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If the transmitter is on a satellite in a circular orbit at Low Earth Orbit with a QPSK modulated waveform at 1 megabaud centered at 12 GHz downlinking to the receiver, which is stationary on the ground. How do we model the channel here?

I was thinking since we need to have a line of sight, Rician fading channel could be a good candidate, but my knowledge of satellite communication is very limited. Also, since the satellite is always moving, we can say that there is always carrier frequency offset caused by the Doppler shift. Am I missing something here? If so, please let me know.

Thanks a lot

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Rician fading is a good candidate since that models multipath with a strong direct path. However it is likely that the direct path is significantly large enough that a standard free-space path loss model is likely sufficient, and then add to that the implementation losses, antenna gain, atmospheric loss, receiver noise figure and modulation accuracy (EVM) to the overall channel loss. Yes there will be Doppler offset but that is not part of the channel model, but added to the budget for range of frequency error to be determined during acquisition. Even without the movement of the satellite you will have frequency offsets regardless inevitably since the transmitter and receiver clocks are not otherwise synchronized.

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  • $\begingroup$ Thanks a lot Dan. For a satellite in distance of 550 Km, and for a carrier frequency of 12 GHz, if I use the standard free-space path loss model, I would get 168 dB loss in power at the receiver side. I'm pretty new at this, and this number seems a bit high for the loss here. Is that correct? If so, how does the satellite solves this issue, since it seems it needs a lot of power to transmit. $\endgroup$
    – Jacob
    Dec 29, 2023 at 2:27
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    $\begingroup$ Yes that sounds right. The answer is high gain antennas (at both the tx and rx side), and power efficient waveforms (with low peak to avg ratio to be able to run the transmit amplifiers at higher transmit power) $\endgroup$ Dec 29, 2023 at 3:48
  • $\begingroup$ Thanks for the help. $\endgroup$
    – Jacob
    Dec 29, 2023 at 18:45

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