[Freedombox-discuss] Serval Mesh Extenders
gnu at toad.com
Fri Jul 12 00:13:15 UTC 2013
> The idea is that it uses the UHF packet radio to mesh over greater
> distances than is possible with Wi-Fi, the trade-off being lower bandwidth.
> In general, we find that the UHF packet radio has a range of about 10x that
> of Wi-Fi when deployed indoors with omni-directional antennae. This means
> it has a range of about a block in a suburban or urban setting compared
> with Wi-Fi's range of about one house or apartment.
> Extending the range in this way is a critical enabler for the adoption of
> mesh communications because it removes the need for skilled installation
> and lowers the required penetration rate from near 100% in a local area if
> using un-aimed Wi-Fi to below 1%:
My guess is that you are getting better range in the 915 MHz frequency
block because fewer people are using that block. Onmidirectional WiFi
used to reach a whole block or more in San Francisco, before everyone
had it (and aiming a dish at an omni would work all the way across the city).
I'm speaking as someone who ran a small wireless ISP using 1-megabit
WaveLan gear in the 1990s, and who ran a public WiFi access point from
my roof in the early 2000s, fed as part of SFLan from across the city
using a second WiFi dish. And who brought Internet to Burning Man and
fed it around the playa with WiFi on towers -- which worked over
*miles* until everybody started bringing wifi phones and wifi laptops.
And who tried using 802.11s-predecessor mesh on the One Laptop Per Child,
which stopped working once you put 30 of them into a classroom.
If you deploy a lot of these, they will stop giving you the advantage
that you designed them for. I would find it hard to recommend this
strategy for widespread deployment.
PS: You don't need to go into the 900 MHz band to get longer range and
lower bandwidth. You can also get better range on WiFi merely by lowering
its bandwidth, using the original 802.11'b' or 'g' protocols.
PPS: "Mesh doesn't scale over radio." is the 5-word summary of my
experience. Merely making mesh work over wired connections is still
a hard research problem that nobody has great solutions for.
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