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NTPC MCQs

Practice NTPC-oriented Electronics & Telecommunication Engineering MCQs with answers and explanations for technical exam preparation. Questions are arranged in pages of up to 100.

Question 1806
Communication SystemsInformation Theory

The mutual information I(X;Y) is zero when X and Y are statistically?

  • AIdentical in every sample
  • BIndependent
  • CGaussian only
  • DPeriodic
Report an error
Correct Answer: B. Independent
Explanation: For statistically independent random variables, observing Y provides no information about X, so mutual information is zero.
Reference: Standard communication systems: mutual information
Question 1807
Communication SystemsInformation Theory

For a discrete memoryless channel, channel capacity is the maximum of mutual information I(X;Y) over?

  • AInput probability distributions
  • BCarrier frequencies only
  • CReceiver temperatures only
  • DSampling phases only
Report an error
Correct Answer: A. Input probability distributions
Explanation: Channel capacity is obtained by maximizing the input-output mutual information over permissible input distributions.
Reference: Standard communication systems: channel capacity definition
Question 1808
Communication SystemsSource Coding

Huffman coding assigns shorter codewords generally to symbols with?

  • ALower probabilities
  • BHigher probabilities
  • CZero probability only
  • DLonger analog durations
Report an error
Correct Answer: B. Higher probabilities
Explanation: Huffman coding minimizes average codeword length by assigning shorter words to more probable symbols.
Reference: Standard communication systems: Huffman coding
Question 1812
Communication SystemsChannel Coding

For a systematic linear block code, a codeword contains?

  • AOnly parity bits
  • BOriginal information bits explicitly plus parity bits
  • COnly carrier samples
  • DNo redundancy
Report an error
Correct Answer: B. Original information bits explicitly plus parity bits
Explanation: In systematic form, the information bits appear unchanged in specified codeword positions and parity bits occupy the remaining positions.
Reference: Standard communication systems: systematic block code
Question 1813
Communication SystemsChannel Coding

For an (n,k) block code, the code rate is?

  • An/k
  • Bk/n
  • Cn-k
  • D1/(n+k)
Report an error
Correct Answer: B. k/n
Explanation: A block code maps k information bits into n coded bits, so its rate is R=k/n.
Reference: Standard communication systems: code rate
Question 1816
Communication SystemsChannel Coding

In polynomial representation of cyclic codes, multiplication by x followed by reduction modulo x^n-1 corresponds to?

  • AA cyclic shift
  • BAmplitude clipping
  • CSampling
  • DFrequency translation only
Report an error
Correct Answer: A. A cyclic shift
Explanation: Multiplication by x shifts polynomial coefficients; modulo x^n-1 wraps the end coefficient around, implementing a cyclic shift.
Reference: Standard communication systems: cyclic-code polynomial representation
Question 1818
Communication SystemsSource Coding

The main objective of source coding is to?

  • AReduce statistical redundancy in the source representation
  • BAdd controlled redundancy for error correction
  • CIncrease receiver thermal noise
  • DCreate image-frequency interference
Report an error
Correct Answer: A. Reduce statistical redundancy in the source representation
Explanation: Source coding represents information efficiently by reducing removable redundancy.
Reference: Standard communication systems: source coding
Question 1819
Communication SystemsChannel Coding

The main objective of channel coding is to?

  • ARemove every redundant bit
  • BIntroduce structured redundancy to improve error detection or correction
  • CSuppress the RF carrier only
  • DReduce sampling rate below Nyquist
Report an error
Correct Answer: B. Introduce structured redundancy to improve error detection or correction
Explanation: Channel coding deliberately adds controlled redundancy so the receiver can detect or correct transmission errors.
Reference: Standard communication systems: channel coding
Question 1820
Communication SystemsSource Coding

A prefix code has the useful property that?

  • ANo codeword is a prefix of another codeword
  • BEvery codeword has exactly one bit
  • CAll source probabilities must be equal
  • DIt cannot be decoded sequentially
Report an error
Correct Answer: A. No codeword is a prefix of another codeword
Explanation: The prefix condition permits instantaneous decoding because a complete codeword cannot be confused with the beginning of another.
Reference: Standard communication systems: prefix code
Question 1821
Communication SystemsChannel Coding

A convolutional encoder is characterized by the fact that its output depends on?

  • AOnly the present input bit
  • BPresent input and encoder memory state
  • COnly receiver noise
  • DCarrier amplitude alone
Report an error
Correct Answer: B. Present input and encoder memory state
Explanation: Convolutional coding has memory: coded outputs depend on the current input and previous input information stored in the encoder state.
Reference: Standard communication systems: convolutional coding
Question 1822
Communication SystemsChannel Coding

The Viterbi algorithm is widely used for?

  • AMaximum-likelihood sequence decoding of convolutional codes
  • BAM envelope detection
  • CFM generation by reactance modulation
  • DAnalog source compression only
Report an error
Correct Answer: A. Maximum-likelihood sequence decoding of convolutional codes
Explanation: The Viterbi algorithm searches a trellis efficiently for the most likely transmitted state sequence of a convolutional code.
Reference: Standard communication systems: Viterbi decoding
Question 1823
Communication SystemsChannel Coding

In a trellis representation of a convolutional code, a path through the trellis represents?

  • AA possible encoder state and output sequence over time
  • BOnly receiver bandwidth
  • CA single analog carrier cycle
  • DThermal-noise temperature
Report an error
Correct Answer: A. A possible encoder state and output sequence over time
Explanation: Each trellis path corresponds to a possible sequence of encoder state transitions and associated coded outputs.
Reference: Standard communication systems: convolutional-code trellis
Question 1824
Communication SystemsError Control

Interleaving in a digital communication system is especially useful for combating?

  • ABurst errors
  • BCarrier generation
  • CQuantization itself
  • DAntenna polarization mismatch only
Report an error
Correct Answer: A. Burst errors
Explanation: Interleaving spreads adjacent corrupted bits or symbols across different codewords so a burst can appear as more manageable separated errors to the decoder.
Reference: Standard communication systems: interleaving
Question 1825
Communication SystemsError Control

A burst-error channel corrupts 12 consecutive coded bits. An idealized block interleaver primarily helps by?

  • ASpreading those errors across separated decoder positions
  • BIncreasing the RF carrier power automatically
  • CChanging every 0 into 1
  • DRemoving the need for channel coding
Report an error
Correct Answer: A. Spreading those errors across separated decoder positions
Explanation: The interleaver rearranges transmission order, so consecutive channel errors are dispersed after deinterleaving.
Reference: Standard communication systems: burst-error interleaving
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Question 1826
Communication SystemsError Control

Automatic repeat request (ARQ) primarily combines error detection with?

  • ARetransmission requests
  • BAnalog frequency modulation
  • CSource entropy maximization
  • DCarrier suppression
Report an error
Correct Answer: A. Retransmission requests
Explanation: ARQ detects erroneous or missing blocks and requests retransmission rather than relying solely on forward correction.
Reference: Standard communication systems: ARQ
Question 1827
Communication SystemsError Control

Forward error correction (FEC) differs from basic ARQ because FEC aims to?

  • ACorrect errors at the receiver without requiring retransmission for each correctable error
  • BEliminate all redundancy
  • COperate only on analog AM signals
  • DMake channel noise exactly zero
Report an error
Correct Answer: A. Correct errors at the receiver without requiring retransmission for each correctable error
Explanation: FEC adds sufficient coding redundancy for the receiver to correct specified error patterns without requesting retransmission.
Reference: Standard communication systems: forward error correction