## EC2301 Digital Communication - Anna University Previous year Question Paper NOV/DEC 2010 for ECE - 5th Semester ...

Posted by R.Anirudhan

Reg. No. :
B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2010
Fifth Semester
Electronics and Communication Engineering
EC 2301 — DIGITAL COMMUNICATION
(Regulation 2008)

Time : Three hours Maximum : 100 Marks
PART A — (10 × 2 = 20 Marks)

1. Which parameter is called figure of merit of a digital communication system
and why?
2. What is meant by distortion less transmission?
3. Why is prefiguring done before sampling?
4. Define quantization noise power.
5. Define Hamming distance and calculate its value for two code words 11100 and
11011.
6. Draw the NRZ and RZ code for the digital data 10110001.
7. What is the need for a demodulator in case of base band signaling when the
8. How does pulse shaping reduce inter symbol interference?
9. Define QAM and draw its constellation diagram.
10. A binary frequency shift keying system employs two signaling frequencies 1 f
and 2 f . The lower frequency 1 f is 1200 Hz and signaling rate is 500 Baud.
Calculate 2 f .

PART B — (5 × 16 = 80 Marks)

11. (a) Draw a neat block diagram of a typical digital communication system and
explain the function of the key signal processing blocks. (Marks 16)
Or
(b) (i) Distinguish between base band and bandpass signaling. (Marks 6)
(ii) Explain Binary symmetric channel and Gaussian channel with
their mathematical models. (Marks 10)
12. (a) State the Nyquist sampling theorem. Demonstrate its validity for an
analog signal x(t) having a Fourier transform x( f ) which is zero outside
the interval [ ] m m - f < f < +f (Marks 16)
Or
(b) Explain in detail the various source coding techniques for speech signal
and compare their performance. (16)
13. (a) For (6,3) systematic linear block code, the code word comprises 1 I , 2 I ,
3 I , 1 P , 2 P , 3 P where the three parity check bits 1 P , 2 P and 3 P are
formed from the information bits as follows : (16)
P1 = I1 ? I2
P2 = I1 ? I3
P3 = I2 ? I3
Find
(i) The parity check matrix
(ii) The generator matrix
(iii) All possible code words.
(iv) Minimum weight and minimum distance and
(v) The error detecting and correcting capability of the code.
(vi) If the received sequence is 10,000.
Calculate the syndrome and decode the received sequence.
Or
(b) (i) Explain how encoding is done by convolution codes with a suitable
example. (Marks 10)
(ii) Explain tree diagram, trellis diagram and state transition diagram
of convolution codes. (Marks 6)

14. (a) (i) Define a matched filter and compare its functioning with a
correlation. (Marks 10)
(ii) Explain how a matched filter can maximize SNR for a given
transmitted symbol. (Marks 6)
Or
(b) What does the term equalization refer to? Explain how it is carried out by
using transverse filters. (Marks 16)
15. (a) (i) Distinguish coherent and non-coherent detection. (Marks 4)
(ii) Explain non-coherent detection methods of binary frequency shift
keying scheme. (Marks 12)
Or
(b) (i) Explain Binary PSK and QPSK with corresponding equations and
constellation diagrams. (Marks 8)
(ii) Obtain the probability of bit error for coherently detected BPSK and
compare its probability of bit error performance with QPSK scheme.
(Marks 8)

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