JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Tech III Year DIGITAL COMMUNICATIONS Previous Question Paper (November/December - 2017 - R13)
Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks and may have a, b, c as sub questions.
PART - A
What are the basic steps involved in the process of analog to digital signal conversion?
Answer
The basic steps in analog-to-digital conversion are Sampling (converting a continuous-time signal into discrete-time samples), Quantization (mapping continuous amplitude values to a finite set of discrete levels), and Encoding (representing the quantized levels as binary digital codes).
Draw the transfer characteristics of midrise Quantizer and write the mathematical expression for quantization error?
Answer
A midrise quantizer has an odd number of quantization levels and the origin is not a quantization level. The transfer characteristic is a staircase function where the input-output mapping is symmetric about the origin. The quantization error e(t) is defined as the difference between the quantized output y(t) and the input x(t):
Differentiate Binary and M-ary signaling schemes.
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Draw the Amplitude Shift Keying and Frequency Shift Keying waveforms for 011011.
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With related equation explain the concept of Entropy.
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A discrete source generates 4 symbols X1, X2, X3 and X4 with probabilities 0.5, 0.25, 0.125 and 0.125. Determine the Entropy?
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Define Hamming distance and calculate its value for two code words 11100 and 11011.
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What is parity check matrix and how it is used?
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What are the Advantages of Spread Spectrum?
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Differentiate between Direct Sequence Spread Spectrum and Frequency Hopping Spread Spectrum.
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PART - B
Explain the principle and operation of Pulse code Modulation.
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A Delta modulation is tested with a 10KHz sinusoid signal with 1V Peak to peak at the input. It is sampled at 10 times the Nyquist rate. What is the step size required to prevent slope over load?
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Draw the block diagram of Delta Modulation and explain each block in detail.
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A six bit single channel PCM system gives an output of 60 kilo bits per second. Determine the bandwidth and number of quantization levels?
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Derive the expression of probability of error for coherent ASK signaling scheme.
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Binary data is transmitted at a rate of 106 bits/sec over a microwave link having a bandwidth of 3MHz. Assume that the noise power spectral density at the receiver input is 10-10 watts/Hz. Find the average carrier power required at the receiver input for coherent PSK, if the signaling scheme maintains Pe is ≤ 10-4 (Q(3.75)=10-4).
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Consider a Binary data11011011 transmitted using DPSK system. Show that the reconstructed data is independent of choice of arbitrary bit in encoded sequence.
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A voice signal is sampled at the rate of 5000 samples/sec and each sample is encoded into 5-bits using PCM system. The binary data is transmitted into free space after modulation. Determine the bandwidth of the modulated signal, if the modulation used is i) ASK ii) PSK iii) FSK where f1=6MHz and f2=8MHz.
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With the example, explain the procedure for Huffman coding technique.
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A source generates four messages m0, m1, m2 and m3 with probabilities 1/3, 1/6 , 1/4 and 1/4 respectively. The successive messages emitted by the source are statistically independent. Calculate entropy of the source.
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State and prove the relation between conditional Entropy and Joint Entropy.
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Apply Shannon -Fano coding procedure to find the coding efficiency for the following message ensemble. X1= 1/4, X2=1/8, X3= 1/16, X4= 1/16, X5= 1/16, X6=1/4, X7= 1/16, X8= 1/8. Obtain the average number of bits/message and coding efficiency.
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With an example explain the decoding process of cyclic codes using polynomial method.
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Consider the (6, 3) linear block code with parity check matrix H. Construct all the possible code vectors.
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Consider a convolutional encoder with K=3 and n=2 and g(1) =( 1,1,1) ; g(2) =(1, 1,0). i) Draw the encoder circuit ii) Draw the State diagram tree diagram and trellis diagram.
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The generator polynomial of a (7, 4) cyclic code is g(x) = 1+x+x3. Find the code word for the binary data 111011 using polynomial division method.
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What are the two spread spectrum techniques and explain each in detail.
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What is the role of Synchronization in spread spectrum systems?
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Differentiate between Fast Frequency Hopping and Slow Frequency Hopping.
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Write short notes on CDMA of DSSS.
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