## Digital Communications Questions and Answers Part-5

1. For a stationary process, autocorrelation function depends on
a) Time
b) Time difference
c) Does not depend on time
d) None of the mentioned

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

2. The autocorrelation function is maximum at
a) Origin
b) Infinity
c) Origin & Infinity
d) None of the mentioned

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

3. Standard deviation is ______
a) Rms value of dc
b) Rms value or ac
c) Either ac or dc
d) Neither dc nor ac

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

4. White noise has _____ mean and ______ variance.
a) Zero and zero
b) Finite and zero
c) Zero and finite
d) One and zero

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

5. The average power of white noise is
a) Zero
b) Unity
c) Infinity
d) Between zero and one

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

6. The process of data conversion along with formatting the data is called as ______
a) Formatting
b) Modulation
c) Source coding
d) Amplifying

Explanation: The process of converting source information to a digital signal and also formatting it is called as source coding.

7. Formatting is the process which includes
a) Pulse code modulation
b) Sampling
c) Quantization
d) All of the mentioned

Explanation: Formatting is the process in which the source information is converted to digital signals using methods like sampling, pulse code modulation etc.

a) Sampling
b) Quantization
c) Coding
d) All of the mentioned

Explanation: Textual information, analog information and digital information undergoes different processes before converting to binary or digital data. The method used for converting analog information are the given methods.

9. The process that transforms text into binary digits is called as _______
a) Binary coding
b) Character coding
c) Data coding
d) Sampling