1. A method of modelling a power amplifier fed by one of a wideband signal and an intra-band carrier aggregated signal, the method comprising: receiving the one of the wideband signal and the intra-band carrier aggregated signal; generating a discrete base band equivalent, BBE, Volterra series based on the received signal, the series having distortion products grouped according to determined shared kernels; and the shared kernels being determined based on a transformation of a real-valued continuous-time pass band Volterra series without pruning of kernels.