Le 26/09/2023 à 23:16, Ulrich Speidel via Starlink a écrit :
On 27/09/2023 8:00 am, David Lang via Starlink wrote:
On Tue, 26 Sep 2023, Jim Forster wrote:
> This is all true (as much as I understand), Worth noting as well,
is that with
> LEOs if one satellite is maxed out serving a cell, then getting a
second
> satellite to help with that cell mean adding *lots* more
satellites. If
> adjacent cells had very different loads then I guess nearby unloaeded
> satellites could help out their busy neighbors. But areas with busy
cells
> close together would mean doubling the number of satellites and
therefore
> platform Capex. Whereas terrestrial towers can be densified in busy
areas.
In 2021 when SpaceX had launched 1800 satellites they said that once
all of them
reached operational altitude they would be able to provide global
coverage.
They now have >4k satellites in operation and (if fully approved) are
aiming at
~10x that number eventually. That leaves a lot of additional
satellites to
provide additional coverage for busy cells or smaller cells.
There's a minor issue that I'm not convinced people take into account.
Simply putting more satellites in orbit doesn't necessarily create
more system capacity - it also takes spectrum to accommodate the up-
and downlink capacity.
I agree, spectrum management is an important aspect in wireless
deployments. But both on sat and ground wireless.
Ground wireless deployments like cellular have the potential of finer
coverage management - it's not simply heaxagonal cells, but more
arbitrary shapes, planned according to visibility and 3D models. (when
done right, because there are also numerous ground cellular deployments,
including new ones, done very wrong with respect to coverage).
The ground wireless and wired deployments have other drawbacks such as
simply too many cables managed by too many people, who simply lost track
of what is where. That situation is only growing alarmly. It leads to
service interruption and bad quality of Internet to subscribers. With
sat LEO Internet such situation (not known cables) does not really
happen - the sat trajectories and orbits are much more planned.
What happens badly with LEO Internet deployments is the new debris added
to the existing large debris. The debris situation is so bad that the
risks of fall out of the sky and injure people or damage property is
considered seriously. There are sites continuously watching and
forecasting the next debris fall. If this situation amplifies, it might
become a factor of societal acceptance.
Alex
And therein lies a bit of a challenge. In terrestrial cellularised
communication, one can leverage proximity between base station and UE
to reduce power emission to a point where neither can be heard too far
away. This allows re-use of the same part of the spectrum a bit
further down the road. But that only works because we can build base
stations within a few hundred metres of where the users are. The
moment we need to project capacity from kilometres away, we're no
longer economical with our spectrum resource. At that point, we're
leveraging low user density.
When cellular networks start out, the base stations tend to be on top
of high vantage points: towers, high buildings, hills. As a network
gains customers, the base stations migrate down the slopes - the hills
now serve as welcome obstacles to isolate the base stations in the
valleys from each other spectrum-wise. Your cells shrink in size and
your transmissions drop in power.
The problem with a LEO system such as Starlink is that migrating down
from orbit is not an option. You have to project your capacity from
many hundreds of km away. You can to an extent use beamforming etc. to
direct your transmissions at targets on the ground, but the side lobes
from your phased arrays pretty much render your transmit frequency
unusable for any other satellite for hundreds of miles around.
Going to E band - fine, but even that is a limited resource, and it
has its other issues, too.
I agree terrestrial towers can be densified more easily in a specific
area.
I'm saying that the crossover point where the density favors
terrestrial towers
is significantly denser than the original author was stating. (and as
more sats
are launched, will move further)
There's also the fact that satellite densification covers all areas,
where
terrestrial tower densification only covers that area. So around the
already
dense areas, you will have tower densification happening, pushing out,
leveraging the nearby wired infrastructure. But you may see a different
situation in areas where small communities are growing and you have
to setup the
tower and wired infrastructure from scratch.
scenario:
a village that is a 30 min drive from the next community and doesn't
have much fiber run to it. As it grows, you can't just put in towers
without
also running tens of miles of fiber to the area, so densification of
towers in
the area is significantly harder than seeing the suburbs of a large
city grow
where fiber is just a couple miles away.
David Lang
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Dr. Ulrich Speidel
School of Computer Science
Room 303S.594 (City Campus)
The University of Auckland
[email protected]
http://www.cs.auckland.ac.nz/~ulrich/
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