On 8/04/2023 12:10 am, David Lang wrote:
I will note that in the Starlink plans, there are plans
to put a layer of satellites at a sigificantly lower altitude.
I should add to this that this would seem like a good strategy, except
of course that this comes with its own set of challenges. Earth
observation satellites in particular are abundant in lower orbits - if
you have a camera on board, you want to be as close to your subject as
you can. So there isn't quite as much space down there as there is
further up.
Residual atmospheric drag at lower altitudes is also higher, which means
you either need to take more fuel to compensate (=heavier satellite &
fewer sats per launch) or you need to replace the satellites more often.
You also need more satellites for global coverage in a shell like this.
Also, as you mostly look at satellites sideways when you're a ground
station, the path length and therefore the path loss isn't necessarily
all that much lower - going from 550 km to 275 km gives you an extra 6
dB of gain if the satellite is straight overhead, but that advantage
shrinks as you move away from zenith.
By launching 10x as many satellites, and each one being able to handle
10x the
data, they _may_ get to 100x, but that is really going to be pushing
it. (note
that this is for ~10x the number of satellites lauched by everyone
other than
SpaceX since Sputnik)
Having seen figures of ~45k sats bandied around for some proposed
mega-constellations, the 10x number of satellites might just work out.
Whether we'll get to 10x the capacity per satellite is another question
altogether given spectral constraints. With ISLs, one could in principle
free up part of the gateway traffic spectrum by putting gateways in
areas that are devoid of other users, but quite how practical that is
given that remote areas are where LEOs will be needed most is a good
question.
One option that could push things a little further in conjunction with
LEOs would be HAPSÂ - high altitude platform systems, essentially
solar-powered UAVs that act as stratospheric cell towers with tours of
duty measured in weeks or months. These could use lasers as backhaul to
LEO networks, yet project comparatively narrow phased array beams to
users on the ground. A HAPS flying at 30 km overhead has a path loss
that's around 25 dB below that of a LEO sat at 550 km, and a clear
optical path to the satellites above. Technology isn't quite there yet -
essentially, we're at the point where solar cells have become performant
enough in conjunction with batteries that have become light enough to
allow sustainable cyclic recharging of a UAV's flight systems. But there
are still issues to be addressed around the excess power required to
operate a cell site in the sky and or course all the regulatory and
safety aspects associated with operating things that don't burn up when
they come down.
If you can get fiber, it's always going to be better than a wireless
option, DSL
is threatened by Starlink in many suburbs, cablemodems depend so much
on the ISP
it's hard to say
This is an interesting comment. Completely agree on the fibre aspect.
DSL I think is threatened more by fibre than Starlink in most places
(except the US perhaps), which has basically displaced most DSL
connections where it became available. We were on DSL here till 2017,
and as fibre was on the horizon for a while, the company that runs the
cable network here on behalf of the telcos stopped investing in new
DSLAM modules, instead preferring to switch customers with problematic
ones to modules that had become available as a result of customers
migrating to fibre. We found ourselves with a weird problem literally
overnight one day - intermittent disconnects lasting a minute or two.
These persisted through a change of DSL router, and logging these for a
few days showed a clear diurnal peak time pattern - so it was obvious we
were dealing with DSLAM-side crosstalk issues here. I asked to be
switched to a different DSLAM. This was an odyssee of support calls
given that you cannot call the lines folk directly - you must call your
retail ISP, who pays someone in India a few rupees to tell you to reboot
your router to make the problem go away. By the time I'd educated their
3rd tier support about what crosstalk was, I'd literally spent many many
hours on the phone to India. Eventually, they switched me over to a new
DSLAM and the problem went away for a few months, just to return as they
kept rewiring more legacy customers.
For those who still have DSL now, VDSL plans start at less than half of
what Starlink charges, with potentially comparable data rates, so not
everyone will want to switch.
Where I see uptake of Starlink in urban areas here is by (a) geeks and
(b) folk who want a (secondary) connection that is independent of local
telcos that run inane call centres in India. The lines company that did
/ does most of the fibre install here was a bit overwhelmed at the time,
so brought crews in from all over the place, as far afield as Zimbabwe.
Installation standards for fibre required them to bury 30 cm (12") deep
and dig under garden walls and hedges, however the crews got paid per
install, and a lot of the time, the standards were interpreted rather
liberally. Our crew arrived anticipating a two hour install and left
after eight hour and more "no-you're-not-going-to-do-it-like-that's"
than I care to count. A colleague of mine observed them laying through
his garden my just brushing the leaves aside. Around Auckland suburbia,
there are countless examples of fibre conduit running over posh volcanic
rock garden walls, through hedges, or along the top of rickety fences.
Cable TV and cable modems are of course pretty much unheard of here -
are there any cable modems / ISPs that do more than a few dozen Mb/s down?
David Lang
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Dr. Ulrich Speidel
School of Computer Science
Room 303S.594 (City Campus)
The University of Auckland
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http://www.cs.auckland.ac.nz/~ulrich/
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