FIELD: data transmission systems. SUBSTANCE: data transmission system has first device and second device, as well as two-way data transmission channel in-between. First device sends user data to second device over data transmission channel and control information, over control channel. This is attained due to the fact that transmission is organized in frames incorporating user data field corresponding to data transmission channel and at least first and second control information fields, both corresponding to control channel. For transmission power control first transmission power level, second transmission power level, and third transmission power level are determined. EFFECT: optimized use of radio interface in radio system. 25 cl, 6 dwg
