M.Sc Electronics (communication Science) (Semester III)
(CGPA) Examination, 2017
DIGITAL COMMUNICATION
Day Date: Thursday, 20-04-2017 Max. Marks: 70
Time: 2:30 PM to 05.00 PM
N.B. Q. No.(1)and are compulsory.
Answer any three questions from Q.3 to Q.7.
All questions carry equal marks.
Use of nonprogrammable calculator is allowed.
Q.1 Select the most correct alternative: 08
1. The square root of variance is called
Mean Random variable
Standard deviation Correlation coefficient
2. Granular noise occurs when
Step size is too small Step size is too large
Interference from the adjacent channel
Bandwidth is too large
3. If minimum distance is means it detect up to
errors.
3 2
1 4
4. For a block code, 7 is the total number of bits and 4 is the
number of
Redundant bits Total bits-information bits
Information bits None of the above
5. The sequence of operations in which PCM is done is.
Sampling, quantizing, encoding
Quantizing, encoding, sampling
Quantizing, sampling, encoding
Sampling, encoding, quantizing
6. In uniform quantization process the step
Remains same
Varies according to the input signal amplitude
Varies according to the input signal phase
Varies abruptly
7. The expected information contained in a message is called

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Entropy Efficiency Coded signal Decoded signal
8. Parity check bit coding is used for
Error correction Error detection
Both a and b Name of the above
State true or false: 06
1. DPCM requires larger bandwidth than PCM.
2. The practically used value of A-law companding is 255.
3. Compression of signal at transmitter and expansion at receiver
is called combinely as companding.
4. Information rate is defined as information per unit time.
5. Probability density function plays a role in describing a
discrete random variable.
6. A random process is said to be stationary in the strict sense
if its statics is not affected by a time shift.
Q.2 Answer the following. (any 14
Explain carrier synchronization. 05
Write a short note on random process. 05
What is a binary cyclic code? 04
What is ergodicity? 04
Q.3 With a neat block diagram, explain in brief a coherent BPSK
system.
08
State and explain Shannon- Hartly theorem. 06
Q.4 What is a matched filter? Derive an expression for its output SNR. 08
With the suitable derivation explain what do you mean by an
optimum receiver.
06
Q.5 Use Shannons encoding procedure for the following symbols and
find the code efficiency.
08
Symbol S1 S2 S3 S4 S5
Probability P1=0.4 P2=0.2 P3=0.2 P4=0.1 P5=0.1
An analog signal bandwidth limited to 10 KHz quantized states are
8 levels of PCM system with probability of and
respectively. Find the entropy and rate of information.
06
Q.6 Explain the adaptive delta modulation with a neat block
diagram.
08
Explain with an example what do you mean by non uniform
quantization?
06
Q.7 The generator polynomial of a cyclic code is
. Find out 16 code words of the above systems.
10
Compare between DM and ADM systems. 04