The input to a binary communication system, denoted by a random variable [tex]x[/tex], takes on one of two values, 0 or 1, with probabilities [tex]\frac{1}{4}[/tex] and [tex]\frac{3}{4}[/tex], respectively. Due to errors caused by noise in the system, the output occasionally differs from the input [tex]x[/tex]. Describe the behavior of the communication system.



Answer :

Sure, I’ll guide you through the solution process step-by-step.

### Step-by-Step Solution:

1. Define Variables and Probabilities:
- The input, [tex]\( x \)[/tex], to the binary communication system takes two values: [tex]\( x = 0 \)[/tex] or [tex]\( x = 1 \)[/tex].
- The probabilities of these inputs are:
[tex]\[ P(X=0) = \frac{1}{4}, \quad P(X=1) = \frac{3}{4} \][/tex]

2. Noise Probabilities:
- Define the probabilities that the output differs from the input due to noise as follows:
[tex]\[ P(Y=1 \mid X=0) = 0.1, \quad P(Y=0 \mid X=1) = 0.2 \][/tex]

3. Correct Transmission Probabilities:
- For [tex]\( x = 0 \)[/tex] to be correctly transmitted, the output should also be 0. This probability is:
[tex]\[ P(Y=0 \mid X=0) = 1 - P(Y=1 \mid X=0) = 1 - 0.1 = 0.9 \][/tex]
- For [tex]\( x = 1 \)[/tex] to be correctly transmitted, the output should also be 1. This probability is:
[tex]\[ P(Y=1 \mid X=1) = 1 - P(Y=0 \mid X=1) = 1 - 0.2 = 0.8 \][/tex]

4. Calculate Joint Probabilities for Correct Transmission:
- For [tex]\( x = 0 \)[/tex] and [tex]\( y = 0 \)[/tex]:
[tex]\[ P(X=0 \text{ and } Y=0) = P(Y=0 \mid X=0) \times P(X=0) = 0.9 \times \frac{1}{4} = 0.225 \][/tex]
- For [tex]\( x = 1 \)[/tex] and [tex]\( y = 1 \)[/tex]:
[tex]\[ P(X=1 \text{ and } Y=1) = P(Y=1 \mid X=1) \times P(X=1) = 0.8 \times \frac{3}{4} = 0.6 \][/tex]

5. Total Probability of Correct Transmission:
- Summing the joint probabilities calculated:
[tex]\[ P(\text{correct transmission}) = P(X=0 \text{ and } Y=0) + P(X=1 \text{ and } Y=1) = 0.225 + 0.6 = 0.825 \][/tex]

6. Probability of Incorrect Transmission:
- Since the output is either correct or incorrect, the probability of incorrect transmission is:
[tex]\[ P(\text{incorrect transmission}) = 1 - P(\text{correct transmission}) = 1 - 0.825 = 0.175 \][/tex]

### Final Results:

- Probability that [tex]\( x = 0 \)[/tex] is correctly transmitted ([tex]\( P(X=0 \text{ and } Y=0) \)[/tex]): [tex]\( 0.225 \)[/tex]
- Probability that [tex]\( x = 1 \)[/tex] is correctly transmitted ([tex]\( P(X=1 \text{ and } Y=1) \)[/tex]): [tex]\( 0.6 \)[/tex]
- Total probability of correct transmission: [tex]\( 0.825 \)[/tex]
- Total probability of incorrect transmission: [tex]\( 0.175 \)[/tex]

These calculations and results provide a complete solution to the question.