text: import commlib as cl
  import numpy as np
  
  TS = 1e-3                   # Symbol duration
  
  # symbols
  ak = np.array([0.5, 0.25, 1.0, 0.5])
  
  t, x = cl.pam_waveform1(ak, TS)
  cl.plot_signal(t, x, plot_type = '-o', close_all = True)
  
  
  