Digital Communications

Direct Sequence and Frequency Hopping

Question 1
Marks : +2 | -2
Pass Ratio : 25%
In direct sequence process which step is performed first?
De-spreading
Demodulation
Despreading & Demodulation
None of the mentioned
Explanation:
In direct sequence process, De-spreading correlator is followed by a modulator.
Question 2
Marks : +2 | -2
Pass Ratio : 25%
The processing gain is given as
Wss/R
R/Wss
Wss/2R
R/2Wss
Explanation:
The processing gain is given by the ratio of the minimum bandwidth of the data to data rate.
Question 3
Marks : +2 | -2
Pass Ratio : 25%
Processing gain is given as
Wss/R
Rch/R
Wss/R & Rch/R
None of the mentioned
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.
Question 4
Marks : +2 | -2
Pass Ratio : 25%
The minimum spacing between consecutive hop positions gives the
Minimum number of chips necessary
Maximum number of chips necessary
Chip rate
None of the mentioned
Explanation:
The minimum spacing between consecutive hop positions given the minimum number of chips necessary in the frequency word.
Question 5
Marks : +2 | -2
Pass Ratio : 25%
Which system allows larger processing gain?
Direct sequence
Frequency hopping
Direct sequence & Frequency hopping
None of the mentioned
Explanation:
Frequency hopping spread spectrum system allows greater processing gain than direct sequence spread spectrum technique.
Question 6
Marks : +2 | -2
Pass Ratio : 25%
The frequency hopping system uses ______ modulation scheme.
FSK
BPSK
MFSK
MPSK
Explanation:
The frequency hopping spread spectrum system uses M-ary frequency shift keying modulation scheme.
Question 7
Marks : +2 | -2
Pass Ratio : 25%
In which technique is phase coherence hard to maintain?
Direct sequence
Frequency hopping
Direct sequence & Frequency hopping
None of the mentioned
Explanation:
In frequency hopping spread spectrum phase coherence is hard to maintain from hop to hop.
Question 8
Marks : +2 | -2
Pass Ratio : 25%
DS/BPSK includes
Despreading
Demodulation
Despreading & Demodulation
None of the mentioned
Explanation:
DS/BPSK is a two step precess which includes despreading and demodulation.
Question 9
Marks : +2 | -2
Pass Ratio : 25%
Chip is defined as
Shortest uninterrupted waveform
Largest uninterrupted waveform
Shortest diversion
None of the mentioned
Explanation:
A chip is defined as the shortest uninterrupted waveform in the system.
Question 10
Marks : +2 | -2
Pass Ratio : 25%
Which modulation scheme is preferred for direct sequence spread spectrum process?
BPSK
QPSK
BPSK & QPSK
None of the mentioned
Explanation:
Both the modulation scheme BPSK and QPSK can be used for direct sequence spread spectrum process.