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Communication System
Random Variable and Random Process

Practice questions from Random Variable and Random Process.

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Q#1 Random Variable and Random Process GATE EC 2025 (Set 1) MCQ +2 marks -0.66 marks

Consider a real-valued random process

 

where  and  is a positive integer. Here,  for  and 0 otherwise. The coefficients  are pairwise independent, zero-mean unit variance random variables.

Read the following statements about the random process and choose the correct option.

(i) The mean of the process  is independent of time .

(ii) The autocorrelation function  is independent of time  for all .

(Here,  is the expectation operation.)

(i) is TRUE and (ii) is FALSE

Both (i) and (ii) are TRUE

Both (i) and (ii) are FALSE

(i) is FALSE and (ii) is TRUE

Explanation:

 are independent

 

Given:  constant

(i) is correct

Auto correlation

We can’t comment on ACF of  however looking at (as no time data given)

 we solve

 

 dependence on  is asked, lets fix  for all z

 

as  for  to  :

Clearly  is a function

(ii) is false

Q#2 Random Variable and Random Process GATE EC 2025 (Set 1) MSQ +2 marks -0 marks

The random variable  takes values in  with probabilities  and , where . Let  denote the entropy of  (in bits), parameterized by . Which of the following statements is/are TRUE?

Explanation:

The entropy of a discrete random variable  is given as,

 

 

 

The entropy function  will thus be:

 

 

For maximum entropy,

 

Thus, at  is near to Maximum.

 

Alternatively,

 

 

 

 

Hence, option (b) & (c) are correct.

Q#3 Random Variable and Random Process GATE EC 2024 (Set 1) MCQ +1 mark -0.33 marks

A white Gaussian noise  with zero mean and power spectral density , when applied to a first-order RC low pass filter produces an output . At a particular time , the variance of the random variable  is _________.

Explanation:

        

For RC LPF

Q#4 Random Variable and Random Process GATE EC 2024 (Set 1) NAT +1 mark -0 marks

Suppose  and  are independent and identically distributed random variables that are distributed uniformly in the interval . The probability that  is _________.

Explanation:

         (Area of triangle from Z>0)

Q#5 Random Variable and Random Process GATE EC 2024 (Set 1) NAT +2 marks -0 marks

Let  be a random process, where amplitude  and phase  are independent of each other, and are uniformly distributed in the intervals  and , respectively.  is fed to an 8 -bit uniform mid-rise type quantizer. Given that the autocorrelation of  is , the signal to quantization noise ratio (in , rounded off to two decimal places) at the output of the quantizer is_________. 

Explanation:

Q#6 Random Variable and Random Process GATE EC 2023 (Set 1) MCQ +2 marks -0.66 marks

A random variable , distributed normally as , undergoes the transformation , given in the figure. The form of the probability density function of  is (In the options given below,  are non-zero constants and  is piecewise continuous function)

Explanation:

Given random variables,

X=N(0,1)

 

 

 

 

 

 is taking discrete set of values and a continuous range of values, so it is mixed random variable. From the given options, density function of '  ' will be.