• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.12A
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• pp.1019-1024
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• 2003

In the thesis, we propose a new type of the predistortion linearizer using frequency multiplier The linearizer utilizing the 2nd and 3th harmonic used the individual control of the 3rd and 5th order intermodulation distortion(IMD) component. This structure is composed of wilkinson power combiner for combine and isolation of output signal, 3rd order IMD product controller using doubler and 5th order IMD product controller using tripler. The proposed predistortion linearizer controlled by individual order is obtained for about -16 dBc and 18 dBc of 3rd order and 5th order IMD components, respectively, over the frequency band 870 MHz to 880 MHz at the output power of 34 dBm/tone.

• Journal of the Korean Society of Radiology
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• v.7 no.4
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• pp.301-305
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• 2013

This thesis intends to analyze tooth distortion by mandibular arch form by reproducing existing panorama image and reconstructed panorama image of Cone Beam CT data with the three-dimensional computer program. The diameter of tooth measured in Cone Beam CT's cross-section image and reconstructed panorama was synchronized without any big change from incisors to posteriors. But, panorama showed serious distortion as going to posteriors after showing a little distortion in incisors. The panorama reconstructed for patients' individual arch showed reduced distortion than panoramas used generally. In addition, panorama showed serious distortion from incisors to posteriors and it means that distortion is reduced in reconstructed panorama.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37C no.12
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• pp.1289-1295
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• 2012

An adaptive digital predistortion (PD) technique is proposed for linearization of power amplifiers (PAs) in multiple-input multiple-output (MIMO) transmitters. We consider a PD structure equipped with only one combined feedback path while conventional systems have multiple feedback paths. Hence, the proposed structure is much simpler than that of multiple feedback paths. Based on the structure, a new PD algorithm is derived. The simulation results show that linearization performance of the proposed method is almost the same as the conventional multiple feedback technique while the former is much simpler to implement than the latter.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.4
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• pp.430-439
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• 2011

In this paper, we design a digital predistortion(DPD) for linearity enhancement of RF power amplifier operating in 900 MHz band. We verify improvement of linearity by comparing the proposed DPD using tanh as a nonlinear indexing function and the DPD using linear indexing function based on signal amplitude. The digital predistortion is realized by look-up table(LUT) method, and the Saleh model is employed for power amplifier modeling, then a commercial power amplifier module is used for measurement. The LUT has 256 tables, and the NLMS(Normalized Least Mean Square) algorithm was utilized for an adaptive algorithm for estimation. As a result, we improve the ACLR(Adjacent Channel Leakage Ratio) by around 15 dB.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.2
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• pp.65-70
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• 2004

This paper presents a novel linearization scheme for a nonlinear RF amplifier It is based on the amplitude modulation with envelope signal. The 3rd order distortion generator is composed of two FETs and it adopts a balanced structure for the purpose of main carrier cancellation. The amplitude and phase of the IM3 component can be controlled at RF band. This predistorter is implemented and tested at the KOREA PCS Tx. band (1840∼1870MHz). Experimental results of two-tone test show that the IM3 cancellation is achieved about 30-40 ㏈ for the wide dynamic range. The adjacent channel power ratio is improved by over 10 ㏈ at the broad-band CDMA signal with a peak to average power ratio of l0㏈, and this improvement is maintained through a wide range of output power levels.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.5
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• pp.475-483
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• 2002

The new architecture for the stabilization of an adaptive linearizer using the RLS algorithm is presented. The delay lock loop is apl)lied to compensate the feedback loop delay of the nonlinear amplifier output, and the Yang's algorithm is used to mitigate the numerical unstability of the RLS algorithm. This method is applied to the linearizer using the polynomial predistorter, and it's efficacy is verified by the simulation of the proposed structure.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.6A
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• pp.587-591
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• 2011

In a visible light communication (VLC) system using LEDs, its nonlinearity degrades the performance. If it is compensated by using predistortion and LED's linear range is extended, then a large signal can be used as an LED input and the performance of VLC will be improved. In this paper, a predistortion curve is made by periodic measurement of LED nonlinearity, and the experimental results of predistorted OFDM is provided.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 1999.11b
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• pp.179-183
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• 1999

일반적인 통신 시스템에서 높은 전력을 가지는 출력 신호를 얻기 위하여 고전력증폭기(HPA)의 사용은 필수적이다. 그러나 HPA를 통과한 신호는 AM/AM 및 AM/PM의 비선형왜곡이 발생하는 단점을 가지고 있다. 그 결과 송신신호의 대역내 신호 스펙트럼이 왜곡되고 신호의 대역폭을 확장시켜 인접채널에 간섭을 유발한다. 본 논문에서는 HPA의 비선형 왜곡 특성을 보상하기 위하여 기저대역에서 룩업테이블(LUT)을 이용한 전치왜곡기의 동작 알고리듬을 제안한다. 먼저, LUT의 빠른 초기화를 위하여 송신신호로부터 HPA의 특성을 예측하여LUT를 초기화 시키는 알고리듬을 제안한다. 그리고 통신중에 HPA의 특성이 변화할 경우에 대비하여 평균자승오차를 최소화하는 적응알고리듬을 제안한다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.1 s.104
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• pp.67-73
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• 2006

This paper proposes a new predistortion linearizer with controlling intermodulation distortion(IMD) signals. This linearizer achieves independent control of third- and fifth-order intermodulation distortion products using amplitude modulation with even harmonic signals. A vector modulator that modulate fundamental signal with both second- and fourth-order harmonic components generated by harmonic generator circuits, generates the inverse characteristics third-and fifth-order intermodulation signals of power amplifier and controls amplitude and phase of them with each other modulation factors. As a results, this linearizer is suppressed IMD signals of power amplifier effectively. The test results show that the third IMD is cancelled more than 25 dB and the fifth order IMD is cancelled about 18 dB for CW two-tone signals. Also, it's improved the adjacent channel power ratio(ACPR) more than 7 dB for IS-95 CDMA signals.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.6 s.97
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• pp.644-651
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• 2005

In this paper, a new predistortion method to reduce nonlinearity or a traveling wave tube amplifiers(IWTAs) is proposed. Nonlinear transfer characteristics of TWTA are analyzed using carrier complex power series. Inverse carrier complex power series or a predistortion linearizer to linearizer TWTA are also proposed. The inverse nonlinear distortion characteristics of predistorter can be realized with reflective structure that is composed of Schottky diode and resistive-terminated transmission line. The AM-to-AM and the AM-to-PM characteristics for TWTA by proposed predistortive linearizer on K-band were improved from -5.825 dB and -37.321^{\circ} to 0.786 dB and 6.742^{\circ}, respectively.