• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.41 no.12
• /
• pp.23-32
• /
• 2004

This research investigates the performance of the optical transmissions systems using the SSB modulation format The focus was on the spectral efficiency of the WDM systems and the transmission penalties due to the fiber nonlinearities. By investigating the performance obtained with ideal SSB signal, we set the upper limit of the performance which can be obtained by SSB technology. Furthermore, we investigated the performance obtainable with SSB signals which can be generated with realizable devices. Since SSB formats are more susceptible to the fiber nonlinearities, SSB formats exhibited inferior transmission performances compared to the DSB format. However, within the 500~1000 km transmission range, which is the focus of this research, it was found that the WDM systems with 12.5 GHz channel spacings might benefit from the SSB modulation techniques.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.41 no.4
• /
• pp.415-423
• /
• 2016

High PAPR (Peak-to-Average Power Ratio) characteristic causes some problems like system performance degradation and OOB (Out-of-Band) power increasement under the HPA (High Power Amplifier) nonlinearity condition. UFMC (Universal Filtered Multi-Carrier) and FBMC (Filter Bank Multi-Carrier) are regarded as 5G(Generation) candidate waveforms. In this paper, we evaluate and analyze performance of these systems with DFT-s (Discrete Fourier Transform Spreading) technique under the nonlinear HPA environment. In this paper, we describe OFDM (Orthogonal Frequency Division Multiplexing), UFMC, FBMC, DFT-s-OFDM, DFT-s-UFMC, and DFT-s-FBMC system, and evaluate BER (Bit Error Rate) performance of these systems. As simulation results, BER performance degradation by HPA nonlinearity of DFT-s-OFDM and DFT-s-UFMC is greatly overcome by DFT spreading technique. However, BER performance degradation by HPA nonlinearity of DFT-s-FBMC system is little overcome.

• Korean Journal of Optics and Photonics
• /
• v.1 no.1
• /
• pp.40-45
• /
• 1990

Optical pulse compression in a high finesse nonlinear Fahry-Perot interferometer made hy a silicon is ohserved. The optical pulse compression and moclul,ltion in a such nonlinear Fabry-Perot interferometer is due to the refractive index change of the silicon hy absorbing the incicknt pulse and generating electron-hole pairs. The pulse is compressed to liS of width of the IIlcicient pulse. And the experimental results are consistent with the results of computer simulation.lation.

• Korean Journal of Optics and Photonics
• /
• v.6 no.2
• /
• pp.115-121
• /
• 1995

본 논문에서는 일체형, Nd:YAG 고리 레이저에서 서로 반대방향으로 진행하는 두 모드의 비선형적인 상호작용에 의한 출력 불안정 현상을 조사하였다. 실험을 통하여 두 모드가 각각 단일 종모드로 발진함을 확인하였고, 레이저가 발진하는 임계치 부근의 낮은 펌핑수준을 유지하여 다중모드간의 경쟁이나 단방향 발진에 의한 출력 불안정이 아님을 확인하였다. 또한 잘 알려진 시스템 고유의 감쇄진동과 구별되는 현상임을 보였다. 두 모드간의 손실차가 클수록 이 출력의 변조주파수는 증가하고 변조폭이 줄어 들어 안정화 되며 단방향 발진이 일어난다.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.39 no.9
• /
• pp.28-34
• /
• 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
• /
• v.26 no.4B
• /
• pp.520-527
• /
• 2001

육상이동위성 채널에서 고속 광대역의 정보를 효율적으로 전송하기 위한 최적 방안으로 OFDM(Orthogonal Frequency Division Multiplexing) M-ary PSK를 들 수 있다. 그러나 가입자 단말기 또는 위성중계기의 송신단 고출력 증폭기(HPA : High Power Amplifier)를 전력효율적인 비선형 mode에서 동작할 때, OFDM M-ary PSK 시스템의 최대 전력 대 평균전력의 비(PAPR : Peak-to-Average Power Ratio)가 부바송파 개수만큼 선형적으로 커져 단일 반송파 변조방식에 비해 비선형 왜곡에 의한 성능 열화가 심각하다. 본 논문에서는 이와 같은 성능 열화를 개선하기 위하여 전송채널에서 대역효율과 BER(Bit Error Rate) 성능이 우수한 PC(Parallel Combinatory) OFDM 방식과 개선된 PAPR을 가지는 PTS(Partial Transmit Sequence) OFDM 방식을 결합한 Combined PC & PTS OFDM 방식을 제안하고 그 성능을 분석하였다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.21 no.11
• /
• pp.1201-1207
• /
• 2010

As the mobile services have been increased, the PIMD(Passive Inter-Modulation Distortion) as well as the active-IMD of the CDMA system should be considered for the design of base station antenna systems, because they have an interference of the neighboring base stations. In this paper, in order to reduce the nonlinearity of current caused by the local point contact, we have investigated an influence of the combination of nuts, contact torque(kgf.cm), and the contact area on the PIMD. We propose the improvement techniques of PIMD by investigating the effects of the distance of nuts, the contact area, and the type of nuts.

• Journal of Ocean Engineering and Technology
• /
• v.24 no.6
• /
• pp.34-40
• /
• 2010

Bragg reflection of nonlinear waves is simulated by a 2D fully nonlinear numerical wave tank (NWT). The developed NWT was based on the Boundary Element Method (BEM) with potential theory and the mixed Eulerian-Lagrangian (MEL) time marching scheme with Runge-Kutta 4th-order time integration. A spatial variation of wave elevations and their Fourier amplitudes of each component are compared to investigate the effect of sea bottom ripples and their relative heights. The incident waves over an undulated sea bottom are partially reflected and changed to partial standing waves due to Bragg reflection. The present results are verified with linear calculations and experimental data. It is found that the 1st-order wave component is mainly affected by Bragg reflection and its spatial modulation is significant in front of the bottom ripples.

• Proceedings of the IEEK Conference
• /
• 1999.11a
• /
• pp.301-304
• /
• 1999

밀리미터파 대역의 아날로그 광전송을 위한 진행파형 (travel ing wave, TW) 전계흡수 광변조기 (electroabsorption modulator, EAM)와 광수신기의 설계에 대해 발표하고자 한다. TW EAM 및 TW 광수신기의 일반적인 형태인 ridge-type의 co-planar waveguide (CPW)구조에서의 마이크로파의 전송특성을 3차원 FDTD로 분석하여 광파와 전파의 속도 정합 등을 이루는 최적화 구조를 설계하였다. TW EAM의 경우 광세기 변조의 비선형 응답특성에 있어서 마이크로파 손실과 소자길이가 RF 신호의 혼변조 왜곡 (intermodulation distortion)과 SFDR (spurious free dynamic range)성능에 미치는 영향도 이론적으로 조사하였다. TW PIN 광수신기의 경우 광파와 마이크로파의 속도정합의 영향과 이전에는 고려되지 않았던 photo-generated 전송자의 진성 영역에서의 transit time이 광수신기의 밴드 폭에 미치는 영향을 분석하여 최적화 설계하였다.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.26 no.6
• /
• pp.352-358
• /
• 2014

Hourly tide-gauge data at 10 tide stations along the West/South coasts were analysed statistically for tidesurge interaction. Interactions were found at all stations except Busan, prominently at the western tip of the South coast near Mokpo and Wando. A well-known interaction pattern which occurs at flood tide was found rarely at domestic coasts, while another pattern of the tide-modulated surge which occurs at low tide was detected frequently. In addition, a new interaction pattern which occurs at ebb tide is discovered. This pattern is found at Mokpo where the ebb dominance is prominent. Finally, the skew surge could be considered as a tool coping with such interactions.