Excess of Fusion Frames: A Comprehensive Approach

Abstract

Computing the excess as a method of measuring the redundancy of frames was recently introduced to address certain issues in frame theory. In this paper, the concept of excess for the fusion frame setting is studied. Initially, a local approach is presented to determine exactly which part of each subspace should be considered as redundancy. Then, several explicit methods are provided to compute the excess of fusion frames and their $Q$-duals. In particular, some upper bounds for the excess of $Q$-dual fusion frames are established. It turns out that each fusion frame and its $Q$-dual may not necessarily have the same excess. Along the way, unlike ordinary frames, it follows that for every $n \in \Bbb{N}$, we can provide a fusion frame together an its $Q$-dual such that the difference of their excess is $n$. Furthermore, the connection between the excess of fusion frames and their orthogonal complement fusion frames are completely characterized. Finally, several examples are exhibited to confirm the obtained results.