For effective use of wireless channels and allowing high-speed data transfers on the reverse link in a mobile communications system, the modulation mode and/or the coding rate can be adaptively adjusted according to changes in the wireless channel conditions. To estimate the channel conditions, the mobile station transmits an access signal via an access channel to the base station. The base station determines a first data transmission rate based upon the signal power level of the access signal and an actual signal power level detected from the access channel, and also determines a second data transmission rate based upon a signal load detected at the base station. The base station selects the appropriate data transmission rate, and applies an adjusted modulation mode and/or channel coding.