Module 9 : Numerical Relaying II : DSP Perspective

Lecture 33 : Discrete Fourier Transform

33.1

Motivation (contd..)

 

Since, we have N-data points [real] and a complex number contains both magnitude and phase angle information in the frequency domain (2-units of information), it is reasonable to expect that we should be in a position to predict atmost transforms for original signal.

 

Now, let

  and   (3)
  then substituting (3) in (1), we get
 
 

Note that our choice of frequency is such that the exponential term in (1) is independent of . The intuition for choosing such is that, in principles we are attempting a transform on discrete samples which may (or) may not have a corresponding analog ‘parent' signal. This suggests to us the following discrete version of Fourier transform for a finite discrete sequence

   
3