# Download GTU B.Tech 2020 Summer 6th Sem 2161001 Digital Communication Question Paper

Download GTU (Gujarat Technological University Ahmedabad) B.Tech/BE (Bachelor of Technology/ Bachelor of Engineering) 2020 Summer 6th Sem 2161001 Digital Communication Previous Question Paper

Seat No.: ________
Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER? VI EXAMINATION ? SUMMER 2020
Subject Code: 2161001 Date:26/10/2020
Subject Name: DIGITAL COMMUNICATION
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.

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

(c) Explain the T1 digital carrier System with frame structure, important
07
parameters and synchronization mechanism.

Q.2 (a) Modul
List ati
out on (D
the M)
im
portance 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

(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

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.
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.
1

(c) A source emits seven messages with probability 1/2, 1/4, 1/8, 1/16, 1/32, 1/64
07
and 1/64 respectively. Find the entropy of the source. 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.

(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) = x3 + x2 +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:
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
(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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