A mobile station (MS) transmits a first data flow to a first group of base stations with a first power offset, transmits a second data flow to a second group of base stations, and further transmits a pilot signal. A radio network controller (RNC) controls the power of the pilot signal power based on reception errors of the second data flow, calculates the first power offset based on signaled required level of the first power offset from base stations (BTS) of the first group which calculate the required level of the first power offset based on an occurrence of retransmission, and signals the calculated first power offset to the mobile station.