Hi Ahsan,
The signal does look good indeed. I'm guessing the problem
is that nothing is output from the OFDM sym acquisition
blocks (both from gr-dvbt and gr-isdbt?). In any case, are
you sure about those transmission parameters? Did you check
other CP lengths? gr-isdbt includes a small grc file to
check both the transmission mode and CP which works both for
ISDB-T and DVB-T (examples/obtaining_parameters.grc, please
refer to the README or the issues section on the git). Maybe
you could test that?