Transmission power offset arbitration between base stations during soft handoff

A transmission power control method for controlling a transmission power of a relative transmission rate control channel including a relative transmission rate of uplink user data, which is transmitted from a cell controlled by a radio base station to a mobile station, comprising:

• notifying, from a radio network controller to a first cell a first offset between a transmission power of a first relative transmission rate control channel and a transmission power of a dedicated physical channel of the first cell, when the mobile station is performing a soft-handover with the first cell and a second cell;
• notifying, from a radio network controller to the second cell, a second offset between a transmission power of a second relative transmission rate control channel and a transmission power of a dedicated physical channel of the second cell, when the mobile station is performing the soft-handover with the first cell and the second cell;
• determining, at the first cell, the transmission power of the first relative transmission rate control channel based on the first notified offset, and transmitting the first relative transmission rate control channel to the mobile station using the determined transmission power;
• and
• determining, at the second cell, the transmission power of the second relative transmission rate control channel based on the second notified offset, and transmitting the second relative transmission rate control channel to the mobile station using the determined transmission power.