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This document is an examination paper for a Digital Communications course. It contains two parts - Part A with short answer questions worth 25 marks total, and Part B with longer answer questions worth 50 marks total. Candidates must answer all of Part A and choose one question from each unit in Part B. The questions cover topics like advantages of digital over analog communication, aliasing, entropy, convolutional codes, matched filters, bandwidth requirements of modulation techniques, PN sequences, sampling, delta modulation, linear block codes, cyclic codes, Shannon-Hartley law, Nyquist criteria, optimal linear receivers, adaptive equalizers, QPSK modulation, DPSK transmission, CDMA, and spread spectrum techniques like frequency hopping.

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Murali Buchammagari
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72 views2 pages

WWW - Manaresults.Co - In: (Electronics and Communication Engineering)

This document is an examination paper for a Digital Communications course. It contains two parts - Part A with short answer questions worth 25 marks total, and Part B with longer answer questions worth 50 marks total. Candidates must answer all of Part A and choose one question from each unit in Part B. The questions cover topics like advantages of digital over analog communication, aliasing, entropy, convolutional codes, matched filters, bandwidth requirements of modulation techniques, PN sequences, sampling, delta modulation, linear block codes, cyclic codes, Shannon-Hartley law, Nyquist criteria, optimal linear receivers, adaptive equalizers, QPSK modulation, DPSK transmission, CDMA, and spread spectrum techniques like frequency hopping.

Uploaded by

Murali Buchammagari
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Code No: 135AK

R16
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
B. Tech III Year I Semester Examinations, November/December - 2018
DIGITAL COMMUNICATIONS
(Electronics and Communication Engineering)
Time: 3 hours Max. Marks: 75

Note: This question paper contains two parts A and B.


Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B
consists of 5 Units. Answer any one full question from each unit. Each question carries
10 marks and may have a, b, c as sub questions.

PART - A
(25 Marks)

1.a) What are the advantages of digital communication over analog communication. [2]
b) What is aliasing and aperture effect and how to eliminate them? [3]
c) A source generates 4 messages with the probabilities 1/3,1/6,1/4,1/4. The successive
messages limited by the sources are statistically independent. Calculate the entropy of
the source. [2]
d) What are the convolutional codes? Explain. [3]
e) Write the properties of the matched filter. [2]
f) What is a correlative level coding? [3]
g) Compare the bandwidth requirements of (i) BPSK (ii) 8QAM (iii) 8PSK. [2]
h) For a tri bit input Q=0, I=0 and C=0(000). Determine the output phase for 8 PSK
modulation. [3]
i) List the applications of the spread spectrum techniques. [2]
j) Write the properties of PN sequence. [3]

PART - B
(50 Marks)

2. Explain the different types of sampling and discuss each technique in detail with neat
sketches. [10]
OR
3.a) Discuss the Delta modulation technique. Also discuss the noises in DM.
b) Discuss the quantization noise in PCM. [5+5]

4.a) Explain the Lempel-Ziv coding with an example.


b) Discuss the Matrix description of the linear bloc codes. [5+5]
OR
5.a) The generator polynomial of a (7,4) cyclic code is G(P)=P3+P+1. Obtain all the code
vectors for the code in non systematic and systematic form.
b) State the Shannon Hartley Law and discuss the properties of entropy. [5+5]

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6.a) Discuss the nyquist criteria for distortion less base band binary transmission.
b) Briefly explain the operation of the optimal linear receiver. [5+5]
OR
7.a) What is the principle of the adaptive equalizer ? Draw the structure.
b) Explain the geometric interpretation of the signals. [5+5]

8. Draw the QPSK modulator? And construct the truth table, phasor diagram and
constellation diagram for it. [10]
OR
9. Explain the transmitter and receiver section of the DPSK techniques in detail. [10]

10.a) Explain the CDMA techniques.


b) What is the use of the spread spectrum techniques? [6+4]
OR
11. Explain in detail the types of frequency hoping spread spectrum techniques. [10]

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