# 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.

a) Degraded, improved**b) Improved, degraded**

c) Improved, improved

d) Degraded, degraded

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