[chbot] Long distance data link, advice from the guru's please

[Helmut Walle]

Hm, where do we start...? Maybe at "There's no free lunch in 
telecommunications."

Let's get some of the basics sorted first:

* Required average bandwidth > 4 GB / week; so that would be at least 53 
kbps flat tack. But probably they want quite a bit more; otherwise they
   would just be happy with the satellite link. To make matters worse, 
they probably want a momentarily much higher rate, so that they don't have
   to sit around waiting for uploading a few pictures. In any case, you 
should find out how much bandwidth they really want (or need) per week or
   month, and _also_ whether there are any momentary (as opposed to 
per-period) bandwidth expectations. The existing satellite link would
   probably be the very minimum in both regards.

* Masts - actually a couple of 90 m masts (one each for the two ends of 
the link) wouldn't even properly get you line of sight at 110 km 
distance. I think
   this is a modest requirement. But obviously it costs. If you want to 
get away without masts you basically have a few other options:
   * Use a wavelength that follows the curvature of the Earth. But the 
trouble with that is that you are looking at lower frequencies and bands 
that may be
     getting a bit narrow and crowded for hauling serious amounts of 
data. Nevertheless, discuss this with a digital radio amateur!
   * Use something cable-based - which probably won't fly for cost reasons.
   * Use a tropo-scatter link, where the troposphere essentially 
replaces your mast: you transmit from ground level, the signal bounces 
off the troposphere,
     and your also ground-level receiver just looks at the area of the 
troposphere targeted by the transmitter. This technology works fine for 
a distance of
    110 km, but it does require a fairly high transmit power and usually 
pretty large antennae. In other words, the two 90 m masts might just be less
    costly. I am also not sure whether there are any readily available 
integrated solutions available on the market. But if there are they will 
cost. And
    you definitely don't want to operate this kind of transmit power 
without a license! (Not that you should transmit at any lesser power 
level without a
    license either for that matter.)
   * Moon bounce is only available when the moon is above the horizon 
for both end points, and is also not practical for other reasons. But it 
must be
     listed for completeness.
   * Use the mail plane that comes by once a fortnight (or whatever the 
schedule is, I don't know) and ship a crate full of locally burnt DVDs 
via snail mail.
     This will quite easily beat the bandwidth of the satellite link by 
several orders of magnitude, however at the expense of incurring some 
latency for
     the users who arrived early in the cycle. Probably not what they 
want...

Ok, so where does that leave us? Well, as I said, no free lunch... but 
have all options using already existing infrastructure been looked at
thoroughly yet? There probably isn't anything wire-based at all there? 
Cellular networks? Ok, there's still the satellite service that they 
already have.
How about simply getting a second satellite modem to double the 
bandwidth? Would they even need a second modem? Or could they just buy more
bandwidth over the already existing link? Possibly not - but if they 
can't then the 2nd-modem solution would give them twice the bandwidth at 
twice the cost. The satellite service provider should know what can be 
done there, and how.

Hope this helps somehow.

Kind regards,

Helmut.

On 10/05/14 21:03, Jasper Mackenzie wrote:
> Good day fellow ROboticisers,
>  I have the privilage of flying off to visit my gf's family in Alaska 
> (you know, the cringing Meet The Family awkward silences...), and her 
> Dad runs a lodge for people to show off their enormous lenses and 
> fancy new gigapixel cameras and glut out on Bears and stuff etc.
>
> Anyway, he has bandwidth issues, all these fancy photographers want to 
> upload photos etc etc and he has one sattelite link limited to 4gb per 
> week. So I was thinking that maybe they could do a VHF (or similar) 
> link to the mainland which is 110km away across the sea. I have found 
> a russian company that had an interesting solution, but all seemed to 
> need towers ~90m tall which would be a massive hazard as small planes 
> are what these outlanders use to get around.
>
> Is there a solution? A data link with usable bandwidth for image 
> uploading, VoIP etc. that could work over 110km without a huge tower, 
> that I could get before june 1st? (Lets deal with licensing later 8)
>
> Cheers
>
> Jasper
>
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