A radio frequency, RF, transmitter (200, 400) characterized by: at least one digital signal processing module (210, 410) comprising at least one digital pre-distortion component arranged to: receive at least one complex input signal comprising information to be transmitted over an RF interface, perform two-dimensional non-uniform mapping of the at least one received complex input signal to a first, in-phase digital pre-distortion control word and a further, quadrature digital pre-distortion control word (212, 214), and output the in-phase and quadrature digital pre-distortion control words; and at least one power amplifier module comprising a first, in-phase, array of switch-mode power cells and at least one further, quadrature, array of switch-mode power cells, wherein the first, in-phase and further quadrature control words (212, 214) are arranged to drive the at least one power amplifier module to output an analogue RF signal that represents the at least one complex input signal and wherein the two-dimensional non-uniform mapping comprises a pre-distortion profile that is at least partly based on an input/output relationship for the at least one power amplifier module, the at least one power amplifier module being arranged to: receive the in-phase and quadrature digital pre-distortion control words output by the at least one digital signal processing module (210, 410), and generate an analogue RF signal for transmission over the RF interface based at least partly on the in-phase and quadrature digital pre-distortion control words. at least one digital signal processing module (210, 410) comprising at least one digital pre-distortion component arranged to: receive at least one complex input signal comprising information to be transmitted over an RF interface, perform two-dimensional non-uniform mapping of the at least one received complex input signal to a first, in-phase digital pre-distortion control word and a further, quadrature digital pre-distortion control word (212, 214), and output the in-phase and quadrature digital pre-distortion control words; and receive at least one complex input signal comprising information to be transmitted over an RF interface, perform two-dimensional non-uniform mapping of the at least one received complex input signal to a first, in-phase digital pre-distortion control word and a further, quadrature digital pre-distortion control word (212, 214), and output the in-phase and quadrature digital pre-distortion control words; and at least one power amplifier module comprising a first, in-phase, array of switch-mode power cells and at least one further, quadrature, array of switch-mode power cells, wherein the first, in-phase and further quadrature control words (212, 214) are arranged to drive the at least one power amplifier module to output an analogue RF signal that represents the at least one complex input signal and wherein the two-dimensional non-uniform mapping comprises a pre-distortion profile that is at least partly based on an input/output relationship for the at least one power amplifier module, receive the in-phase and quadrature digital pre-distortion control words output by the at least one digital signal processing module (210, 410), and generate an analogue RF signal for transmission over the RF interface based at least partly on the in-phase and quadrature digital pre-distortion control words.