Digital Communication System MCQs

Question 1

The auto-correlation function of a function x(t) is defined as 1 f?T

Accepted Answer

R (to) =j 0 x (t) x (t +to) dt

Answer

R (to) =foT x (t) x (t to) dt

Answer

R (to) = -TI-, 01. x (t - to) x (t + to) dt

Answer

R (to) = -TI TT X (t ? to) X (t + to) dt

Question 2

The auto-co-relation function of an ergodic random process is given by IT

Accepted Answer

Lt -x (t) (t ? dt T--Ko 2T 0

Answer

Lt x (t) (t - t) dt T--*co T 0 1 cr

Answer

Lt x (t) (t - ?r) dt T 0 f T

Answer

Lt -x (t) (t ? dt T-400 21 oI

Question 3

If n is the positive-frequency power density, the power density spectrum white noise S(co) is equal to

Accepted Answer

02-Jan

Answer

1/1

Answer

ri

Answer

21

Question 4

Which of the following is not true regarding auto-correlation function :

Accepted Answer

it is defined only for periodic signals

Answer

it is an average function

Answer

it is a measure of both time variation and statistical dependence

Answer

it is non-unique description of signals.

Question 5

Probability density function of thermal noise is

Accepted Answer

Gaussian

Answer

Binomial

Answer

Poisson

Answer

None of the above

Question 6

The Gaussian probability density is defined as

Accepted Answer

2fc a e?(x?m)

Answer

2/2 cr2

Answer

f(x)=2

Answer

f(x) = 27c a2

Question 7

The auto-correlation function of white noise is a

Accepted Answer

impulse function

Answer

step function

Answer

Gaussian function

Answer

constant

Question 8

The auto-correlation function for the function x(t) = V sin cot is given by

Accepted Answer

-2 V', cos cot

Answer

V2 cos cot

Answer

V2 cos2 cot

Answer

2V2 cos cot

Question 9

If x and y are two independent Gaussian random variables, each with average value zero and with variance 152, the joint density function is defined as :

Accepted Answer

gx, y)= f(x) ? gy)

Answer

gx, y)= f(x) + f(y)

Answer

gx, y)= f(x)- f(y)

Answer

gx, y) = f(x)/ f(y)