GUJARAT TECHNOLOGICAL UNIVERSITY
BE- SEMESTER-VI (NEW) EXAMINATION - WINTER 2020
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Subject Code:2161001 Date:20/01/2021Subject Name:Digital Communication
Time:02:00 PM TO 04:00 PM Total Marks: 56
Instructions:
1. Attempt any FOUR questions out of EIGHT questions.
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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 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. [04]
(c) Explain Quantization noise in a PCM. For a PCM signal, determine L if the compression parameter µ=100 and the minimum SNR required is 45 dB. [07]
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Q.2 (a) Describe “Timing Extraction” required to sample incoming pulses at precise instants in regenerative repeater. [03]
(b) Explain an M-ary FSK digital modulation technique in brief. [04]
(c) Explain the operation of Delta Modulation using block diagram and waveforms. Discuss the need of Adaptive Delta Modulation. [07]
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 PSD of a polar signaling. [04]
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(c) Explain Differential Phase-Shift Keying (DPSK) modulation technique in detail. What is advantage of DPSK over Binary-Phase Shift Keying (BPSK)? [07]
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 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? [03]
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(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, 0.1, 0.1, and 0.1. Find binary Huffman code and determine the code efficiency of the code. [07]
Q.6 (a) P(x)=0.5|x| e-|x| Explain Chebyshev’s Inequality. [04]
(b) For a (7,4) linear block code, the generator matrix G is
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G = [ 1 0 0 0 1 1 00 1 0 0 1 0 1
0 0 1 0 0 1 1
0 0 0 1 1 1 1 ]
1. Construct the code table generated by this matrix.
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2. Prepare a suitable decoding table. [07]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 Function (PDF) of random variable in detail. [07]
Q.8 (a) Show that for finite signal and noise powers, the channel capacity always remains finite in the case of AWGN channel. [03]
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(b) Explain syndrome decoding of systematic cyclic codes. [04]
(c) Derive expression for channel capacity of discrete memory-less channel with an arbitrary number of inputs. [07]
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