Novel Data Pre-Distorter for APSK Signals in Solid-State Power Amplifiers

A computationally efficient data pre-distorter suitable for the 16 amplitude and phase-shift keying (APSK) constellation transmitted through a memoryless non-linear power amplifier is introduced. The proposed method is based on estimating the optimum value of the ring ratio that enables compensation for the power amplifier (PA) distortion occurring at each input back-off (IBO) level of a memoryless behavioral model. Previous results for data pre-distortion rely on iterative numerical optimization techniques which require increased computational resources. Instead, the proposed approach is numerically efficient and further provides insight on the generation of non-linear distortion. Computed and measured bit-error rate (BER) results for 16-APSK in additive white Gaussian noise (AWGN) channel and the presence of a PA are presented to prove the validity of the method. The performance evaluation of the pre-distorter based on a measured non-linear characteristic of a commercial power amplifier showed a BER reduction of up to four orders of magnitude at low IBO levels.