dc

e received code word 110110. Comment on error detection capability of this code. [15]
7. a) Explain how you would draw the trellis diagram of a convolutional encoder given its
state diagrams.
b) For the convolutional encoder shown in figure7, draw the state diagram and the trellis
diagram. [15]
Figure: 7
8. a) What are the advantages of spread spectrum technique.
b) Compare direct sequence spread spectrum and frequency hopped spread spectrum
techniques and draw the important features of each. [15]
B. Tech III Year II Semester Examinations, April/May - 2012
DIGITAL COMMUNICATIONS
(ELECTRONICS AND COMMUNICATION ENGINEERING)
Time: 3 hours Max. Marks: 75
Answer any five questions
All questions carry equal marks
---
1. a) State and discuss the Hartley-Shannon law.
b) The terminal of a computer used to enter alpha numeric data is connected to the computer
through a voice grade telephone line having a usable bandwidth of 3 KHz and a output SNR
of 10 dB. Determine:
i) The capacity of the channel
ii) The maximum rate at which data can be transmitted from the terminal to the computer
without error.
Assume that the terminal has 128 characters and that the data sent from the terminal consists
of independent sequences of characters with equal probability.
[15]
2. a) What is hunting in delta modulation? Explain.
b) Differentiate between granular and slope overload noise.
c) A signal band limited within 3.6 KHz is to be transmitted via binary PCM on a channel
whose maximum pulse rate is 40,000 pulses/sec. Design a PCM system and draw a block
diagram showing all parameters. [15]
3. a) Derive an expression for the spectrum of BFSK and sketch the same.
b) Explain operation of differentially encoded PSK system. [15]
4. a) What is an inter symbol interference in base band binary PAM system? Explain.
b) Give the basic components of a filter in baseband data transmission and explain.
[15]
5. a) State the significance of H(Y/X) and H(X/Y).
b) Given six messages with probabilities, P() = 123456x, x, x, x, x, x1x13, 21P(x) = , 4
31P(x) = , 8 41P(x) = , 8 51P(x) = , 12 61P(x) = 12. Find the Shannon-Fano code.
Evaluate the coding efficiency. [15]
6. a) State and explain the properties of cyclic codes.
b) The generator polynomial of a (7, 4) cyclic code is x 3 +x+1. Construct the generator
matrix for a systematic cyclic code and find the code word for the message (1101)
using the generated matrix. [15]
7. a) What is a convolutional code? How is it different from a block code?
b) Find the generator matrix G(D) for the (2, 1, 2) convolutional encoder of figure shown 7.
[15]
Figure: 7
8. a) What are the PN sequences? Discuss their characteristics.