A radio system comprising: a radio unit comprising a modulator configured to modulate a digital data signal and a signal interface; an antenna unit comprising a signal interface, the antenna unit being physically separate from the radio unit and located remote from the radio unit; and a cable coupling the signal interface of the radio unit to the signal interface of the antenna unit; wherein the antenna unit further comprises: a digital pre-distortion engine configured to receive the modulated digital data signal and to pre-distort the modulated digital data signal; a digital to analog converter configured to convert the pre-distorted digital data signal to a pre-distorted analog data signal; and a power amplifier configured to amplify the pre-distorted analog data signal, wherein the power amplifier distorts the pre-distorted analog data signal, the distortion introduced by the power amplifier being opposite to the pre-distortion introduced by the digital pre-distortion engine such that the pre-distortion introduced by the digital pre-distortion engine cancels the distortion introduced by the power amplifier; wherein the radio unit further comprises a coefficient computation engine configured to calculate coefficients used by the digital pre-distortion engine to pre-distort the modulated digital data signal; wherein the digital pre-distortion engine is configured to receive a feedback signal and the antenna unit further comprises a feedback loop comprising a down converter and an AD converter and wherein the output of the power amplifier is connected to the input of the down converter and the output of the AD converter is connected to the digital pre-distortion engine, the output of the AD converter having a sampling rate wherein the digital pre-distortion engine is configured to compute feedback data based on the feedback signal and to output the feedback data to the coefficient computation engine in the radio unit for use in re-calculating the coefficients, wherein the data rate of the feedback data is less than the sampling rate a radio unit comprising a modulator configured to modulate a digital data signal and a signal interface; an antenna unit comprising a signal interface, the antenna unit being physically separate from the radio unit and located remote from the radio unit; and a cable coupling the signal interface of the radio unit to the signal interface of the antenna unit; wherein the antenna unit further comprises: a digital pre-distortion engine configured to receive the modulated digital data signal and to pre-distort the modulated digital data signal; a digital to analog converter configured to convert the pre-distorted digital data signal to a pre-distorted analog data signal; and a power amplifier configured to amplify the pre-distorted analog data signal, wherein the power amplifier distorts the pre-distorted analog data signal, the distortion introduced by the power amplifier being opposite to the pre-distortion introduced by the digital pre-distortion engine such that the pre-distortion introduced by the digital pre-distortion engine cancels the distortion introduced by the power amplifier; a digital pre-distortion engine configured to receive the modulated digital data signal and to pre-distort the modulated digital data signal; a digital to analog converter configured to convert the pre-distorted digital data signal to a pre-distorted analog data signal; and a power amplifier configured to amplify the pre-distorted analog data signal, wherein the power amplifier distorts the pre-distorted analog data signal, the distortion introduced by the power amplifier being opposite to the pre-distortion introduced by the digital pre-distortion engine such that the pre-distortion introduced by the digital pre-distortion engine cancels the distortion introduced by the power amplifier; wherein the radio unit further comprises a coefficient computation engine configured to calculate coefficients used by the digital pre-distortion engine to pre-distort the modulated digital data signal; wherein the digital pre-distortion engine is configured to receive a feedback signal and the antenna unit further comprises a feedback loop comprising a down converter and an AD converter and wherein the output of the power amplifier is connected to the input of the down converter and the output of the AD converter is connected to the digital pre-distortion engine, the output of the AD converter having a sampling rate wherein the digital pre-distortion engine is configured to compute feedback data based on the feedback signal and to output the feedback data to the coefficient computation engine in the radio unit for use in re-calculating the coefficients, wherein the data rate of the feedback data is less than the sampling rate