Digital Communication System MCQs

Question 1

For a periodic function, the spectral density and the auto-correlation functions are

Accepted Answer

Fourier transform pair

Answer

Laplace transform pair

Answer

One and the same thing

Answer

None of the above

Question 2

The channel capacity C of a band limited Gaussian channel equals, where B is the channel bandwidth

Accepted Answer

B log2(1 --)

Answer

B log2 (-) 1

Answer

log2 (S/N)

Answer

? lo2g (1B

Question 3

Spectral density of white noise

Accepted Answer

is constant

Answer

varies with frequency

Answer

varies with bandwidth

Answer

none of the above

Question 4

A random process is defined as ergodic if

Accepted Answer

All types of ensemble average are interchangeable

Answer

All types of ensemble averages are not changeable

Answer

All types of ensemble averages are constant

Answer

None of above

Question 5

Auto correlation function of a random process is defined as

Accepted Answer

R (t1 t2) = E (X, ) = ffx y p (x, y) dX dY

Answer

E (X, Y)= fx2 y2 dX dY

Answer

R t2) = ix2 y2 dX dY

Answer

none of the above

Question 6

Spectral density expresses

Accepted Answer

Average power in a waveform as a function of frequency

Answer

Average voltage

Answer

Average current

Answer

None of the above

Question 7

For a Gaussian process, auto-correlation also implies

Accepted Answer

statistical independence

Answer

statistical dependence

Answer

ergodic process

Answer

none of the above

Question 8

The auto-correlation function of a signal (t) at to = 0 is equal to

Accepted Answer

average power of the signal

Answer

zero

Answer

infinite

Answer

average voltage of the signal

Question 9

The auto-correlation function is

Accepted Answer

an even function in to

Answer

an odd function in to

Answer

an exponential function in to

Answer

none of the above