Digital Communications Questions and Answers – Direct Sequence and Frequency Hopping

This set of Digital Communications Multiple Choice Questions & Answers (MCQs) focuses on “Direct sequence and frequency hopping”.

1. DS/BPSK includes
a) Despreading
b) Demodulation
c) Despreading & Demodulation
d) None of the mentioned
View Answer

Answer: c
Explanation: DS/BPSK is a two step precess which includes despreading and demodulation.

2. In direct sequence process which step is performed first?
a) De-spreading
b) Demodulation
c) Despreading & Demodulation
d) None of the mentioned
View Answer

Answer: a
Explanation: In direct sequence process, De-spreading correlator is followed by a modulator.

3. The processing gain is given as
a) Wss/R
b) R/Wss
c) Wss/2R
d) R/2Wss
View Answer

Answer: a
Explanation: The processing gain is given by the ratio of the minimum bandwidth of the data to data rate.
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4. Chip is defined as
a) Shortest uninterrupted waveform
b) Largest uninterrupted waveform
c) Shortest diversion
d) None of the mentioned
View Answer

Answer: a
Explanation: A chip is defined as the shortest uninterrupted waveform in the system.

5. Processing gain is given as
a) Wss/R
b) Rch/R
c) Wss/R & Rch/R
d) None of the mentioned
View Answer

Answer: c
Explanation: Processing gain is given as both as the ratio of the minimum bandwidth of the data to data rate and also the by the ratio of code chip rate and data rate as minimum bandwidth is approximately equal to code chip rate.
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6. Which modulation scheme is preferred for direct sequence spread spectrum process?
a) BPSK
b) QPSK
c) BPSK & QPSK
d) None of the mentioned
View Answer

Answer: c
Explanation: Both the modulation scheme BPSK and QPSK can be used for direct sequence spread spectrum process.

7. The frequency hopping system uses ______ modulation scheme.
a) FSK
b) BPSK
c) MFSK
d) MPSK
View Answer

Answer: c
Explanation: The frequency hopping spread spectrum system uses M-ary frequency shift keying modulation scheme.
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8. The minimum spacing between consecutive hop positions gives the
a) Minimum number of chips necessary
b) Maximum number of chips necessary
c) Chip rate
d) None of the mentioned
View Answer

Answer: a
Explanation: The minimum spacing between consecutive hop positions given the minimum number of chips necessary in the frequency word.

9. Which system allows larger processing gain?
a) Direct sequence
b) Frequency hopping
c) Direct sequence & Frequency hopping
d) None of the mentioned
View Answer

Answer: b
Explanation: Frequency hopping spread spectrum system allows greater processing gain than direct sequence spread spectrum technique.
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10. In which technique is phase coherence hard to maintain?
a) Direct sequence
b) Frequency hopping
c) Direct sequence & Frequency hopping
d) None of the mentioned
View Answer

Answer: b
Explanation: In frequency hopping spread spectrum phase coherence is hard to maintain from hop to hop.

11. Which type of demodulator is used in the frequency hopping technique?
a) Coherent
b) Non coherent
c) Coherent & Non coherent
d) None of the mentioned
View Answer

Answer: b
Explanation: As it is difficult to maintain phase coherence, non coherent demodulator is used.

12. Robustness gives the inability of a signal to withstand the impairments.
a) True
b) False
View Answer

Answer: b
Explanation: Robustness gives the ability of a signal to withstand the impairments such as noise, jamming etc.

13. Chips are the
a) Repeated symbols
b) Non repeated symbols
c) Smallest length symbols
d) None of the mentioned
View Answer

Answer: a
Explanation: The repeated symbols are called as chips.

14. Slow frequency hopping is
a) Several hops per modulation
b) Several modulations per hop
c) Several symbols per modulation
d) None of the mentioned
View Answer

Answer: b
Explanation: Slow frequency hopping is several modulation per frequency hop.

15. Fast frequency hopping is
a) Several modulations per hop
b) Several modulations per symbol
c) Several symbols per modulation
d) None of the mentioned
View Answer

Answer: d
Explanation: Fast frequency hopping is several frequency hops per modulation.

16. Which duration is shorter?
a) Hop duration
b) Symbol duration
c) Chip duration
d) None of the mentioned
View Answer

Answer: a
Explanation: In frequency hopping technique hop duration is shorter than the symbol duration.

Sanfoundry Global Education & Learning Series – Digital Communications.

To practice all areas of Digital Communications, here is complete set of 1000+ Multiple Choice Questions and Answers.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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