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Transmit Diversity Schemes for MUD based CDMA TDD Systems
Younglok Kim 에스케이텔레콤 (주) 2003 Telecommunications Review Vol.13 No.6
In CDMA TDD wireless systems, the major requirement for data detection is the cancellation of both MAI as well as ISI. Multiuer detection (MUD) technique is one of the joint detection techniques that satisfy this requirement with its complexity low enough to support the real-time processing and feasible for the practical implementation. The performance requirements can be satisfied even with the lower transmission power by improving the transmission media. Transmit diversity is the antenna diversity technique that provides more efficient use of the spectrum and hence improve the transmission performance without the significant complexity increase at the receiver. This paper reviews the multiuser detection algorithm that can be applied to any TD-CDMA systems, and introduces the various transmit diversity schemes that are applicable to this MUD-based receivers. The performance gains and the complexity evaluations are provided for each transmit diversity scheme associated to a specific physical channel.
자본시장법상 미공개중요정보이용행위와 법적규제에 관한 고찰
김영록 ( Kim Younglok ) 제주대학교 법과정책연구원 2017 국제법무 Vol.9 No.2
Legislative efforts to regulate insider trading have continued in the Financial Investment Services and Capital Markets Act (“Capital Markets Act”) as well as the former Securities Exchange Act, under the recognition that insider trading undermines the soundness and hinders the credibility of the capital market. In particular, the title of Article 188-2 of the former Securities Exchange Act was partially supplemented and revised from ‘restriction of insider trading’ to ‘prohibition of insider trading’. And this was succeeded by Article 174 of the Capital Markets Act, ‘Prohibition on Use of Material Nonpublic Information’, so that the regulatory framework for insider trading was strengthened as it is now. Not only in Korea but in the United States, the United Kingdom, and Japan, insider trading has been recognized as an important criminal offense, and criminal punishment and civil liability have been strengthened. However, although there has been legal restructuring in order to prevent unauthorized use of material information in the Capital Markets Act, and regulatory system restructuring(e.g. introduction of the fast-track) for early blocking and investigation of unfair trading practices, insider trading is increasing rather than decreasing due mainly to the lack of compliance awareness among the employees of listed corporations. Also, in relation to the act of providing the internal material information of listed corporations to other persons in the status of insiders and quasi-insiders, there are a lot of cases in which the information recipients use the information for transactions because there is a lack of guilt that such an act is a criminal act. Furthermore, due to the development of means for delivering information using mobile devices, undisclosed material information received from insiders, etc. is transmitted to the first information receiver, the second information receiver, and the like, resulting in a large number of information receivers. However, it is fortunate that the regulatory authority has enacted Article 178-2(Prohibition on Market Disturbances) of the Capital Markets Act, enabling the Financial Services Commission to collect undue profits arising from the position of second or above information recipient as penalty surcharges, thereby preventing the insider trading that takes advantage of information asymmetry. As a result, it is now possible to regulate the act of using market information, press information or policy information as well as inside information which was difficult to regulate under Article 174. Therefore, in the future, it is expected that unfair transactions such as market manipulation, acts of using inside information by insiders, etc. will be reduced.
김승환(Seunghwan Kim),이진범(Jinbeom Lee),이진용(Jinyong Lee),김영록(Younglok Kim) 한국통신학회 2008 韓國通信學會論文誌 Vol.33 No.6A
유럽형 지상파 디지털 방송 표준인 DVB-T 시스템에서는 OFDM방식을 사용하여 신호를 전송하며, 주파수 선택적 페이딩 환경과 충격 잡음 채널에서도 향상된 성능을 제공 할 수 있다. 그러나 이동성이 가정된 시변 채널에서는 도플러 확산의 영향 때문에 한 OFDM 심볼 안에 존재하는 부반송파 사이의 직교성의 파괴, 즉 inter-carrier interference(ICI)가 발생하여 심각한 성능 열화가 발생한다. 본 논문에서는 시간 및 주파수 축에서 채널의 특성과 ICI를 분석하고, OFDM시스템에서 구현이 간단한 LS 알고리즘과 이를 이용한 잡음 및 ICI 감쇄 기법을 사용한 LS 방식을 단말기의 속도에 따라 선택하여 사용하는 적응형 채널 추정 방식을 제안한다. 단말기의 속도를 추정하는 방법을 제안하여 COST207의 TU6 채널 모델을 적용한 시뮬레이션을 통하여 그 동작을 확인하였다. 또한 속도 추정을 위한 연산을 최소화한 알고리즘을 제안하여 하드웨어의 증가를 무시할 정도로 줄였다. 제안된 적응형 채널 추정 알고리즘은 속도가 약 70 ㎞/h 이하인 경우에 잡음 및 ICI 감쇄기법을 위한 하드웨어를 동작시키지 않음으로서 전력의 소모가 현저하게 줄어든다. In digital video broadcasting-terrestrial (DVB-T), which is the European digital terrestrial television standard, the orthogonal frequency division multiplexing (OFDM) has been adopted for signal transmission. The main reasons using OFDM are to increase the robustness against the frequency selective fading and impulse noise, and to use available bandwidth efficiently. However, channel variation within an OFDM symbol destroys orthogonality between subcarriers, resulting in inter-carrier interference (ICI), which increases an error floor in proportional to maximum Doppler spread. This paper provides an ICI analysis in both time and frequency domains while existing literatures analyze the ICI effects mainly in frequency domain and proposes the algorithms that estimate the channel impulse response and channel variation using least square (LS) algorithm which is the most simple channel estimation technique. And we propose adaptive channel estimation algorithm that estimates the velocity of terminals. The simulation results show that proposed algorithm has similar performance with about 1.5% computational complexity of noise and ICI reduction LS algorithm in low speed environments.
Three-level 하이브리드 몽고메리 감산을 통한 ARM Cortex-M7에서의 CSIDH-512 최적화
최영록(Younglok Choi),허동회(Donghoe Heo),홍석희(Seokhie Hong),김수리(Suhri Kim) 한국정보보호학회 2023 정보보호학회논문지 Vol.33 No.2
NIST PQC 표준화 작업 Round 4에 올라 있던 유일한 아이소제니 기반 KEM 알고리즘인 SIKE에 대한 효율적인 키 복구 공격이 발표됨에 따라, 이를 대체할 수 있는 키 교환 알고리즘인 CSIDH가 다시 주목받고 있다. CSIDH는 현재까지 알려진 공격에 안전한 아이소제니 기반 키 교환 알고리즘으로, CRS 스킴을 현대화하여 효율적인 NIKE를 제공한다. 본 논문에서는 CSIDH-512를 ARM Cortex-M7에서 구현하고 three-level 하이브리드 몽고메리 감산을 적용하여 최적화한 성능을 측정한 뒤 그 결과 및 한계에 대해 서술하고 향후 연구 방향을 제시한다. 이는 기존에 제시되지 않았던 32-bit 임베디드 기기에서의 CSIDH 구현으로, 향후 다양한 임베디드 환경에서 CSIDH 및 파생 암호 알고리즘을 구현하는데 본 논문의 결과를 이용할 수 있을 것으로 기대한다. As an efficient key recovery attack on SIDH/SIKE was proposed, CSIDH is drawing attention again. CSIDH is an isogeny-based key exchange algorithm that is safe against known attacks to date, and provide efficient NIKE by modernizing CRS scheme. In this paper, we firstly present the optimized implementation of CSIDH-512 on ARM Cortex-M7. We use three-level hybrid Montgomery reduction and present the results of our implementation, limitations, and future research directions. This is a CSIDH implementation in 32-bit embedded devices that has not been previously presented, and it is expected that the results of this paper will be available to implement CSIDH and derived cryptographic algorithms in various embedded environments in the future.