A problem with my digital communication code

6 views (last 30 days)
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?

Accepted Answer

Rick Rosson
Rick Rosson on 19 Oct 2014
Edited: Rick Rosson on 19 Oct 2014
Please try using the General QAM Modulator and Demodulator system objects.
  2 Comments
Rick Rosson
Rick Rosson on 19 Oct 2014
Please try:
[ ~, SER ] = symerr(symdecoded,databits)
[ ~, BER ] = biterr(symdecoded, databits)

Sign in to comment.

More Answers (1)

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

Sign in to comment.

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by