[Starlink] [LibreQoS] Starlink cell capacity (was; tarana strikes back)

[David Lang]

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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>
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