Digital Communications Multiple Choice Questions on “Modulation Techniques”.
1. Average energy per bit is given by
A. average energy symbol/log2 M
B. average energy symbol * log2 M
C. log2 M/ Average energy symbol
D. none of the mentioned
Answer: A
Clarification: Average energy per bit is given by average energy symbol divided by log2 M.
2. Which FSK has no phase discontinuity?
A. Continuous FSK
B. Discrete FSK
C. Uniform FSK
D. None of the mentioned
Answer: A
Clarification: Continuous frequency shift keying has no phase discontinuity between symbols.
3. FSK reception is
A. Phase Coherent
B. Phase non coherent
C. Phase Coherent & non coherent
D. None of the mentioned
Answer: C
Clarification: Reception of FSK can be either phase coherent or phase non coherent.
4. FSK reception uses
A. Correlation receiver
B. PLL
C. Correlation receiver & PLL
D. None of the mentioned
Answer: C
Clarification: Frequency shift keying uses correlation receiver and phase locked loop.
5. In non coherent reception _____ is measured.
A. Phase
B. Energy
C. Power
D. None of the mentioned
Answer: B
Clarification: In non coherent reception of FSK, energy in each frequency is measured.
6. Every frequency has ____ orthogonal functions.
A. One
B. Two
C. Four
D. Six
Answer: B
Clarification: Every frequency has two orthogonal functions – sine and cosine.
7. If we correlate the received signal with any one of the two orthogonal function, the obtained inner product will be
A. In phase
B. Quadrature
C. Zero
D. Cannot be determined
Answer: C
Clarification: If we correlate the received signal with only one of the orthogonal function for example sine, the inner product obtained will be zero.
8. If we correlate the received signal with both orthogonal function the inner product will be
A. In phase
B. Quadrature
C. In phase and quadrature
D. Unity
Answer: C
Clarification: If we correlate the received signal with both the orthogonal function, the two inner products obtained will be in phase and quadrature.
9. Simulation is used to determine
A. Bit error rate
B. Symbol error rate
C. Bit error
D. Symbol error
Answer: A
Clarification: A simulation of digital communication system is used to estimate bit error rate.
10. Matched filter is a _____ technique.
A. Modulation
B. Demodulation
C. Modulation & Demodulation
D. None of the mentioned
Answer: B
Clarification: Matched filter is a demodulation technique with LTI.
11. Which is called as on-off keying?
A. Amplitude shift keying
B. Uni-polar PAM
C. Amplitude shift keying & Uni-polar PAM
D. None of the mentioned
Answer: C
Clarification: Amplitude shift keying and uni-polar PAM both schemes are called as on off keying.
12. QAM uses ______ as the dimensions.
A. In phase
B. Quadrature
C. In phase & Quadrature
D. None of the mentioned
Answer: C
Clarification: QAM uses in phase and quadrature which is cosine and sine respectively as the dimensions.
13. Which has same probability of error?
A. BPSK and QPSK
B. BPSK and ASK
C. BPSK and PAM
D. BPSK and QAM