  We present results of a feasibility study of a model-independent way to
measure the angle phi_3 of the unitarity triangle. The method involves B->DK
decays where the neutral D decays to the K_S Pi+ Pi- final state, together with
the sample of decays of CP-tagged D mesons (produced, e. g. in psi(3770)->DDbar
process) to the same final state. We consider different approaches to the
extraction of phi_3 and obtain the expected statistical accuracy of the phi_3
measurement as a function of B and D_CP statistics.
