[Starlink] starlink at sea

[Sebastian Moeller]

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.
>>