• Journal of information and communication convergence engineering
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• 제14권3호
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• pp.147-152
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• 2016

In radio-over-fiber (RoF) systems, nonlinear compensation is essential to improve performance. Among the several existing nonlinear compensation techniques, we investigate a predistortion technique for a directly modulated laser in an RoF system. First, we obtain the input-to-output response of a directly modulated laser at 160, 820, and 1,540 MHz. The results show that the laser response is dependent on the frequency band. Second, we design an optimal predistortion circuit to compensate for the nonlinear responses of three frequency bands. We design the predistortion circuit with two options: each predistortion circuit for each frequency band and one single predistortion circuit for all the three frequency bands. Finally, we present the simulation results of the predistortion system obtained using a commercial simulator. These results show that the third intermodulation distortion (IMD3) is improved by 0.6-9 dB for the three frequency bands with only a single predistortion circuit.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1998년도 하계종합학술대회논문집
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• pp.98-101
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• 1998

The intermodulation distortion(IMD) due to laser diode nonlinearity of an asynhcronous direct sequence code diviion multiple access(DS/CDMA) system in wireless-optical transmission system model is analzed. A third order polynomial is used to represent laser diode nonlinearity. In DS/CDMA system, only one harmonic of the third-order intermodulation term falls on the signal frequency band and influences the system performance characteristics. To cancel multi-user interference and nonlinear distortion in a DS/CDMA wireless-optical transmission system model, the simple transversal filter structure with N-taps of (N-1) tap delay of 1 chip time delay line is used. It is necessary to select an optimal modulation index that provides a maximum signal-to-noise ratio and the results are useful for CDMA system design.

• 전자공학회논문지A
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• 제31A권1호
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• pp.9-16
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• 1994

In this paper, we propose a frequency assignment algorithm to minimize intermodulation effect which is caused by nonlinear amplipification of the satellite transponder. Allmost all of the published algorithms up to now are applicable to one-level SCPC systems, the application range of those algorithms is very restricted from the viewpoint of actual practice. In this paper, we develope and propose a new frequency assignment algorithm which utilize the basic concept of Okinaka's DELINS-INSDEL algorithm to extend its applicabilty from one-level SCPC systems to multi-level systems. The proposed TDTI algorithm provides considerable generality in reducing intermodulation effect in practical satellite communication systems because of its alpplicability to multi-level and multi-bandwidth systems as well as one-level systems. Besides the TDTI algorithm which shows excellent characteristics in performance but requires somewhat long excution time. the WTDI-SDELINS algorithm is proposed in this paper to compensate TDTI's demerits in excution time. Considering the fact that there are very little published sterategies for multi-level and muti-bandwidth systems. the algorithm proposed in this paper is quite meaningful.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 학술대회 논문집 정보 및 제어부문
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• pp.475-477
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• 2005

We simulated 3rd order intermodulation distortion (IMD3) induced Carrier-to-Intermodulation Ratio (CIR) of laser diodes over a wide range of optical modulation index, and compared the results with commercial IMD3 induced CIR specification such as Composite Triple Beat (CTB) of DFB laser transmitter for CATV networks. It shows that the simulation results are in good agreement with the CATV CTB specification within 3dB margin. The results can be used to predict IMD3 induced CIR performance for various analog optical transmission systems with given optical modulation index and the number of transmission channels.

• ETRI Journal
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• 제29권4호
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• pp.536-538
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• 2007

We propose and describe the fabrication of a linear power amplifier (LPA) using a new analog feedforward method for the IMT-2000 frequency band (2,110-2,170 MHz). The proposed analog feedforward circuit, which operates without a pilot tone or a microprocessor, is a small and simple structure. When the output power of the fabricated LPA is about 44 dBm for a two-tone input signal in the IMT-2000 frequency band, the magnitude of the intermodulation signals is below -60 dBc and the power efficiency is about 7%. In comparison to the fabricated main amplifier, the magnitude of the third intermodulation signal decreases over 24 dB in the IMT-2000 frequency band.

• Journal of the Optical Society of Korea
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• 제18권4호
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• pp.330-334
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• 2014

In this paper, we present an incoherent dual-parallel modulation linearized optical link employing two different optical wavelengths. Comparing with previous dual-parallel modulation, this linearization method prevents the recreation of distortion products and can be readily implemented. Furthermore, a dual-wavelength dual-parallel modulation linearized optical link constructed with the commercially available devices is experimentally demonstrated with a spurious-free dynamic range of $122.5dB.Hz^{4/5}$. More than 25 dB suppression of the intermodulation distortion, 15.6 dB improvement of spurious-free dynamic range and 1.5 dB improvement of compression dynamic range are achieved after linearization.

• 전자공학회논문지A
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• 제30A권9호
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• pp.14-23
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• 1993

In this paper, we present analysis results of various intermodulation products (IMPs) evaluation methods previously proposed for nonlinear systems. The results indicate that out of these methods, Fuenzalida and Simbo's method is the best for efficient evaluation of IMPs. Also, we present a detailed mathematical analysis of IMP and show how to apply the equations related to IMP to actual program implementations with examples. In this paper, we newly introduce three methods to reduce the IMP calculation time and improve the accuracy of the outputs :1) TWTA curve fitting method by LS (Least Square), 2) IMP evaluation technique which is based on a look-up table 3) Gaussian spectral shaping for PSK signal instead of convolution. The IMP evaluation results obtained by the new approaches introduced in this paper resulted in a good match with the published outputs in the open literature and showed improved performance especially in the TWTA curve .

• 대한전자공학회논문지TC
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• 제38권5호
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• pp.1-8
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• 2001

본 논문은 광무선 (fiber-radio)링크를 통한 OFDM(orthogonal frequency division multiplexing) 신호 전송 시스템의 성능을 분석한다. 전체 시스템에 대한 기저대역 등가 모델을 유도했으며 광링크 상에서의 혼변조왜곡(IMD : intermodulation distortion) 전력과 OFDM 신호의 부반송파 개수 사이의 상관 관계를 증명하였다. 이를 이용해서 전체 시스템의 CNR을 유도하였으며 각 변복조 방식의 요구되는 CNR 관점에서 OFDM 신호의 최대 부반송파 개수를 시뮬레이션에 의해 추출하였고 여러 시스템 파라메타와 CNR과의 관계를 조사하였다.

• JSTS:Journal of Semiconductor Technology and Science
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• 제8권4호
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• pp.283-288
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• 2008

A post-linearization technique for the differrential CMOS LNA is presented. The proposed method uses an additional cross-coupled common-source FET pair to cancel out the third-order intermodulation ($IM_3$) current of the main differential amplifier. This technique is applied to enhance the linearity of CMOS LNA using $0.18-{\mu}m$ technology. The LNA achieved +10.2 dBm IIP3 with 13.7 dB gain and 1.68 dB NF at 2 GHz consuming 11.8 mA from a 1.8-V supply. It shows IIP3 improvement by 6.6 dB over the conventional cascode LNA without the linearizing circuit.

• 한국전자파학회논문지
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• 제12권5호
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• pp.734-739
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• 2001

본 논문에서는 동축선로 공진기를 이용한 필터에서 발생하는 수동 상호변조 왜곡신호의 분석 및 최적화 기법을 제시하였다. 개발한 시뮬레이션 기법은 필터의 치수 변화를 통해 필터의 선형응답 특성에 영향을 주지 않고 수동 상호변조 왜곡신호 수준을 낮출 수 잇다. 필터의 수동 상호변조 왜곡신호 수준은 필터를 형성하는 각 공진기를 통해 흐르는 전류의 양에 의해 결정되며, 이러한 전류의 제어를 통해 공진기형 필터의 수동 상호변조왜곡 신호를 감소시킬 수 있다.