Transmission signal power control apparatus, communication apparatus and predistortion coefficient updating method

A communication apparatus comprising:

• a baseband processing unit which generates a transmission signal;
• a transmission signal power control unit which amplifies the transmission signal;
• and
• an antenna which emits the amplified transmission signal,
• wherein the transmission signal power control unit comprises:
• a power amplifier which amplifies the transmission signal;
• a first low-pass filter which attenuates a frequency component of a feedback signal, which is higher than a certain sampling frequency, the feedback signal being part of a signal that is output from the power amplifier;
• an analog-to-digital converter which digitizes the feedback signal output from the first low-pass filter by the certain sampling frequency;
• a predistortion unit which generates a predistortion signal to input to the power amplifier, by multiplying the transmission signal by predistortion coefficients which represent an inverse characteristic of an input-output characteristic of the power amplifier;
• a power amplifier model unit which generates a learning digital signal by multiplying part of the predistortion signal by model coefficients which tentatively represent the input-output characteristic of the power amplifier;
• an inverse unit which calculates the predistortion coefficients from the model coefficients;
• a second low-pass filter which generates a pseudo feedback signal by attenuating the high frequency component of the learning digital signal by multiplying the learning digital signal by weighting coefficients;
• and
• a subtractor which calculates an error between the pseudo feedback signal and the digitized feedback signal,
• wherein
• the power amplifier model unit updates the model coefficients such that the error is minimized, and
• the second low-pass filter is an adaptive filter which updates the weighting coefficients such that the error is minimized.

A predistortion coefficient updating method for updating predistortion coefficients which represent an inverse characteristic of an input-output characteristic of a power amplifier, the predistortion coefficient updating method comprising:

• attenuating a frequency component of a feedback signal, which is higher than a certain sampling frequency, the feedback signal being part of a signal that is output from the power amplifier by a first low-pass filter;
• digitizing the feedback signal whose the high frequency component is attenuated by the certain sampling frequency;
• generating a predistortion signal by multiplying a transmission signal by the predistortion coefficients;
• generating a learning digital signal by multiplying the predistortion signal by model coefficients which tentatively represent the input-output characteristic of the power amplifier;
• generating a pseudo feedback signal by attenuating a high frequency component of the learning digital signal by multiplying the learning digital signal by weighting coefficients of an adaptive low-pass filter;
• calculating an error between the pseudo feedback signal and the digitized feedback signal;
• updating the model coefficients such that the error is minimized;
• updating the weighting coefficients such that the error is minimized;
• and
• calculating the predistortion coefficients from the updated model coefficients.