Lysario – by Panagiotis Chatzichrisafis

"ούτω γάρ ειδέναι το σύνθετον υπολαμβάνομεν, όταν ειδώμεν εκ τίνων και πόσων εστίν …"

In [1, p. 61 exercise 3.5] we are asked to show that for the conditions of Problem [1, p. 60, exercise 3.4] the CR bound is
var(\hat{\mu}_x) \geq \frac{\sigma_x^2}{N}

and further to give a statement about the efficiency of the sample mean estimator. read the conclusion >
In [1, p. 60 exercise 3.4] we are asked to prove that the estimate
\hat{\mu}_x = \frac{1}{N}\sum\limits^{N-1}_{n=0}x[n] (1)

is an unbiased estimator, given \left\{x[0],x[1],...,x[N]\right\} are independent and identically distributed according to a N(\mu_x,\sigma^{2}_x) distribution. Furthermore we are asked to also find the variance of the estimator. read the conclusion >
In [1, p. 60 exercise 3.3] we are asked to prove that the complex multivariate Gaussian PDF reduces to the complex univariate Gaussian PDF if N=1. read the conclusion >
In [1, p. 60 exercise 3.2] we are asked to proof by using the method of characteristic functions that the sum of squares of N independent and identically distributed N(0,1) random variables has a \chi^{2}_{N} distribution. read the conclusion >
In [1, p. 60 exercise 3.1] a 2 \times 1 real random vector \mathbf{x} is given , which is distributed according to a multivatiate Gaussian PDF with zero mean and covariance matrix:
\mathbf{C}_{xx}=
\left[
\begin{array}{cc} 
\sigma_{1}^2 & \sigma_{12} \\ 
\sigma_{21} & \sigma_{2}^2
\end{array}\right]

We are asked to find \alpha if \mathbf{y}=\mathbf{L}^{-1}\mathbf{x} where \mathbf{L}^{-1} is given by the relation:

y_{1}=x_{1}
y_{2}=\alpha x_{1}+x_{2}

so that y_{1} and y_{2} are uncorrelated and hence independent. We are also asked to find the Cholesky decomposition of \mathbf{C}_{xx} which expresses \mathbf{C}_{xx} as \mathbf{L}\mathbf{D}\mathbf{L}^{T}, where \mathbf{L} is lower triangular with 1′s on the principal diagonal and \mathbf{D} is a diagonal matrix with positive diagonal elements. read the conclusion >

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