A high-speed packet data communication system, wherein a channel condition determiner measures a signal-to-interference ratio (SIR) of a first uplink dedicated channel signal received from a UE, and calculates a difference between the measured SIR and a preset target SIR; a transmission power determiner compares the difference with preset thresholds, and determines an uplink power offset to be applied to a second uplink dedicated channel transmitting control information for packet data received at the UE according to a result of the comparison; and a transmitter transmits over a downlink the determined uplink power offset to the UE.