JNTU
JNTU B.Tech III DIGITAL COMMUNICATIONS Previous Question Paper (May - 2018 - R15)
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.
Part A
The PCM signal is generated by carrying out three basic operations. What are those operations?
Answer
The three basic operations required to generate a Pulse Code Modulation (PCM) signal are:
- Sampling: The continuous-time analog signal is sampled at discrete time intervals to convert it into a discrete-time signal.
- Quantization: The sampled amplitude values are mapped to a finite set of discrete levels, approximating the continuous amplitude range.
- Encoding: Each quantized level is represented by a unique binary code word, resulting in a digital pulse stream.
State sampling theorem.
Answer
The Sampling Theorem, also known as the Nyquist-Shannon sampling theorem, states that a band-limited signal with a maximum frequency component of fm Hz can be completely reconstructed from its samples if it is sampled at a rate fs that is at least twice the maximum frequency.
The minimum sampling rate, fs = 2fm, is referred to as the Nyquist rate. If the sampling frequency is less than this value, aliasing occurs, resulting in the loss of information and the inability to perfectly reconstruct the original signal.
Draw OOK signal for binary data 101010.
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Give the graphical representation of QPSK signal constellations.
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Which information is provided by the eye pattern?
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Define entropy of a source.
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Give some examples of error correcting codes.
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For linear codes, define the minimum distance and minimum weight.
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What are the different spread spectrum techniques?
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Draw the six-stage generator of a maximum length PN sequence.
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Part B
Explain the following terms: i) Granular noise ii) Slope-overload distortion
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Consider binary PCM transmission of a video signal. Calculate the signalling rate needed to achieve.
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What are the advantages of digital communication system over analog communication system? Explain.
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A signal is ideally sampled. If the signal is passed through an ideal low-pass filter with a cut-off frequency of 250 Hz, what frequency components will appear in the output?
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Draw the block diagram of DPSK transmitter and determine its output when fed with a message sequence 1 1 0 0 1 1 0 0.
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Plot and compare the probabilities of error for the non-coherent detection of binary ASK, binary FSK and binary DPSK signals.
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Describe the non-coherent detection of binary FSK signals.
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Describe the working principle of non-coherent BFSK receiver.
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Determine the impulse response of matched filter for the given signal and sketch the matched filter output as a function of time.
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A message source generates one of four independent messages randomly every second. The probabilities of these messages are 0.35, 0.3, 0.25 and 0.1. Find the source entropy.
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Draw the typical eye diagram and label it. What are the measures that can be extracted from eye diagram regarding signal quality?
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A source has an alphabet with corresponding probabilities. Design a Huffman code for the source and compare the average length of the Huffman code with the entropy of the source.
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If G and H are the generator matrix and the parity-check matrix of a linear block code, show that GH^T = 0.
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Considering g(x) as the generator polynomial for the (7, 4) cyclic linear block code, determine the code vectors in systematic form for the following message sequences: i) 1011 ii) 1111
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Find a generator polynomial for a (7, 4) cyclic code and find code vectors for the following data vectors: 1010, 1111.
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A convolutional encoder is shown. Draw the state diagram of it.
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Draw the block diagram of FHSS system and explain.
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With a neat block diagram, explain the operation of CDMA system based on DSSS.
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What is the need for synchronization in SS systems? Explain.
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What are the applications of FHSS?
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