On Wed, 27 Sep 2023, Ulrich Speidel via Starlink wrote:
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.
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.
yep, this is why when I'm setting up wifi for a conference, I put out lots of
APs, one the ground, under seats, etc so that the shielding provided by the
attendees reduces the range that each AP covers
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.
the fact that you have directional antennas on both ends helps mitigate this
quite a bit. with normal cell servce and wifi your end user stations are
omnidirectional, but with Starlink they are quite directional.
you are correct to note this as an issue to be aware of.
David Lang
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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