Re: [Starlink] Main hurdles against the Integration of Satellites and Terrestial Networks

[Ulrich Speidel <u.speidel@auckland.ac.nz>]

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On 15/09/2023 11:29 pm, Alexandre Petrescu via Starlink wrote:
>
> I must say that I dont know whether the original 'DISHY' is simply a
> dish antenna with an analog amplifier and maybe some mechanical motor
> steering, or whether DISHY includes a computer to execute some protocol,
> some algorithm.

It's a phased array, not a dish, even if it looks like one. It consists 
of 100's of fingernail-sized antenna elements that:

  * during transmissions, have an individual phase delay added to the
    signal transmitted from that element, in order to permit
    transmission of the combined signal from all elements into a
    particular direction.
  * during reception, have an individual phase delay added to the signal
    collected by that element, before the signals are added to obtain
    the combined received signal. This allows reception from a
    particular direction.

Dishy's main direction of transmission / reception is therefore not its 
surface normal - this simply points to the area of the sky where Dishy 
expects to see most satellites (a function of geographical latitude and 
constellation design - essentially straight up in the tropics, and 
elsewhere in the direction of the 53rd parallel, which corresponds to 
the predominant orbital inclination in the Starlink fleet). The actual 
tracking is then done with the phased array without mechanical movement 
by Dishy.

 From what I've seen, Dishy seems to consume more power on receive than 
on transmit - that's if you actually download stuff. This is somewhat 
counter-intuitive if you're used to putting link budgets together. But 
I'd attribute that to a higher degree of digital signal processing 
required on the receive and demodulation path.

-- 

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Dr. Ulrich Speidel

School of Computer Science

Room 303S.594 (City Campus)

The University of Auckland
u.speidel@auckland.ac.nz  
http://www.cs.auckland.ac.nz/~ulrich/
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