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A problem with my digital communication code

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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?

Risposta accettata

Rick Rosson
Rick Rosson il 19 Ott 2014
Modificato: Rick Rosson il 19 Ott 2014
Please try using the General QAM Modulator and Demodulator system objects.
  2 Commenti
DM
DM il 19 Ott 2014
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
Rick Rosson il 19 Ott 2014
Please try:
[ ~, SER ] = symerr(symdecoded,databits)
[ ~, BER ] = biterr(symdecoded, databits)

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Più risposte (1)

Rick Rosson
Rick Rosson il 19 Ott 2014
Instead of
hH.PhaseOffset = pi/4;
please try
H.PhaseOffset = pi/4;
  1 Commento
DM
DM il 19 Ott 2014
Thanks I did, do you happen to know how to generalize such a program to the QAM case?

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