## Wednesday, November 4, 2009

B.E / B.Tech. Degree Examinations |

III Semester |

IF 244 PRINCIPLES OF COMMUNICATION |

Time: 3 Hours Max Marks: 100 |

Answer all questions |

PART – A |

(10 x 2 = 20 Marks) |

1. Determine the Fourier Series representation of x(t)=Cos4pt + sin 8pt. |

2. What is the relation between the autocorrelation and power spectr al density of a |

random signal? Explain. |

3. Calculate the transmission bandwidths required when voice signal having a |

bandwidth of 4KHZ is transmitted using amplitude modulation and frequency |

modulation. Assume b=5. |

4. What do you understand by FM threshold? Explain. |

5. State and explain sampling theorem for band limited signals. |

6. What are the causes of Inter Symbol Interface(ISI)?. Explain how eye pattern is |

used to measure ISI. |

7. Differentiate between coherent and non-coherent demodulation. |

8. Compare the performances of M-ary PSK and M-ary PSK modulation schemes. |

9. List the properties of Pseudo Noise Sequence used in direct sequence spread |

spectrum system. |

10. What are the advantage of cyclic block codes over linear block codes? |

PART - B |

(5 x 16=80 Marks) |

11. Consider an amplitude modulated signal S(t)=5 (1+0.5 cos 2000pt +0.5 cos |

4000pt+cos 6000pt) cos 25,000pt. |

a. Sketch the frequency of spectrum of S(t) |

b. Find the total power , the sideband power and power efficiency |

c. Find the modulation index. |

12a. i) State the Dirichlet condition to be satisfied for Fourier Series and Transform |

representation . |

ii) Find the Fourier co-efficient of a periodic pulse train of period T0. |

(OR) |

12b. Explain direct method FM signals generation and slope detector for |

demodulation. |

13a. i) Draw the block diagram of Pulse code Modulator and explain. |

ii) Differentiate between granular noise and slope overload noise and slope overload |

noise in delta modulation. |

(OR) |

13b. Derive an expression for the impulse response of a matched filter working under |

white noise and hence show that it is equivalent to the time. correlate |

14a. Explain Binary PSK and Binary FSK modulation and demodulation with the help |

of block diagrams. |

(OR) |

14b. Derive an expression for bit error probability for quadrate PSK receiver and draw |

the block diagrams for the modulator and demodulator. |

15a. Draw the block diagrams of Direct Sequence and Frequency Hopping spread |

spectrum transmitters and explain. |

(OR) |

15b. Write notes on the following |

i. Cyclic codes |

ii. Adaptive Delta Modulation. |

http://www.ziddu.com/download/7216990/POC.pdf.html