• 전력전자학회논문지
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• 제22권4호
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• pp.285-296
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• 2017

This paper proposes an improved modulation scheme for the medium voltage modular multi-level converter (MMC), which operates in the nearest level control and applies in the medium voltage direct current (MVDC) system. In the proposed modulation scheme, the offset (neutral-to-zero output) voltage is adjusted, with the phase voltage magnitude, thereby maintaining a constant value with N+1 level in the controllable modulation index (MI) range. In order to confirm the proposed scheme's validity, computer simulations for the 22.9 kV - 25 MVA MMC were performed with PSCAD/EMTDC, as well as hardware experiments for the 380 V - 10 kVA MMC. The proposed modulation scheme offers to build a constant pole voltage regardless of the MI value, and to build a phase voltage with improved total harmonic distortion (THD).

• 전자공학회논문지
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• 제52권1호
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• pp.17-23
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• 2015

본 논문에서는 FTN (Faster than Nyquist) 방식을 이용한 데이터 전송기법에서 효율적으로 ISI (Inter Symbol Interference)를 제거하기 위한 기법을 제안한다. FTN 방식을 이용한 통신 시스템은 나이퀴스트 (Nyquist) 율 보다 빠르게 신호를 전송하는 방식으로 필연적으로 ISI가 발생한다. FTN 시스템에서 ISI를 제거하기 위한 여러 방안들이 제안되었으며 대표적으로 BCJR (Bahl-Cocke-Jelinek-Raviv) 알고리듬 기반의 ISI 제거 기법을 들 수 있다. 그러나 제안된 기법들은 매우 큰 구현 복잡도를 갖으며, 특히 고차 변조 기법을 사용할 경우 복잡도는 변조 차수에 따라 지수적으로 증가하는 단점이 있다. 구현복잡도를 줄이기 위하여 길쌈부호가 적용된 시스템에서 SIC (Successive Interference Cancellation) 기법을 이용하여 ISI를 제거하는 기법이 제안되었다. 본 논문에서는 반복 복호가 가능한 채널 부호화 기법과 고차 변조가 적용된 시스템에서 복호기에서 생성된 정보를 이용하여 FTN 복조를 효율적으로 수행할 수 있는 기법을 제안한다. 제안하는 기법은 기존에 제안된 기법들에 비하여 낮은 구현 복잡도를 나타낼 뿐만 아니라 우수한 ISI 추정 성능으로 인하여 주어진 신호 대 잡음비 (Signalto-Noise Ratio) 영역에서 보다 나은 비트오율 (Bit Error Rate) 성능을 나타낸다. 또한 고차 변조 기법이 적용된 시스템에서도 큰 복잡도 증가 없이 적용이 가능하다.

• Journal of Communications and Networks
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• 제11권3호
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• pp.271-278
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• 2009

A new modulation scheme called multicoded-pulse position modulation (MC-PPM) is proposed for an ultrawideband (UWB) impulse radio communication system. The multicoded signal is generated by using several orthogonal codes for transmitting data simultaneously. Then, each multi-level value of the multicoded signal is converted to pulse position which results in not only an improved data rate, but also a processing gain in reception, delivering the power-efficient benefit of PPM and guaranteeing the low pulse energy for UWB systems. We notice that the modulation of multi-level values of the multicoded signal to pulse position is more efficient in terms of achievable data rate than the modulation of transmitting data based on other PPM schemes within given bandwidth and pulse energy. Therefore, as a performance measure, we focus on the achievable data rate (link capacity) of the proposed scheme and analyze it theoretically. Through simulation, we compare the link capacity of the MC-PPM scheme and other PPM schemes, such as M -ary PPM and multiple PPM. With the fixed bandwidth and same pulse energy condition, the UWB system based on the proposed MC-PPM scheme shows good link capacity and an increased data rate as L increases, which is contrary to other PPM schemes.

• Journal of the Optical Society of Korea
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• 제16권2호
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• pp.107-114
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• 2012

In this paper, we propose a new modulation scheme called multi-coded variable pulse position modulation (MC-VPPM) for visible light communication systems. Two groups of signals (Pulse Width Modulation (PWM) and Pulse Position Modulation (PPM) groups) are multi-coded by orthogonal codes for transmitting data simultaneously. Then, each multi-level value of the multi-coded signal is converted to pulse width and position which results in not only an improved data rate, but also a processing gain in reception. In addition, we introduce average duty ratio and cyclic shift concepts in PWM through which dimming control for light illumination can be supported without any degradation in communication performance. Through simulation, we confirm that the proposed MC-VPPM shows a comparable BER curve and much greater achievable data rate than the conventional VPPM scheme using a visible light optical channel environment.

• Current Optics and Photonics
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• 제2권6호
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• pp.532-539
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• 2018

Multiple LED arrays can be utilized in visible-light communication (VLC) to improve communication efficiency, while maintaining smart illumination functionality through dimming control. This paper proposes a modulation scheme called "Spatial Intensity Modulation" (SIM), where the effective number of turned-on LEDs is employed for data modulation and dimming control in VLC systems. Unlike the conventional pulse-amplitude modulation (PAM), symbol intensity levels are not determined by the amplitude levels of a VLC signal from each LED, but by counting the number of turned-on LEDs, illuminating with a single amplitude level. Because the intensity of a SIM symbol and the target dimming level are determined solely in the spatial domain, the problems of conventional PAM-based VLC and related MIMO VLC schemes, such as unstable dimming control, non uniform illumination functionality, and burdens of channel prediction, can be solved. By varying the number and formation of turned-on LEDs around the target dimming level in time, the proposed SIM scheme guarantees homogeneous illumination over a target area. An analysis of the dimming capacity, which is the achievable communication rate under the target dimming level in VLC, is provided by deriving the turn-on probability to maximize the entropy of the SIM-based VLC system. In addition, a practical design of dimmable SIM scheme applying the multilevel inverse source coding (MISC) method is proposed. The simulation results under a range of parameters provide baseline data to verify the performance of the proposed dimmable SIM scheme and applications in real systems.

• 조명전기설비학회논문지
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• 제22권12호
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• pp.64-70
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• 2008

종래의 준 랜덤 주파수 캐리어(PRC : Pseudo-Randomized Frequency Carrier) 변조기법을 3상 H-브리지 멀티레벨 인버터(HBML: H-Bridge Multi-Level Inverter)에 적용하는 경우, 스위칭 주파수의 2배 주파수 영역에서 큰 스펙트럼 클러스터가 그대로 존재하는 문제점이 있다. 본 연구에서는 서로 2배의 주파수 비율을 갖는 2개의 고정주파수 삼각파 캐리어와 3단계 멀티플렉서(MUX : Multiplexer)를 이용하여 종래의 PRC기법의 고조파 스펙트럼 확산 효과를 개선하였다. 제안된 기법은 1.5[kw]급 3상 HBML인버터 구동시스템에 적용하였으며, 종전의 방법과 제안된 방법의 전압 및 전류 고조파 스펙트럼을 비교 검토하였다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1999년도 추계종합학술대회 논문집
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• pp.775-779
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• 1999

This paper presents design of AGC(Automatic Gain Control) and DC offset remover suitable for cable modem which makes use of QAM(Quadrature Amplitude Modulation) scheme. Since QAM has multi-level signal characteristic, for high-order QAM, the constellation is dense and the distance of decision boundary between adjacent symbols is short. So AGC and DC offset remover must be designed optionally for preventing performance degradation. AGC is designed into feedback type and is related to the STR(Symbol Timing Recovery)and Paff interpolation algorithm. Whereas AGC need to perform average power detection during many symbols by comparison with the reference power, DC offset remover uses only the instant polarity decision such that simple implementation can be achieved with good performance. Though the AGC and DC offset remover are simulated here only for 256 QAM scheme for convenience'sake, it can be applied to other multi-level QAM or PSK modulation scheme.

• Journal of the Optical Society of Korea
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• 제20권1호
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• pp.29-35
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• 2016

This paper deals with a design method and capacity loss of an efficient multi-level modulation scheme for dimmable visible light communications (VLC) systems that use light-emitting diodes (LEDs) with efficiency droop. To this end, the impact of such an impairment on dimmable VLC is addressed with respect to multi-level modulations based on pulse-amplitude modulation (PAM) via data-rate optimization formulation.

• 한국통신학회논문지
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• 제21권9호
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• pp.2470-2480
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• 1996

The energy efficiency and bandwidth efficiency are two important criterion in designing a modulation scheme Especially the constant envelope property must be considered as in the non-linear channel tht exit, for example in the nonlinear amplifiers for satellite repeater. The Q$^{2}$AM(Quadrature Quadrature Amplitude Modulation) is a new modulation scheme which combines the Q$^{2}$PSK(Quadrature Quadrature Phase Shift Keying) scheme which increases the signal space dimension and the QAM scheme which increases the bandwidth efficiency using the multi-level signal. The Q$^{2}$AM scheme has by far superior spectrum efficiency compared with the existing modulation schemes. Applying this scheme in the non-linear communication system increses the bandwidth efficiency but cannot envelop property. In this paper, a new system architecture is suggested which satisfies the large spectrum efficiency and constant envelope property by implementing the linear block coding prior to the Q$^{2}$AM modulation. the system has improved in performance by gaining the constant envelope and the additional coding gain. We able to observe the performance improvement of the suggested system(at BER=10$^{-5}$ ) of 4.4 dB for the 16-QAM and 0.7 dB for the Q$^{2}$PSK under the exact spectrum efficiency.

• Journal of Communications and Networks
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• 제8권1호
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• pp.1-7
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• 2006

Quadrature amplitude modulation-spread spectrum (QAM-SS) and code division multiplexing (CDM) are multi-level modulation schemes with high performance but they cause a large peak-average power ratio (PAPR). Therefore, this paper proposes a novel modulation scheme for high-rate transmission which follows a sequence of CDM-mapping-CDM not only to correct the above-mentioned problem but also offer a high flexibility in obtaining arbitrary multilevel modulation with very low implementation complexity and high performance.