Re: [Starlink] SpaceX/Starlink says it's ready for a fall satellite-to-cell service with T-Mobile

[Mike Puchol <mike@starlink.sx>]

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The doppler shift will change as the satellite transitions overhead, this is very clear if you look at a spectrum capture of the narroband beacons with a static LNB, and can be corrected by the user terminal, as it is expecting this shift and has software written specifically to deal with it.

In the case of e.g. LTE, a UE is not designed to cater for a changing doppler shift, so this is compensated by the satellite. In a theoretical MIMO configuration where multipath is achieved by using beams from multiple satellites towards a UE’s location, the signals such as P-SS and S-SS from each satellite would arrive at the UE at different times, frequencies, and power levels.

Here is an interesting paper that discusses the topic: https://arxiv.org/pdf/1706.06013

Best,

Mike
On Jun 4, 2024 at 21:47 -0700, Sebastian Moeller <moeller0@gmx.de>, wrote:
> Curious, is that doppler correction applied individually per dishy, or per cell? If the latter do cells extend ahead or behind the satellite's projection onto the globe, or is there one or more beams ahead an another one or more behind?
>
>
> > On 5 June 2024 06:16:02 CEST, Mike Puchol via Starlink <starlink@lists.bufferbloat.net> wrote:
> > > Yes, they correct doppler in a single stream - what I was alluding to is the MIMO advantage of terrestrial networks which cannot be easily replicated from multiple satellites, as the UE cannot correct multiple doppler shifts and timing advances unless it implements an NTN-specific approach.
> > >
> > > Best,
> > >
> > > Mike
> > > On Jun 4, 2024 at 20:17 -0700, David Lang <david@lang.hm>, wrote:
> > > > Mike Puchol wrote:
> > > >
> > > > > Something else that's much harder to implement is MIMO, as you don't get path
> > > > > diversity from a satellite. AST claims they will do this by using more than
> > > > > one satellite, however they haven't answered basic questions such as how will
> > > > > the UE compensate the huge differences in doppler shift on top of the multiple
> > > > > paths.
> > > >
> > > > for the starlink version, the satellite adjusts it's transmit/receive
> > > > frequencies to correct for the doppler shift so that the phones don't need to.
> > > >
> > > > David Lang
> > > >
> --
> Sent from my Android device with K-9 Mail. Please excuse my brevity.

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