FACULTY OF ENGINEERING B.E. 3/4 (ECE) II Semester (Suppl.) Examination, December 2012 Subject: Digital Communication Systems Time: 3 Hours
Max.Marks: 75
Note : Answer all questions from Part A. Answer any Five questions from Part B. PART – A (25 Marks) 1. List the advantages and disadvantages of digital communication system. 2. What is companding in PCM system? Why do you need it? 3. What is meant by concept of information and average information? 4. Define entropy with reference to information theory? 5. Justify need for error control coding. 6. What are advantages of convolutional codes over block codes? 7. Draw neat diagrams of ASK, FSK and PSK signals. 8. What is correlation receiver and explain. 9. List the properties of PN sequences. 10. Define direct sequence spread spectrum and frequency hoping spread spectrum.
(3) (3) (2) (2) (3) (2) (3) (2) (3) (2)
PART – B (50 Marks) 11.(a) What is quantization noise and derive the expression for the same.
(6)
(b) A PCM system uses a uniform quantizer followed by a 7 bit encoder. The bit rate of the system is 50x106 bits/sec. What is the maximum band width for which system operates satisfactorily? What is its output SNR in dB. (4) 12.(a) Explain Shannon Fano encoding with an example. (b) A DMS X has four symbols x1,x2,x3 and x4 with probabilities p(x1 ) = and p(x3 ) = p(x4 ) = 13.
(4) 1 1 , p(x2 ) = 2 4
1 . Construct Huffman code for x and calculate the efficiency. 8
(6)
The generator polynomial of (7,4) cyclic code is g(x) = 1+x+x3. Find the code words in systematic and non systematic methods for the message vectors 1010, 1100 & 1101. (10)
14.(a) With the help of block diagrams explain the generation and detection of QPSK signal. (b) Compare DM and DPCM.
(7) (3)
15.(a) Explain acquisition and tracking of FHSS. (b) Explain how ranging using direct sequence spread spectrum.
(6) (4)
16.(a) What is meant by m-ary signaling? What are the advantages and disadvantages of m-ary signaling over binary signaling. (6) (b) Describe the sequential decoding of convolutional codes. (4) 17.
Write short notes on the following: (a) Adaptive Delta Modulation (b) Optimum Receiver (c) BCH codes.
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Define direct sequence spread spectrum and frequency hoping spread spectrum. (2). PART â B (50 Marks). 11.(a) What is quantization noise and derive the ...
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