General QAM Modulation-Demodulation Compatibility Considerations

Replace instances of modem.genqammod and modem.genqamdemod with genqammod and genqamdemod. To generate soft decision output, use comm.GeneralQAMModulator and comm.GeneralQAMDemodulator.

• This code sample shows you bit input and multichannel input support for general QAM modulated signals:

  %% Bit Input
  % Multichannel input
  x = randi([0,1],16,3);
  
  M = 16;
  nBits = log2(M);
  inSize = size(x);
  outSize = inSize;
  % nBits bits make one symbol
  outSize(1) = outSize(1)/nBits;
  
  % M-QAM constellation
  const = qammod((0:M-1)',M);
  
  % Modulate
  m1 = modem.genqammod('InputType','Bit','Constellation',const);
  ym1 = m1.modulate(x);
  
  % Convert bit input to integer
  % Each column is a bit representation of an integer
  xTmp = reshape(x,nBits,numel(x)/nBits);
  % each row is a bit representation of an integer, left-MSB
  xTmp = xTmp'; 
  xIntCol = bi2de(xTmp,'left-msb');
  xIntMat = reshape(xIntCol,outSize);
  
  % Compare modulator function output
  yf1 = genqammod(xIntMat,const);
  err = max(abs(ym1(:) - yf1(:)))

  err =
  
       0

• This code sample shows you how to simulate multichannel input/output and soft decision output for general QAM-modulated signals:

  %% Soft decision output
  % Multichannel input
  x = randi([0,1],16,3);
  
  M = 16;
  nBits = log2(M);
  inSize = size(x);
  outSize = inSize;
  % nBits bits make one symbol
  outSize(1) = outSize(1)/nBits;
  
  % 16-QAM constellation
  const = qammod((0:M-1)',M);
  
  % Modulate
  m1 = modem.genqammod('InputType','Bit','Constellation',const);
  ym1 = m1.modulate(x);
  
  % Convert bit input to integer
  % Each column is a bit representation of an integer
  xTmp = reshape(x,nBits,numel(x)/nBits);
  % Each row is a bit representation of an integer, left-MSB
  xTmp = xTmp'; 
  xIntCol = bi2de(xTmp,'left-msb');
  
  % Compare System object output
  s1 = comm.GeneralQAMModulator('Constellation',const);
  ysTmp = s1(xIntCol);
  ys1 = reshape(ysTmp,outSize);
  
  err1 = max(abs(ym1(:) - ys1(:)))
  
  % Demodulate (LLR)
  m2 = modem.genqamdemod('Constellation',const,'OutputType','Bit', ...
      'DecisionType','LLR','NoiseVariance',0.2);
  ym2 = m2.demodulate(ym1);
  
  s2 = comm.GeneralQAMDemodulator('Constellation',const,'BitOutput',true, ...
      'DecisionMethod','Log-likelihood ratio','Variance',0.2);
  % Columnize ys1 as System object supports only column vector input
  ys2 = s2(ys1(:));
  ys2 = reshape(ys2,inSize);
  err2 = max(abs(ym2(:) - ys2(:)))
  

  err1 =
  
       0
  
  err2 =
  
       0