# M-ary Signalling

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

2. M-ary signalling produces _______ error performance with orthogonal signalling and _______ error performance with multiple phase signalling.
c) Improved, improved

3. Which is more vulnerable to noise?
a) 2-ary system
b) 4-ary system
c) Binary system
d) None of the mentioned

4. In which system, bit stream is portioned into even and odd stream?
a) BPSK
b) MSK
c) QPSK
d) FSK

5. The error performance of MPSK ______ as M or k increases.
a) Increases
b) Decreases
c) Stays constant
d) None of the mentioned

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

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

8. For FSK signalling, WT is equal to
a) 0
b) 1
c) 0.737
d) Infinity

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)

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

11. As limit of k increases, the ratio of PB/PE becomes
a) 1:2
b) 2:1
c) 1:3
d) 3:1