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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."
This is extremely interesting, if not tried before. I wonder what FCC/ologopolies will have to say when someone else starts using their hard lobbied/bribed frequencies.
FP?
Live for the present, learn from the past, and dream of the future!
Every few years somebody renames ultra wideband CDMA and acts like it's new technology.
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.
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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.
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”
I work as an engineer in the broadcast industry, and I concur. This is nothing new or amazing, just another implementation of spread-spectrum. I found this acticle's pseudo-science quite entertaining. Especially the use of quoted words in this paragraph:
What is unique about the system is that it can emit signals that are too weak to be picked up by normal antennas, but that can be "heard" by special aerials which know where to "listen", thus enabling dual usage of the same scarce radio spectrum.
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All of whose base are belong to the what-now?
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).
While partially true, you also underestimate the sensitivity of radio telescopes. Sadly I don't remember the exact values, but I think a few nanowatt signal could still be detectable for Arebico. Basically an earth like civ within 10 ly could probably be detected,
What does that mean in practise, not many stars within that range, so it isn't to much help. So to have any real chance you would need a space based telescope that is much much larger to seriously increase sensitivity. But that won't happen for atleast a few decades.
> A very noisy planet will still stand out since
> it will be generating much more radio noise than
> the surroundings.
Not true. The total output of all the radio transmitters in use today is much less than the thermal radiation from the Earth integrated over the same band. If all those transmitters were using UWB the effect would be to raise the apparent noise level by an imperceptible amount.
> Saying that wide band communications is less
> visible than narrow band communications is like
> saying that white light is less visible than red
> light.
No, it's like saying that a dim laser is visible against a bright white background, but a dim white light is not.
Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.
The point is lower power. Since signal decreases as a square of distance, even small reductions in transmit power will have a dramatic difference in the noise signature of the Earth at multi-light-year distances. Ultra wideband allows lower power.
As an aside, the transition to heavily encoded packet RF also reduces our signature to ET. Anyone with a long enough wire and a speaker can pick up analog TV or radio and recognize it as synthetic. Can the same be said for highly dense encrypted digital traffic? Even my 56k modem sounds like white noise to me.
Build a man a fire, he's warm for one night. Set him on fire, and he's warm for the rest of his life.
Also interesting to note that the Navy rejected her invention for 17 years after her and her partner received a patent. WWII completely missed out on spread spectrum military applications because of thick-headed Navy officials. Nice.
Isn't she the one on the Corel Draw 8 ad?