West Bengal Institute of Technology (WBIT) 2008-5th Sem B.Tech Electronics and Communications Engineering Electronics & Comm ( - ) Digital Communication - Question Paper
CS/.TKCH (EC*-KEW)/8EM-B/EC-503/0/(09) 3
ENGINEERING & MANAGEMENT EXAMINATIONS, DECEMBER - 2008 DIGITAL COMMUNICATION SYSTEM SEMESTER -5
Time : 3 Hours ] { Full Marks ; 70
GROUP-A
(Multiple Choice Type Questions)
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Choose the correct alternatives for any ten of the following : 10 x 1 = 10
i) The frequency spectrum of a square wave or rectangle wave in time domain Is a) Impulse function b) Sine function
c) Sine, function d) Gaussian function.
ii) In quantization has 8 bit code, then SMR will be a) 32 dB b) 16 dB
c) 48 dB d) 8 dB.
f '
ill) In Hofmann coding, the probabilities are arranged in
- 1 - r "
a) ascending order
b) descending order
c) no specification.
iv) How many bits would be required to represent a 256 level quantization in PCM ? a) 6 b) 8
c) 5 d) 7.
v) In PCM, the amplitude levels are transmitted in a 7-unit channel code. The sampling is done at the rate of 10 Hz. The bandwidth preferred minimum should be
a) 5 kHz b) 35 kHz
c) 70 kHz d) 85 kHz. 1
vi) If the quantization has 4 levels which occurs with probability Pj = P4 = and
8
p2 s P3 = , then the information rate is 8
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a) 1-8 bits/message b) d) c) 1 -v6 bits / message |
3-8 bits/message 2-6 bits/message. |
vli) The Nyquist rate of the composite signal x (/) * 5 cos 1000 nt cos 3000 nt is
a) 3000 Hz b) 1000 Hz
c) 4000 Hz d) 2000 Hz.
viii) The channel capacity of a band-limited Gaussian channel is
a) C - B log2 (l+|)
c> c4'Mf)
C-B
b)
d)
ix) Which of the following system is digital ?
pulse-code modulation pulse-frequency modulation.
PCM generation requires LPF (low-pass filter ) at the beginning to
a) eliminate aliasing effect
b) eliminate quantization noise
c) eliminate decoding noise
d) none of these.
xi) Spread spectrum scheme Increases
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a) processing gain c) transmission gain xli) Eye pattern is used to study a) ISI c) Error rate |
b) spectral efficiency d) none Of these. b) Quantization noise d) None of these. |
GROUP-B (Short Answer Type Questions )
Answer any three of the following.
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2. |
a) |
What are the proportion of line coding. |
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b) |
Draw the Manchester coding and PNRZ coding for m = 1001011 | |
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c) |
Write down the PSD function of PNRZ signal. | |
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3. |
a) |
Explain the advantages of digital communication system. |
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b) |
Draw block diagram and explain such a system briefly. | |
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4. |
a) |
What is direct sequence spread spectrum ? |
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b) |
Explain the generation of DSSS. | |
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5. |
What is eye pattern ? | |
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b) |
How is it generated in CRO. | |
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c) |
What information we get from it ? | |
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6. |
Explain the principle of operation of QPSK modulator. | |
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7. |
a) |
Explain the implication 'aliasing1. |
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b) |
How is the 'aliasing' effect removed. | |
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GROUP-C (Long Answer Type Questions ) Answer any three of the following questions. | ||
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8. |
a) |
What are the disadvantages of DPSK. |
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b) |
What are the disadvantages of BPSK and how is it improved ? | |
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c) |
What is BFSK ? | |
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d) |
Describe orthogonal BFSK. | |
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9. |
a) |
State sampling theorem and explain its important. |
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b) |
What is Nyquist rate of sampling. | |
CS/B.TECH (ECE-NEW)/SEM-B/EC-503/OS/(09) 6 1Va/ E
c) Explain how an analogue signal is converted into a digital signal noising PCM system. 6
d) A television signal has a bandwidth of 4*5 MHz. The signal is sampled and converted into PCM signal. Determine the sampling rate if the signal is to be sampled at a rate 20% above Nyqulst rate. 3
10. a) What is quantization ? Classify them. 3
b) How is non-uniform quantization utilised. 2
c) Deduce the relation of signal to quantization noise. 4
d) Calculate the number of quantization levels for the signal x{t) = 5 sin (500 n + 0) 4
e) What are therelated laws for non-uniform quantization. 2
11. a) What do you mean by matched filter for digital reception ? 5
b) Derive an expression for error probability of a matched filter ? 3
c) State and explain Nyqulst criterion for zero ISI. 3
d) What is the roll of an equalizer ? 4
12. a) Define information. 2
b) Define'Discrete Memoryless Source'. 2
c) What is 'Entropy1 ? 2
d) Calculate amount of information if binary digits occur with equal llkelyhood in a binary PCM system. 3
e) A discrete source emits one of the five symbols once every millisecond with
probabilities , , , and . Determine source entropy and information
2 4 8 16 32
rate. 6
13. Write sh6rt notes for the following :
a) Compounding 5
b) Differential Encoding 5
c) Linear Prediction Coder. 5
END
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Attachment: |
| Earning: Approval pending. |
