In a wireless communications system, after a high data rate user is admitted and a supplemental channel is assigned to the user, a control message is sent to a receiver to communicate for power ramp-up and ramp-down profiles. The control message contains parameters of a data rate, a starting time and a duration of time as group in assigned fields in the message which is provided by a control signal source. In response to the control message, a controller provides a rate controllable signal with reference to the parameters of the control message to a data encoder. A bursty input data stream is fed to a buffer. The data encoder withdraws the data from the buffer in response to the rate controllable signal. The bit rate transitions in the bursty input data stream are smoothed with reference to the parameters. There is provided an output data stream having smoother data rate transitions than the input data stream. It is possible to solve problems with 3G CDMA systems which have sudden interference changes resulting from the bursty nature of high-speed data transmissions.