Universal frame set for rational functions

Abstract

Let $g \in L^2(\mathbb{R})$ be a rational function of degree $M$, i.e. there exist polynomials $P, Q$ such that $g = {{P} \over {Q}}$ and $deg(P) < deg(Q) \leq M$. We prove that for any $\varepsilon>0$ and any $M \in \mathbb{N}$ there exists universal set $\Lambda \subset \mathbb{R}$ of density less than $1+\varepsilon$ such that the system $$\left\{ e^{2\pi i \lambda t } g(t-n) \colon (\lambda, n) \in \Lambda \times \mathbb{Z} \right\}$$ is a frame in $L^2(\mathbb{R})$ for any well-behaved rational function $g$.

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