A Nonlinear Distortion Compensation Method with Adaptive Predistorter and Negative Feed-Back for a Narrow-Band Signal
ABSTRACT As a method to compensate for the nonlinear distortion of a power amplifier, the adaptive predistorter and the negative feed-back system are known. Although the feedback method is a simple technique, its instability becomes a problem for a high feedback gain to achieve a high compensation effect. On the other hand, the predistorter needs long time to calculate the suitable parameters. In this paper, we propose a nonlinear distortion compensation method for a narrow-band signal. In this method, adaptive predistorter and negative feedback are combined. With computer simulations, we show that the proposed scheme achieves both five times faster convergence speed than that of the predistorter and three times longer permissible delay time in the feed-back amplifier than that of a negative feed-back only amplifier, while keeping the required compensation performance.
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ABSTRACT: Adaptive predistorter is an effective technique to compensate for nonlinear distortion in a power amplifier. As a method to improve the parameter convergence speed in the predistorter, a series expansion technique with an orthogonal polynomials has been investigated. In this paper, we present an adaptive predistortion linearization method based on orthogonal polynomial expansion for a nonlinear power amplifier affected by memory effect in OFDM systems, where both memory and memoryless predistorter are constructed by the weighted sum of orthogonal polynomials. In addition, to achieve the parameter optimization speed improvement of the predistorter, we propose a method to determine step-size in a recursive calculation. The parameter convergence performance of the predistorter is investigated in OFDM systems with and without peak-to-average power ratio (PAPR) reduction, where the partial transmit sequence (PTS) technique is employed to reduce PAPR. Computer simulation results show that the proposed adaptive predistorter achieves faster parameter convergence time than that of non-orthogonal one in OFDM systems with nonlinear power amplifier affected by memory effect, even though PAPR of OFDM signal is reduced by using PTS. It is also confirmed that power added efficiency is further improved by combining the adaptive predistortion with PAPR reduction technique.Communications and Signal Processing (ICCSP), 2011 International Conference on; 03/2011