Apparatus, comprising a first number of input ports (1610-1 to 1610-n), each adapted to input a respective input signal, wherein the first number is at least two; a second number of noise generator output ports (1620-1 to 1620-m), each corresponding to a respective different one of the input ports and adapted to provide a respective noise, wherein the second number is one less than the first number or equal to the first number; the second number of mixers (1630-1 to 1630-m), each corresponding to a respective different one of the noise generator output ports and adapted to mix the respective input signal with the respective noise to generate a respective mixed signal; the first number of pre-distorters (1640-1 to 1640-n), each corresponding to a respective different one of the input ports and adapted to apply a respective preliminary pre-distortion on the respective mixed signal if one of the noise generator output ports corresponds to the respective input port and to apply a respective preliminary pre-distortion on the input signal if none of the noise generator output ports corresponds to the respective input port, in order to obtain a respective pre-distorted signal; the first number of signal paths (1650-1 to 1650-n), each corresponding to a respective different one of the input ports and adapted to modify the respective pre-distorted signal in order to obtain a respective modified signal; a combiner adapted to combine the modified signals from the signal paths in order to obtain an output signal; a contribution separator adapted to separate, for each of the input signals, from a feedback signal and based on the respective noise and the respective input signal, a contribution of the respective input signal to the output signal, wherein the feedback signal is based on the output signal; a determinator adapted to determine a respective pre-distortion for at least one of the input signals and to replace the respective preliminary pre-distortion by the respective determined pre-distortion such that, if the determined respective pre-distortion is applied by the respective pre-distorter to the respective mixed signal or input signal, the respective contribution will correspond to the respective mixed signal or input signal on which a predefined function is applied, wherein the predefined function is at least one of non-linear and dynamic and has a third number of predefined parameters. a first number of input ports (1610-1 to 1610-n), each adapted to input a respective input signal, wherein the first number is at least two; a second number of noise generator output ports (1620-1 to 1620-m), each corresponding to a respective different one of the input ports and adapted to provide a respective noise, wherein the second number is one less than the first number or equal to the first number; the second number of mixers (1630-1 to 1630-m), each corresponding to a respective different one of the noise generator output ports and adapted to mix the respective input signal with the respective noise to generate a respective mixed signal; the first number of pre-distorters (1640-1 to 1640-n), each corresponding to a respective different one of the input ports and adapted to apply a respective preliminary pre-distortion on the respective mixed signal if one of the noise generator output ports corresponds to the respective input port and to apply a respective preliminary pre-distortion on the input signal if none of the noise generator output ports corresponds to the respective input port, in order to obtain a respective pre-distorted signal; the first number of signal paths (1650-1 to 1650-n), each corresponding to a respective different one of the input ports and adapted to modify the respective pre-distorted signal in order to obtain a respective modified signal; a combiner adapted to combine the modified signals from the signal paths in order to obtain an output signal; a contribution separator adapted to separate, for each of the input signals, from a feedback signal and based on the respective noise and the respective input signal, a contribution of the respective input signal to the output signal, wherein the feedback signal is based on the output signal; a determinator adapted to determine a respective pre-distortion for at least one of the input signals and to replace the respective preliminary pre-distortion by the respective determined pre-distortion such that, if the determined respective pre-distortion is applied by the respective pre-distorter to the respective mixed signal or input signal, the respective contribution will correspond to the respective mixed signal or input signal on which a predefined function is applied, wherein the predefined function is at least one of non-linear and dynamic and has a third number of predefined parameters.