Varying the time-frequency lattice of Gabor frames

Abstract

A Gabor or Weyl-Heisenberg frame for L 2 (R d ) is generated by time-frequency shifts of a square-integrable function, the Gabor atom, along a time-frequency lattice. The dual frame is again a Gabor frame, generated by the dual atom. In general, Gabor frames are not stable under a perturbation of the lattice constants; that is, even for arbitrarily small changes of the parameters the frame property can be lost. In contrast, as a main result we show that this kind of stability does hold for Gabor frames generated by a Gabor atom from the modulation space M 1 (R d ), which is a dense subspace of L 2 (R d ). Moreover, in this case the dual atom depends continuously on the lattice constants. In fact, we prove these results for more general weighted modulation spaces. As a consequence, we obtain for Gabor atoms from the Schwartz class that the continuous dependence of the dual atom holds even in the Schwartz topology. Also, we complement these main results by corresponding statements for Gabor Riesz sequences and their biorthogonal system.