• 한국통신학회논문지
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• 제40권11호
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• pp.2121-2130
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• 2015

본 논문에서는 단일 RF 단을 사용하여 다중 스트림을 전송할 수 있는 LM-MIMO (load-modulation multiple-input multiple-output) 시스템에 대하여 알아보고, 이 시스템에서 사용하는 부하변조 (load modulation) 방법이 고차 m-PSK (phase shift keying) 심볼이나 고차 m-QAM (quadrature amplitude modulation) 심볼을 효과적으로 생성할 수 있는지 확인한다. 그리고 부하변조를 사용하는 LM-MIMO 시스템의 성능을 평가한다. LM-MIMO 시스템은 안테나가 확장되어도 단일 RF 단만을 요구하기 때문에 저복잡도, 저전력의 시스템 구성을 할 수 있다. 시뮬레이션의 결과를 살펴보면, T 모델 (model)을 사용하는 부하변조는 고차 m-PSK 변조와 고차 m-QAM 변조를 효과적으로 지원할 수 있다. 또한 부하변조를 사용하는 LM-MIMO 시스템이 기존의 이상적인 m-PSK나 m-QAM 변조를 사용하는 MIMO 시스템과 유사한 성능을 낼 수 있음을 확인하였다. 또한 $4{\times}4$ LM-MIMO 시스템이 기존의 $4{\times}4$ MIMO 시스템과 유사한 성능을 내는 것을 확인하였다.

• Journal of Power Electronics
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• 제17권6호
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• pp.1413-1421
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• 2017

In order to control the output voltage in a dual active bridge converter, this paper establishes a theoretical inductor current equation for a dual-pulse-width-modulation scheme that ensures low switching loss. It also proposes a modulation strategy that minimizes conduction loss. When compared to the conventional single-pulse-width-modulation strategy, the proposed approach can reduce the inductor current RMS and improve efficiency in the low power region, as verified through simulation and experimental results.

• 전자공학회논문지
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• 제50권8호
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• pp.21-27
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• 2013

본 논문에서는 Turbo coded BICM-ID (bit-interleaved coded modulation with iterative decoding)의 구현 복잡도를 개선하기 위한 기법을 제안한다. 터보 부호는 Shannon 한계에 근접하는 우수한 성능을 나타내는 오류정정부호 (error correction code)이며 터보 부호와 고차원 변조 (high order modulation)를 결합하여 전송효율을 개선할 수 있다. BICM (bit-interleaved coded modulation)은 채널 부호와 고차원 변조 사이에 이진 인터리버를 사용하는 기법이며 복호기와 복조기 간에 정보를 주고받으며 반복 복호 (iterative decoding)를 수행하는 BICM-ID를 이용하여 성능을 개선 할 수 있다. BICM-ID는 BICM과 비교하였을 때 반복 복호로 인하여 비트오율 (bit error rate) 성능이 개선되지만 구현 복잡도가 크게 증가하는 단점이 있다. 본 논문에서는 Turbo coded BICM-ID에서 구현 복잡도를 개선하기 위한 기법을 제안한다. 제안하는 기법은 기존에 제안된 Turbo coded BICM-ID 기법과 유사한 비트오율 (bit error rate) 성능을 나타내면서 구현 복잡도를 크게 감소시킬 수 있는 장점이 있다.

• 한국군사과학기술학회지
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• 제17권3호
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• pp.336-341
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• 2014

When using a higher-order modulation scheme, there are variations in bit-reliability depending on the bit position in a modulation symbol. Variations of bit-reliability in the codeword block lower the decoding performance. Also, the decoding performance increases as the sum of the bit-reliabilities in the codeword block increases. This paper presents a novel hybrid automatic repeat request scheme that increases the sum of the reliabilities of the transmitted bits by lowering the modulation order, and decreases the variations of bit-reliability in the codeword block by preferentially retransmitting bits with low reliability. The proposed scheme outperforms the constellation rearrangement scheme. Furthermore, the proposed scheme also provides a good solution in cases where the size of the retransmission block is smaller than the size of the initial transmission block.

• 한국음향학회지
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• 제40권5호
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• pp.428-438
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• 2021

심해 장거리 통신에서는 전달 손실이 적은 낮은 반송 주파수가 효율적이지만, 좁은 대역폭을 가지는 제약이 따른다. 대역폭의 감소는 전송률의 감소를 의미하며, 제한된 대역폭을 가진 환경에서 전송률을 증가시키기 위해서는 고차 변조 기법으로 설계될 필요가 있다. 본 논문은 고차 변조 기법으로 설계된 장거리 수중음향통신 데이터 분석 결과를 제시한다. 2020년 10월 동해에서 예인 음원을 이용한 장거리 해상실험 (23 km ~)이 수행되었고, 수직 선 배열을 통해 데이터를 획득하였다. 본 연구팀은 위상 변조 방식이 적용된 Phase Shift Keying (PSK) 계열 신호와 위상 및 진폭 변조 방식이 적용된 Quadrature Amplitude Modulation (QAM) 계열의 신호를 송신하였으며, 구체적으로 각 계열별 두 종류의 신호를 설계하였다; 1) PSK : quadrature PSK and 8PSK, 2) QAM : 8QAM and 16QAM. 데이터 분석을 위해 수신 신호와 채널 임펄스 응답 사이의 상관성을 활용하여 심볼 간 간섭을 완화시키는 시역전 처리가 적용되었다. 23 km 거리 데이터에 대해 모든 변조 방식이 성공적으로 복조됨으로써 장거리 환경에서 고차 변조 기법의 활용 가능성을 실험적으로 확인하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권11호
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• pp.5381-5399
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• 2016

Currently, the quantize-and-forward (QF) scheme with high order modulation and quantization has rather high complexity and it is thus impractical, especially in multiple relay cooperative communications. To overcome these deficiencies, an improved low complex QF scheme is proposed by the combination of the low order binary phase shift keying (BPSK) modulation and the 1-bit and 2-bit quantization, respectively. In this scheme, the relay selection is optimized by the best relay position for best bit-error-rate (BER) performance, where the relays are located closely to the destination node. In addition, an optimal power allocation is also suggested on a total power constraint. Finally, the BER and the achievable rate of the low order 1-bit, 2-bit and 3-bit QF schemes are simulated and analyzed. Simulation results indicate that the 3-bit QF scheme has about 1.8~5 dB, 4.5~7.5 dB and 1~2.5 dB performance gains than those of the decode-and-forward (DF), the 1-bit and 2-bit QF schemes, at BER of $10^{-2}$, respectively. For the 2-bit QF, the scheme of the normalized Source-Relay (S-R) distance with 0.9 has about 5dB, 7.5dB, 9dB and 15dB gains than those of the distance with 0.7, 0.5, 0.3 and 0.1, respectively, at BER of $10^{-3}$. In addition, the proposed optimal power allocation saves about 2.5dB much more relay power on an average than that of the fixed power allocation. Therefore, the proposed QF scheme can obtain excellent features, such as good BER performance, low complexity and high power efficiency, which make it much pragmatic in the future cooperative communications.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1988년도 추계학술대회 논문집 학회본부
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• pp.32-35
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• 1988

Simultaneous control of active and reactive power for superconducting magnetic energy storage is possible by a current source inverter with paise - width modulation. And a current source inverter is useful to reduce low order harmonics. In this paper, paise generating method for pulse - width modulation is studied and harmonics with and without paise - width modulation is compared.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2004년도 하계종합학술대회 논문집(1)
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• pp.11-14
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• 2004

Digital Video Broadcasting - Satellite (DVB-S) [1] (EN 300 421(bibliography)) was introduced as a standard in 1994. However, by combing with higher order modulation, promise more powerful alternatives to the DVB-S / DVB-DSNG coding and modulation schemes. Variable rate coding and modulation (VCM) may employed to provide different levels of error protection to different service components. Adaptive coding and modulation (ACM) provides more exact channel protection and dynamic link adaptation to propagation conditions, targeting each individual receiving terminal. By these reasons, DVB-S2 introduced. This paper derives exact symbol error rate(SER) of 16-Amplitude Phase Shift Keying(APSK) modulation by using Craig's formula. 16-APSK modulation is used in DVB-S2. The difference between Union Bound and Craig's formula is 1.26dB in low SNR and 0.1dB in high SNR.

• Journal of Power Electronics
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• 제17권5호
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• pp.1186-1194
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• 2017

This paper proposes an improved low frequency Selective Harmonic Mitigation-PWM (SHM-PWM) technique. The proposed method mitigates the low order harmonics of the output voltage up to the $50^{th}$ harmonic well and satisfies the grid codes EN 50160 and CIGRE-WG 36-05. Using a modified criterion for the switching angles, the range of the modulation index for non-linear SHM equations is improved, without increasing the switching frequency of the CHB converter. Due to the low switching frequency of the CHB converter, mitigating the harmonics of the converter up to the $50^{th}$ order and finding a wider modulation index range, the size and cost of the passive filters can be significantly reduced with the proposed technique. Therefore, the proposed technique is more efficient than the conventional SHM-PWM. To verify the effectiveness of the proposed method, a 7-level Cascaded H-bridge (CHB) converter is utilized for the study. Simulation and experimental results confirm the validity of the above claims.

• Journal of Power Electronics
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• 제11권2호
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• pp.132-139
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• 2011

The selective harmonic elimination pulse width modulation (SHEPWM) switching strategy has been applied to multilevel inverters to remove low harmonics. Naturally, the related equations do not have feasible solutions for some operating points associated with the modulation index (M). However, with these infeasible points, minimizing instead of eliminating harmonics is performed. Thus, harmful harmonics such as the $5^{th}$ harmonic still remains in the output waveform. Therefore, it is proposed in this paper to ignore solving the equation associated with the highest order harmonics. A reduction in the eliminated harmonics results in an increase in the degrees of freedom. As a result, the lower order harmonics are eliminated in more operating points. A 9-level inverter is chosen as a case study. The genetic algorithm (GA) for optimization purposes is used. Simulation results verify the proposed method.