RTU 2016 Question Paper Semester VI Electronics and Communication Engineering Digital Communication

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B. Tech. VI-Sem. (Main/Back) Exam., April/1Vlay-2016
Electronics & Communication Bngineering
EI 6EC4A Digital Communication
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Time: 3 Hours Maximum Marks: 80
Min. Passing Marks (Main & Back): 26
Instructions to Candidate s : -

Attempt any five questions, selecting one qaestion from each anit. All
Questions carry equal marks. Schematic diagrams must be shown
wherever necessary. Any data you feel missing may suitably be assumed
and stated clearly.
Units of quantities used,/ calculated must be stated clearly.
Use of following supporting material is permitted during examination.
(Mentioned in form No. 205)
I. NIL 2. NIL

UNIT.I
Q.l (a) Explain the quantization error and derive an expression for maximum signal to
noise ratio in PCM system that uses linear quantization. t8l
(b) A television signal having a bandwidth of 4.2 MHz is transmitted using a binary
PCM system. Given that the number of quantization level is 512, determine- [8]
(i) Code Word Length
(ii) TransmissionBandwidth
(iii) Final Bit Rate
(iv) Output Signal to Quantization Noise Ratio

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OR
Q.1 (a) What are the drawbacks of Delta Modulation and how it is removed in
ADM? t8l
(b) In a DM system, the voice signal is sampled at a rate of 64,000 samples/ second.
The maximum signal amplitude A-u* = 1

(i) Determine minimum value of step size to avoide slope overload l2l
(ii) Determine quantization noise power if voice signal bandwidth is 3.5 kHz.[3]
(iii) Assuming voice signal to be a sine wave, determine Soand the SNR t3l
UNIT.II
Q.2 (a) Explain Inter - Symbol Interference (ISI) in detail. t8l
(b) Given that the bit sequence given below is to be transmitted - l4x2=8)
Bit sequence = 10110010
Draw the resulting waveform, if the sequence is transmitted using
(i) Unipolor RZ & NRZ
(ii) Bipolor RZ & NRZ
(iii) Polor RZ & NRZ
(iv) AMI & M -a:ray when M = 4
OR
Q.2 (a) Explain the Nyquist criterion for distortion less baseband binary transmission. t8l
(b) Explain the following formats with equation (assume suitable data for
diagram). [4x2=8]
(i) Unipolor RZ & NRZ
(ii) Bipolor RZ & NRZ
(iii) Manchasterformat
(iv) Polor Quaternary NRZ format

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Q.3 (a) Explain MSK transmitter and receiver. What are the advantages of MSK as
compared to epSK?
t10l
(b) In a digital continuous time communication system, the bit rate of NRZ data
stream is lMbps and carrier frequency of transmission is 100 MHz. Find the

symbol rate of transmission and bandwidth requirement of the channel in

following cases of different techniques used :
13x2=61

(a) BPSK sysrem
(b) QPSK system

(c) 16 ary PSK system

OR
Q.3 (a) Explain M - ary and PSK in Detail.
tt2)
(b) For the following data stream, show the phase states of carrier and draw
epSK
Signal Data stream = 10110001
l4l

Q.4 (a) Explain entropy and prove the following:
tgl
0 < H (X) < log2 m, where m is the size of the a$habet in X

(b) Given a telegraph source having two symbols, dot and dash. The dot duration
is
0.2 second. The dash duration is three times the dot duration. The probability
of
the dots occurring is twice that of the dash and the time between symbols
is 0.2
second.

Calculate the information rate of telegraph source.
t8l

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OR
Q'4 (a) A discrete memory ress source (DMs)
X has four symbors x1 x2 x3 xa with
probabilities P (x1)
= 0.4,P (xz) = 0.3, p (xs) = 0.2 and.p (x.)
= g.1
(i) Calculate H (X)
L4l
(ii) Find the amount of information contained
in the ffiessage x1 x2 X1 x3 and
X4 X3 X2 X3
t4l
(b) Explain channel capacity and prove S ')

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C = B rog, [r
N/ t8l

UNIT-V
Q.5 Write short notes on: (Any Four)
(a) Hamming code L4x4=161

(b) Signal parity bit code
(c) Linear block code
(d) Cyclic code
(e) Convolutional code
OR
Q'5 A DMs has seven symbols X1 x2
X3 x4 X5 X6 x7 with probabilities
P (xr) = 0'05' p (xz)
- 0.05, p (xs) = 0.1, p (xa) = 0.15, p (xs)
= 0.3, p (xo) =0.2andp
(xz) = o'15'
[2x8=161
(a) Construct a Shannon fano code for
X, and calculate the efficiency
of code
(b) Repeat for the Huffman code and
compare the result

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