A radio communication system comprising a primary station and a plurality of secondary stations has a communication channel for the transmission of information from a secondary station to the primary station. The secondary station can adjust its output transmission power at a plurality of different rates, and the primary station can instruct the secondary station which of the plurality of rates it should use. The primary station determines the optimum rate for the secondary station to use by measurement of characteristics of signals received from the secondary station, for example the average signal to interference ratio, and instructs the secondary station accordingly. Other indications may be used to determine or verify the optimum rate, for example further properties of the received signals or information on the speed of the secondary station.