• 한국전자파학회논문지
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• 제11권3호
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• pp.484-491
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• 2000

DS-CDMA 방식의 이동통신 시스댐에서 계속 증가하는 가입자의 용량 증대 및 향후 예상되는 광대역 고속 데이터 서비스를 수용하기 위해 대역 사용효율이 높은 SSB변조 방식을 적용할 펼요가 있다. 그러나, SSB 변조 방식을 BPSK - DS/CDMA방식에 적용하면 대역 사용효율은 증가하나 다중 사용자 간섭의 증가로 성능이 감소 한다. 따라서 증가된 다중 사용자 간섭을 제거하기위해 연속간섭제거 기법을 적용한 SSB/BPSK-DS/CDMA방 식을 제안하고, 성능분석 및 용량분석을 하였다. 주어진 시스템의 가용 대역폭에서 연속간섭제거 기법을 적용한 S SSB/BPSK -DS/CDMA기볍이 종래의 연속간섭제거 기법이 적용된 BPSK -DS/CDMA 보다 더 많은 가입자 수 용량을 제공할 수 있음을 분석하였다.

• 한국정보통신학회논문지
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• 제5권2호
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• pp.251-256
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• 2001

OFDM 방식은 전통적인 단일 반송파 전송방식과는 달리 전송할 데이터를 병렬적으로 변조하여 주어진 다중전송채널에 다수의 반송파를 실어보내므로 고속의 데이터전송을 수행하고 주파수를 직교적으로 오버랩 시킴으로써 높은 스펙트럼 효율을 제공할 수 있어 여러 분야에서 적용되고 있으며 계속해서 연구되고 있다. 본 논문에서는 컴퓨터 시뮬레이션을 통해서 변조방식에 따른 OFDM 무선통신시스템의 성능을 평가하였으며 변조방식으로서는 M-PSK, M-QAM을 사용하였다. 시뮬레이션은 다중로지연확산, 가우시안채널잡음, Peak Power Clipping, Frame Start Time Error 등이 포함된 가상의 채널환경과 실제채널환경에서 적용되었다. 시뮬레이션 결과 OFDM 시스템에서의 변조방식으로는 M-QAM 방식이 M-PSK 방식보다 우수함을 확인하였다.

• 한국통신학회논문지
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• 제38C권9호
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• pp.787-796
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• 2013

고속 광 센싱과 송신기로부터 넓은 범위의 가시광 수신에 적합한 가시광 통신 응용 서비스를 위해서 본 논문에서는 캐리어 변조 기반 가시광 통신 방식을 생각하고 32.768 kHz 저주파 캐리어와 4 MHz 고주파 캐리어 변조 기반 가시광 통신 회로를 각각 설계와 구현하여 설계된 회로의 신호 파형을 관측한다. 또한 구현된 캐리어 변조 기반 가시광 통신 프로토타입을 사용하여 여러 가지 성능 실험도 한다.

• International Journal of Computer Science & Network Security
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• 제23권5호
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• pp.121-127
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• 2023

A 500 km/h linear motor high speed terrestrial transportation service is planned to launch 2027 in Japan. In order to support 5G service in the train, the Sub-carrier spacing frequency of 30 kHz is planned to be used instead of common 15 kHz sub-carrier spacing to mitigate Doppler effect in such high-speed transportation. In addition, to increase the cell size of 5G mobile system, plural Base Station antenna will transmit the identical Down Link (DL) signal to form the expanded cell size along the train rail. In this situation, forward and backward antenna signals will be Doppler shifted by reverse direction respectively and the receiver in the train might suffer to estimate accurate Channel Transfer Function (CTF) for its demodulation. In this paper, Delay and Doppler Profiler (DDP) based Channel Estimator is proposed and it is successfully implemented in signal processing simulation system. Then the simulated performances are compared with the conventional Time domain linear interpolated estimator. According to the simulation results, QPSK modulation can be used even under severe channel condition such as 500 km/h, 2 path reverse Doppler Shift condition, although QPSK modulation can be used less than 200 km/h with conventional Channel estimator.

• Journal of Power Electronics
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• 제14권1호
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• pp.61-73
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• 2014

Multiphase machines are characterized by high power density, enhanced fault-tolerant capacity, and low torque pulsation. For a voltage source inverter supplied multiphase machine, the probability of load imbalances becomes greater and unwanted low-order stator voltage harmonics occur. This paper deals with the PWM control of multiphase inverters under unbalanced load conditions and it proposes a novel near-five-vector SVPWM algorithm based on the five-phase six-leg inverter. The proposed algorithm can output symmetrical phase voltages under unbalanced load conditions, which is not possible for the conventional SVPWM algorithms based on the five-phase five-leg inverters. The cause of extra harmonics in the phase voltages is analyzed, and an xy coordinate system orthogonal to the ${\alpha}{\beta}z$ coordinate system is introduced to eliminate low-order harmonics in the output phase voltages. Moreover, the digital implementation of the near-five-vector SVPWM algorithm is discussed, and the optimal approach with reduced complexity and low execution time is elaborated. A comparison of the proposed algorithm and other existing PWM algorithms is provided, and the pros and cons of the proposed algorithm are concluded. Simulation and experimental results are also given. It is shown that the proposed algorithm works well under unbalanced load conditions. However, its maximum modulation index is reduced by 5.15% in the linear modulation region, and its algorithm complexity and memory requirement increase. The basic principle in this paper can be easily extended to other inverters with different phase numbers.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.319-320
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• 2012

Large aperture optical modulator called optical shutter is a key component to realize time-of-flight (TOF) based three dimensional (3D) imaging systems [1-2]. The transmission type electro-absorption modulator (EAM) is a prime candidate for 3D imaging systems due to its advantages such as small size, high modulation performance [3], and ease of forming two dimensional (2D) array over large area [4]. In order to use the EAM for 3D imaging systems, it is crucial to remove GaAs substrate over large area so as to obtain high uniformity modulation performance at 850 nm. In this study, we propose and experimentally demonstrate techniques for backside etching of GaAs substrate over a large area having high uniformity. Various methods such as lapping and polishing, dry etching for anisotropic etching, and wet etching ([20%] C6H8O7 : H2O2 = 5:1) for high selectivity backside etching [5] are employed. A high transmittance of 80% over the large aperture area ($5{\times}5mm^2$) can be obtained with good uniformity through optimized backside etching method. These results reveal that the proposed methods for backside etching can etch the substrate over a large area with high uniformity, and the EAM fabricated by using backside etching method is an excellent candidate as optical shutter for 3D imaging systems.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권8호
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• pp.3772-3790
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• 2016

It is well known that the constant modulus algorithm (CMA) presents a large steady-state mean-square error (MSE) for high-order quadrature amplitude modulation (QAM) signals. In this paper, we propose a low-complexity hybrid adaptive blind equalization algorithm, which augments the CMA error function with a novel constellation matched error (CME) term. The most attractive advantage of the proposed algorithm is that it is computationally simpler than concurrent CMA and soft decision-directed (SDD) scheme (CMA+SDD), and modified CMA (MCMA), while the approximation of steady-state MSE of the proposed algorithm is same with CMA+SDD, and lower than MCMA. Extensive simulations demonstrate the performance of the proposed algorithm.

• 한국통신학회논문지
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• 제35권4C호
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• pp.371-376
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• 2010

본 논문에서는 고차의 QAM 시스템을 위한 새로운 고속 반송파 복원 알고리즘을 제안한다. 제안된 방식은 수신 심볼 간 위상차를 이용하여 반송파 주파수 오프셋을 직접 검출하며, 이를 기존의 반송파 복원 방식에 적용함으로써 넓은 주파수 추적 범위와 빠른 수렴 속도를 제공하는 반송파 복원을 수행할 수 있다. 시뮬레이션을 통하여 제안된 반송파 복원 방식이 주파수 오프셋이 크고 신호 대 잡음비가 낮은 상황에서도 짧은 수렴 시간을 가지는 것을 확인하였다.

• 전기학회논문지P
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• 제60권1호
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• pp.19-26
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• 2011

In this paper, we designed Interpolation FIR(Finite Impulse Response) filter and 1-bit SDM(Sigma- Delta Modulator) for small digital audio speaker, which has low power consumption and high output characteristics. In order to achieve high linearity and low distortion performance of the systems, we adopt Type I Chevychev FIR filter which has equiripple characteristics in the pass band and proposed high efficient FIR filter structure. SDM is the most efficient modulation technique among the noise shaping techniques. In this paper, we implemented SDM using CIFB(Cascade of Intergrators, Feed-Back) which is generally used in DAC of small digital audio speakers. The proposed SDM structure can achieve high SNR, high-efficiency characteristics and low power consumption in mobile devices. Also considering manufacture of SoC(System on Chip), we performed simulation with Matlab and Verilog HDL to obtain optimal number of operational bits and verified a good experimental results.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1999년도 전력전자학술대회 논문집
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• pp.469-471
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• 1999

In this paper, the method of Space-Vector Pulse Width Modulation(SVPWM) with Fuzzy Logic Regulator(FLR) is proposed. In a conventional SVPWM, the procedures of phase transformation and choosing PWM patterns are complex. So, it should be implemented with high performance processor like Digital Signal Processor(DSP). In order to reduce a calculation burden, a proposed system adopts FLR. Using a linguistic contro strategy based on expert knowledge, FLR relieves the processor from a heavy computations. In simulations, the proposed system is validated.