A problem with my digital communication code

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DM 2014-10-19

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https://ww2.mathworks.cn/matlabcentral/answers/159232-a-problem-with-my-digital-communication-code

评论： Rick Rosson 2014-10-19

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?

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Answer 1

Rick Rosson 2014-10-19

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https://ww2.mathworks.cn/matlabcentral/answers/159232-a-problem-with-my-digital-communication-code#answer_155769

编辑：Rick Rosson 2014-10-19

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

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DM 2014-10-19

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 2014-10-19

在 MATLAB Online 中打开

Please try:

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

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Answer 2

Rick Rosson 2014-10-19

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/159232-a-problem-with-my-digital-communication-code#answer_155764

在 MATLAB Online 中打开

Instead of

hH.PhaseOffset = pi/4;

please try

H.PhaseOffset = pi/4;

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DM 2014-10-19

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

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