Dear all, can anyone help me on to fix the following

Error using comm.APPDecoder/step
Complexity mismatch with input 2; expected real, got complex.
-tmp is QPSK complex signal+noise 
Error in G_NOMA_IDMA_SAMSON_ZITHA>CBCReceiever (line 297)
                    [outSoftData outLLR]= step(hAppDec,ini,transpose(tmp));

In fact i want the hAppDec to decode complex signal, how do i define that in the hAppDec matlab function

e.g

   hAppDec = comm.APPDecoder(...
                                  'TerminationMethod','Truncated','TrellisStructure',poly2trellis(3,[5 7]), ...
                                  'Algorithm','True APP','CodedBitLLROutputPort',true);