다중 사용자 DS/CDMA 시스템에서 채널간 전력 할당

홍대기,홍대식,강창언 한국통신학회 2002 韓國通信學會論文誌 Vol.27 No.12B

버스트 MPSK 전송에서 시스템 파라미터들의 동시 추정 성능의 개선을 위한 이산 푸리에 변환의 보간기법

홍대기,이영조,홍대식,강창언 한국통신학회 2002 韓國通信學會論文誌 Vol.27 No.1A

비동기 복조 DS/CDMA 역방향 링크에서 채널 추정 및 다중 사용자 검파를 이용한 성능 개선

홍대기,윤석현,홍대식,강창언 한국전자파학회 2001 한국전자파학회논문지 Vol.12 No.5

본 논문에서는 M-ary 직교 변조를 사용하는 직접 확산 코드 분할 다중 접속 (DS/CDMA: Direct Sequence/Code Division Multiple Access) 시스템을 위한 최대 근사 (Maximum Lkelihood : ML) 결정 궤환 채널 추정(Decision Feedback Channel Estimation : DFCE) 시스템을 제안한다. 제안된 시스템은 결정 궤환 정보로서 RAKE 수신기의 최대 결합 출력을 사용한다. 제안된 시스템으로부터 추정된 채널 값을 이용하면 파일럿의 삽입없이 RAKE 수신기에서 동기 검파 (coherent demodulation)를 할 수 있고, 동시에 최대 비 결합(Maximum Ration Combining : MRC) 기법을 사용할 수 있다. 그러나 제안된 DFCE 다중 사용자 환경에서 다중 사용자 간섭 (Multiple Access Interference: MAI)으로 인해 심각한 성능의 저하가 발생한다. 이런 문제를 해결하기 위해 다단 병렬 간섭 제거기(Multistage Parallel Interference Cancellation : PIC)를 제안된 시스템과 결합해 본다. 제안된 DFCE에서 추정된 정확한 채널 값은 동기식 검파뿐 아니라 PIC에서 다중 사용자 간섭 신호의 재 생성(regeneration)을 위해서도 쓰인다. 이럴 경우 PIC와 EFCF간에 서로 도움을 주는 이중 효과를 얻게 된다. 실험결과에 의하면 제안된 시스템은 기존의 비동기 검파(noncoherent demodulation) 방식에 비해 다단 PIC를 쓰지 않는 동기 검파의 경우 IE-02의 E$_{b}$/N$_{0}$에서 수용 가능한 사용자 수가 5명에서 약 10으로 2배 증가함을 확인할 수 있었으며, 다단 PIC를 사용한 동기 검파의 경우 약 30명으로 6배 정도가 증가함을 확인할 수 있었다. In this paper, we propose maximum likelihood (ML) decision feedback channel estimation (DFCE) for M-ary orthogonal modulation in direct sequence/code division multiple access (DS/CDMA) systems. The proposed DFCE uses the maximum combiner output in a RAKE receiver as decision feedback information, enabling M-ary orthogonal signals to be demodulated coherently and a RAKE receiver to use a em maximal ration combining (MRC) scheme. However, the performance of the proposed DFCE in the multiuser environment is severely degraded due to multiple access interference (MAI). To overcome this problem, a multistage parallel interference cancellation (PIC) scheme is combined with the proposed DFCE for multiuser environments. Accurate knowledge of the channel coefficient estimated by the proposed DFCE is used to regenerate the signal of each user for the multistage PIC scheme. According to the results of our simulations, the performance of coherent demodulation using the proposed system is significantly improved in comparison with conventional noncoherent demodulation.

The effect of surgery with cul de sactomy (douglasectomy) for endometriois on quality of Life

홍대기,박내윤,정근오,조영래,박일수,이윤순 대한산부인과학회 2011 대한산부인과학회 학술대회 Vol.97 No.-

WAVE 시스템에서 선택 다이버시티를 위한 선택 기준에 대한 연구

홍대기 한국반도체디스플레이기술학회 2015 반도체디스플레이기술학회지 Vol.14 No.2

In this paper, selection criterions on selection diversity are researched. The diversity is applied to the multiple antenna system based on wireless access in vehicular environment (WAVE) standard for rapid varying channel. Least squares (LS) based decision feedback equalizer (DFE) are used for channel equalization. Received signal is regenerated by means of the decision feedback path. In the selection diversity, the regenerated signal as well as the received signal is selected according to selection criterion. The decision feedback algorithm can follow the fast speed of WAVE fading channel. To control the tracking speed of the time-varying channel, simple low pass filter is used. Finally, the estimated channel value recovers the distorted payloads. Signal power before automatic gain control (AGC) in analog stage can be used as a selection criterion. In the digital stage, signal power after AGC, noise power after AGC, signal to noise ratio after AGC and cross-correlation method can be used as selection criterions. According to the simulation results, the performance of the selection diversity is improved in comparison with that of the combining diversity for the WAVE fading channel.

Survival benefit of laparoscopic surgical staging-guided radiation therapy in locally advanced cervical cancer

홍대기,박내윤,정근오,조영래,박일수,이윤순 대한부인종양학회 2010 Journal of Gynecologic Oncology Vol.21 No.3

Objective: This study was designed to evaluate the survival benefit of laparoscopic surgical staging (LSS)-guided tailored radiation therapy (RT) in locally advanced cervical cancer (LACC). Methods: We retrospectively reviewed 89 LACC patients’ medical records who primarily received non-surgical treatment,of which pretreatment LSS was performed in 20 (LSS group) and primary chemoradiation therapy (CCRT) without LSS (CCRT group) was carried out in 69 from January 2000 to January 2006. We analyzed clinical characteristics, pretreatment imaging study results and survival outcomes including disease free survival (DFS) and overall survival (OS) to compare them between the two groups. Results: There were as many as eight cases (40%) of LSS related complications. The mean time interval between LSS and RT or CCRT was 26.6 days (±18.8 days). Six out of twenty (30%) in LSS group and 10 out of 69 (14.5%) in CCRT group received extended field RT when paraaortic lymph nodes (LNs) were positive based on the pathologic findings after LSS and the results of imaging studies, respectively. Three-year DFS and OS were both better in 33imaging-negative CCRT group patients than those in 4 imaging-negative/pathology-positive (false negative) patients after LSS (3-year DFS, 50% vs. 87%, p=0.022; 3-year OS, 50% vs. 84%, p=0.033). The 5-year DFS rates were 52%and 55% in LSS group and in CCRT group, respectively (p=0.28). The 5-year OS rates were 68% in LSS group and 62% in CCRT group without significant difference between the two groups (p=0.79). Conclusion: We found that LSS-based RT tailoring did not show survival benefit in LACC despite inaccuracy of imaging-based RT tailoring. Further studies are required to find new method to overcome this inaccuracy and improve survival outcomes.

포커스 메커니즘이 적용된 소형 위성 카메라의 제작 및 성능 실험

홍대기,황재혁 항공우주시스템공학회 2019 항공우주시스템공학회지 Vol.13 No.4

The precise alignment between optical components is required in high-resolution earth observation satellites. However, the misalignment of optical components occurs due to external factors such as severe satellite launch environment and space environment. A satellite optical system with a focus mechanism is required to compensate for the image quality degraded by these misalignments. This study designed, fabricated, aligned precisely, and carried out a performance tests for the image quality of the system. The satellite optical camera performance tests were carried out to check the image quality change by operating the focus mechanism and to analyze the satellite optical system MTF by photographing USAF target using the autocollimator. According to the experimental results, the misalignments can be compensated sufficiently with the focus mechanism. Finally the basic data for re-focusing algorithm of the optical system was obtained through this study. 고해상도 지구 관측위성에서는 광학 부품간 정밀한 위치 정렬도가 요구된다. 그러나, 가혹한 위성 발사환경 및 우주환경 같은 외부 요인에 의해 광부품의 정렬오차가 발생한다. 이러한 정렬오차에 의해 저하된 영상품질을 보상하기 위해 포커스 메커니즘이 적용된 위성광학계의 설계가 필요하다. 본 논문에서는 위성카메라 정렬오차 보상이 가능한 목표광학계의 제작 및 성능 실험에 대한 연구를 수행하였다. 먼저 설계된 목표광학계를 제작/조립/정렬하였으며, 이 완료된 목표 광학계를 사용하여 영상 촬영 실험을 수행하였다. 영상 촬영 실험은 포커스 메커니즘에 의한 상의 변화를 이미지로 확인하는 실험과 오토콜리메이터를 이용하여 USAF 타깃을 촬영해 MTF를 분석하는 실험을 수행하였다. 실험 결과를 통해 포커스 메커니즘을 통하여 정렬오차를 충분히 보상할 수 있음을 확인하였으며, 궤도상에서 정렬오차를 보상할 수 있는 리포커싱의 기초자료를 확보하였다.

3GPP WCDMA 모뎀 계측장비를 위한 신호계측 알고리듬

홍대기 한국반도체디스플레이기술학회 2011 반도체디스플레이기술학회지 Vol.10 No.1

In this paper, we implement measurement functionality for the 3GPP (Third Generation Partnership Project) WCDMA (Wideband Code Division Multiple Access) modem. Generally speaking, the receiving algorithms in normal modems cannot be used directly to the measurement system due to the lack of the measurement accuracy. In this paper, we propose the new measurement algorithm for precise 3GPP WCDMA signal measurements. In the measurement algorithm, 4-stage parameters estimation scheme is used. To improve the measurement accuracy, we increase the number of the received signal samples by interpolation. The proposed 3GPP WCDMA signal measurement algorithm can be used for verifying and implementing SoC/FPGA modem measurement systems.

Benign Gynecologic Surgery

홍대기 대한산부인과학회 2016 연수강좌 Vol.56 No.-

정진폭 다중 부호 이진 직교 변복조기의 FPGA 설계 및 SoC 구현

홍대기,강성진,김용성,김선희,조진용 한국통신학회 2007 韓國通信學會論文誌 Vol.32 No.11