JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III DIGITAL COMMUNICATIONS Previous Question Paper (August/September - 2024 - R16)
Note: Part A is compulsory (25 Marks). In Part B, answer any one question from each unit (10 Marks each).
Part A
List key advantages of digital communication systems over analog systems.
Answer
- Robustness to noise: Digital signals are less susceptible to noise and interference compared to analog signals because they can be regenerated at repeaters.
- Error correction: Digital systems allow for the implementation of error detection and correction codes, ensuring high data integrity.
- Ease of multiplexing: Time-division multiplexing (TDM) is more efficiently implemented in digital systems.
- Storage and processing: Digital data is easily stored and processed using sophisticated digital signal processing (DSP) algorithms.
A PCM system uses a uniform quantizer followed by a 7-bit binary encoder. The bit rate of the system is equal to 50x10^6 bits/sec. What is the maximum message bandwidth for which the system operates satisfactorily?
Answer
Given: Bit rate (Rb) = 50 Mbps, Number of bits per sample (n) = 7.
The sampling rate (fs) is calculated as:
According to the Nyquist criterion, the maximum message bandwidth (W) is half the sampling frequency:
What is the parity-check matrix, and how is it used in error detection?
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Why is understanding the bandwidth-S/N trade-off important in system design?
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What is the role of a correlation receiver in digital communication systems?
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Explain the concept of an optimal linear receiver.
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What are the advantages of using a PLL for FSK detection?
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How do higher-order PSK schemes like 8-PSK and 16-PSK increase data rates? Explain.
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How does FHSS enhance resistance to interference and jamming?
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How does CDMA allow multiple users to share the same frequency band? Explain.
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Part B
Compare and contrast the three types of sampling techniques in terms of the characteristics, advantages, and disadvantages.
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Describe Adaptive Differential Pulse Code Modulation and how it extends the concept of DPCM.
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Describe the Lempel-Ziv coding algorithm and its significance in data compression with an example.
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Discuss with a detailed example of decoding a convolutionally encoded sequence using the Viterbi algorithm.
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Discuss the principles of baseband M-array Pulse Amplitude Modulation (PAM) transmission and also explain the advantages and limitations of M-array PAM compared to binary PAM.
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Discuss the geometric interpretation of signals in digital communication systems with an example.
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Binary data is transmitted over a telephone line with a usable bandwidth of 2400 Hz using the FSK signaling scheme. The transmit frequencies are 2025 Hz and 2225 Hz, and the data rate is 300 bits/sec. The average signal to noise power ratio at the output of the channel is 6 dB. Calculate the Probability of error for the coherent and non-coherent demodulation schemes.
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Explain in detail about QPSK and find the probability of Error.
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Derive the necessity of DSSS techniques. Draw the transmitter and receiver block diagram and explain.
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Explain about PN-Sequences generation and their characteristics.
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What is meant by Synchronization? Why we require synchronization in spread spectrum? Explain in detail.
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