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Australian Researchers Push Near-Broadband IP Over VHF
Curmudgeon Rick writes "A research group at the Australian National University is getting symmetrical 250K bps at 20km, using "empty" 7MHz-wide broadcast TV allocations in the 45MHz band. Story here, project homepage here. Aim is to put some bandwidth out beyond the reach of the wires, where users are few and far between."
i allways thought broadband was at least 10mbit, this is 'only' as fast as 4 isdn lines, sure better than dialup but nowhere near broadband..
Isn't "nearbroadband" almost the same concept as being "almost pregnant"?
This could be a nice alternative for those of us who still aren't able to get broadband (No DSL where I am and Rogers Cable never bothered to run cable to the last three houses. Guess where I am! GRR), without all the potential problems with broadband over power lines (signal leakage, interfering with ham radio).
Sorry, but speaking from purely a capitalist's point of view, the keyword here is few. As cool as the technology is, it'll never take off.
IWARS.
People, in general, disappoint me. Politicians even more so.
only problem is in the US these frequencies are not for broadcasting TV. 7Mhz is for Amateur radio frequencies. US Radio Frequency Allocations
30% Troll, 50% Underrated, 10% Interesting
Score:5, Troll
But the term "broadband" has come to mean "fast" in the common language. Thank the media for that.
In the olden days, the highest speed things tended to be broadband, so the meaning just got twisted.
I'd say, considering speeds and waht is noramlly known as broadband in the US... 250kbps qualifies as "near broadband"... people usually think 1mbps is broadband.
As a frequency this low will generally pass through buildings and obstructions much more effectively, it's probably a more likely candidate for inner-city wireless broadband than 802.11 -- on a commercial level.
If some ISP can obtain the correct licenses and find an existing 802.11 chipset with firmware-programmable frequency, they'd be the winners of all time.
I rather suspect that anyone attempting to use the proposed Aussie gear in the US would be caught and flayed alive in very short order.
Do a little research and you'll find out who the incumbent users are in that part of the spectrum are, and you'll see why...
(HINT: Many of them are public employees at various levels of government, and many others are taxpayers, either individually, or corporate)
The article is distinctly light on technical details. It might be full duplex, ie 250Kbps in both directions at the same time, even that is a poor data rate to bandwith ratio.
The quote from Dr Borg says they are not channelising though that dosn't rule out the 250Kbps figure being a timeslice allocated to a paticular station.
I'd like to know what modulation scheme they are using for this. I suspect they are compensating for a low signal to noise ratio at the receiver by using more bandwidth. Shannon's law (if I'v worked it out correctly) says that you need a minimum of -16dB signal to noise ratio to send 250Kbps over a 7MHz wide channel.
That gives it plenty of margin to cope with high path loss and in channel noise.
40Km is a good distance with 20watts at 45MHz. There will be a little bit of groundwave propagation past the horizon but not much. They will need to get the antenna's pretty high up or operate hilltop to hilltop.
Any aussies here know what would be using channels 0 and 1? Did Australia follow the US when it reallocated the frequencies back in the sixties? I can't even remember what channel 1 got reused for here in the states. I think it was business band radio like for taxicabs and such.
Liberals call everyone Nazis yet they are the closest thing to it.
If they were using direct-sequence spread spectrum, they could deal with multipath, too. Just don't be on the frequency when the echo arrives.
Bruce
Bruce Perens.
You would get more bandwidth as well.
AU has few people so they have more unused spectrum to play with.
I would think a higher frequency and better enginering would yield better results.
At around 45 Mhz the antennas are still quite large though the signal does tend to travel well over hilly terain in this frequency range and it can propigate via the E layer at the right time of year as well.
Well at least it's not in the middle of the Ham bands for once (being a Ham myself.)
If you don't like what I write don't be a CS and mod it down. Refute it.
Yea I can't spell. So what is your point?
Bruce
Bruce Perens.
Many posters seem to assume they're using all 7 MHz for a single carrier, or maybe pair of carriers. I did too, at first. But maybe not.
'Dumb modulation' would be what, BPSK? They could just as easily design around an off the shelf spread spectrum chipset and reap the benefits.
Grad students I know like to try out new things, not reinvent the wheel. That's boring. I'll give 'em the benefit of the doubt.
This VHF solution looks interesting, and in most cases could be a good idea, but some of these kids are 2-3 days 4WD travel from Pt Augusta. I shudder to think how far they are from the exchanges. It might be a silver bullet for the eastern states however with the denser population.