Communications Toolbox

Adding Noise

According to the definition of baseband QASK modulation, modsignal is a complex matrix having len*Fs/Fd rows and two columns. The command below adds normally distributed random numbers to the real and imaginary parts of modsignal, to produce a noisy signal noisy. The randn function is a built-in MATLAB function.

Notice that the command adds to modsignal an entire real matrix of the appropriate size and an entire imaginary matrix of the appropriate size. Using a loop to add noise to individual scalar entries of modsignal would be less efficient, because MATLAB is optimized for matrix operations.

• % Add noise to real and imaginary parts of the modulated signal.
  noisy = modsignal+.5*randn(len*Fs/Fd,2)...
  +j*.5*randn(len*Fs/Fd,2);
  

Modulating the Signal

Demodulating the Signal