A problem with my digital communication code

I have a problem in writing in MATLAB a program that modulates data bits, adds noise, then demodulates it and calculates the bit error and the symbol error rate. The modulation used first should be QPSK. I have done the following:

N=100;
databits = randi([0 3],N,1);
hModulator = comm.QPSKModulator;
hModulator.PhaseOffset = pi/4;
txsig = step(hModulator, databits);
scatterplot(txsig)
grid on
SNRdB=-10
rxsig = awgn(txsig,SNRdB);
H = comm.QPSKDemodulator
hH.PhaseOffset = pi/4;
symdecoded=step(H,rxsig)
symerr(symdecoded,databits)
biterr(symdecoded, databits)

My first question is I don't think I am doing the bit error rate and symbol error rate correctly, can someone help me spot where the problem is? Where am I missing out?

I am then asked to repeat the same problem but make the changes needed to make it work with 16-QAM and 64-QAM by changing a parameter called CONSTELLATION.

I have tried using demod() and ddemodce() but these two functions have been removed from MATLAB? Does anyone know how to proceed?

Answer 1

[Rick Rosson]

Please try using the General QAM Modulator and Demodulator system objects.

[DM]

Thank you very much, one more question, do you think the way I do my symbol error and bit error rate is correct? I am basically taking the error between the data bits and the decoded symbol for both types of errors, is that correct?

[Rick Rosson]

Please try:

[ ~, SER ] = symerr(symdecoded,databits)
[ ~, BER ] = biterr(symdecoded, databits)

Answer 2

[Rick Rosson]

Instead of

   hH.PhaseOffset = pi/4;

please try

   H.PhaseOffset = pi/4;

[DM]

Thanks I did, do you happen to know how to generalize such a program to the QAM case?