## Digital Communications Questions and Answers Part-4

1. Autocorrelation function of periodic signal is equal to _______
a) Energy of the signal
b) Power of the signal
c) Its area in frequency domain
d) None of the mentioned

Explanation: Autocorrelation function of a real valued signal is equal to the energy of the signal and auto-correlation function of the periodic signal is equal to the average power of the signal.

2. Autocorrelation is a _______ function.
a) Real and even
b) Real and odd
c) Complex and even
d) Complex and odd

Explanation: According to properties of autocorrelation function it a even function when the frequency value f is real.

3. Autocorrelation function of white noise will have?
a) Strong peak
b) Infinite peak
c) Weak peak
d) None of the mentioned

Explanation: Autocorrelation function curve of continuous time white noise signal has a strong peak.

4. 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 occurrence

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

5. 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)

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.

6. The value of the probability density function of random variable is
a) Positive function
b) Negative function
c) Zero
d) One

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

7. The distribution function of -(infinity) and (infinity) is _____
a) 0 and 1
b) 1 and 0
c) Both 0
d) Both 1

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

8. Which gives the measure of randomness of the random variable?
a) Mean
b) Pdf
c) Standard variance
d) Variance

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

9. 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