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

dan dandenson at gmail.com
Tue Sep 26 19:05:51 EDT 2023

I'd like to question those numbers as stated by Tarana.

Firstly, no provider can possibly get 100% utilization based on average
use.  If average use is 10M and you have 2200Mbps on an AP, you can only
possibly serve 220 users that have 10Mbps plans.   If you have 100Mbps
plans you cannot have 220 users though as there has to be a substantial
reserve to accommodate their bursty traffic up to plan speed.  From our
networks, I would say this is approximately 1 maximum plan speed reserved
every 25 subscribers. I am of course just picking on a single AP, Tarana
has pitched a 4 APs per tower all using the same frequency (which is a
really nice trick) aka 'reuse of 1' so you can multiple any numbers I say
here by 4 to accommodate a full tower and you could potentially double that
and have 8 Tarana APs on a tower and then triple that when 6Ghz is
available and so on.

So 100 subscribers with 100M plans needs a ~400Mbps reserve.  This is well
supported in our statistics and lots of operators will land at a somewhat
similar number when looking at their oversells.
Of Tarana's 2200M stated speeds (which are more like 1400 per operators
I've talked to but I digress...) 400Mbps per 100 subs needs to be scraped
off the top and you need 1000M for average use, so that's fine at 1400M
needed to 2200M claimed (but again, many operators will say 1400M available
so..... about a 100x100M subscribers on this math).  however, 200 subs is
2Gbps use but needs an 800Mbps reserve so that's well oversold and the AP
will certainly see congestion during peak hours.  2800M needed on 2200M
*or* 2800M needed on 1400M...  Likely nightly congestion that could be 50%
of sold capacity.

Now, in support of Tarana's claims.  LEO satellites have a much more
limited geometry to work with, with a service cone of not more than about
15% of the satellites' view being of earth, the rest being of space....
which. means the antenna has to handle far more in far less.  Terrestrial
towers however have up to 360 degrees and up to about 50 degrees in
elevation, only blocked by obstructions and tarana's tech overcomes a good
part of that.  At the borders of that service area, build another tower.
LEO can try to put more satellites up, but these satellites are
broadcasting down and even with really advanced beamforming each one
creates more noise at the ground stations.  They also need to have at least
about 20 degrees separation for the ground stations to effectively utilize
beamforming and nulling to avoid the noise.   ie, it's not so simple to
just add more LEO birds and get linear results, however it is relatively
easy to add more towers and get a linear increase in capacity because
client radios tend to be facing away from all towers except the one they
are aimed at.

There are definitely use cases for both techs, but if we're talking about
capacity in any given area with enough population to support terrestrial
towers, there really is no competition, terrestrial can out perform LEO by
an order of magnitude because geometry says so.    however, LEO gear like
starlink is a godsend for people that are outside of that footprint.

I can rant all day about the inherent limitations to LEO based purely on
physics as well as the absolute requirement for dedicated spectrum that is
much better handled with terrestrial towers but I'll save you all's eyes.

On Tue, Sep 26, 2023 at 1:00 PM David Lang via LibreQoS <
libreqos at lists.bufferbloat.net> 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.
> 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
> _______________________________________________
> LibreQoS mailing list
> LibreQoS at lists.bufferbloat.net
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