Anna University Coimbatore 2010 B.E Electronics & Communication Engineering Digital Communications - Question Paper
ANNA UNIVERSITY COIMBATORE B.E. I B.TECH. DEGREE EXAMINATIONS : MAY I JUNE 2010 REGULATIONS : 2007 SIXTH SEMESTER: ECE ,
070290071 - DIGITAL COMMUNICATION TIME : 3 Hours Max.Marks : t00
PART - A
(20 x 2 = 40 MARKS)
ANSWER ALL QUESTIONS
1. Find the Nyquist rate and Nyquist interval for the signal g(t) = sine 200t. 1
2. What is Delta modulation?
-3r Determine the SNR of PCM system if the number of quantization levels is
28? [
t
4. Differentiate uniform and non-uniform quantizer.
5. Compare PAM and PCM.
6. What is Intersymbol interference? Explain
7. What is an ideal Nyquist channel? |
8. Give the application of Raised Cosine channels. I
9. Compare the probability of error of PSK with that of FSK. i
10. What is the need for bit synchronization?
11. Draw the ML partitioning space for BFSK.
12. What is bit error probability?
13. What are Hamming codes?
14. Mention the properties of cyclic codes.
15. What are Reed Solomon codes?
16. Define spread spectrum.
17. What is anti-jam?
18. Slow hop FH/MFSK system has number of bits/MFSK symbol as 4 and number of MFSK symbols/hop as 5. Calculate processing gain of the system.
19. What is frequency hopping spread spectrum?
20. Sketch the model of spread spectrum communication system.
PART - B
(5x12 = 60 MARKS)
ANSWER ANY FIVE QUESTIONS
21. A sinusoidal signal is transmitted using PCM. An output SNR of 66.7 dB is required. Find the number of representation levels required to achieve this
performance.
22. a Explain the STDM and ASTDM with neat illustrations. 6 b Derive the expression for quantization error due to DM. 6
23. a Derive the condition for Nyquist criterion for zero ESI. 6 b Write short notes on Correlative coding. 6
24. a Explain briefly about FSK system with a neat signal space diagram. 6
b In a PSK system, the received waveforms S1(t)=A coswt and 6 S2(t)= -A coswt are coherently detected with a matched filter. The value of A is 20mV and the bit rate is 1Mbps. Assume that the noise power spectral density h/2=10-11W/Hz. Find the probability of error Pe
25. a Derive an expression for error probability of a BPSK system. 8
26. a Explain Viterbi decoding algorithm in detail with an example. 6
b For a (2,1,3) convolution code with g1 = ( 1 0 1 1) and g2 = ( 1 1 1 1), 6 design the encoder and find the following.
(i) Generator matrix
(ii) Transfer function matrix Compute the coded output using both the methods assuming the input u = (101101).
27. a Describe Trellis coded modulation in detail with an example. 3 b Derive an expression for Jamming margin for direct sequence spread 6
spectrum system with BPSK modulation
28. a Discuss the method of generation and properties of Pseudo Noise 6
sequences in detail.
b An PN sequence is generated using a feed back register of length m = 8. 6 The chip rate is 127 chips per sec. Find the length, chip duration and the period of the PN sequence
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| Earning: Approval pending. |
