I have been trying to implement a transmitter receiver flow graph which uses 16 QAM. I am using a USRP B200 as the transmitter and a RTL-SDR as the receiver.
I used uhd_packet_tx.grc and uhd_packet_rx.grc found in gnuradio examples. I changed the packet_rx block to work with 16 QAM by replacing the Costas Loops from the packet_rx with Constelation receivers (I read in GNURadio tutorials that Costas loop does not work with QAM) and also, added a CMA equalizer and a LMS DD equalizer following the PolyPhase Clock Sync block. I'm posting the screenshot of the my flowgraphs and the plot of the output from the LMS DD Equalizer to a constellation sink here. I would be really grateful, if someone could point out the mistake I'm making. Am I missing something?
I'm not a signal processing person, so kindly pardon me for any mistakes in my flowgraph.