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Cognitive Radios Could Increase Wireless Spectrum
schliz writes to tell us that a new intelligent radio technology, dubbed "cognitive radio," is being developed that adjusts operation based on input from its surroundings. Consumers wont likely see practical implementations of this tech for another five years, but it could have wide reaching applications from wireless networking to public safety devices. "Adaptive, cognitive radios could enable techniques such as dynamic frequency sharing, in which radios automatically locate unused frequencies, or share channels based on a priority system. In public safety, cognitive radios also could be used to provide interoperability between various signals and automatically adjust radio performance."
But as with any system of resource sharing (especially bandwidth), some devices/users will simply ignore the rules to improve their own performance: flag every transmission as ultra-high-priority and so forth. You can't expect users, or even manufacturers, to "play fair." And I'm not convinced that regulation can force people to play fair. Unlike objective measures like antenna transmission power, things like "priority" are more open to interpretation (or misinterpretation, if you prefer). I suppose the same solution as for cell-phones could be applied: if you charge someone for every transmission, they are forced to conserve bandwidth.
I love technology... but when it comes to safety and emergency systems, it's usually best to use the lowest-tech solution possible: cheaper, easier to repair/maintain, more robust, more reliable, and better understood. I don't know if I want my emergency call negotiating interoperability with other devices to reach someone (since any such operation is error-prone). The simplest solution (e.g. full-power transmission on a reserved channel) is probably better in such a case.
Motorola have been working on this for years and I suspect so have all the other mobile handset makers. Frequency agile, power agile systems are used in all cell phones, base stations can direct and use a focused beam to reach a faint handset - this is in service stuff. Walk through hand off from a handset that uses DECT, then dials out and goes cellular seamlessley has been demonstrated, as have handsets that can ask others to dial power down etc. The only thing holding this back has been market forces - customers just haven't wanted it. Yet.
And then, we run into a problem - the standard phantom transmitter. You have three stations, A talking to B on frequency F. Then we have your station, C, closer to B than A, and as such, can't pick up A's transmission. But C starts saying "F isn't used, I'll use it!" and blasts something out. If you use the same power as A, it's unlikely that A will notice, but B certainly will.
The big problem is, this can happen a lot on the "unused" frequencies. Also, you have the issue that they may suddenly be in use at a random time, and you really shouldn't wipe out its transmissions (it may be a fleapower transmitter from some remote sensor - one way, so it can't even detect if there's interference).
To do this properly requires cooperation from everyone, and bi-directional control, which means battery powered transmitters now need receivers and processors to "slot in nicely". And radios that are somewhat frequency agile so they can move to another frequency if their primary one is jammed.
And we all know from 802.11 how well things cooperate. When it works, it works great. But then you get people who twist the spec about ("Super G", "Turbo G") so they can sell "faster!" or "more range!". Or early first-gen N devices that were reknown for wiping out the entire band by not cooperating with existing installations. Sure they conformed to the spec, provided you were on their network, but damned be everyone else. (Which is unusual, since 802.11 forces the MAC to cooperate with everyone, including those using the band but on another network, but as usual, it's an implementation problem, not a spec problem. The same happens for the 40MHz channels issue on present-gen draft-N - the radios don't listen on the sub channel, and just assume it's free when the main channel is free).
As a telecommunications engineer, I do not understand what is new with this.
If you want to check out something that will have a real impact on such video/radio applications, have a look at SVC.
I have some printet material here from this year's IBC where it seems NTT actually already have a software implementation of it.