I am currently doing a project in the area of optical inter-satellite communication (GEO-LEO).

I am using a optical carrier of 281 THz, and the Doppler shift corresponding to it is ±7 GHz. I introduced this Doppler shift in the transmitted signal $S$ as an offset like

$$ S \cdot e^{j 2 \pi f_\mathrm{doppler}} $$

At the receiver, I am using a Costas Loop as a demodulator. I have to do Doppler shift compensation to recover the signal. Guess, I have to add an offset compensator in the local oscillator.

Can anybody help me in doing this?

  • $\begingroup$ You say "have introduced this doppler shift in the transmitted signal as an offset ...". I'm guessing that you are doing this in your model, in order to model the expected shift? Are you using a reference laser to measure the Doppler shift optically? What rate of Doppler shift change do you anticipate? A 14 GHz swing might be challenging to account for in the LO, particularly if the swing is fast. The following paper includes quite a few references that might provide information on a practical solution: spbu.ru/images/avtoref/Marat-cut.pdf $\endgroup$ – user2338215 Jul 1 '14 at 14:46
  • $\begingroup$ Thanks for the link. Yes, I am including the laser to measure the Doppler shift optically since it is coherent detection. The maximum Doppler shift rate is 10 Mhz/second. The only doubt I have is that whether I need to have a frequency offset compensator before the LO (which can be done very easily) or should I include it LO module (which is quite difficult I think). If it has to be done in the LO, then how? Thanks in advance. Sharma $\endgroup$ – Seetharama Jul 8 '14 at 17:02
  • $\begingroup$ Just another curious question: if a frequency offset compensator can easily be added before the LO, why consider putting that function in the LO? I am not an authority in this area. But if you are measuring the shift with a reference laser, and can account for the shift before the LO, then it would seem the best option. But there may be advantages to LO compensation that I am not aware of. Sorry, but I cannot provide help with how to do it. Please update with the answer you find. It is a very interesting subject. $\endgroup$ – user2338215 Jul 9 '14 at 0:04
  • $\begingroup$ Hi! @user2338215 as of now I am compensating as Sexp(-j*2*piFdoppler) which is a child's play. I am still trying to do the Compensation inside the LO. Will post it once I come up with the answer. $\endgroup$ – Seetharama Jul 15 '14 at 9:54

I think the main issue will be targeting the sat. The receiver should handle the flux in frequency based on the carrier. leading the sat target depending on how far the sat is from each other. Geo sync sates are 28k miles and signal takes 28000 / 186000 seconds to reach earth and twice that to reach back. So you have to lead the target by a few hundred yards before the sat will even pickup the focused signal.

  • 1
    $\begingroup$ You say "The receiver should handle the flux in frequency" but that is exactly what the question is about. This does not answer the question. $\endgroup$ – Kevin Reid AG6YO Jan 26 '16 at 22:27

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