Gabor Dual Frames with Characteristic Function Window

The duals of Gabor frames have an essential role in reconstruction of signals. In this paper we find a necessary and sufficient  condition for two Gabor systems (X[c1,d1),a,b) and (X[c2,d2),a,b) to form dual frames for L_2(R), where a and b are positive numbers and c1,c2,d1 and d2 are real numbers such that c1 d1 and c2 d2.