Digital Communications Multiple Choice Questions on “Modulation and Entropy”.
1. PCM includes the process of
A. Amplitude discretization
B. Time discretization
C. Amplitude & Time discretization
D. None of the mentioned
Answer: C
Clarification: Time discretization and amplitude discretization are the two processes done in PCM system.
2. For which quantization process is used?
A. Amplitude discretization
B. Time discretization
C. Amplitude & Time discretization
D. None of the mentioned
Answer: A
Clarification: Sampling process is used for time discretization and quantization process is used for amplitude discretization.
3. Modulation process corresponds to ______ the amplitude, frequency or phase.
A. Switching
B. Keying
C. Switching or keying
D. None of the mentioned
Answer: C
Clarification: Modulation process corresponds to switching or keying the amplitude, frequency or phase of CW carrier.
4. Matched filter
A. Is a non linear filter
B. Produces maximum output SNR
C. All of the mentioned
D. None of the mentioned
Answer: B
Clarification: Matched filter is a linear filter which produces maximum output SNR for a given transmitted signal.
5. Which has same probability of error?
A. ASK and FSK
B. ASK and PSK
C. PSK and FSK
D. None of the mentioned
Answer: C
Clarification: Uni-polar base-band signalling, PSK and FSK has same probability of error.
6. Which has higher error probability performance?
A. Uni-polar base-band signalling
B. Bipolar base-band signalling
C. ASK
D. FSK
Answer: B
Clarification: Bipolar base-band signalling has high error probability performance than the others. The probability of error value is A2T.
7. Time division multiplexing uses
A. High pass filter
B. Commutator
C. High pass filter & Commutator
D. None of the mentioned
Answer: B
Clarification: Time division multiplexing uses low pass filter and commutator.
8. In TDM, at the receiver end, ____ filter is used.
A. Low pass
B. High pass
C. Band pass
D. Band stop
Answer: A
Clarification: In TDM, at the receiver end low pass filtering is done to obtain individual signals.
9. Which provides more secure communication?
A. CDMA
B. FDMA
C. TDMA
D. None of the mentioned
Answer: A
Clarification: CDMA provides more secure communication than TDMA and FDMA.
10. Entropy is the measure of
A. Randomness
B. Information
C. Randomness & Information
D. None of the mentioned
Answer: C
Clarification: Entropy can be defined as the measure of randomness or information.
11. Entropy calculation returns
A. Random variable
B. Deterministic number
C. Random number
D. None of the mentioned
Answer: B
Clarification: Entropy calculation returns a deterministic number and not a random variable.
12. Entropy of N random variables is the _____ of the entropy of individual random variable.
A. Sum
B. Product
C. Sum of squares
D. Average
Answer: A
Clarification: Entropy of N random variables is the sum of the entropy of individual random variable.
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