In this paper, adaptive baseband polynomial predistortion techniques are introduced to counter-balance the AM/AM and AM/PM non-linear effects of the transmit power amplifier. The proposed polynomial predistortion scheme is based on polar coordinate representation. Both LMS and RLS concepts are used to derive the adaptive algorithms. An enhanced LMS-based algorithm with fast convergence and low complexity is proposed. For very fast convergence, a cascaded RLS-based adaptive polynomial predistorter structure is introduced. The performance of the proposed schemes in terms of intermodulation distortion, spectral regrowth, and convergence rate are examined. The obtained results show that the polynomial predistortion schemes can be used in M-QAM transmitters with power amplifiers operating near saturation to achieve a highest power efficiency.

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