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I'm in the process of implementing a general purpose baseband system for modulation schemes (Linear + CPM) commonly used satellite and deep-space TT&C as shown in the functional flow block diagram (FFBD) below. enter image description here So far, I have implemented most of the blocks (in GNU Radio). At the moment, I'm testing the BPSK implementation. In the tests, the software is able to receive transmitted frames when the blocks are arranged according to the figure or when I changed the position of the equalizer. i.e both [--- Matched filter-> equalization -> demodulation -> timing -> phase -> decision] and [--- Matched filter-> demodulation -> timing -> equalization -> phase -> decision] works fine. Phase recovery is done by the Costas loop. The timing recovery block uses a TED based on maximum likelihood. I use a blind equalizer (constant modulus algorithm (CMA)). I still have doubts about my approach in the FFBD and thoughts regarding the following questions will be highly appreciated:

  1. A suggestion for the optimum location for the equalizer in relation to time and phase recovery.
  2. Any thoughts on improving the overall approach in the FFBD.

I will happily provide clarification if needed.

Regards,

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    $\begingroup$ The main question is: what type of equalizer is it, and what is it equalizing (depends on signal bandwidth and channel response)? If the response is fairly benign and you can get by with a simple MMSE eq, I don't think it matters as much where you put it. However, if you are doing a sequence-detector-based equalizer (e.g. SOVA or RSSE/DFE/etc followed by MAP), then residual frequency error should be removed before eq, and timing offset is a part of the impulse response used in the eq anyway. $\endgroup$ – user35336 May 4 '18 at 4:50
  • $\begingroup$ I should add that I presumed you do not have a lot of excess BW and TX pulse that needs to be matched to recover that excess BW energy (given your mention of CPM). $\endgroup$ – user35336 May 4 '18 at 5:38

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