Identification of true-static predistorter using a sine wave and accurate quantification of memory effects in broadband wireless transmitters

Abstract

This study proposes a new technique for the extraction of static non-linearities in wideband transmitters by launching a simple sinusoidal wave within the bandwidth of the system. The transmitter is first characterised under a two-carrier wideband code division multiple access (WCDMA) drive signal and modelled using a memory polynomial model. Two types of memoryless digital predistorters are then synthesised and applied to the amplifier model. The first predistorter is derived from the averaging of the measured data under the two-carrier WCDMA signal, while the second is derived using a sinusoidal wave signal excitation. Discrepancies between the two predistortion functions are illustrated, demonstrating that the predistorter using the averaging technique is biased by the presence of linear memory effects. The results show that the residual distortions at the output of the linearised power amplifier are different and more present when using the sine wave excitation technique compared with the averaging technique. This finding indicates that the sine wave-based technique is more rigorous for de-embedding the static non-linearity from the overall non-linear behaviour, which corroborates the validity of the proposed approach in extracting the true static behaviour of the system and its pertinence for the accurate extraction and quantification of memory effects.