  In a frequency selective slow-fading channel in a MIMO system, the channel
matrix is of the form of a block matrix. We propose a method to calculate the
limit of the eigenvalue distribution of block matrices if the size of the
blocks tends to infinity. We will also calculate the asymptotic eigenvalue
distribution of $HH^*$, where the entries of $H$ are jointly Gaussian, with a
correlation of the form $E[h_{pj}\bar h_{qk}]= \sum_{s=1}^t
\Psi^{(s)}_{jk}\hat\Psi^{(s)}_{pq}$ (where $t$ is fixed and does not increase
with the size of the matrix). We will use an operator-valued free probability
approach to achieve this goal. Using this method, we derive a system of
equations, which can be solved numerically to compute the desired eigenvalue
distribution.
