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'Whispering' Wireless Internet
Zondar writes "MSNBC is reporting about a new radio filtering technology allows an ISP to use already-occupied frequencies to transmit and receive data. From the article: 'xMax, the latest innovation in broadband communications, is a very quiet radio system that uses radio channels already filled up with noisy pager or TV signals ...' and 'xMax is trespassing radio frequencies, although trespassing is not the right word, because we're allowed to transmit a signal if it doesn't interfere with other, stronger signals...' Too good to be true? Sounds like it would just raise the noise floor, to me."
I didn't see any mention of the FCC in this article at all, something that may be indicative of a lack of approval from the relevant bodies. It's all very well the inventors/creators saying that this is technically ok, but when the people who are allocated the frequency range this technology operates in have problems with the raised noise or extra signals, or even just object to something else intruding on their licenced spectrum, I wonder what will happen.
Business Voyeur
I'm surprised that no-one's actually tried something like this before. What with the prevalence of radios that can adjust themselves to noise conditions, it seems that it would be fairly obvious to build one that could listen to the frequency (or frequencies) it wanted to transmit on and intelligently avoid stomping on other, old-fashioned signals in the vicinity. It's interesting, 'cause I just got done reading about something like this in this rather weird, but oddly compelling book.
Or will the TV stations roll out internet service themselves, since they have the license?
An area of 40 square miles is a circle of radius 3.6 miles (5.8 km). Is that really more than a digital phone tower can manage, for example?
I’m old enough to remember 16K of memory being described as “whopping”
If you know the characteristics of a signal exactly, you can recover it from below quite a bit of noise. One of the experiments I have my students do is to recover a signal 20 dB below the noise. It is trivially easy to do. The amount of data you can send, on the other hand, is approximately zilch.
Shannon's law describes the amount of data you can send as a function of the signal to noise ratio. As long as you are willing to put up with low bit rates it is no problem to use a signal below the noise floor.
Several of the posters have assumed that these guys have re-invented cdma. That's not necessarily the case (although it might be).