This set of Digital Communications Multiple Choice Questions & Answers (MCQs) focuses on “Random signals”.

1. Random variables give relationship between _____

a) Two random events

b) Probability of occurence of two random events

c) Random event and a real number

d) Random event and its probability of occurence

View Answer

Explanation: A random variable gives functional relationship between a random event and a real number.

2. The distribution function of random variable is

a) P(X less than or equal to x)

b) P(X greater than or equal to x)

c) P(X less than x)

d) P(X greater than x)

View Answer

Explanation: The distribution function of a random variable is the probability that the value taken by the random variable is less than or equal to the real number x.

3. The distribution function of -(infinity) and (infinity) is _____

a) 0 and 1

b) 1 and 0

c) Both 0

d) Both 1

View Answer

Explanation: F(minus infinity) is 0 and F(infinity) is 1.

4. The value of probability density function of random variable is

a) Positive function

b) Negative function

c) Zero

d) One

View Answer

Explanation: The probability density function is always greater than 0. It is a non negative function with the area of 1.

a) Mean

b) Variance

c) Standard variance

d) Pdf

View Answer

Explanation: Variance gives the randomness of the random variable. It is the difference between the mean square value and square of the mean.

6. Random process is a function of ______

a) Random event and time

b) Random event and frequency

c) Random event and real number

d) None of the mentioned

View Answer

Explanation: Random process is a function of two variables : a random event and its time of occurence.

7. A random process is called as stationary in strict sense if

a) Its statistics vary with shift in time origin

b) Its statistics does not vary with shift in time origin

c) Its autocorrelation vary with shift in time

d) Its autocorrelation does not vary with shift in time

View Answer

Explanation: A random process is defined to be stationary in strict sense if its statistics varies with shift in time origin.

8. For stationary process, autocorrelation function depends on

a) Time

b) Time difference

c) Does not depend on time

d) None of the mentioned

View Answer

Explanation: Autocorrelation function depends on time difference between t1 and t2.

9. Autocorrelation function is maximum at

a) Origin

b) Infinity

c) Both of the mentioned

d) None of the mentioned

View Answer

Explanation: On substituting different values in the formula for autocorrelation function it wil be maximum at the origin.

a) Rms value of dc

b) Rms value or ac

c) Either ac or dc

d) Neither dc nor ac

View Answer

Explanation: The standard deviation of a random variable gives the rms value of an ac component.

11. The average power of white noise is

a) Zero

b) Unity

c) Infinity

d) Between zero and one

View Answer

Explanation: The average power of white noise is infinity because its bandwidth is infinite.

12. White noise has _____ mean and ______ variance.

a) Zero and zero

b) Finite and zero

c) Zero and finite

d) One and zero

View Answer

Explanation: White noise is a zero mean function with infinite average power, finite variance and infinite bandwidth.

**Sanfoundry Global Education & Learning Series – Digital Communications.**

To practice all areas of Digital Communications, __here is complete set of 1000+ Multiple Choice Questions and Answers__.