MATLAB: A problem with the digital communication code

communication

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?

Best Answer

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