0
$\begingroup$

am trying to implement OQPSK modulation with half sine pulse shaping. If I simulate the OQPSK modulation without pulse shaping, the simulated curve is similar to the theoretical value. However, when I introduce pulse shaping, the simulated values are lesser than the theoretical case. I am not sure where I am going wrong. Below is the code where I am using pulse shaping:

  Rc = 2e6;       % Chip rate
  Tc = 1/Rc;      % inverse of chip rate
  Fs = 12e6;      % sampling frequency
  dt = 1/Fs;
  over = Fs/Rc;   % sampling factor
  TSim = 0.01;
  N = floor(TSim/4e-6);
  data = randi([0 1],N,1); 

  hMod = comm.OQPSKModulator('BitInput',true);
  modulated_data = step(hMod, data);

   %% Upsample
  over_data = upsample(modulated_data,over);

  %% Pulse Shape
  time = 0:dt:2*Tc;
  hSineflt = sin(pi*time/(2*Tc)); 
  tx=conv(over_data,hSineflt,'same');

  %% AWGN channel
  hAWGN = comm.AWGNChannel('EbNo',SNR);
  noisy_signal = step(hAWGN, tx); 

  %% Matched filter
  rx=conv(noisy_signal,hSineflt,'same');

  %% Downsample
  downsampled_signal = rx(1:over:end);

  %% OQPSK Demodulation
  hDemod = comm.OQPSKDemodulator('BitOutput',true);
  demod_data = step(hDemod,downsampled_signal);

  %% BER 
  hError = comm.ErrorRate('ReceiveDelay',2);
  errors = step(hError,data, demod_data);
  BER_sim = errors(1);

This is the part where I calculated the theoretical value

  BER_Theo = berawgn(SNR,'oqpsk','nondiff');

I expect both BER_sim and BER_Theo to be almost the same. But I am unable to figure out where I am going wrong.

$\endgroup$
2
  • 1
    $\begingroup$ The pulse shape has absolutely no bearing on the bit-error rate in an AWGN channel. If you get different results, then you're doing something wrong. $\endgroup$
    – MBaz
    Commented May 28, 2015 at 23:40
  • $\begingroup$ I figured out that the power of the half sine wave that I was using was high, which was the reason for the deviation. $\endgroup$
    – smyslov
    Commented May 29, 2015 at 6:48

0

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Browse other questions tagged or ask your own question.