Abstract: The present invention provides a method, a mobile terminal device and a system for determining a transmission power factor. During an uplink of data between a mobile terminal device and a base station via a code division multiple access (CDMA) system supported by automatic repeat request (ARQ) first transmission containing original data and re-transmissions of different order containing supplementary information are communicated. The i-th re-transmissions are based on the automatic repeat request (ARQ). The transmission power factor to be determined is operable with an i-th re-transmission. A first and a second error quantity are obtained from an evaluation of status information items received in accordance with the automatic repeat request (ARQ). The first error quantity and the second error quantity allow for deriving an i-th error ratio so as to calculate a transmission power correction factor.