Download GTU (Gujarat Technological University Ahmedabad) B.Tech/BE (Bachelor of Technology/ Bachelor of Engineering) 2020 Winter 6th Sem 2161001 Digital Communication Previous Question Paper
Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE- SEMESTER?VI (NEW) EXAMINATION ? WINTER 2020
Subject Code:2161001 Date:20/01/2021
Subject Name:Digital Communication
Time:02:00 PM TO 04:00 PM Total Marks: 56
Instructions:
1. Attempt any FOUR questions out of EIGHT questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1 (a) Derive Bay's rule.
03
(b) Five telemetry signals, each of bandwidth 1kHz, are to be transmitted 04
simultaneously by binary PCM. The maximum tolerable error in sample
amplitudes is 0.2% of the peak signal amplitude. The signal must be
sampled at least 20% above the Nyquist rate. Framing and synchronizing
requires an additional 0.5% extra bits. Determine the minimum possible
data rate (bits per second) that must be transmitted and minimum
bandwidth required to transmit this signal.
(c) Explain Quantization noise in a PCM. For a PCM signal, determine L if 07
the compression parameter ?=100 and the minimum SNR required is 45
dB.
Q.2 (a) Describe "Timing Extraction" required to sample incoming pulses at 03
precise instants in regenerative repeater.
(b) Explain an M-ary FSK digital modulation technique in brief.
04
(c) Explain the operation of Delta Modulation using block diagram and 07
waveforms. Discuss the need of Adaptive Delta Modulation.
Q.3 (a) Compare the On-off and Bipolar signaling for transmission of digital data. 03
(b) Using general expression for finding Power Spectral Density (PSD), find 04
PSD of a polar signaling.
(c) Explain Differential Phase-Shift Keying (DPSK) modulation technique in 07
detail. What is advantage of DPSK over Binary-Phase Shift Keying
(BPSK)?
Q.4 (a) Explain Noise temperature and Noise figure in brief.
03
(b) Compare QPSK and MSK modulation techniques.
04
(c) Describe non-coherent detection of Amplitude-Shift Keying (ASK) signal. 07
Q.5 (a) We have two boxes. Box-1 contains 1000 components of which 5% are 03
defective. Box-2 contains 200 components of which 20% are defective.
We select at random one of the boxes and we remove at random a single
component then, what is the probability that the selected component is
defective?
(b) Explain coherent detection of Frequency-Shift keying (FSK) signal.
04
(c) A zero-memory source emits six messages with probabilities 0.4, 0.2, 0.1, 07
0.1, 0.1, and 0.1. Find binary Huffman code and determine the code
efficiency of the code.
1
Q.6 (a) Determine mean and the variance of the RV x whose PDF is given by
03
p (x) 0.5
x
x e
.
x
(b) Explain Chebyshev's Inequality.
04
(c) For a (7,4) linear block code, the generator matrix G is
07
1 0 0 0 1 1 0
0 1 0 0 0 1 1
G
0 0 1 0 1 1 1
0 0 0 1 1 0 1
1. Construct the code table generated by this matrix.
2. Prepare a suitable decoding table.
Q.7 (a) Explain Interlaced code for burst error correction.
03
(b) Explain code tree for Convolutional codes with suitable example.
04
(c) Explain Cumulative Distribution Function (CDF) and Probability Density 07
Function (PDF) of random variable in detail.
Q.8 (a) Show that for finite signal and noise powers, the channel capacity always 03
remains finite in the case of AWGN channel.
(b) Explain syndrome decoding of systematic cyclic codes.
04
(c) Derive expression for channel capacity of discrete memory-less channel 07
with an arbitrary number of inputs.
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This post was last modified on 04 March 2021