[Starlink] Comprehensive Measurement Study on Starlink Performance Published

Tue Feb 27 09:02:08 EST 2024

Hi,

Will quickly jump in for one of the points discussed here.

but as I understand the reverse-engineering of the starlink system, a given cell 
is currently only serviced by one satellite at a time.
Are we sure here? One (classic) Dishy is served by one satellite at a time, but a cell (which can contain multiple DIshys) almost has to be serviced by multiple sats to get around obstruction issues (Starlink is now quite tolerant of these. Try to put it in a tight spot where it can't see the northern sky at your place in LA and tell me whether it still connects. If it does, then your cell gets served by multiple sats).

A cell is definitely served by more than one sats. In the paper I shared, we did exactly this experiment where we shielded our dish in Edinburgh from the south side so it doesnt receive connectivity from dense 53 deg orbit. The dishy received connection as long as there was a sat in 70 and 97.6 deg orbit in LoS (see fig 4). From our calculations, if your location is covered by all orbital shells of Starlink, you might receive connectivity from 15-20 sats in LoS at any given time.  

Thanks and Regards

Nitinder Mohan
Technical University Munich (TUM)
https://www.nitindermohan.com/

From: Ulrich Speidel via Starlink <starlink at lists.bufferbloat.net>
Reply: Ulrich Speidel <u.speidel at auckland.ac.nz>
Date: 27. February 2024 at 11:16:45
To: David Lang <david at lang.hm>
Cc: starlink at lists.bufferbloat.net <starlink at lists.bufferbloat.net>
Subject:  Re: [Starlink] Comprehensive Measurement Study on Starlink Performance Published

On 27/02/2024 7:21 pm, David Lang wrote:
...snip
> The point though is that these sparsely populated areas aren't where the  
> scalability issue arises. Capacity needs to be where the demand for it is.

I only partially agree with you here. Yes, capacity that isn't needed doesn't  
matter, but I think that the capacity where there aren't other options matters  
more than in the more densly populated areas where there are other options (and  
I say this as a starlink user living in the Los Angeles area, a fairly densely  
populated area) I use Starlink as a backup now, but I do periodically test it  
and verify that it is acceptable for work + other uses.
The pinchpoint thus far seems to have been the suburban and lifestyle block belts - basically where fibre doesn't reach for whatever reason, but where people with the wealth to afford Starlink (or fibre if it were offered) live. My bog standard example here in NZ are your IT project manager who wants to live on a lifestyle block out bush. They're dime a dozen here and Starlink serves them now even when they couldn't previously get fibre.
>>> 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 get fibre, you should get fibre (with starlink as a possible  
>> backup). SpaceX has said many times that Starlink is never going to be  
>> competitive to fibre
>>  
>> if you can get fibre, you aren't under-connected.
> Tick. But 2 billion plus can't, or at least not yet. The question is how many  
> of them might Starlink & Co be able to assist in due course?

what information do you have about the distribution of these 2B under-connected?
My particular "pet case" are Pacific Islanders on islands with populations too small / poor to afford a submarine fibre connection. These are a somewhat interesting case in that they are just a couple of million all up I guess, with numbers shrinking as fibre does get laid. Essentially, anyone with 10k plus population and under 1000 km (~600 miles) to the next cable access point is now a member of the club - having a rich nation or large diaspora backing you helps, but beyond that it's distance, GDP and politics that govern the game. Starlink can (and does now) serve most of the remaining islands, however what makes life interesting here is that these islands are often quite densely populated, which with growth in Starlink endpoints makes for reduced capacity per user. Kiribati for example currently sees around 10 Starlink kits arriving on every flight into Tarawa in the western part of the country (3 flights a week). I'm sure some more arrive by boat every few weeks - air freight is expensive (around US$400 per unit). Some of these will no doubt go to the outer islands, but Starlink is now having a visible presence on roofs there (my PhD student was up there and installed one for his family as well as two as part of our project). There is no official service yet but regional roaming works well (while the power is on, which it hasn't always been lately).

(and as someone who just a couple years ago was on a 8m down/1m up connection,  
what is the definition of 'under-connected'?,
That's under-connected in my book.

but as I understand the reverse-engineering of the starlink system, a given cell  
is currently only serviced by one satellite at a time.
Are we sure here? One (classic) Dishy is served by one satellite at a time, but a cell (which can contain multiple DIshys) almost has to be serviced by multiple sats to get around obstruction issues (Starlink is now quite tolerant of these. Try to put it in a tight spot where it can't see the northern sky at your place in LA and tell me whether it still connects. If it does, then your cell gets served by multiple sats).

>>>  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.
>>  
>> the cell service is not intended to compete with the Dishy, just be an  
>> emergancy contact capability
>
> Here's how one of the local partner organisation here spins it. Much more  
> than just an emergency contact capability:
>
> https://one.nz/why-choose-us/spacex/
>
> (Judge for yourself whether this instils the impression that you're going to  
> get 5G level service off this. You really need to read the small print!)

yeah, that does seem to imply more than it can offer. Elon has been pretty vocal  
that each cell is something like 70 miles in diameter, and the available  
bandwidth needs to be shared across all users. Text messages should always work,  
voice will probably work, and as the system gets built out, data will happen,  
but will be slow due to the sharing.
Yep, that's what I'd expect also.

> It's not that easy. Adding satellites in the first instance is just adding  
> transmitters, and unless you have spectrum to accommodate these, then even if  
> the satellites' on-board bandwidth is higher, it doesn't translate into as  
> much extra capacity. Spectrum comes in terms of extra Hertz, and in terms of  
> spatial beam separation. The former is limited in that they don't make any  
> more of it, and the latter is a matter of antenna size and getting antenna  
> side lobes sufficiently far down. And we know that SpaceX are running close  
> to spectral capacity in some areas.

I am assuming that the fact that they have planned for 10x satellites (~45k  
satellites up from the ~5k they have now) means that they have a plan to be able  
to use that many efficiently. I have no inside knowlege, so I am speculating  
about this.
A lot of what is meant to go up there is meant to use higher bands, which means "more bandwidth" but with caveats relating to obstruction by atmospheric phenomena. So that wouldn't quite scale I guess.

There are also other reasons for why you'd want more birds: 

Path diversity on ISLs to avoid "busy center" issues
Having each satellite look after fewer users on the ground allows for more bandwidth per user overall due to spatial diversity.
Better illumination of the ground.
Higher capacity in equatorial areas (where GSO protection takes a good chunk out of what's directly overhead).
Redundancy.

> Assuming that the spatial distribution of the under-connected is somewhat  
> similar to Starlink's current customer base in terms of densities, we need  
> that factor of 1000.

I think there are a lot of early adopters for who Starlink is a luxury, not a  
lifeline.
I think we're well past that point here. Last year's cyclone was the best sales push Elon could have hoped for. You no longer get a discount here for living rurally like last year. But you can get deprioritised service.
I think the under-connected are going to be in more sparse areas than  
the early adopters. I have friends and family in rural areas, and awareness of  
Starlink is only slowly penetrating there.
The slow penetration of modernity into US rural areas seems to be a particularly American problem - it's not been an issue here or in the Pacific.

I'm seeing increased use for mobile applications here in the US, including in  
built-up areas.
Interesting.

> So which factor in terms of capacity growth should we expect of Starlink & Co  
> over today?

not enough information. I agree it's something to watch, I'm just more  
optomistic about it than you are.
OK, let's see how this pans out.

>>> 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.
>>  
>> True, although if you can setup a community gateway of some sort to share  
>> one satellite connection, you gain efficiency (less housekeeping overhead  
>> or unused upload timeslots), and have a place that you can implement  
>> caches.
>
> Indeed. Or if you provide a feed to a local ISP. But Starlink still focuses  
> on direct to site, as does every other LEO provider FAIK.

SpaceX is diversifying thier offerings, including boats, planes, and very  
high-performance community gateways.
The latter run under "business" here and the data rates they talk about aren't all that appealing given that this is what I see on a roaming subscription already. But who knows!

I'd love to see more tech folks supporting this sort of thing.

I would especially like to see us put together disaster kits that can take one  
uplink and spread it around. We've seen SpaceX being willing to donate dishy  
kits, but being able to spread the hotspot island out from direct wifi range of  
the dishy to be able to cover a larger area would be worth quite a bit (and  
don't forget the need for power for the system)
Yes - that's a lesson that's been learned here.

After last year's cyclone, a lot of local civil defence posts and marae here have acquired Starlink kits and generators (NB: marae are compound facilities operating as a focal point for indigenous Māori life. Most are capable of housing and feeding large groups of people at relatively short notice, and they are almost everywhere. Often used for conferences, retreats, weddings, funerals, public meetings, and not just by Māori).

One of the problems with disaster kits is their power use. Dishy uses between 40 and 100W when "idle" with a laptop connected via Ethernet, but uses noticeably more power (up to around 150 W on RX and slightly less on TX) when receiving significant data volumes, most likely due to the complex DSP needed to decode from the phased array.

Half that and you could power it off a car cigarette lighter socket with some ease. Would be interesting to hear how the latest generation Dishy stacks up there. Oleg - have you measured?

--
****************************************************************
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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