Stabilization of Direct Learning Algorithm for Wideband Signals

An apparatus for controlling a power amplifier, comprising:

• a pre-distorter;
• at least one processor, and
• at least one memory for storing instructions to be executed by the processor, wherein
• the at least one memory and the instructions are configured to, with the at least one processor, cause the apparatus at least to perform
• inputting a signal to be amplified to a pre-distorter provided for compensating for non-linearity of the power amplifier;
• forwarding the pre-distorted output signal from the pre-distorter to the power amplifier;
• adapting parameters of the pre-distorter based on an error between the linearized signal output from the power amplifier and the signal to be amplified using an adaptive direct learning algorithm;
• and
• solving the linear system of equations formed by the direct learning algorithm using a conjugate gradient algorithm,
• wherein, once per direct learning algorithm adaptation, at least one of the initial residual and the initial direction of the conjugate gradient algorithm are set based on the result of the previous adaptation.