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Memoryless polynomial adaptive predistortion [TV transmitters]

In this paper we investigate algorithms to adaptively adjust the coefficients of memoryless polynomial structures used to precompensate for the nonlinear amplitude and phase distortion of the high-power amplifier in a terrestrial digital television transmitter. The results of the investigation are twofold. First the phase error is a non-Euclidean measure of the absolute symbol error. For small inputs, noise causing a small Euclidean change can create a large phase error. We compensate for this heuristically by not updating the predistorter coefficients for small inputs. This thresholding is shown to decrease the residual error of the phase predistorter. Second, the pre-compensation nature of the amplitude correction requires a modification to the traditional LMS algorithm. This modification will be seen to produce a smaller residual error than traditional LMS. We demonstrate the superior performance of our algorithms via simulations based on the measured characteristics of production high-power amplifiers.