An apparatus is configured to allocate an IDentification (ID) cell to avoid duplication of a preamble Pseudo Noise (PN) code in a broadband wireless communication system. The apparatus selects one sector inside the system. A temporary ID cell for the selected sector is selected. Whether an ID cell of a sector to which an ID cell has been already allocated inside a minimum unit group for ID cell allocation is the same as the temporary ID cell is determined. Whether PN codes of sectors inside a neighbor list of the selected sector are the same as temporary PN codes determined using the temporary ID cell are determined. When the temporary ID cell is not duplicated and the temporary PN codes are not duplicated, the selected temporary ID cell is allocated as an ID cell of the selected sector.