Gabor frames, unimodularity, and window decay

  • Helmut Bölcskei
  • J. E. M. Janssen


We study time-continuous Gabor frame generating window functions g satisfying decay properties in time and/or frequency with particular emphasis on rational time-frequency lattices. Specifically, we show under what conditions these decay properties of g are inherited by its minimal dual γ0 and by generalized duals γ. We consider compactly supported, exponentially decaying, and faster than exponentially decaying (i.e., decay like |g(t)|≤Ce−α|t|1/α for some 1/2≤α<1) window functions. Particularly, we find that g and γ0 have better than exponential decay in both domains if and only if the associated Zibulski-Zeevi matrix is unimodular, i.e., its determinant is a constant. In the case of integer oversampling, unimodularity of the Zibulski-Zeevi matrix is equivalent to tightness of the underlying Gabor frame. For arbitrary oversampling, we furthermore consider tight Gabor frames canonically associated to window functions g satisfying certain decay properties. Here, we show under what conditions and to what extent the canonically associated tight frame inherits decay properties of g. Our proofs rely on the Zak transform, on the Zibulski-Zeevi representation of the Gabor frame operator, on a result by Jaffard, on a functional calculus for Gabor frame operators, on results from the theory of entire functions, and on the theory of polynomial matrices.

Math Subject Classifications

42C15 94A12 

Key words and Phrases

Gabor frame Zak transform entire function polynomial matrix unimodularity 


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Copyright information

© Birkhäuser 2000

Authors and Affiliations

  • Helmut Bölcskei
    • 1
    • 2
  • J. E. M. Janssen
    • 3
  1. 1.Information Systems LaboratoryStanford UniversityStanford
  2. 2.Dept. of CommunicationsVienna University of TechnologyViennaAustria
  3. 3.Philips Research Laboratories EindhovenAA EindhovenThe Netherlands

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