[Starlink] Comprehensive Measurement Study on Starlink Performance Published

Ulrich Speidel u.speidel at auckland.ac.nz
Mon Feb 26 19:16:37 EST 2024


On 27/02/2024 12:19 pm, David Lang wrote:
> On Tue, 27 Feb 2024, Ulrich Speidel via Starlink wrote:
>
>> My most serious concern about Starlink as a system remains the fact 
>> that it puts a pipe between the end user and the first network hop 
>> (the satellite) that is in principle very difficult to scale: There's 
>> only so much extra spectrum one can use, spatial diversity 
>> (beamforming) has limited potential, and unlike in cellular networks, 
>> you can't really shrink the cell size to accommodate more end users 
>> through frequency re-use as your cell size is determined to a good 
>> part by orbital altitude. That all but rules out the scaling effects 
>> that CDNs have brought to the rest of the Internet, which keep orders 
>> of magnitude worth of traffic off long distance cables. There simply 
>> isn't an obvious place in LEO topology to put a cache that'll produce 
>> a decent number of hits while being able to serve this content to end 
>> users through a large collective bandwidth.
>>
>> The interesting question for me is how much we can scale Starlink and 
>> its up-and-coming cousins from the few million users Starlink has 
>> now. To 100 million? To 200 million? Half a billion even?
>
> If you are in an area where the cell companies are investing in 
> smaller cells, then you are not in a Starlink target area. 

Hm. I'm in Auckland, which is where cell companies are investing in 
smaller cells, and Starlink did a leaflet drop here last year trying to 
get customers.

> There are large areas with poor or non-existant cell coverage.
>
> Outside the US, scaling of Starlink can happen just by providing 
> coverage to locations that don't yet have coverage with no additional 
> satellites.
But what's the population of these areas? Generally quite sparse. (Or 
politically disinclined to accept Starlink service)
>
> In terms of scaling existing areas, larger antennas can reduce cell 
> size, you can have more than one satellite cover a given cell, they 
> are looking at eventually having lower satellites, which again will 
> let them reduce the cell size.

Lower orbit = more drag = shorter lifetime, and the reduction in 
footprint isn't actually that significant. Larger antennas = fewer sats 
per launch = more expensive system.

If you put in fibre today, you know that by upgrading the endpoints over 
time, you can get orders of magnitude of extra bandwidth if needed. If 
you can reduce distance between satellite and ground station by a factor 
of 2, all else being equal, theoretically you'd also reduce footprint to 
a quarter, but that's assuming you don't need to worry about antenna 
sidelobes. But say we can, and then that gives us a factor of 4 in terms 
of capacity as long as our user density is the same. It also buys us an 
extra 6 dB in received signal power and hence an extra 2 bits per 
symbol. That's another factor of 4 at best if you go from 1 to 3 
bits/symbol. Larger antennas: Doubling antenna size gives you 3 dB in 
gain or an extra bit per symbol. So that turns into a game of 
diminishing margins pretty quickly, too. But now you want to serve 
cellphones on the ground which have smaller antennas by a factor of I'd 
say about 16:1 aperture-wise. So you need to make your antennas in space 
16 times larger just to maintain what you had with Dishy. That's a far 
cry from what is needed to get from two million or so customers to 
supply two billion unconnected or under-connected. For that, we need a 
factor of 1000.

And then you need to provision some to compete with extra capacity you 
wanted, and then some to cope with general growth in demand per client. 
And then you have to transmit that same viral cat video over and over 
again through the same pipe, too.

-- 

****************************************************************
Dr. Ulrich Speidel

School of Computer Science

Room 303S.594 (City Campus)

The University of Auckland
u.speidel at auckland.ac.nz
http://www.cs.auckland.ac.nz/~ulrich/
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