GATE EC 2019 Set 1 — Question 54
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Question
Let be a length-7 discrete-time finite impulse response filter, given byand is zero for . A length-3 finite impulse response approximation of has to be obtained such thatis minimized, where and are the discrete-time Fourier transforms of and , respectively. For the filter that minimizes , the value of , rounded off to 2 decimal places, is ________.
Correct answer
-27.01
Solution
By Parseval's theorem, the error in the frequency domain is proportional to the error in the time domain:To minimize this sum, should be equal to for the three indices where is non-zero, and those indices should be chosen to capture the maximum energy of .
The magnitudes of are:
.
The three largest magnitudes are at . Thus, the optimal length-3 filter is:
The required value is:
The magnitudes of are:
.
The three largest magnitudes are at . Thus, the optimal length-3 filter is:
The required value is:
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