A base station, a mobile station, a radio communications system, and a radio transmission method are disclosed. The base station includes a control information determining unit configured to determine control information that includes a spreading factor, the number of chip repetitions, and a phase unique to the mobile station, based on at least one of information about the type of cell environments in which the mobile station is present, information about the number of mobile stations that are present in the cell, information about information rate required by the mobile station, information about a type of traffic, information about a radio parameter of the mobile station, information about a propagation path condition, and information about interference from an adjacent cell, and configured to transmit the spreading factor, the number of chip repetitions, and the unique phase of the mobile station that is determined to the mobile station.