The FCC allowed them 2Ghz of bandwidth for the satellite to user
terminal. 20Gbps must assume 10 bits/hz. Or maybe they mean a
different sense of "capacity". The journalistic sources are never
precise about these things.
I've been assuming that just like any other wireless you can't put the
same channel into the exact same location at the same time, or else they
would interfere. So they might simplify and say "20 Gbps per
satellite", but I think it's really going to be "20Gbps for a given
geographic area". I don't know how big that area will be, but the
smaller the satellite is, the smaller the antenna has to be, and then of
course the wider the beam is. I imagine each satellite won't use the
full 2ghz, but maybe dozens of satellites over a certain area will each
use their own non-interfering chunk.
....I'll freely admit that I'm filling in blanks left by the articles
I've seen. Maybe there are additional details to explain how they're
solving these problems, but I suspect the 20Gb per satellite is not
going to be meaningful. It'll be 20Gb total for a region of some size.
On 7/15/2020 1:32 PM, Colin Stanners wrote:
Doing some math:
40K subscribers on 60 satellites is 666 subs/satellite if equally
loaded. But load is far from equal, the planet surface is 70% water. I
don't know how much the "standard" orbit is over water but let's say
50% as it's further from the poles. Say that at any point in time,
around half the satellites will be barely useful (except for cruise
ships, and overseas aircraft service) due to being over water and
ground obstructions.
So a more accurate number is 1300 subs/well-positioned satellite,
assuming for simplicity that subs are equally physically spread out.
The numbers that I saw state that every satellite has 20Gbps capacity,
let's assume that that is downlink subscriber capacity at maximum
modulation, and that the backhaul to the ground station is fully
available to that satellite and also 20Gbps at max modulation. 20Gbps
/ 1300 subs is 15mbit per sub, assuming that everyone's using it
simultaneously.
But there are the issues with wireless in general, added to those
about customer self-installs (shudder), and satellite service: mainly
subs having trees or obstructions in the way, blocking or reducing LoS
to at least part of the sky where their hand-off satellite should be,
and rain. I'd say that altogether that a more realistic number with
those is 8-12mbit per user.
Being generous, 12Mbit average per sub: not bad these days,
considering the traffic patterns at peak time (1/3rd subscribers using
Netflix / D+ / etc with 1-3 streams at HD or 4K) I'd assume that from
that they could sell mostly 30-70mbit download speed plans without too
much consternation. But as traffic keeps increasing, over time they
may run out of capacity for the higher plans and decide to reduce.
On Wed, Jul 15, 2020 at 11:58 AM Bill Prince <part15...@gmail.com
<mailto:part15...@gmail.com>> wrote:
There are some details in this story that were new to me. One of the
ones that popped up was that each group of 60 Starlink satellites is
expected to support ~~ 40,000 subscribers.
That puts the 800 satellite "moderate service level" at supporting
about
half a million subscribers (~~ 533,000).
In order to support a million subscribers, they will need about 1500
satellites.
https://www.tesmanian.com/blogs/tesmanian-blog/starlink-router-fcc?_pos=19&_sid=a6c7fff07&_ss=r
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