GTU BE/B.Tech 2019 Winter Question Papers || Gujarat Technological University
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER- VI (Old) EXAMINATION - WINTER 2019
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Subject Code: 161001 Date: 11/12/2019
Subject Name: Digital Communication
Time: 02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
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| MARKS | |
|---|---|
| Q.1 (a) Explain the advantages of digital communication over analog communication. | 07 |
| (b) What is a line code? Describe the desirable properties of line codes | 07 |
| Q.2 (a) Draw neat diagram of delta modulator, delta demodulator, input waveform, output waveform and error waveform. Define slope overload and write the condition to avoid slope overload in delta modulation. | 07 |
| (b) Derive an equation of signal-to noise ratio for a uniform quantizer. | 07 |
| OR | |
| (b) State Nyquist sampling theorem. Write the condition and name of the circuit to avoid aliasing. Discuss the applications of sampling theorem. | 07 |
| Q.3 (a) Explain HDB3 signaling with an example. Draw it PSD. | 07 |
| (b) What is a regenerative repeater? Draw its block diagram and state the function of each block in 2-3 sentences. | 07 |
| OR | |
| Q.3 (a) Draw neat waveforms of data, carrier and modulated signals for ASK; FSK and PSK modulations. What is the difference in PSDs of ASK and PSK. | 07 |
| (b) State the Nyquist criterion for zero ISI. Draw time and frequency domain waveforms for the pulse that satisfies this criterion. Define roll-off factor. | 07 |
| Q.4 (a) Define the following mathematically with reference to probability and random variables: Conditional probability, joint probability, CDF, PDF, Statistical mean, variance, correlation. | 07 |
| (b) State and explain central limit theorem. | 07 |
| OR | |
| Q.4 (a) Find the mean square value of quantization error in PCM considering uniform random variable approach | 07 |
| (b) Give mathematical expression of Gaussian PDF and CDF. Also, draw the curves for the CDF and PDF of Gaussian random variable. Define Q function and express the probability that Gaussian random variable is greater than some value x in terms of Q function. | 07 |
| Q.5 (a) Derive the expression for the channel capacity of a Binary Symmetric Channel. | 07 |
| (b) Define following with reference to error detecting and correcting codes: Code efficiency, Hamming bound, perfect code, generator polynomial, interlaced code, code tree, burst error-detecting/correcting code. | 07 |
| OR | |
| Q.5 (a) Design an optimum binary receiver and compute error probability for 16-QAM system. Assume all messages are equi-probable and AWGN channel. | 07 |
| (b) Explain the coherent detection of ASK signal with neat diagram, waveforms and relevant expressions. | 07 |
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