Key points are not available for this paper at this time.
Sergej Kuksin, Jurgen Poschel, Invariant Cantor Manifolds of Quasi-Periodic Oscillations for a Nonlinear Schrodinger Equation, Annals of Mathematics, Second Series, Vol. 143, No. 1 (Jan., 1996), pp. 149-179
Kuksin et al. (Mon,) studied this question.