 MHz. If you want to do TV broadcasting with a single transmitter over a range of 100 miles, you are probably limited to 50 - 1000 MHz, and so on.
The problem is that governments, not knowing anything better to do, have carved up the spectrum into fixed allocations to various "services" - broadcasting, police & fire, military, amateur, etc. But if you listen with a wide coverage receiver, you will find most of the frequencies are empty most of the time. That is a real waste.
Theoretically, "software defined radio" lets you divide up frequency and time and modulation type in arbitrary dynamically programmable ways. The problem with that is that both ends have to agree on the algorithm and everybody has to agree to use the minimum power necessary. (Because there IS interference if you use too much power.) The price of flexibility is a huge burden of coordination. Of course, this is great for covert communications.
To paraphrase one of my profs, if you pave all of Delaware County, you don't need stop lights anymore.
-Martin
Sig of the day: What became of humble foreign policy?
pi IS rationnal... in some strange bases (Score:2, Interesting)
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...
Not a great article (Score:3, Interesting)
Interference, as it says, is not a law of nature. It's what happens when you are trying to listen to, say, a 1.1Mhz signal coming from over there and someone over here is also transmitting on 1.1Mhz. How can the radio receiver tell the difference between those signals? As the article hints, it's an engineering issue; but it's a non-trivial one. Radio engineers all over the world will not read this article and rejoice. Reclassifying the problem in some bizarre colour analogy has not magically solved it.
Now as for the politics of spectrum allocation and the potential improvements of a free spectrum policy: now that's a more interesting issue, but one the article doesn't address in any but the most superficial of ways.
Bah, I say to it.
Johnny Mnemonic (Score:2, Interesting)
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?
Re:Someone hand this guy a physics book, stat! (Score:1, Interesting)
You've got to be kidding. Few things annoy me more than people who aren't educated in a discipline drawing conclusions about the theories of people who are. You obviously aren't an electrical engineer. If you can't comment intelligently, shut the hell up.
Look, this guy's physics are hardly revolutionary. If you'd taken an undergraduate EE signal analysis class (or if you have taken one, understood it) or even an ordinary differential equations class, you'd remember the nifty little mathematical construct behind the theory for every single reciever known to man. The Laplace transform.
Crazy interference waveform in, summation of constituent frequencies out.
What? That can't happen, you say? Interference destroys the information of the constituent frequencies? You're ignoring the time-varying, distributed-over-time nature of any meaningful electromagnetic signal. The point is to transmit information, not enjoy the constant-color waveform coming off a soap bubble.
All these CS- and humanities-major
Re:complete bunk (Score:2, Interesting)
Re:The Economics of RF and 'smart radio' (Score:3, Interesting)
Yawn, nothing new here at all. (Score:2, Interesting)
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.
Um, no... (Score:5, Interesting)
Note that the GNU Radio project recently achieved ATSC (US digital TV) demodulation.
Using $1000+ worth of hardware
40x slower than realtime.
Compare that to the MyHD HDTV tuner card, which can do realtime demodulation, MPEG decoding, and display scaling for $300. Why? Because it's designed for the task. It's somewhat reconfigurable, but you can't take a Palm Pilot and turn it into a software-defined radio.
Real citations (Score:3, Interesting)
All of these elements increase the efficiency of radio spectrum use.
Optimal Operation of Wireless Networks [comsoc.org]
Combined Space Time Diversity and Interference Cancellation for MIMO Networks [vt.edu]
Information Theory at the Extremes [cornell.edu]
Linear Multiuser Receivers: Effective Interference, Effective Bandwidth and User Capacity [nec.com]
Abstract: Multiuser receivers improve the performance of spread-spectrum and antenna-array systems by exploiting the structure of the multiaccess interference when demodulating the signals of a user.
Reed is Right but for the Wrong Reasons (Score:2, Interesting)
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.
Re:Why do the UWB cranks think... (Score:2, Interesting)
None of the claims that I've seen coming out of the major players (Intel, TDI, etc) has violated Shannon's Law. The problem here lies in the way that most people interpret the Law, and their stake in the existing wavelenth coordiation scheme.
In the wavelength scheme, one uses the average, or peak information rate to determine spectral occupancy, as one cannot completely predetermine the stochastic nature of the information transfer. As a result, you occupy spectrum even if you're not using it, because you might use it. In contrast, when a UWB transmitter is not in use, it doesn't emit RF, thereby decreasing the noise floor, and thus increasing the available information rate for other stations.
Aside from being a better match to the stochastics of the information, there's a true RF advantage to UWB -- the elimination of Rayleigh Fading due to multipath. Any narrowband link has to take into account destructive interference resulting in multiple RF wave paths; the resulting increase in required power reduces the spectral efficiency. However, in a time-based system, where the pulse length is shorter than the path difference, the receiver is able to easily reject reflections which arrive outside the time window.
Sorry, but in thise case, the trolls are on the other side of the bridge...
Re:Interesting thing about radio signals (Score:1, Interesting)
After the demo, the place went ballistic with applause...
It's partly true & here is a better article/an (Score:2, Interesting)
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.