code: def time_step(z,Ns,t_step,Nstep):
      
      z_step = np.hstack((z[:Ns*Nstep], z[(Ns*Nstep+t_step):], np.zeros(t_step)))
      return z_step
docs: Create a one sample per symbol signal containing a phase rotation
      step Nsymb into the waveform.
  
      :param z: complex baseband signal after matched filter
      :param Ns: number of sample per symbol
      :param t_step: in samples relative to Ns
      :param Nstep: symbol sample location where the step turns on
      :return: the one sample per symbol signal containing the phase step
  
      Mark Wickert July 2014