I have a real orthogonal design for codeword...
$$ \begin{bmatrix} s1 & s2 \\ -s2 & s1 \end{bmatrix} $$
$$ s=\begin{bmatrix} s1\\ s2 \end{bmatrix} $$
$$ Y^T=\sqrt{\frac{P}{Mt}} h^T X + n^T $$
...and receive signal:
$$ Y1=\begin{bmatrix} y1\\ y2 \end{bmatrix} $$
So for:
$$ X = \begin{bmatrix} x1 & x2 \\ -x2 & x1 \end{bmatrix} $$
and $$ Y = \begin{bmatrix} y1 & y2 \end{bmatrix} $$
...i have:
$$ Y=\sqrt{\frac{P}{Mt}} \cdot \begin{bmatrix}h1 & h2\\ h2 & -h1\end{bmatrix}\cdot \begin{bmatrix}x1 & x2\end{bmatrix}^T+N $$
...right?