The invention relates to a cellular radio system wherein a communication terminal receives servo power instruction from a base station with which a radio communication comprising first uplink and downlink channels is established. In response to an instruction for changing a channel (13), the terminal records a first power level received from the base station and a reference power on which the terminal transmitted when the instruction was received. The terminal endeavours to continue communication on new uplink and downlink channels interrupting the transmission on the first uplink channel. If failed, the terminal evaluates a second power level received from the base station and restarts to transmit through the first uplink channel at a power determined according to the reference power and a variation between the first and second power level.