6. We transmit a random variable X, which satisfies the distribution N(0, 1). The variable is corrupted in the channel by a N(0, 1) noise Y and becomes Z. In other words, Y~ N(0, 1), X and Y are independent, and Z = X + Y. (a) Find E[(X - aZ)²], and find a to minimize this expectation. (b) Find the conditional pdf fz|x(z|x). (c) Find the joint probability density function fx,z(x, z) = fz|x(z|x)ƒx(x). (d) Find the conditional probability density function fx|z(x|z). (e) Find E[X|Z].

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### Problem 6: Analysis of a Corrupted Random Variable

We transmit a random variable \( X \), which satisfies the distribution \( \mathcal{N}(0, 1) \). The variable is corrupted in the channel by a \( \mathcal{N}(0, 1) \) noise \( Y \) and becomes \( Z \). In other words, \( Y \sim \mathcal{N}(0, 1) \), \( X \) and \( Y \) are independent, and \( Z = X + Y \).

#### (a) Find \( \mathbb{E}[(X - \alpha Z)^2] \), and find \( \alpha \) to minimize this expectation.
 
#### (b) Find the conditional pdf \( f_{Z|X}(z|x) \).

#### (c) Find the joint probability density function \( f_{X,Z}(x,z) = f_{Z|X}(z|x) f_X(x) \).

#### (d) Find the conditional probability density function \( f_{X|Z}(x|z) \).

#### (e) Find \( \mathbb{E}[X|Z] \).

---

### Solution Outline

1. **Objective**: Given the model where \( Z = X + Y \), with \( X \sim \mathcal{N}(0, 1) \) and \( Y \sim \mathcal{N}(0, 1) \), figure out various statistical properties and relationships between \( X \) and \( Z \).

2. **Key Concepts**:
    - Probability Density Functions (PDFs)
    - Expectation and Minimization of functions
    - Conditional Distributions
    - Joint Distributions

3. **Steps**:
    - Calculate the expected value \( \mathbb{E}[(X - \alpha Z)^2] \).
    - Derive the conditional probability density function \( f_{Z|X}(z|x) \).
    - Use the above to find the joint PDF \( f_{X,Z}(x,z) \).
    - From the joint PDF, derive the conditional PDF \( f_{X|Z}(x|z) \).
    - Finally, find the conditional expectation \( \mathbb{E}[X|Z] \).

The problem touches on fundamental concepts in probability theory and will often appear in courses related to random
Transcribed Image Text:### Problem 6: Analysis of a Corrupted Random Variable We transmit a random variable \( X \), which satisfies the distribution \( \mathcal{N}(0, 1) \). The variable is corrupted in the channel by a \( \mathcal{N}(0, 1) \) noise \( Y \) and becomes \( Z \). In other words, \( Y \sim \mathcal{N}(0, 1) \), \( X \) and \( Y \) are independent, and \( Z = X + Y \). #### (a) Find \( \mathbb{E}[(X - \alpha Z)^2] \), and find \( \alpha \) to minimize this expectation. #### (b) Find the conditional pdf \( f_{Z|X}(z|x) \). #### (c) Find the joint probability density function \( f_{X,Z}(x,z) = f_{Z|X}(z|x) f_X(x) \). #### (d) Find the conditional probability density function \( f_{X|Z}(x|z) \). #### (e) Find \( \mathbb{E}[X|Z] \). --- ### Solution Outline 1. **Objective**: Given the model where \( Z = X + Y \), with \( X \sim \mathcal{N}(0, 1) \) and \( Y \sim \mathcal{N}(0, 1) \), figure out various statistical properties and relationships between \( X \) and \( Z \). 2. **Key Concepts**: - Probability Density Functions (PDFs) - Expectation and Minimization of functions - Conditional Distributions - Joint Distributions 3. **Steps**: - Calculate the expected value \( \mathbb{E}[(X - \alpha Z)^2] \). - Derive the conditional probability density function \( f_{Z|X}(z|x) \). - Use the above to find the joint PDF \( f_{X,Z}(x,z) \). - From the joint PDF, derive the conditional PDF \( f_{X|Z}(x|z) \). - Finally, find the conditional expectation \( \mathbb{E}[X|Z] \). The problem touches on fundamental concepts in probability theory and will often appear in courses related to random
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