Yes I don’t think that you have set up the proper OutputPort1 data structure. Typically the best way to start is with:
OutputPort1 = InputPort1;
To set it up exactly the same as the input, however you will need to make changes as your input is a M-ary signal and your output is an electrical signal. Although I probably already mentioned it we have videos about the Matlab component here:
It shows you how to view the data structures in Matlab and setup the input/output ports.
Regards