Summary
Marcin Bownik and Ole Christensen (2007) Characterization and perturbation of Gabor frame sequences with rational parameters. J. Approx. Theory, 147(1):67–80. 
Bibtex entry
@ARTICLE { MR2346803,
AUTHOR = { Marcin Bownik and Ole Christensen },
TITLE = { Characterization and perturbation of {G}abor frame sequences with rational parameters },
JOURNAL = { J. Approx. Theory },
FJOURNAL = { Journal of Approximation Theory },
VOLUME = { 147 },
YEAR = { 2007 },
NUMBER = { 1 },
PAGES = { 67--80 },
ISSN = { 0021-9045 },
CODEN = { JAXTAZ },
MRCLASS = { 42C15 (42C40) },
MRNUMBER = { 2346803 (2008k:42092) },
MRREVIEWER = { Jean-Pierre Gabardo },
DOI = { 10.1016/j.jat.2007.01.002 },
URL = { http://dx.doi.org/10.1016/j.jat.2007.01.002 },
}