16-APSK NDA Carrier Synchronization Problem
Symbol timing and carrier synchronization are two separate &quot;tasks&quot; in a demodulator.
There is lot of literrature on the internet to understand synchronization on a DVB-S2 signal.
But not sure that GNU Radio has the good ready block for it.
For symbol timing synchronization, there is Gardner timing error detector that suits well for QPSK modulation. An adapted version of it for 16APSK and 32APSK in a second order control loop could do the job.
For carrier synchronization, if you try to look at the 16APSK and 32APSK in polar representation (the constellation), the angle value modulo a constant gives you a phase error. Also in a second order control loop you can track the carrier this way. The modulo constant depends on the order of the modulation scheme you use. That is probably also why the one in GNU Radio may not work.
What I described before is called fine synchronization. Which means that it can be not enough to lock on large offsets.
You also need a coarse synchronization to help the fine one to lock. Depends on your requirements.
I hope this helps