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Open Spectrum: The New Wireless Paradigm
prostoalex writes ""Almost everything you think you know about spectrum is wrong." - starts Kevin Werbach in his working paper Open Spectrum: The New Wireless Paradigm. He touches the possibilities of using open spectrum, and then dwells on such innovative products like software-defined radios, spread spectrum or cooperative wireless networking. Truly informative insight into where the U.S. government stands on the issues of wireless spectrum, where it should be, and how it will benefit society and individuals."
One thing I do know about it that I am fairly certain is not wrong: the government will attempt to regulate it. It doesn't matter what shape it takes the government will make sure it makes a profit from it.
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I wouldn't say he ignores it, but there is one assumption about underlay that is incorrect. The proposed mechanism of underlay is for the the underlay system to detect that it is causing interference and cease to do so within a few milliseconds.
However, the ideas of Open Spectrum, applied carefully and with good engineering understanding, can indeed significantly increase the usage of spectrum. However, unlike many of the subsequent posters on this thread will assume, it will *not* work without appropriate regulation (as the author recognizes). It is a different and superior method of spectrum management, not spectrum anarchy.
The idea of setting aside spectrum "parks" for the unlicensed services, and then applying strict technical regulations to those systems is the most promising. Setting aside channels 60-69 would free up 60 MHz of very useful bandwidth for mobile and portable applications. The appropriate standards would allow proper sharing of the underlying spectrum without licensing individual users or sites.
However, some of the techniques that allow this sort of operation may not be that inexpensive to create. They will require substantial processor power and probably power consumption. This will limit their use in extremely inexpensive uses (such as keychain transmitters for auto alarms). For these kinds of uses, different spectral parks may be required.
In other words, one may need some spectrum for dirt cheap devices (where an additional $.01 is a significant cost increase), and other spectrum for sophisticated devices where the value allows greater costs. Likewise one may want different spectrum and rules for wide area systems than local ones. Furthermore some systems can tolerate significant random interruption (remote meter reading, for example) while others must work well all of the time in real time (police communications, air traffic control, etc). These may again require different parts of the spectrum in order to be protected from inadvertent interference from nearby non-cooperating unlicensed systems.
Furthermore, one needs to make sure that failure modes of these devices don't screw up a whole area!
Hmmm... this starts to sound a lot different from just turning folks loose on unlicensed bands! It illustrates the complexity and the need for sophisticated standards and associated regulation.
Underlay is IMHO much more dubious than the author lets on.
In practice it can be very hard to do well. Existing narrow-band systems use techniques that *cannot be used* in wideband receivers. The techniques (such as very high Q low loss RF filters) allow the narrow band receiver to operate with very weak signals, signals which could not be adequately detected by a wideband underlay system, and which would then be interfered with by that system. These existing systems are engineered, and regulated, to use the minimum power needed - and thus are inherently susceptible to this new interference.
There are a number of physical factors that limit receiver sensitivity. They range from thermal noise in the receiver to exotic topics such as intermodulation, desensitization, and quantization noise. It is not possible to optimize for all of these in a frequency agile receiver to nearly the degree one can in a narrow band receiver.
In addition, some of the techniques are inherently expensive. Moore's law doesn't apply to the fabrication of precision metal resonators, for example.
What this means is that for an underlay service to be truly non-interfering, it requires either a very expensive, big and power consuming receiver, or it needs to be on a portion of the spectrum where these techniques are not applied by existing users of that spectrum.
Other approaches, such as using spread spectrum - or wideband as the autho prefers -(so you don't have to detect systems you are interfering with) have different problems. A wideband system distributes its power across a wide spectrum, but that power is still not zero. This means that if it is too close to a traditional narrow band receiver, or another wideband receiver it will cause damaging interference.
Overall, however, the Open Spectrum initiative is a good thing and can have enormous economic value. But it should not be viewed as a magic solution or one that can rely strictly on anarchy or unregulated cooperative development.
The only good weather is bad weather.
It's a bit of both. The existing protocols lack some features you really need to make best use of the bandwidth, for example, node routing and power control are both absolutely critical, and WiFi does neither out of the box.
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"Actually, you need to be aware that the unlicensed bands ARE regulated - for example, you can only use channels a certain width at max (say 1MHz), and need to use a spectrum conserving modulation, such as FHSS (frequency hopping spread spectrum). You also have maximium tranmission power requirements and so on.
No, I don't trust in god. He'll have to pay up front, like everybody else.
*insipid childrens show music*
:)
Welcome to the Slashkids Fun-Filled Fallacy Post!
Slashkids:Yay!
Today we're going to learn about The Post Hoc (Ergo Propter Hoc) Fallacy!
Slashkids:What's that?
Well kids, that's Latin for "after this therefore because of this."
For example, you could easily say that eating breakfast causes car accidents, because most people that have had a car accident had breakfast that day.
Slashkids:Ha ha ha!
Or that you started a new job, and then your hair fell out.
Slashkids:Then what caused the hair loss?
Who knows? It could be something in the water, it could be any number of other factors. How do we avoid this type of thinking?
Slashkids:With control group studies, double-blind and random tests!
That's right!
Remember Slashkids, sequential patterns != causation AND correlation != causation!
Next lesson: The ad hoc hypothesis
Slashkids:Yay!
*insipid childrens show music, credits, cut to commercial*
(Sorry, I'm a prick and I couldn't resist
Robots are everywhere, and they eat old people's medicine for fuel.
... say node A is visible to base B and base C but base B and ase C are out of each others range. If B and C don't "hear" each other they can't work in unison without a third party. So when Node A (mobile presumably) hunts for a connection, both B and C try to talk at the same time to A, thus hampering the usable bandwidth.
But mobile node A can BE the "third party". If base stations B and C have unique (or at least non-colliding) identifiers then mobile node A can say, as part of its transmission, "I'm talking to B." or "I'm talking to C."
There are variants that work even if mobile node A is saying "Who's out there for me to talk to?". Look at the IP address resolution protocols for working examples. For starters, the a similar case arises on an Ethernet when a machine that wants to be booted uses RARP, broadcasting its Ethernet address and asking potentially redundant servers for its IP address. (Granted the servers COULD hear each other. But the protocol works even if they can't.)
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
The rules of and assumptions underlying the way the FCC is carving up spectrum are based on 1930's technology. It assumes transmitters and receivers have poor filters, and cannot tolerate adjacent or overlapping signals. It assumes no spread spectrum or channel agility / frequency hopping technology. Fast forward 70 years. Technology has marched on. Spread spectrum and channel agility are cheap and commonplace. Transmitters meet much stricter tolerances for sideband and out-of-band emissions. Receivers can pick up weaker signals, and much more successfully distinguish their signal from other overlapping or closely adjacent signals. Thus we can now pack several times the data per unit of spectrum than the current rules assume we can. Yet the rules prevent us from doing this on a large scale because the unlicensed bands in which we can operate are so few and small. Users of the licensed bands (most of them anyway, cell phones being the one big exception) have little incentive to deploy these technologies and make maximum use of their spectrum because the rules guarantee them enough free spectrum that they can use older, less efficient technology with abandon, and still get done everything they want to.
THAT is the point of this paper. We shouldn't be asking what if both nodes are at 2.4GHz. We should be asking why does the guy at 2.3GHz get to be so wasteful with his bandwidth when technology now makes it cheap and easy for him to get more done with less, and we're all crammed in here together at 2.4GHz?
-----Chaz