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Sharing the Airwaves: Spread-Spectrum Broadcasting
NaDrew writes "From the SFGate: Hal Plotkin writes about how Spread-Spectrum broadcasting technology could revolutionize the way we listen to the radio, and make it incredibly easy for neo-broadcasters to start their own services. Sadly, he writes, the "often technically inept U.S. Congress has complicated the situation in recent years by shortsightedly instructing the FCC to sell or lease additional bands of spectrum that had been reserved for other uses." Not to mention "the media conglomerates that own most of the nation's TV and radio stations have a vested interest in the status quo and won't easily give up their hammerlock on what, in the end, are public airwaves." A fascinating article that also includes some history of Spread-Spectrum technology (did you know it was patented by Hedy Lamarr?)." A good primer to spread spectrum if you're new to the issue.
Using spread spectrum technology greatly increases bandwidth available. We are figuring this out 75 years after the invention of radio, so wouldn't any one else out there be doing the same thing? Are we wasting time looking for a strong signal from space when a spread spectrum signal would look just like increased static coming from a planet.
Free cell phone tracking
That's what Pulsars are, basically a big galactic GPS / messaging system.
try { do() || do_not(); } catch (JediException err) { yoda(err); }
The european Digital TV and Radion systems already
use spread spectrum technology (though not
frequency hopping AFAIK) and have been since
they came online years ago. Time for the US to
play catch up (again).
It's not a noise floor if I can route through them or they route through me; it's called CONNECTIVITY. Don't forget that radiowaves get absorbed in most cases; we don't live in freespace on the earth's surface; so the concept of 'noise floor' is flawed; atleast, at the higher frequencies.
I'm a big fan of the idea of ad-hoc wireless networks. I think it will give us almost 100% coverage for IP services of all kinds. Wireless is a solution to the last mile issue of how you reach the internet backbones; and firewalls are a solution for how you charge for bandwidth and avoid 'leaching'.
If a particular service requires priority in certain situations (e.g. military, rescue services etc.), then their packets should be given priority on the network, and handled as such.
I think we are gradually evolving towards this model, but there's a lot of equipment out there...
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"Personally I think the solution is tightly collimated beams and making sure that you're not leaking radiation everywhere. Broadcast spread spectrum is annoying - it does raise the noise floor. If you're talking about for IP services, and you have highly directional antennas, yah, spread spectrum should be OK. Less interference, more stable signal, should be good. But if you're talking about for cell phone use, no way, and unfortunately, I think that's in general what people want. Put a big tower broadcasting spread spectrum, and that WILL raise the noise floor. Broadcast from inside your house, and no, that won't.
:) )
You can't give wireless things priority, unfortunately. Wireless is wireless, and the only way to make certain things a priority is to use a different frequency. The problem with spread spectrum is that if you're allowed to broadcast it (the cell tower thing I was talking about) then you futz EVERYONE's frequencies, and it really sucks.
This only applies to ultra spread spectrum, in any case - the stuff that's spread over many GHz of frequency space. Ugh.
Be careful - the raising of the noise floor idea is real, and it will suck. But you are right that for personal things, it's fine - even an ad-hoc wireless over an entire city would be fine, because probably the connections between each "house" would be weak, but inside the house they'd be fine.
The worry is for commercial services, and people broadcasting (that is, intention omnidirectional broadcasting) - that will raise the noise floor.
If we set up an ad-hoc wireless network across a city, that's cool. If everyone decides to broadcast their own spread-spectrum 'SSFM' radio station, that would suck.
(do I get kudos for using 'suck' a lot?
spread spectrum is noisy, tears up vital communications necessary for storm chasing, wipes out or interferes with repeater operations, and is a general nuisance to the Amatuer radio community. We provide many disaster relief services, not to mention the tornado and heavy storm tracking to help the weathermen confirm or deny potential problems shown on doppler and other radar systems. The ARRL and several other ham friendly organizations have been fighting the spread spectrum lobbyers as well as the little leo (low earth orbit) sattelites that infringe on our allocated spectrum. and..... lets not even get started on lowjack.......... Seriously, this is a budding problem that needs to be fixed!!!
I think the #1 thing the Electrical Engineers out there are missing is the impact of data compression algorithms. I'll grant them for now that its less efficient (how about some numbers as to how inefficient it is), but with proper compression/decompression algorithms, the same signals today should be ten times smaller, or, the same frequency can broadcast 10 stations more than it used to. That opens up a lot of space if the "property rights" aspects of transmission were shattered. If a concept like spread is used which fundamentally is less efficient but destroys the monopolies is implemented, I think data compression can bypass any inefficiencies.
Hey, I'm just your average shit and piss factory.
Yes, I would wonder that, if there were any truth to it. My Motorola CDMA Vader is just as small as the GSM Vader. And I have an 802.11b card (Symbol's CF Wi-Fi) that's smaller than any GSM phone. Don't overgeneralize.
When it comes down to it, Spread Spectrum is nothing more than a spectrum allocation algorithm that depends on the orthogonality of the chipping sequences. This orthogonality is further degraded by Rayleigh fading (aka multipathing), which is why ACPR or diversity reception is essential to CDMA. The primary benefit, however, is that that as an allocation scheme, spread spectrum is time based, and can take advantage of the bursty nature of most communications, be they human-to-human or machine-machine. And that's why time domain approaches are more efficient.
...-.-