Don't forget that these are LEO. I don't know for certain, but I
get the impression that each group of 60 satellites represents a
ring of sorts. That would put about 6° of separation between each
of the sats in one ring. There will also be overlapping rings at
some point.
In watching a few of the "trains" going by, it looks like each satellite goes from horizon to horizon in a maximum of roughly 6 minutes. How much time you might spend on a single satellite probably can't be more than that. So a lot of hopping is going to be going on. I also imagine that once enough rings are filled in, there will be multiple satellites to choose from at any given moment.
bp
<part15sbs{at}gmail{dot}com>
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> 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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bp
<part15sbs{at}gmail{dot}com>
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