Seat No.: ________                                              Enrolment No.
___________
             GUJARAT TECHNOLOGICAL UNIVERSITY
                BE - SEMESTER–IV (NEW) EXAMINATION – WINTER 2023
Subject Code:3141005                                                    Date:17-01-2024
Subject Name:Signal & Systems
Time:10:30 AM TO 01:00 PM                                                Total Marks:70
Instructions:
        1. Attempt all questions.
        2. Make suitable assumptions wherever necessary.
        3. Figures to the right indicate full marks.
        4. Simple and non-programmable scientific calculators are allowed.
                                                                                            Marks
Q.1    (a)   Find discrete Convolution of following pairs of signals.                        03
             and x(n) = {1,3,5,7} and h(n) = {2,4,6,8}
       (b)   Prove Commutative property of Convolution.                                      04
       (c)   What is ROC with respect to z- transform? What are its properties?              07
Q.2    (a)   Find the DFT of the sequence x(n) = {1, 1, -2, -2}                              03
       (b)   Enlist frequency shifting and time differentiation properties of Fourier        04
             transform. Prove any one of them.
       (c)   State the sampling theorem. Also explain the reconstruction of a signal from    07
             its samples using interpolation.
                                                OR
       (c)   Determine the Z – Transform & ROC of the following sequence                     07
             x(n) = (3)n u(n) - (2)n u(-n-1)
Q.3    (a)   Explain Scaling property in the z -Domain.                                      03
       (b)   State Dirichlet condition for Fourier Series Representation                     04
       (c)   Determine the convolution sum of two sequences using graphical method           07
             x(n) = {1, 4, 3, 2}; h(n) = {1, 3, 2, 1}
                        ↑                 ↑
                                                    OR
Q.3    (a)   Find even and odd parts of 𝑥(𝑡)=𝑢(𝑡).                                           03
       (b)   Bring out difference between DFT and Fourier Transform (FT).                    04
       (c)   Explain following property for the system                                       07
              y(t) = 10 x(t) + 5.
             (i) Linearity (ii) Time-invariance (iii) Causality (iv) Dynamicity
Q.4    (a)   Explain the trigonometric Fourier series.                                       03
       (b)   Define energy and power. Hence, define energy signal and power signal.          04
       (c)   Calculate the DFT of a sequence 𝑥[𝑛]={1,1,0,0} and check the validity of        07
             DFT by calculating its IDFT.
                                                   OR
Q.4    (a)   Explain the Differentiation property of Z-Transform.                            03
       (b)   Determine whether the following system with impulse response                    04
             h(t) = e-3 t u(t) is stable or not.
       (c)   Find the Fourier series coefficients for the continuous time periodic signal    07
             x(t) = 1.5 for 0 ≤ t < 1
                 = -1.5 for 1 ≤ t < 2
             with fundamental frequency W0 = π.
                                                                                                  1
Q.5   (a)   State and prove a condition for a discrete time LTI system to be stable.           03
      (b)   Find the natural response of the system described by difference equation           04
            y(n) – 1.5 y(n - 1) + 0.5 y(n - 2) = x(n) ; y(-1) = 1; y(-2) = 0.
      (c)   Obtain the Fourier Transform of following signals:                                 07
            1. 𝑥(𝑡) = cos𝜔0𝑡
            2. 𝑥(𝑡) = sin𝜔𝑐𝑡 𝑢(𝑡)
                                                   OR
Q.5   (a)   Explain relation between Fourier transform and z transform using necessary         03
            equations.
      (b)   Prove that DT LTI system is causal if and only if h(n) = 0 for n < 0.              04
      (c)   Find whether the given signals are periodic or not? If yes, give its fundamental   07
            period.
            (i) x(t) = 3 sin 200πt + 4 cos 100t
            (ii) x(n) = e j (π / 2) n
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