A method and apparatus of signaling radio resource allocation in a wireless communication system includes establishing groups of mobile stations which monitor a shared group scheduling bitmap; transmitting a group scheduling bitmap to the mobile stations, wherein the group scheduling bitmap contains a mobile station presence bitmap and an SDMA bitmap, wherein the SDMA bitmap is used to divide the group members into two or more subgroups; and transmitting packets to the mobile stations or receiving packets from the mobile stations using the radio resource which is derived from the value indicated in the group scheduling bitmap.