1. A system, comprising: a digital pre-distortion circuit in a transmission path between a system input and a transmission circuit; a feedback circuit coupled between the output of the transmission circuit and a training module, the feedback circuit providing feedback signal samples from the output of the transmission circuit at a feedback sampling rate that is lower than an input sampling rate used for signals at the system input; and a training circuit coupled to the system input and coupled to an output of the feedback circuit, the training circuit comprising a feedback-model circuit operating to modify the system input signals to match characteristics of the feedback signal samples, the training circuit providing operating parameters to the digital pre-distortion circuit.