$k$-Homogeneous Equiangular Tight Frames

Abstract: Equiangular tight frames (ETFs) are optimal packings in projective space which also yield useful decompositions of signals. Paley ETFs are constructed using number theory. In this article, we present the doubly homogeneous automorphism groups of the Paley ETFs of prime order. We also prove some properties of doubly homogeneous frames, namely that they are always ETFs and that their short circuits -- i.e., dependent subsets of minimum size -- form a balanced incomplete block design. We additionally characterize all $k$-homogeneous ETFs for $3 \leq k \leq 5$. Finally, we revisit David Larson's AMS Memoirs \emph{Frames, Bases, and Group Representations} coauthored with Deguang Han and \emph{Wandering Vectors for Unitary Systems and Orthogonal Wavelets} coauthored with Xingde Dai with a modern eye and focus on finite-dimensional Hilbert spaces.