Method for carrying out handoff between macrocell and microcell in hierarchical cell structure

A method for carrying out an idle handoff from a macrocell to a microcell (picocell) in a hierarchical cell structure includes the steps of: a) allocating different frequency assignments (FA) to the macrocell and the microcell in a same service band, to construct the hierarchical cell structure; b) transmitting cell structure information of neighboring base stations and pseudo noise (PN) code from base station to mobile station; c) checking whether the mobile station is in the hierarchical cell by using the cell structure information of neighboring base station; and d) checking whether a value of the pseudo noise (PN) code is greater than T_ADD and greater than Ec/Io of the macrocell by periodically searching the pseudo noise (PN) code of the microcell, to carry out an idle handoff to the microcell, wherein the T_ADD represents a value of base station pilot strength required for the base station of neighboring set to be included in a candidate set, the Ec represents an pilot energy accumulated during one pseudo noise (PN) chip period, and the Io represents a total power spectrum density within a reception bandwidth.