Re: [Starlink] musk: 28ms median latency on starlink

[David Lang <david@lang.hm>]

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If the ground stations were omnidirectional antennas, you would be correct, but 
since they are phased array directional antennas, they can steer the beam to 
receive one satellite even while a different one is transmitting on the same 
frequency to the same cell.

David Lang


On Mon, 3 Jun 2024, Ulrich Speidel via Starlink wrote:

> Date: Mon, 3 Jun 2024 22:40:24 +1200
> From: Ulrich Speidel via Starlink <starlink@lists.bufferbloat.net>
> Reply-To: Ulrich Speidel <u.speidel@auckland.ac.nz>
> To: starlink@lists.bufferbloat.net
> Subject: Re: [Starlink] musk: 28ms median latency on starlink
> 
> Getting the satellite density up will help, but it will only improve things 
> so far.
>
> The problem on user downlink in particular is that there's a limit on the 
> maximum spectral power flux density that arrives from the satellite in space 
> on the ground. If you point all (mutually compatible) user downlink beams 
> from a single satellite at a single cell, you all but reach that limit there. 
> In fact, where SpaceX want to use two beams on the same frequency but with 
> opposite polarisations to the same cell, they must reduce the transmit power 
> on each beam by 3 dB (50%) in order to stay within the limit. More satellites 
> would give you more beams, but you can't point them at cells that already 
> have a beam on the same frequency in use from another satellite (unless you 
> de-rate on the power front, I guess). That seriously limits what you can 
> receive in terms of total capacity within a single cell to what a single 
> satellite's mutually compatible beams can deliver, which appears to be about 
> 12 Gb/s on V1 and V1.5 birds, and 20 Gb/s on V2 (on Ku, if you add in Ka-band 
> and anticipate Dishys that can do Ka, then it's a lot more for Ka). In 
> practice, we know that a cell gets served by beams from different satellites, 
> but the overall constraint still applies - if you deploy beam X from sat A 
> and beam Y from sat B to the same cell, this makes the same contribution to 
> PFD as deploying both from the same satellite. Note that Starlink sats do 
> have multiple mutually incompatible beams that they can only point at 
> different cells, bringing Ku user downlink capacity up to 16 Gb/s on V1 and 
> 1.5, and 48 Gb/s on V2. But that only ups your chances of getting a larger 
> slice of those 12 or 20 Gb/s in your cell.
>
> Your best bet for continuing good service at the moment is literally to tell 
> your neighbours that Starlink is useless, so they don't sign up and you can 
> have your cake all to yourself ;-)
>
> On 3/06/2024 5:13 am, Dave Taht via Starlink wrote:
>> Via elon musk:
>> 
>> Starlink just achieved a new internal median latency record of 28ms 
>> yesterday! Great work by the engineering and operations teams.
>> 
>> - https://twitter.com/elonmusk/status/1797282250574184587
>> 
>> I of course, am very interested in y'all´s external measurements of how 
>> well starlink is doing. For me, it is fantastic - 30Mbit uploads nowadays, 
>> 0
>> latency on the upload (how?) 
>> https://www.waveform.com/tools/bufferbloat?test-id=2a1d139b-87cb-4ba4-a829-e2167801cffe
>> 
>> I also keep hoping that the rest of the ISP industry is now paying 
>> attention and deploying stuff like fq_codel and cake and libreqos, but, ah 
>> well - I will settle for starlink blowing past a lot of dsl and cable and 
>> finding ways to get their density up.
>> 
>> Anyone going to the Starship launch on the 6th?
>> 
>> 
>> 
>> -- 
>> https://www.youtube.com/watch?v=BVFWSyMp3xg&t=1098s 
>> <https://www.youtube.com/watch?v=BVFWSyMp3xg&t=1098s> Waves Podcast
>> Dave Täht CSO, LibreQos
>> 
>> _______________________________________________
>> Starlink mailing list
>> Starlink@lists.bufferbloat.net
>> https://lists.bufferbloat.net/listinfo/starlink
>
>

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