Gabor systems and almost periodic functions
  We give a construction of Gabor type frames for suitable separable subspaces of the non-separable Hilbert spaces $AP_2({\mathbb R})$ of almost periodic functions of one variable. Furthermore we determine a non-countable generalized frame for the whole space $AP_2({\mathbb R}).$ We show furthermore that Bessel-type estimates hold for the $AP$ norm with respect to a countable Gabor system using suitable almost periodic norms of sequencies. 
Paolo Boggiatto, Carmen Fern\'andez, Antonio Galbis
math.FA