Thank you Tom,
I found a note in documentation of the Packet Encoder block where it declares that the Packet Encoder is for use with the gnuradio modulator blocks: GMSK, DPSK, QAM. I don't know why only these modulator blocks are supported, but not some popular things like BPSK or QPSK. Another thing is that my task requires the use of OFDM.
Suppose now I have a simple flow graph as below:
File Source -------> Packet Encoder -------> Packet Decoder ---------> File Sink
I wonder what types of file can be loaded and processed properly in the File Source block (text, image, or video ...), and the same question for the File Sink block :-)
Thank you so much