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Digital Communications MCQs set-15
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1. Which should be used first to decrypt?
Public key
Private key
Public & Private key
None of the mentioned
2. The digital signature provides authentication to the
Sender
Message
Sender & Message
None of the mentioned
3. In hash function output length is fixed.
True
False
4. The hash function
Is collision free
Has manageable collision
Has high unmanageable level of collision
None of the mentioned
5. DSA protocol is based on
Discrete logarithm problem
Continuous logarithm problem
Discrete & Continuous logarithm problem
None of the mentioned
6. What is the source for performance degradation?
Thermal noise
Man made noise
Natural noise
All of the mentioned
7. The received power is attenuated by a factor called
Path loss
Free space loss
Path & Free space loss
None of the mentioned
8. Scintillation describes the fading caused by
Atmospheric changes
Physical changes
Thermal noise
Propagating effects
9. Large scale fading refers the attenuation in
Amplitude
Phase
Signal power
None of the mentioned
10. Small scale refers to changes in
Amplitude
Phase
Amplitude & Phase
None of the mentioned
11. Small scale fading manifests due to
Signal dispersion
Time variant behavior
Signal dispersion & Time variant behavior
None of the mentioned
12. The parameters used to describe large scale fading are
Reference distance
Path loss exponent
Standard deviation of random variable
All of the mentioned
13. Small scale fading occurs due to
Doppler shift
Time delay
Doppler shift & Time delay
None of the mentioned
14. What are the types of small scale fading that occurs due to Doppler shift?
Slow fading
Fast fading
Slow & Fast fading
None of the mentioned
15. Multiple isolated peaks in multipath components is called as
Fingers
Returns
Fingers & Returns
None of the mentioned
16. If delay time is greater than symbol time, _______ fading occurs.
Frequency selective
Time selective
Frequency non selective
None of the mentioned
17. If delay time is lesser than symbol time, ______ fading occurs.
Frequency non selective
Flat
Frequency non selective & Flat
None of the mentioned
18. When channel coherence bandwidth is greater than the transmitted signal bandwidth ______ occurs.
Time selective
Frequency selective
Frequency non selective
None of the mentioned
19. Channel’s time spreading properties are
Coherence bandwidth
Signal dispersion
Coherence bandwidth & Signal dispersion
None of the mentioned
20. When channel coherence time is less than the time duration of a transmission symbol, then ______ fading occurs.
Fast
Slow
Time selective
None of the mentioned
21. Minimum time required for magnitude change or phase change is called as
Shift time
Coherence time
Delay time
None of the mentioned
22. When a user’s moving, the user’s velocity causes shift in frequency. This is called as
Doppler shift
Frequency shift
Velocity shift
None of the mentioned
23. Coherence time is _______ to Doppler spread.
Directly proportional
Inversely proportional
Not dependent
None of the mentioned
24. Block fading occurs in
Frequency domain
Time domain
Frequency & Time domain
None of the mentioned
25. If coherence bandwidth is smaller than the bandwidth of the signal, _____ fading occurs.
Flat
Frequency selective
Fast fading
Time selective
26. Flat fading can be avoided or stopped by
Error coding
Equalization
Adaptive bit loading
All of the mentioned
27. The effect of Doppler shift can be counterattacked by
OFDM
By using two receivers with separate antennas
By using diversity receiver
All of the mentioned
28. When transmitter and receiver moves towards each other, the magnitude of frequency shift is
Positive
Negative
Zero
Infinity
29. If signalling rate is less than fading rate, _____ fading occurs.
Slow
Fast
Time selective
None of the mentioned
30. Frequency tracking loop can minimize irreducible error rate by using
GMSK
DMSK
MSK
QAM
31. The technique for combining diversity signals are
Feedback
Maximal ratio
Equal gain
All of the mentioned
32. Diversity technique is used for combating
Fading
Error bursts
Co-channel interference
All of the mentioned
33. Diversity technique is applied at
Base station
Mobile receiver
Base station & Mobile receiver
None of the mentioned
34. Which is more effective and commonly preferred technique?
Time diversity
Spatial diversity
Frequency diversity
None of the mentioned
35. What are the modes of adaptive equalizer?
Training mode
Tracking mode
Training & Tracking mode
None of the mentioned
36. Which signalling scheme is preferred for fading channel?
Frequency based modulation
Phase based modulation
Frequency & Phase based modulation
None of the mentioned
37. Uncorrelated fading occurs when
Time span is small
Time span is large
Does not depend on time span
None of the mentioned
38. Interleaving does
Forward error correction
Backward error correction
Forward & Backward error correction
None of the mentioned
39. Rake receiver does
Counter effects multi-path fading
Resembles equalizer
Resembles equalizer & Counter effects multi-path fading
None of the mentioned
40. Information reliability depends on
Magnitude of each component
Time of arrival of each component
Magnitude & Time of arrival of each component
None of the mentioned
41. A rake receiver uses multiple
Delay circuits
Correlators
Detectors
None of the mentioned
42. Rake receivers are used in
Radio astronomy
CDMA
W-CDMA
All of the mentioned
43. The rake receivers functions are similar to
Equalizer
Matched filter
Equalizer & Matched filter
None of the mentioned
44. Fading channel has memory.
True
False
45. How can frequency selective distortion be minimized?
By using pilot signal
By adaptive equalization
By spread spectrum
All of the mentioned
46. How can slow fading be minimized?
By diversity technique
Error correcting codes
By diversity technique & Error correcting codes
None of the mentioned
47. Fast fading can be minimized by
Robust modulation
Coding and interleaving
Robust modulation, Coding and interleaving
None of the mentioned
48. The decision feedback equalizer has a linear traversal filter which is
Feed forward section
Feedback section
Feed forward section & Feedback section
None of the mentioned
49. The ISI and adjacent channel interference is removed by
Cancelling filter
Port processing equalizer
Cancelling filter & Port processing equalizer
None of the mentioned
50. The inter-leaver is more effective if the vehicle is
Fast
Slow
Fast & Slow
None of the mentioned
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