The HRT conjecture for two classes of special configurations

TL;DR

This paper proves two special cases of the HRT conjecture involving specific configurations of time-frequency shifts, using ergodic theorems, and fully resolves the case where three points are collinear.

Contribution

It establishes the HRT conjecture for configurations with points on a lattice plus one arbitrary point, and for points on a line with an external point, using ergodic theory methods.

Findings

Proves HRT conjecture for N+1 points with N on a lattice and one arbitrary point.

Proves HRT conjecture for N points on a line with an external point.

Resolves the case of three collinear points in the HRT conjecture.

Abstract

The HRT (Heil-Ramanathan-Topiwala) conjecture stipulates that the set of any finitely many time-frequency shifts of a non-zero square Lebesgue integrable function is linearly independent. The present work settles two special cases of this conjecture, namely, the cases where the set of time-frequency shifts has cardinality $N+1$ such that either $N$ of the points lie on some integer lattice and the last point is arbitrary, or $N$ of the points are on a line, while the last point does not belong this line. In both cases, we prove that the HRT conjecture holds appealing mainly to various forms of the ergodic theorem. We note that, in recent years, the latter case has been the subject of many investigations -- notably, the subcase where $N=3$ -- and our work completely resolves it.