Measurement and correction of residual nonlinearities in a digitally predistorted power amplifier

A reduced cost method for the measurement and correction of residual nonlinearities in a digitally predistorted transmitter is proposed. The original system uses a calibration signal applied off-line and a cancellation loop with a square law detector to measure residual nonlinearities. The approach is improved by replacing the calibration signal with the actual signal transmitted, resulting in an on-line measurement system. A further extension integrates several measurements over the input envelope range to adapt a fourth-order polynomial predistorter. Simulation results for a WCDMA input with a 101 carrier configuration show that the proposed approach for measuring residual nonlinearities and estimating predistortion coefficients is effective.