GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER- VI EXAMINATION — SUMMER 2020
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Subject Code: 2161001 Date:26/10/2020
Subject Name: DIGITAL COMMUNICATION
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
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MARKS
Q.1 (a) What are the Nyquist criteria for the sampling of signal in communication? 03 Which kind of effect is observed if Nyquist criteria doesn’t follow? Explain with example.
(b) State the difference between PCM, DPCM and Delta modulation. 04
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(c) Explain the T1 digital carrier System with frame structure, important 07 parameters and synchronization mechanism.
Q.2 (a) List out the importance characteristic of line codes and compare the On- 03 Off, Polar and Bipolar codes in terms of their Power Spectral Density (PSD).
(b) Discuss the Trade-off between transmission rate and transmission power 04 for M-ary signal.
(c) State the importance of Regenerative repeater in digital communication 07 and discuss briefly about the significance of individual components of Regenerative repeater.
OR
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(c) What is the pulse shaping? Shed the light on Nyquist first and second 07 criteria for pulse shaping.
Q.3 (a) Establish the relationship between PDF and CDF and enlist the properties 03 of CDF.
(b) What is marginal probability? Explain with mathematical background 04
(c) Explain central limit theorem in a brief and draw the Probability 07 distribution function (PDF) and CDF for the Random Variable (R.V.) obtain as a sum of large number of R.V.
OR
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Q.3 (a) What is conditional probability? State the equation of conditional 03 probability for two variable case.
(b) A binary source generates digits 1 and 0 randomly with probabilities 04 P(1)=0.8 and P(0) =0.2.
(a) What is the probability that two 1's and three 0's will occur in a five-digit sequence?
(b) What is the probability that at least three 1's will occur in a five-digit sequence?
(c) How many types of correlation does exists between two sets of R.V. ? 07 Explain with diagram and mathematical background.
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Q.4 (a) Derive the equation for Shannon capacity and describe the tradeoff between 03 signal to noise ratio and bandwidth.
(b) What is entropy of message? In which case, Entropy will be maximum 04 explain with the mathematical background.
(c) A DMS has five symbols x1, x2, x3, x4 and x5 with probabilities 1/2, 1/4, 1/8, 1/16 and 1/16 respectively. Obtain the compact binary code and find the average length of the code word. Determine the efficiency and redundancy of the code.
OR
Q.4 (a) State the difference between ASK, FSK and PSK in terms of their 03 important parameters.
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(b) Explain the concept of GMSK with their transmitter and receiver block 04 diagram.
(c) What is QAM, ?. Draw Constellation diagram of 16- QAM. Discuss their 07 merits and demerits. Draw and explain the transmitter and receiver structure of QAM.
Q.5 (a) Construct a (7,4) systematic cyclic code for data vector d= 10101 for the 03 Generator matrix g(x) = x²+ x+1.
(b) Derive the Hamming bound condition for error correcting codes. 04
(c) For a (6,3), Linear block code the parity check digits c4, c5 and c6 are as 07 follows:
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c4=d1+d2+d3, c5= d1+d2, c6= d1 +d3. (+ sign is consider as X-OR Operation)
Draw the line block encoder, Generate the Matrix G and find the code vector for following data vector : 001, 111, 010, 101. Comment on maximum error correcting capacity of the code.
OR
Q.5 (a) What is the trade-off between code efficiency and reliability? Explain with 03 example.
(b) Explain Burst error detecting and correcting codes. 04
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(c) What is convolution code? How it is differ than linear block code ? Draw 07 the encoder if out put V1 = S1 + S2 +S3 and V2 = S1 +S3 where S1, S2 and S3 are the number of shift register, Entering data is fetching S1 first. What is the output of convolution encoder if applied input is 10110. Draw the state diagram for this encoder. (+ sign is consider as X-OR Operation)
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