**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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