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Digital Communications MCQs set-10
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1. Turbo code is a
Serial concatenation code
Parallel concatenation code
Block code
None of the mentioned
2. The minimum nyquist bandwidth needed for baseband transmission of Rs symbols per second is
Rs
2Rs
Rs/2
Rs2
3. The capacity relationship is given by
C = W log2 ( 1+S/N )
C = 2W log2 ( 1+S/N )
C = W log2 ( 1-S/N )
C = W log10 ( 1+S/N )
4. Which parameter is called as Shannon limit?
PB/N0
EB/N0
EBN0
None of the mentioned
5. Entropy is the measure of
Amount of information at the output
Amount of information that can be transmitted
Number of error bits from total number of bits
None of the mentioned
6. Equivocation is the
Conditional entropy
Joint entropy
Individual entropy
None of the mentioned
7. For a error free channel, conditional probability should be
Zero
One
Equal to joint probability
Equal to individual probability
8. Average effective information is obtained by
Subtracting equivocation from entropy
Adding equivocation with entropy
Ratio of number of error bits by total number of bits
None of the mentioned
9. Turbo codes are
Forward error correction codes
Backward error correction codes
Error detection codes
None of the mentioned
10. Components used for generation of turbo codes are
Inter leavers
Punching pattern
Inter leavers & Punching pattern
None of the mentioned
11. Decoders are connected in series.
True
False
12. The inter leaver connected between the two decoders is used to
Remove error bursts
Scatter error bursts
Add error bursts
None of the mentioned
13. In soft decision approach what does -127 mean?
Certainly one
Certainly zero
Very likely zero
Very likely one
14. In soft decision approach 100 means?
Certainly one
Certainly zero
Very likely zero
Very likely one
15. In soft decision approach 0 represents
Certainly one
Certainly zero
Very likely zero
Could be either zero or one
16. QPSK is a composite of
Two BPSK
Three BPSK
Two FSK
Two M-ary PSK
17. The IF transmission bandwidth of MFSK is
M/T
T/M
2M/T
M/2
18. The bandwidth efficiency of MFSK is
M/log2M
log2M/M
M/log10M
log10M/M
19. The bandwidth efficiency increases as M increases.
True
False
20. The bandwidth efficiency of QFSK is _______ that of BFSK.
Greater than
Less than
Equal to
None of the mentioned
21. Which modulation is the most efficient one?
BPSK
BFSK
QPSK
QAM
22. The primary communication resource is
Transmitted power
Received power
Efficiency
None of the mentioned
23. Greater the redundancy lesser is the bandwidth expansion.
True
False
24. Which modulation scheme uses nonlinear transponders?
MSK
Offset QPSK
MSK & Offset QPSK
None of the mentioned
25. Which modulation requires more bandwidth?
QPSK
OQPSK
BPSK
BFSK
26. Which modulation has lower side lobe levels?
QPSK
OQPSK
BPSK
MSK
27. Which modulation is spectrally more efficient?
BPSK
MSK
QPSK
OQPSK
28. Which modulation spectrum has narrow main lobe?
QPSK
OQPSK
BPSK
MSK
29. Which technique can be used for bandwidth reduction?
BPSK
QPSK
MPSK
MFSK
30. QPSK amplitude modulates
Sine function
Cosine function
Sine & Cosine function
None of the mentioned
31. QAM is a combination of
ASK and FSK
ASK and PSK
PSK and FSK
None of the mentioned
32. Which refers to the presence of error correction coding scheme?
Coded
Uncoded
Coded & Uncoded
None of the mentioned
33. The system will be more bandwidth efficient as WTb decreases.
True
False
34. In MPSK, R/W
Increases with increase in M
Increases with decrease in M
Decreases with increase in M
Is not dependent on M
35. In MFSK, R/W
Increases with increase in M
Increases with decrease in M
Decreases with increase in M
Is not dependent on M
36. Which modulation is selected for power limited system?
MPSK
MFSK
MPSK & MFSK
None of the mentioned
37. The transmission rate is given as
R/log2M
log2M/R
R/log10M
log10M/R
38. Code’s redundancy is given as
n/k
k/n
nk
None of the mentioned
39. For more than two quantization level, _______ is used.
Hard decision
Soft decision
Hard & Soft decision
None of the mentioned
40. How can the throughput of the system be increased?
Increasing EIRP
Increasing channel bandwidth
Decreasing system losses
All of the mentioned
41. In which technique spot beam antennas are used to point the radio signals in different directions?
Code division
Space division
Frequency division
None of the mentioned
42. In polarization division technique ______ polarization is used.
Orthogonal
Non orthogonal
Orthogonal & Non orthogonal
None of the mentioned
43. Channelization characterized by orthogonal spectra is called as
Time division multiplexing
Frequency division multiplexing
Time division & Frequency division multiplexing
None of the mentioned
44. In double side band spectrum which side-band is called as inverted side-band?
LSB
USB
LSB & USB
None of the mentioned
45. The mixing and filtering of DSB removes
LSB
USB
LSB & USB
None of the mentioned
46. The super group is made up of
Five groups
Sixty channels
Five groups & Sixty channels
None of the mentioned
47. The orbital period of communication satellites is _______ as that of earth’s rotational period.
Same
Greater
Lesser
None of the mentioned
48. Adding improvement to the signal subset choice by starting with the densest possible lattice for the space is called as
Optimum signal constellation boundaries
Higher density lattice structures
Trellis coded modulation
None of the mentioned
49. Choosing a closely packed signal subset from any regular lattice or array of candidate points is called as
Optimum signal constellation boundaries
Higher density lattice structures
Trellis coded modulation
None of the mentioned
50. Trellis coded modulation uses
Non binary method
Uses redundant bits
No expansion of bandwidth
All of the mentioned
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