Abstract: A mobile communication system using an orthogonal frequency division multiplexing (OFDM)/orthogonal frequency division multiple access (OFDMA) scheme. The method for assigning ranging codes in the OFDM/OFDMA communication system includes classifying rangings between a base station and a mobile subscriber station (MSS) of the OFDM/OFDMA communication system into an initial ranging, a periodic ranging, a bandwidth request ranging, and a handover ranging. A first number of ranging codes used for the rangings are created and a second number of ranging codes selected from the first number of ranging codes are assigned as handover ranging codes used for the handover ranging.

Abstract: A method for transmitting common control information from a base station to a plurality of subscriber stations in a wireless communication. The common control information includes first information transmitted in common to all of the subscriber stations and second information separately transmitted to the subscriber stations according to channel states of the subscriber stations. The first information is transmitted using an MCS (Modulation and Coding Scheme) level having a modulation scheme with a lowest order and a coding scheme with a lowest coding rate among all MCS levels available in the base station. The second information is transmitted using MCS levels that are adjusted by a predetermined level against MCS levels corresponding to channel states of the subscriber stations.