Conference Paper

A Nonlinear Distortion Compensation Method with Adaptive Predistorter and Negative Feed-Back for a Narrow-Band Signal

Grad. Sch. of Inf. Sci. & Electr. Eng., Kyushu Univ., Fukuoka
DOI: 10.1109/VTCF.2006.603 Conference: Vehicular Technology Conference, 2006. VTC-2006 Fall. 2006 IEEE 64th
Source: IEEE Xplore


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
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    ABSTRACT: Digital Predistorter is a cost-effective solution to compensate for the nonlinear distortions appearing in the RF power amplifiers (PAs). The indirect learning scheme is widely implemented because of its flexibility to eliminate the requirement for building a closed-loop real time system, which dramatically reduces the complexity for measurement setup. However, such scheme is sensitive to the measurement noise that may cause biasing in the coefficients estimation. To minimize the influence of measurement noise and simultaneously enable the open-loop implementation, we propose a predistortion technique that first model the PA and then generates predistorted signal iteratively through a feedback configured structure to avoid using the noisy signal when performing the inverse model estimation. Unlike the indirect learning which estimates the postinverse of the PA, our predistortion is based on the preinverse of the PA. Both simulations and measurements show that utilizing the proposed predistortion can obtain adjacent channel power ratio (ACPR) improvement in wideband code division multiple access (WCDMA) signal test compared with the conventional memory polynomial predistortion based on indirect learning. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.
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