[email protected] wrote:
> if gardner can't works for QAM what kind of symbol synchronisation
> could we use for QAM ?

Who said it can't work? As long as the excess bandwidth is more than
something like 25%, it works quite well. Problems occur with narrowing
bandwidth, so it certainly can't work for some people.

Where Gardner it won't work various things are possible, You could try
something like cross-correlating the outputs from two narrow bandpass
filters centred at the band edges.

Steve