ANALOG AND DIGITAL COMMUNICATION(ADC) 141304 ANNA UNIVERSITY QUESTION PAPER MODEL QUESTION PAPER NOV/DEC 2011

B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2011.

B.E. Computer Science and Engineering

Third Semester

141304 — ANALOG AND DIGITAL COMMUNICATION

(Regulation 2010)

Time : Three hours Maximum : 100 marks

Answer ALL questions.

PART A — (10 ´ 2 = 20 marks)

1. Consider an AM signal ) 2 cos( . ) 2 cos( 5 . 0 ) 2 cos( 2 ) ( t f t f t f t x c m c p p p + = . Find the modulation index used to generate the signal

2. Draw the block diagram of FM signal generator that uses phase modulator in it.
3. Distinguish between power efficiency and spectral efficiency.
4. Find the capacity of a channel having 50 kHz bandwidth and produces SNR of
1023 at the output.
5. A PCM system uses sampling frequency of 16 k. samples/s. Then, find out the
maximum frequency of the signal upto which the signal can be perfectly
reconstructed.
6. What is IST? What is the reason for it occurance?
7. List the layers presented in ISO–OSI reference model.
8. What is modem?
9. Differentiate TDMA and CDMA.
10. Differentiate multiplexing and multiple access.

PART B — (5 ´ 16 = 80 marks)

11. (a) Write the equation of single tone amplitude modulation. Derive the
Fourier transform of the signal and plot the signal in time domain and
frequency domain for the modulation index
(i) lesser than unity,
(ii) equal to unity
(iii) greater than unity Also calculate the power of each frequency component
Or
(b) (i) Briefly discuss the method of deriving wideband FM signal. (12)
(ii) State and apply Carson’s rule to calculate the bandwidth occupied
by a 3kHz message signal frequency modulated with modulation
indext = 5. (4)
12. (a) (i) Draw the block diagram of QPSK modulator, demodulator and
explain the principle of operation. (8)
(ii) With neat constellation diagram, explain the operation of QAM
transmitter. List out its merits over PSK. (8)
Or
(b) (i) Explain the operation of the binary FSK modulator and
demodulator with its constellation diagram. (10)
(ii) Brief the carrier recovery with squaring loop. (6)
13. (a) (i) Draw the block diagram of pulse code modulation system and write
short notes on each blocks. (8)
(ii) Explain in details on the criterions need to be satisfied in its
sampling and quantization blocks. (4+4)
Or
(b) (i) Draw the block diagram of delta modulation system and explain. (6)
(ii) With suitable diagram and example, explain the noise associated
with DM. (5)
(iii) Derive the condition on step size to avoid slope overload error. (5)
14. (a) (i) What is CRC? Draw the encoder of the same and explain its
operation. (8)
(ii) Write short notes on forward error correction and backward error
correction techniques. (8)
Or
(b) Draw the block diagram of modem and explain the operation with the
importance of each block in the diagram.
15. (a) (i) List three properties of pseudo-noise signal and explain them with
an example. (8)
(ii) With neat block diagram, explain the DS-spread spectrum with
coherent BPSK. (8)
Or
(b) (i) With neat diagram, describe the operation of CDMA. (8)
(ii) Compare the features of FDMA, TDMA and CDMA. (8)
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