Nothing could possibly go wrong though, after all this is OFFCOM, that bastion of reliability and integrity.
Ofcom has laid out the rules regarding White Space devices, kicking off a consultation process which could see devices on the shelves around the end of next year. The rules are complicated, because devices operating in White Spaces have to consult with an online database for usable frequencies, and check back regularly to …
It's all based on all devices voluntarily and correctly checking with the database, owning up who they are, where they are and what power/frequency they will use, and doing that again, honestly and correctly, every day. The naivety is touching, I suppose. A bit like the early days of the internet, when no-one could ever see why IP would need security, QoS, authentication, policing, etc.
Dusting off my old blackhat for a while, I have think... would it not be a very impressive achivement for someone to make a virus that can firmware-flash or otherwise hack a popular model of white-space device such that on a predetermined date (Big Brother series premiere!) they all switch to the TV spectrum and start transmitting on full power?
> The suggestion that the devices check locally for transmissions seems sensible.
Except that it isn't sufficient. Just because a device can't hear a signal on a given frequency doesn't mean that it won't cause interference it it transmits on the frequency. Google "hidden transmitter syndrome" for one of the problems.
But the TV receivers and set-boxes are not reporting which TV mast they hear. Which in 10s of thousands of cases is not the one the Database thinks they are on.
Also in many cases the propagation of the "White Space" device may be x2 to x10 more than expected. "White Space" is a deliberate Euphemism. These gadgets are going to transmit on actually used TV channels. Not separate Spectrum.
Mobile 3G and 4G/LTE has white space in exactly the same sense as TV. Why doesn't Ofcom try this at 800, 900, 1800, 1900 (DECT Phones) and 2100 MHz phone bands?
DECT phones work on auto channel assignment because they are used for short periods and indoors and only share the spectrum with other smart phones.
These "White Space" devices can only be deployed on a dedicated band. It's Criminal vandalism to deploy them IN the TV band as proposed.
I wasn't suggesting that STBs or the like report anything - they are listening on well defined channels. I was talking about the white space devices themselves reporting amongst themselves what they can each hear there by extending their listening range and, to some extent, mitigating the hidden transmitter problem.
There is certainly a case to be made for testing the viability of a white space devices antenna(s) ability to pick up polarized weak signals from distant transmitters. I would also be interested to see how a DVB STB copes with white space devices active locally during a channel scan. I expect it would be pretty much as it did with the analogue channels - ignore them.
Transmit power could be varied to suit the conditions. Transmit power would also depend on the desired goal. I would think any high powered application would be a better candidate for a look-up table as the overall cost would be higher and the cost of implementing internet access would be negligible for such a system. If cost isn't an over riding factor then both approaches could be used with that device adding what it can hear to the look-up.
The 'unused' spaces are those not used locally. They are in use somewhere else. That doesn't mean they can't be used at a lower power in the places where they aren't already.
Checking back for geographic lists? How very 80s. Some degree of exclusion is necessary, but 100m granularity? LOL.
Surely we are at the point where the device can determine its own white space and configure accordingly? Software radio capability is way beyond checking back against a database, move with the times.
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"The suggestion that the devices check locally for transmissions seems sensible."
It's not. I am picking up TV stations from 70 miles away or more daily, because there are only a couple local channels. The little "rubber duck" on a access point would not see anything, let alone some wifi-device-sized client, and would gleefully blast signals right over my channels given a "device checks by itself" scenario.
I just hope that any database used is very conservative in determining what is freespace, not just assuming people will use the nearest stations and forget the rest. (I admit, I think this is different in the UK than here in the US, where there aren't just almost the same stations at each TV transmission site.)
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