Information for different subscribers of a service with the same modulation and channel encoding method is transmitted by allocating radio resources in a wireless portable Internet system. Also, identifier information on the subscriber of a concurrently allocated radio resource is transmitted through common control information. Therefore, information for a plurality of subscribers coexists in a single radio resource block, and it can be easily transmitted. Since a subscriber station which has received downlink information can know to which radio resource block the information for the corresponding station is allocated through the subscriber identifier information transmitted as common control information, the subscriber station can access desired information by accessing a specific radio resource block to which information for the subscriber is allocated in the received frame.