Re: [Starlink] starlink at sea

[Nitinder Mohan <mohan@in.tum.de>]

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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@lists.bufferbloat.net>
Reply: Sebastian Moeller <moeller0@gmx.de>
Date: 14. July 2022 at 14:35:16
To: Mike Puchol <mike@starlink.sx>
Cc: Dave Taht via Starlink <starlink@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@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@gmx.de>, wrote:
>> Hi Mike,
>>  
>>> On Jul 14, 2022, at 13:15, Mike Puchol via Starlink <starlink@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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