  It is well known that while forward scattering has no effect on the
conductance of one-dimensional systems, backscattering off a static impurity
suppresses the current. We study the effect of a time-dependent point impurity
on the conductance of a one-channel quantum wire. At strong repulsive
interaction (Luttinger liquid parameter g<1/2), backscattering renders the
linear conductance greater than its value e^2/h in the absence of the impurity.
A possible experimental realization of our model is a constricted quantum wire
or a constricted Hall bar at fractional filling factors nu=1/(2n+1) with a
time-dependent voltage at the constriction.
