Characterizations of function spaces on the sphere using frames

Abstract

In this paper we introduce a polynomial frame on the unit sphere $\sph$ of ${\mathbb{R}}^d$, for which every distribution has a wavelet-type decomposition. More importantly, we prove that many function spaces on the sphere $\sph$, such as $L^p$, $H^p$ and Besov spaces, can be characterized in terms of the coefficients in the wavelet decompositions, as in the usual Euclidean case ${\mathbb{R}}^d$. We also study a related nonlinear $m$-term approximation problem on $\sph$. In particular, we prove both a Jackson--type inequality and a Bernstein--type inequality associated to wavelet decompositions, which extend the corresponding results obtained by R. A. DeVore, B. Jawerth and V. Popov (``Compression of wavelet decompositions'', {\it Amer. J. Math.} {\bf 114} (1992), no. 4, 737--785).

23 pages