Applying the Riemann geometric machinery of volume estimates in terms of
curvature, bounds for the minimal distance of packings/codes in the Grassmann
and Stiefel manifolds will be derived and analyzed. In the context of
space-time block codes this leads to a monotonically increasing minimal
distance lower bound as a function of the block length. This advocates large
block lengths for the code design.Comment: Replaced with final version, 11 page