This set of Digital Communications Multiple Choice Questions & Answers (MCQs) focuses on “M-ary signalling and performance”.
1. The limit which represents the threshold Eb/N0 value below which reliable communication cannot be maintained is called as
a) Probability limit
b) Error limit
c) Shannon limit
d) Communication limit
View Answer
Explanation: Eb/N0 curve has waterfall shape. Shannon limit gives the threshold value below which reliable communication cannot be maintained.
2. M-ary signalling produces _______ error performance with orthogonal signalling and _______ error performance with multiple phase signalling.
a) Degraded, improved
b) Improved, degraded
c) Improved, improved
d) Degraded, degraded
View Answer
Explanation: In M-ary signalling as k increases, the curve moves towards the degraded error performance. It produces improved error performance in case of orthogonal signalling and degraded error performance in case of multiple phase signalling.
3. Which is more vulnerable to noise?
a) 2-ary system
b) 4-ary system
c) Binary system
d) None of the mentioned
View Answer
Explanation: The minimum energy noise vector for 4-ary system is smaller than 2-ary system. So 4-ary system is more vulnerable to noise.
4. In which system, bit stream is portioned into even and odd stream?
a) BPSK
b) MSK
c) QPSK
d) FSK
View Answer
Explanation: In QPSK bit stream is portioned into even and odd stream, I and Q bit streams. Each new stream modulates as orthogonal component at half bit rate.
5. The error performance of MPSK ______ as M or k increases.
a) Increases
b) Decreases
c) Stays constant
d) None of the mentioned
View Answer
Explanation: The error performance of MPSK degrades as M or k increases.
6. In MPSK adding new signals _______ make it vulnerable to noise and in MFSK _______ make it vulnerable.
a) Does, does not
b) Does not, does
c) Does, does
d) Does not, does not
View Answer
Explanation: In MPSK adding new signals that is on crowding the signals it makes it vulnerable to noise where as in MFSK it does not.
7. In orthogonal signalling with symbols containing more number of bits we need ____ power.
a) More
b) Less
c) Double
d) None of the mentioned
View Answer
Explanation: In orthogonal signalling with symbols having more number of bits need more power but requirement per bit is reduced.
8. For FSK signalling, WT is equal to
a) 0
b) 1
c) 0.737
d) Infinity
View Answer
Explanation: For FSK signalling the detection bandwidth is typically equal to symbol rate 1/T that is WT is nearly equal to 1.
9. Energy per symbol Es is given as
a) Es=Eb(log2M)
b) Es=Eb/(log2M)
c) Es=2Eb(log2M)
d) Es=Eb/2(log2M)
View Answer
Explanation: In M-ary PSK signalling, the energy per symbol is given as Es=Eb(log2M).
10. The relation between the probability of bit error and probability of symbol error in M-ary orthogonal signalling is
a) M/M-1
b) 2M/M-1
c) (M/2)/M-1
d) M/M+1
View Answer
Explanation: The relationship between the probability of bit error and probability of symbol error is (M/2)/M-1 in M-ary orthogonal signalling.
11. As limit of k increases, the ratio of PB/PE becomes
a) 1:2
b) 2:1
c) 1:3
d) 3:1
View Answer
Explanation: As the limit of k increases, the ratio of PB/PE becomes 1:2.
Sanfoundry Global Education & Learning Series – Digital Communications.
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