# Analog and Digital Communication 3rd ND11 CS2204

B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2011.
B.E. Computer Science and Engineering
Third Semester
CS2204 - 141304 - ANALOG AND DIGITAL COMMUNICATION
(Regulation 2010)

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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 Carsons 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)