Download AKTU B-Tech 6th Sem 2014-2015 Digital Communication Question Paper

Download AKTU (Dr. A.P.J. Abdul Kalam Technical University (AKTU), formerly Uttar Pradesh Technical University (UPTU) B-Tech 6th Semester (Sixth Semester) 2014-2015 Digital Communication Question Paper

Printed Pages :4
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(Following Paper ID and Roll No. to be ?lled In yourAnsw'er Book)
PAPER 10' . 131601
R011 No.2; ' B: J
B. Tech.
(SEM. VI) THEORY EXAMINATION, 2014-15
DIGITAL COMMUNICATION
rm : 3 Hows} . [Total Mm : 100
Note: Attempt all' questions.
1 Attempt 'any two questions : I ' ZXIO=20
(a) Explain the rise of scrambler and unscrambler in
digital Communication system. Draw the block
' .diagramofanumcmnblerusmgshi?regista'sand
explain its operation with suitable example.
(b) Write short note on following digital modulalion
V techniquw:
(i) Di?'erential phase shift "keying (DPSK)
(i1) Quadrature phase shift keying (QPSK).
(c) How FSK modulatio? and demodulatim is done?
Explain using block diagrams of modulator and
demodulator.
131601] 1 [ Contd...

' (a)
(b)
(C)
(a)
(b)
(0)
(a)
131601]
Attempt any two questions ZXIO=20
Write'short note on following :
O CDF (ii) PDF (iii) random precess.
De?ne mean, variance and standard deviation for
random variables
Also prove the following theorem on variance
6) 62 = E(X2)-p.2
(ii) Pizr(CA9= C2Var(X)
(n1) Var(X?=)9 Varm+Varm
The probability density function is given as
fx(x)=ae?bl?1 where x is a random van'able.
Find : y
(1) relationship between a and b
(i) CDF
(ii) the probability that outcome lies between
1 and 2.
Attempt any two questiom ZXIO=20
Whatdo youunderstandbymatched?lterahd
whatare?ieproper?es ofmatched?lter?
Derive an expression for the probability of ermr
of the binary phase shi? keying (BPSK) signal.
Derive an expressidn for error probability of a
matched ?lter.
Attempt any four questions 4XS=20
What is PN sequence? Draw suitable PN
sequence generator and prove the properties of
PN sequence and sketch its autoea'relation
?mction
2 [Contd...
(b) With the help of block diagram and suitable
expressions explain the generation and reception
of direct Sequence spread spectrum (DS-SS)
signal using BPSK modulation.
(c) Explain the following tenns for spread spectrum
system.
(1) Processing gain (P G)
Oi) Probability of error of DS/BPSK system
(Iii) Jammingnwgin
(d) Explain the operation of ?equency hop spread-
spectmm (F H-SS) with the help of block diagram
and waveforms. .
(e) Explain how spread spectrum communication can
? beusedforprovidingnml?pdntoomwdivityusing
CDMA techniques?
Attempt any ?ve questions ' 5X4=20
(a) An event has six possible outcomes with the
probabilities p1=l/2, p2: 1/4, p3= 1/8 p4=l/16,
p5=l/32, p6=l/32. Find the entropy of the
systemAlso?ndtheinformatimrateifthereai-e
32 outcomes per second.
? (b) Consider a sequence of symbols emitted by a
source with their probabilities as given below:
Symbol xlxzxsx4xsx6x7xs
Hobbility 0.1 0.5 0.15 0.05 0.15 0.1 0.05 0.15
Compute the Hu?nan code for the above source
symbols. Also ?nd the average codeword length
and e?iciency. .
(c) The generator polynomial of a (7, 4) cyclic code
isG(p)p3+p+l?ndtheeodevectorsfor
messagesOlll & lllO. Ifoode is in systematic
fonn.
131601] 3 [ Contd...

(d) The parity check matrix ofa (7, 4) hamming code
00
(0
131601]
is given
1110100
[H] = 1101010
1011001,
Find :
(i) Generatormatrix
(11) code vector for message 1011
(i) draw the encoder diagram?
Thepa?tycheckmah?ixofa?, 4)hammingoode
is given. '
1110100 ?
[H] = 1101010
1011001
Calculate the syndrome vectors for
(i) No error in received code vector
(11) Error in third bit of received code vector.
A rate 1 f3 convolution encoder has generating
vectors as
g1 = (110), g2 = (110) and g3 = (101)
(i) Sket0h the encoder con?guration
(ii) Draw the trellis diagram
(iii) If input message sequence is 11010;
determine the output sequence of the
? encoder?
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