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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."
Mesh networking would be a better idea than all of this. More bandwidth, more parallelism, less power.
It doesn't sound as if they are really ready to talk about frequency coordination with other users. I hope they don't go about asking for spectrum for anything but experimentation this early in their project.
Bruce
Bruce Perens.
In Australia the ACCC defines BroadBand as 200kps and over.
Narrowband: less than 2Mbps (POTS, ISDN, etc)
Broadband: greater than or = 2Mbps.
Most DSL lines work at under 1Mbps (home users don't need more and it's damned expensive if telcos offer it at all), but in full flight, it can reach around 8Mbps, so it's technically broadband.
One man's *near* broadband is another man's 2B+D.
This might fly in Australia, but probably not in the US or other large nations. The radio spectrum is a limited resource and as such, a highly competitive one. Amateur radio operators (myself included) are constantly trying to defend our allocated bands here in the US against commercial entities who would like to have it for their own usage. I don't see a system that uses this much bandwidth being practical for US usage.
That's not entirely true.
In the land Down Under, Telstra is the dominant telco, and it's currently 51% government owned. The current Liberal Party (think: nice Republicans)-National Party (think: farmers) coalition government really wants to flog off the rest. The problem is that Telstra provides many services to the underpopulated areas (aka "the Bush", who are generally represented by the National Party half of the Coalition) that really don't make much economic sense but make a lot of political sense. Also, it's sort of halfway decent that the outback farmers get at least a phone service. Anyway, every man and his dog knows that if Telstra gets fully privatised, *bang* there goes any semblance of service to the bush, since it is just not econmical.
To that end, the government has brought in a Service Guarantee (including Universal Service Obligations) that says (amongst other things) Telstra must provide certain minimum standards to all subscribers, and if they don't they get smacked. The government hopes that after a few years we'll all see what a good corporate citizen Telstra is and give the Libs the OK to flog off the other 51% of Telstra.
Now, one big complaint from the bush is that they get bugger all access to broadband. Even getting net access at all can be tricky for them. Satellite (if available) is very expensive. This would almost certainly not improve under a toally privatised Telstra. However, if Telstra could provide near-broadband to the bush without having to string up hundreds of miles of cable, things would again be looking promising for the privatisation thing to be on the agenda again.
Speaking from a purely Australian voter/taxpayer POV, the keyphrase is the National Party might be the junior member of the coalition but they can wield a fair amount of power over the Libs when they want to.
.When they came for the communists, I said "He's next door. Take him away. Goddam commies."
Analogue television channels in Australia are 7MHz wide. The channels of interest are between 45 and 75MHz. BushLAN is not necessarily tied to using a particular block of spectrum, or an entire television channel. BushLAN subdivides available spectrum into 300kHz channels. As always, there is a tradeoff between transmitter power, communications range, and the data rate.
Using two 300kHz channels [for a symmetric full-duplex connection] low power, relatively short range links with a raw data rate of 115.2kbps have already been created.
As to propagation. VHF achieves beyond line of sight range whereas microwave links are limited to LOS. Long distance propagation is largely due to diffraction over hill tops. Atmospheric attenuation is much smaller at VHF (wavelength is roughly 6 metres) than it is at microwave frequencies (wavelength: ~10cm). This allows greater reliability during adverse weather conditions.