[Starlink] starlink at sea

Thu Jul 14 11:28:23 EDT 2022

Hi Mike,

On 14 July 2022 16:56:21 CEST, Mike Puchol via Starlink <starlink at lists.bufferbloat.net> wrote:
>The handovers are clear from the RF traces, 

         Can you estimate how long a handover takes? And are these linked somehow to either the 4second or 15second intervals visible in starlink latency traces?

Regards
        Sebastian

but they won’t indicate per se what satellite is being used. I have a cunning plan for a rotating vertical metal plate which, given the right calculations, would block 10° of the FOV, which would allow inference of the satellite in use. There are also narrowband uplink signals that are likely used for channel sounding and basic signaling between terminal and satellite.
>
>The other interesting observation is that the power spike (~200W for 1-2 seconds) that happens at boot time, corresponds to a burst of these narrowband transmissions on various frequencies at once.
>
>Best,
>
>Mike
>On Jul 14, 2022, 15:33 +0200, Nitinder Mohan <mohan at in.tum.de>, wrote:
>> Hi Jared,
>>
>> Turns out that SpaceX has deprecated the API calls to get satelliteID and cellID over gRPC so that information is no longer available. See https://github.com/danopstech/starlink/issues/27
>>
>> Too bad since those would have been quite useful to understand performance trends.
>>
>> Thanks and Regards
>>
>> Nitinder Mohan
>> Technical University Munich (TUM)
>> https://www.nitindermohan.com/
>>
>> From: Nitinder Mohan <mohan at in.tum.de>
>> Reply: Nitinder Mohan <mohan at in.tum.de>
>> Date: 14. July 2022 at 15:05:42
>> To: Jared Mauch <jared at puck.nether.net>
>> Cc: Dave Taht via Starlink <starlink at lists.bufferbloat.net>, Mike Puchol <mike at starlink.sx>
>> Subject:  Re: [Starlink] starlink at sea
>>
>> > Hi Jared,
>> >
>> > Thanks much for the pointer. This seems promising!
>> >
>> > We have a stationary dish available locally so we can try pulling information at our end.
>> >
>> > Thanks and Regards
>> >
>> > Nitinder Mohan
>> > Technical University Munich (TUM)
>> > https://www.nitindermohan.com/
>> >
>> > From: Jared Mauch <jared at puck.nether.net>
>> > Reply: Jared Mauch <jared at puck.nether.net>
>> > Date: 14. July 2022 at 14:57:25
>> > To: Nitinder Mohan <mohan at in.tum.de>
>> > Cc: Mike Puchol <mike at starlink.sx>, Dave Taht via Starlink <starlink at lists.bufferbloat.net>
>> > Subject:  Re: [Starlink] starlink at sea
>> >
>> > > I haven’t poked hard, but it does seem you can get it:
>> > >
>> > > currentCellId current_cell_id
>> > >
>> > > Seem to be in the GRPC proto dump from the dish.
>> > >
>> > > https://github.com/sparky8512/starlink-grpc-tools/blob/main/extract_protoset.py
>> > >
>> > > This should pull it out, if you want from my (stationary) dish I bet I can run something to pull/dump the info.
>> > >
>> > > - jared
>> > >
>> > > > On Jul 14, 2022, at 8:49 AM, Nitinder Mohan via Starlink <starlink at lists.bufferbloat.net> wrote:
>> > > >
>> > > > Hi Mike,
>> > > >
>> > > > Do you happen to have a tool that can extract the current uplink channel of Starlink and (more importantly) which staellite it is connected to at any given time? I wanted to track the handovers in Starlink and try to find its impact on network performance but cannot seem to get those values.
>> > > >
>> > > > Thanks and Regards
>> > > >
>> > > > Nitinder Mohan
>> > > > Technical University Munich (TUM)
>> > > > https://www.nitindermohan.com/
>> > > >
>> > > > From: Sebastian Moeller via Starlink <starlink at lists.bufferbloat.net>
>> > > > Reply: Sebastian Moeller <moeller0 at gmx.de>
>> > > > Date: 14. July 2022 at 14:35:16
>> > > > To: Mike Puchol <mike at starlink.sx>
>> > > > Cc: Dave Taht via Starlink <starlink at lists.bufferbloat.net>
>> > > > Subject: Re: [Starlink] starlink at sea
>> > > >
>> > > >> Hi Mike.
>> > > >>
>> > > >> Thanks a lot. This is intersting.
>> > > >>
>> > > >> > On Jul 14, 2022, at 14:02, Mike Puchol <mike at starlink.sx> wrote:
>> > > >> >
>> > > >> > The uplink is an OFDM signal with 128 subcarriers, looking at the signal in the time domain reveals a frame length corresponding to 14% (from memory, 1,1 us frame vs 6.7 us pause). I have two terminals 1 meter apart and they can each achieve 30 Mbps at the same time over the same uplink channel. I would expect the satellite to assign a particular set of slots to a terminal.
>> > > >>
>> > > >> So assuming the 30 Mbps being gross rate and not measured goodput:
>> > > >>
>> > > >> 30Mbps -> 30 / (1.1/(6.7+1.1)) = 212.73 Mb/s while actively sending, and
>> > > >> 1000000µs/s / (6.7+1.1)µs = 128205.128205 slots/sec
>> > > >> (30 / (1.1/(6.7+1.1))) * 1000^2 / (1000000 / (6.7+1.1)) = 1659.27 bits/slot 1659.27/8 = 207.41 Bytes/slot
>> > > >>
>> > > >> with 128 subcarriers that would be approximately an average
>> > > >>
>> > > >> 1659.27/128 = 12.96 or ~ 13 bit/subcarrier
>> > > >>
>> > > >> if all carriers are loaded equally (which is unlikely, I expect some re-arrangement ot bits between subcarriers to account for different levels of noise and what not).
>> > > >>
>> > > >>
>> > > >> > If there are any OFDM blind analysis experts in the room, shout!
>> > > >>
>> > > >> Please do!
>> > > >> Regards
>> > > >> Sebastian
>> > > >>
>> > > >> >
>> > > >> > Best,
>> > > >> >
>> > > >> > Mike
>> > > >> > On Jul 14, 2022, 13:33 +0200, Sebastian Moeller <moeller0 at gmx.de>, wrote:
>> > > >> >> Hi Mike,
>> > > >> >>
>> > > >> >>> On Jul 14, 2022, at 13:15, Mike Puchol via Starlink <starlink at lists.bufferbloat.net> wrote:
>> > > >> >>>
>> > > >> >>> On the multiple terminals, I have verified that the duty cycle of a consumer terminal is 14%, thus, you could have 7 terminals on a single uplink channel with some guard time.
>> > > >> >>
>> > > >> >> Could you elaborate how that works.how the terminals will be interleaved in that situation?
>> > > >> >>
>> > > >> >> Regards
>> > > >> >> Sebastian
>> > > >> >>
>> > > >> >>
>> > > >> >>> I have seen 30 Mbps up, so you’d be able to push 210 Mbps in uplink, or a spectral efficiency of about 3.4 bps/Hz.
>> > > >> >>
>> > > >>
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