• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.10C
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• pp.1027-1031
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• 2002

In this paper, the non linear characteristics of HPA (High Power Amplifier) is improved by using predistorter. Predistorter consists of 0 degree and 90 degree couplers, complementary amplifier, shottky diodes, and attenuators. Gain of the Linearized HPA is 54㏈ at 1960㎒ - 1980㎒. IMD (Inter Modulation Distortion) characteristic shows -58㏈c at 39㏈m/tone ⓐ1.23㎒. The IMD performance of this predistorter is improved by 14㏈.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.7
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• pp.1102-1109
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• 2001

This paper presents the new architecture of an adaptive predistortion linearizer using the polynomial type predistorter. In the proposed linearizer, most of the processes, including the predistortion, are performed with a digital signal processor(DSP). The recursive least squares(RLS) algorithm is employed for the optimization process to minimize the errors between the predistorter and postdistorter output signals. Simulation results demonstrate that the adjacent channel power ratio(ACPR) is improved by greater than 40 dB at the band edge with linearization. The convergence and reconvergence performance of the linearizer is also satisfactory.

• Proceedings of the IEEK Conference
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• 2001.09a
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• pp.605-608
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• 2001

This paper proposes LUT based predistorter using interpolater to reduce nonlinear distortion which was generated by HPA. We minimized performance degradation from the reduced LUT size with linear interpolation. We updated LUT using LMS algorithm using input data as reference data. As a result, it is shown that when the size of the LUT is 8, linear interpolation is the most outstanding performance in the view of performance and H/W complexity.

• Proceedings of the IEEK Conference
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• 2002.06a
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• pp.339-342
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• 2002

In this paper, the structure of OFDM system is studied, and causes of inter carrier interference (ICI) are analyzed. Based on analysis, this paper shows a technique to prevent a distortion due to nonlinearity of high Power amplifier. The proposed scheme is a predistorter for high power amplifier linearization in orthogonal frequency division multiplexing (OFDM) system used in wireless local area network(WLAN). This is verified by comparing BER characteristics of OFDM system, between used PD and not used PD.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.9
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• pp.28-34
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• 2002

In this paper, a new type predistorter using a low frequency intermodulation signals terms of harmonic generator is proposed. A vector modulator, in which fundamental signal is modulated with low frequency intermodulation signals derived from harmonic generator, generates predistorted third and fifth IM components. Using predistorted signals, intermodulation distortion signals of power amplifier suppressed. The suggested predistorter has been manufactured to operate in Korean PCS base-station transmitting band (1840~1870MHz). The test results show that the third IMD signal level is reduced more than 20dB and the fifth IMD signal is reduced about 10dB for CW two-tone signals. The predistorter improves the Adjacent Channel Power Ratio (ACPR) more than 10dB for CDMA (IS-95) signals.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.2C
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• pp.191-199
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• 2006

In this paper, we propose a method to implement a predistorter of the $rho$-th order inverse filter structure to prevent signal distortion and spectral re-growth due to the high PAPR (peak-to-average ratio) of the OFDM signals and the non-linearity of high-power amplifiers. We model the memory-less non-linearity of the high-power amplifier with a polynomial model and utilize the inverse of the model, the $rho$-th order inverse filter, for the predistorter. Once the non-linearity is modeled with a polynomial, since we can determine the $rho$-th order inverse filter only with the coefficients of the polynomial, large memory is not required. To update the coefficients of the non-linear high-power amplifier model, we can use LMS or RLS algorithms. The convergence speed is high since the number of coefficients is small, and the computation is simple since manipulation of complex numbers is not necessary.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.8
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• pp.740-747
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• 2015

Recently, mobile communication systems using the millimeter-wave frequency band have been proposed, and the importance of efficient compensation of the nonlinearity caused by 60 GHz high-power amplifiers(HPAs) is increasing. In this paper, we propose a predistorter structure based on multiple coefficient sets which are separately used to different ranges of input power values. These ranges correspond to varying levels of nonlinearity characteristics. The structure is applied to the 60 GHz HPA FMM5715X and the performance of correcting the nonlinearity of LTE signals is evaluated. Evaluation results using a hardware testbed demonstrate that the proposed predistorter structure achieves the maximum of 6 dB gain over the conventional method in terms of the adjacent channel leakage ratio(ACLR).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1C
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• pp.65-76
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• 2010

Orthogonal frequency division multiplexing (OFDM) is an attractive technique for achieving high-bit-rate wireless data transmission. However, multicarrier systems such as OFDM show great sensitivity to nonlinear distortion. The OFDM structure requires a summation of a large number of subcarriers for multicarrier modulation, and as a result of this summation large signal envelope fluctuations occur. These fluctuations make OFDM systems to be very sensitive to nonlinear distortion introduced by the high power amplifier (HPA) at the transmitter. In this paper, we propose a canonical piecewise-linear (CPWL) model based digital predistorter to compensate for nonlinear distortion introduced by the high peak-to-average power ratio (PAPR) and the HPA in OFDM systems. The performance of the new predistortion scheme for OFDM systems is evaluated in terms of total degradation (TD) and bit error rate (BER). The simulation results demonstrated that the proposed predistorter achieves significant performance improvement by effectively compensating for the nonlinear distortion introduced by the HPA.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.10
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• pp.97-102
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• 2004

In this paper, a new predistorter controlling modified individual order jntermodulation distortion signals is proposed. The proposed predistorter generates and controls predistorted third and high order IM signals independently. Using predistorted signals, jntermodulation distortion signals of power amplifier are suppressed effectively. The predistortion linearizer has been implemented to operate in Korean PCS basestation transmitting band (1840～1870MHz). The test results show that IMD3 and IMD5 (C/I) of power amplifier are improved more than 40dB and 23dB for CW two tone signals, respectively. The predistorter improves the adjacent channel power ratio (ACPR) more than 10dB at 885KHz offset point for CDMA (IS-95) signals.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.2
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• pp.9-18
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• 2004

OFDM is a special case of multicarrier transmission, where a high-rate datastream is transmitted over a number of lower rate subcarriers. In this paper, the structure of ORM system is studied, and causes of inter carrier interference (ICI) are analyzed. Based on analysis, this paper shows a technique to prevent a distortion due to nonlinearity of high power amplifier. The proposed scheme is a predistorter(PD) for high power amplifier linearization in OFDM system. This is verified by comparing BER characteristics of OFDM system, between used PD and not used PD, and superiority is shown by comparing BER characteristics of OFDM system, between used the proposed PD and used some other PDs.