Cochin University of Science and Techology (CUST) 2005-6th Sem B.Tech Electronics and Communications Engineering (Supplementary) ,, EC 603 Digital Communication - Question Paper

B. Tech Degree VI Semester (Supplementary) Examination

November 2005

BTS(Q -VI-(S) -05 - 074 (E)

		EC 603 DIGITAL COMMUNICATION
		(2002 Admission Onwards )
Time:	3 Hours	Maximum MarksrIOO
1.	(a)	State and prove sampling theorem for low pass signals. What do you mean by
		aliasing and guard band	(8)
	<b)	Explain any two pulse modulation schemes.	(12)
		OR
11.	(a)	With neat diagram explain differential pulse code modulation scheme. What is the
		significance of predictor circuit in DPCM.	(8)
	(b)	Explain adaptive delta modulation.	(8)
	(c)	What is the need for companding network in a PCM system? Draw the transfer
		characteristics of a companding network.	(4)
m.	(a)	With neat waveforms and required derivations and expressions explain minimum
		shift keying scheme (MSK)	(12)
	(b)	Explain inter symbol interference.	(8)
		OR
IV.	(a)	Explain QPSK transmitter-receiver scheme with relevant block diagram and waveforms.
		Obtain the distance between signal points in QPSK scheme.	(10)
	(b)	Write notes on
		(i) raised cosine spectrum
		(ii) eye patterns	(10)
V.	(a)	Apply Shannon Fano coding procedure for the following message ensemble

(*]*(*.*: *i ** ** *.]

, , fl 1 1 1 1 I I I 1*1

"[4 I 16 16 16 4 4 16 8J    <^l0)

(i) Find tbe avenge length per code word (!) ^w Entropy N [x]

Efficiency of coding o\

(Take M - 2)

(b) Write notes on

(i)    Shannons Theorem

(ii)    Entropy

(iii)    Channel capacity    (10)

OR

(Turn Over)

2

X1

0.04

VI. (a) Explain various type* of channel in communication systems.

(b) By using Huffman coding obuin the code word C4 for the message x.

Message    X_t X₂ x> X4 xj x*

Probability 0.4 0.2 0.12 0.08 0.08 0.08

Also find the average length per code word.

VII.    (a) The generator polynomial of a (7,4) cyclic code is g(x) I +x+x*. Generate a systematic

code word for the message vector Ml0l1 (b) Explain various methods for bunt etror correction.

OR

VIII.    (a) The b sub matrix for a (7,4) systematic linear block code is given by

1110

I I 0 I

10 11

the generator matrix show that GH^t - 0

Compute the syndrome for the received vector

(0 0 I 0 II 1]

Discuss on various types of ARQ and its performance.

IX.    (a) Explain Gram Schmidt Ortbogonalization procedure.

(b) In estimation theory what do you mean by Bayes estimation and maximum a posteriori (MAP) estimate.

OR

X.    What do you mean by matched filter? Derive its transfer function. Also obtain its probability of error. Explain its properties.

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Earning:   Approval pending.