This set of Digital Communications Multiple Choice Questions & Answers (MCQs) focuses on “Effects of fading and decision theory”.
1. Fading channel has memory.
a) True
b) False
View Answer
Explanation: Fading channel has memory and the received samples are correlated with each other in time.
2. How can frequency selective distortion be minimized?
a) By using pilot signal
b) By adaptive equalization
c) By spread spectrum
d) All of the mentioned
View Answer
Explanation: Frequency selective distortion can be minimized by using adaptive equalization, by using spread spectrum, by using pilot signal and also by using orthogonal FDM modulation.
3. How can slow fading be minimized?
a) By diversity technique
b) Error correcting codes
c) By diversity technique & Error correcting codes
d) None of the mentioned
View Answer
Explanation: Slow fading can be minimized by using error correcting codes and also by using diversity technique to get additional uncorrelated estimates of a signal.
4. Fast fading can be minimized by
a) Robust modulation
b) Coding and interleaving
c) Robust modulation, Coding and interleaving
d) None of the mentioned
View Answer
Explanation: Fast fading can be minimized by using coding and interleaving, by using robust modulation and by introducing signal redundancy to increase signalling rate.
5. The decision feedback equalizer has a linear traversal filter which is
a) Feed forward section
b) Feedback section
c) Feed forward section & Feedback section
d) None of the mentioned
View Answer
Explanation: The decision feedback filter has a feed forward section which is a linear traversal filter.
6. The ISI and adjacent channel interference is removed by
a) Cancelling filter
b) Port processing equalizer
c) Cancelling filter & Port processing equalizer
d) None of the mentioned
View Answer
Explanation: The known ISI which is introduced deliberately and the adjacent channel interference is removed by cancelling filter and post processing equalizer.
7. The inter-leaver is more effective if the vehicle is
a) Fast
b) Slow
c) Fast & Slow
d) None of the mentioned
View Answer
Explanation: The inter-leaver is more effective in fast running vehicles.
8. Channel noise is
a) Additive
b) White and stationary
c) Has infinite bandwidth
d) All of the mentioned
View Answer
Explanation: Channel noise is stationary, additive and white with infinite bandwidth.
9. Which noise component plays a role in decision making?
a) Relevant noise
b) Non relevant noise
c) Relevant & Non relevant noise
d) None of the mentioned
View Answer
Explanation: Only the relevant noise components play an important role in decision making. It does not depend on non relevant noise components.
10. Decision making needs
a) Priors
b) Likelihoods
c) Priors & Likelihoods
d) None of the mentioned
View Answer
Explanation: Decision making needs both priors and likelihoods and Bayes decision rule combines them to achieve minimum probability of error.
11. In matched filter _______ is performed.
a) Convolution
b) Correlation
c) Convolution & Correlation
d) None of the mentioned
View Answer
Explanation: In matched filter a known signal is correlated with an unknown signal. It is similar to convolving a unknown signal with time reversed version of it.
12. Which needs more signal power?
a) BPSK
b) 16-QAM
c) BPSK & 16-QAM
d) None of the mentioned
View Answer
Explanation: 16-QAM needs ten times more signal power than BPSK to attain the same probability of error.
13. Which has higher transmission rate?
a) BPSK
b) 16-QAM
c) BPSK & 16-QAM
d) None of the mentioned
View Answer
Explanation: The rate of transmission of bits in 16-QAM is four times that of BPSK.
14. Symbol error probability can also be determined using upper bound.
a) True
b) False
View Answer
Explanation: Certain signals lacks symmetry in representation. For those signals symbol error probability can be determined by using upper bound.
15. Which signal sets are called as equivalent signal sets?
a) Simplex
b) Bi-orthogonal
c) Simplex & Bi-orthogonal
d) None of the mentioned
View Answer
Explanation: Simplex signals and bi-orthogonal signals are examples of equivalent signal sets.
16. For neyman pearson decision criterion, which are important?
a) Probability of false alarm
b) Probability of miss
c) Probability of false alarm & miss
d) None of the mentioned
View Answer
Explanation: For neyman pearson decision criterion two probabilities are important – probability of false alarm and probability of miss.
17. What are the parameters calculated for an estimator?
a) Error
b) Mean square error
c) Variance
d) All of the mentioned
View Answer
Explanation: Some of the parameters calculated for an estimator are error, mean square error, variance, sampling deviation etc.
Sanfoundry Global Education & Learning Series – Digital Communications.
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