Digital Communications

M-ary Signalling and Performance

Question 1
Marks : +2 | -2
Pass Ratio : 100%
In MPSK adding new signals _______ make it vulnerable to noise and in MFSK _______ make it vulnerable.
Does, does not
Does not, does
Does, does
Does not, does not
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.
Question 2
Marks : +2 | -2
Pass Ratio : 100%
Which is more vulnerable to noise?
2-ary system
4-ary system
Binary system
None of the mentioned
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.
Question 3
Marks : +2 | -2
Pass Ratio : 100%
The error performance of MPSK ______ as M or k increases.
Increases
Decreases
Stays constant
None of the mentioned
Explanation:
The error performance of MPSK degrades as M or k increases.
Question 4
Marks : +2 | -2
Pass Ratio : 100%
Energy per symbol Es is given as
Es=Eb(log2M)
Es=Eb/(log2M)
Es=2Eb(log2M)
Es=Eb/2(log2M)
Explanation:
In M-ary PSK signalling, the energy per symbol is given as Es=Eb(log2M).
Question 5
Marks : +2 | -2
Pass Ratio : 100%
In which system, bit stream is portioned into even and odd stream?
BPSK
MSK
QPSK
FSK
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.
Question 6
Marks : +2 | -2
Pass Ratio : 100%
For FSK signalling, WT is equal to
0
1
0.737
Infinity
Explanation:
For FSK signalling the detection bandwidth is typically equal to symbol rate 1/T that is WT is nearly equal to 1.
Question 7
Marks : +2 | -2
Pass Ratio : 100%
The limit which represents the threshold Eb/N0 value below which reliable communication cannot be maintained is called as
Probability limit
Error limit
Shannon limit
Communication limit
Explanation:
Eb/N0 curve has waterfall shape. Shannon limit gives the threshold value below which reliable communication cannot be maintained.
Question 8
Marks : +2 | -2
Pass Ratio : 100%
The relation between the probability of bit error and probability of symbol error in M-ary orthogonal signalling is
M/M-1
2M/M-1
(M/2)/M-1
M/M+1
Explanation:
The relationship between the probability of bit error and probability of symbol error is (M/2)/M-1 in M-ary orthogonal signalling.
Question 9
Marks : +2 | -2
Pass Ratio : 100%
M-ary signalling produces _______ error performance with orthogonal signalling and _______ error performance with multiple phase signalling.
Degraded, improved
Improved, degraded
Improved, improved
Degraded, degraded
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.
Question 10
Marks : +2 | -2
Pass Ratio : 100%
In orthogonal signalling with symbols containing more number of bits we need ____ power.
More
Less
Double
None of the mentioned
Explanation:
In orthogonal signalling with symbols having more number of bits need more power but requirement per bit is reduced.