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

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.

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

홍대기,이영조,홍대식,강창언 한국통신학회 2002 한국통신학회논문지 Vol.27 No.1A

한국인 여성에서 자궁근종 발생에 관여하는 인자들에 대한 연구 - 후향적 연구 -

홍대기,정민지,김보섭,이정미,조영래,이택후,전상식,Hong, D.G.,Chung, M.J.,Kim, B.S.,Lee, J.M.,Cho, Y.L.,Lee, T.H.,Chun, S.S. 대한생식의학회 2006 Clinical and Experimental Reproductive Medicine Vol.33 No.3

Objective: The purpose of this study is to find out risk factors related to uterine leiomyoma in Korean women and to compare with the results of previous western studies. Methods: A retrospective analysis was carried out. All the cases of uterine leiomyoma (n=244) were diagnosed surgically or sonographically between Jannuary 1998 and December 2004. Total of 269 controls not having uterine leiomyoma were collected from patients who visited Kyungpook national university hospital for routine gynecologic check-up or treatment of their gynecologic or obstetric diseases other than uterine leiomyoma. Data were collected through review of medical records and interviews and analyzed with $x^2$ and logistic regression model. Results: In multivariate analysis, patient's age (OR 1.070; 95% CI 1.041~1.099), number of artificial abortion (OR 1.182; 95% CI 1.018~1.374) and alcohol drinking (OR 1.865; 95% CI 1.231~2.824) had significantly positive correlation with uterine leiomyoma. The duration of lactation was the only factor which had negative correlation (OR 0.985; 95% CI 0.972~0.998). BMI, parity, age at menarche, the duration and interval of menstruation, caffeine consumption and marital status did not show any correlations. Conclusion: In this study, patient's age, number of artificial abortion, and alcohol drinking were the risk factors of uterine leiomyoma in Korean women and the result was similar to that of western studies. Though we couldn't find out the specific risk factors related to the development of uterine leiomyoma in this study, but it has a great meaning to be the first trial in Korean women. The role of information bias should be carefully evaluated and further multicentered, randomized, controlled prospective studies will be needed to know the possible risk factors among Korean women. 목 적: 본 연구의 목적은 한국인 여성에서 자궁근종 발생과 관련된 인자를 찾고 기존 연구 결과와 비교 하는데 있다. 연구방법: 1998년 l월부터 2004년 12월 사이에 경북대학교병원을 정기 검사 및 산부인과 질환을 가진 환자로 치료를 위해 방문한 환자 중 외과적 또는 초음파검사상 자궁근종이 진단된 244명과 자궁근종이 없는 269명을 대조군으로 후향적인 연구를 시행하였다. 자료는 의료기록 조사로 이루어졌으며 통계분석은 $x^2$ 검정과 로지스틱 회귀분석을 시행하였다. 결 과: 다변량분석상 나이, 인공유산 횟수, 음주는 자궁근종 발생과 양의 상관관계를 나타내었으며, 수유기간에 따라서는 그와 반대의 관계를 나타내었다. BMI, 분만력, 초경 나이, 월경기간 및 간격, 카페인 섭취, 결혼 상태는 연관성을 나타내지 않았다. 결 론: 이번 연구는 한국인 여성에서 자궁근종 발생에 관련된 인자에 대한 첫 후향적인 연구로서 의의를 가지지만, 한국인 여성에서의 구체적인 발생인자에 대한 결론을 내리기에는 부족하였다. 따라서 한국인 여성에서의 자궁근종의 발생인자에 대한 향후 장기간에 걸친 대규모의 전향적인 연구가 필요하리라 여겨진다.

무선 이동 통신을 위한 잡음 예측 결정 궤환 등화기

홍대기,김선희,김용성,조진웅,강성진,Hong, Dae-Ki,Kim, Sun-Hee,Kim, Young-Sung,Cho, Jin-Woong,Kang, Sung-Jin 한국정보통신학회 2008 한국정보통신학회논문지 Vol.12 No.1

디지털 통신에서는 전송 채널의 왜곡을 보상해 주는 적응 등화기가 필수적이다. 이러한 적응 등화기는 요구되는 비트 오율 (BER: Bit Error Rate)을 얻기 위해서 이동통신 시스템의 특성에 적합하고 최적의 성능을 가지는 적응 알고리즘이 필요하게 된다. 본 논문에서는 무선 이동 채널에서 성능이 우수한 잡음 예측 결정 궤환 등화기 (NPDFE: Noise-Predictive Decision Feedback Equalizer)를 제안한다. 제안된 NPDFE는 직교 위상 변조 (QPSK; Quadrature Phase Shift Keying) 방식을 사용하는 시스템에 대해 가산성 백색 가우스 잡음 (AWGN: Additive White Gaussian Noise)이 발생한다는 기본 가정하에 라이시안 페이딩, 유럽 표준 (ETSI: European Telecommunications Standards Institute) 페이딩, 그리고 레일리 페이딩 채널에서의 성능을 분석한다. 시뮬레이션에서 사용되는 등화기 구조는 선형 등화기(LE: Linear Equalizer), 결정 궤환 등화기 (DFE: Decision Feedback Equalizer), 그리고 제안된 NPDFE이다. 각 등화 알고리즘을 사용하는 QPSK 변조 방식의 성능 비교는 BER을 통하여 이루어진다. Adaptive equalizers are inevitable schemes in digital communication systems for compensating the transmission channel distortion. Additionally, to obtain the required BER(Bit Error Rate), the adaptive algorithms appropriate to the mobile communication channels are required. In this paper, we propose the NPDFE (Noise-Predictive Decision Feedback Equalizer) for communication systems performance improvement in mobile communication channels. The performance of the proposed NPDFE with QPSK (Quadrature Phase Shift Keying) is simulated under AWGN (Additive White Gaussian Noise), Ricean fading, ETSI (European Telecommunications Standards Institute) fading, and Rayleigh fading channels. The equalizers used in simulations are a LE (Linear Equalizer), a DFE (Decision Feedback Equalizer), and a NPDFE. Moreover, the equalizer performance criterion of the QPSK is the BER.

WAVE 시스템에서 미드엠블을 이용한 채널 등화 방식

홍대기,강법주,Hong, Dae-Ki,Kang, Bub-Joo 한국정보통신학회 2010 한국정보통신학회논문지 Vol.14 No.10

차량 간 통신을 위한 직교 주파수 분할 다중화 (OFDM: Orthogonal Frequency Division Multiplexing)기반 WAVE (Wireless Access for Vehicular Environment) 시스템의 물리계층 표준은 기존에 정지환경을 기반으로 표준화된 IEEE802.11a 무선랜 (WLAN: Wireless Local Area Network)의 물리계층 표준을 따르는 것으로 되어 있다. 따라서 이동환경에 기반한 WAVE 시스템에서 단순한 등화방식을 적용할 경우 빠른 페이딩의 영향으로 인하여 프레임 초기 채널특성과 말기 채널특성의 변화가 초래되어 시스템의 수신 성능이 저하되게 되고, 특히 고차 변조방식에서는 더욱 문제가 된다. 따라서 본 논문에서는 WAVE 시스템의 64-직교진폭변조 (QAM: Quadrature Amplitude Modulation)과 같은 고차 변조에서 채널 등화성능을 향상시키는 방식에 대해 연구하였다. 훈련 심볼을 이용하는 기존의 채널추정방식을 기반으로 하되 WAVE 채널처럼 빠르게 변화하는 채널특성을 추적하기 위해 일정한 주기 마다 미드엠블을 삽입하는 전송구조를 제안하였다. 또한 미드엠블 사이의 심벌들의 채널 변화는 다양한 보간법을 적용한 등화 알고리듬을 제안하였다. A Wireless Access for Vehicular Environment (WAVE) system based on Orthogonal Frequency Division Multiplexing (OFDM) is made for vehicle to vehicle wireless communications. The physical layer standard of the WAVE system is very similar to that of the IEEE802.11a wireless local area network (WLAN). Therefore, the performance of the WAVE system is degraded by continual channel variation in the WAVE multipath fading channels after starting initial channel estimation. In this paper, we research the performance improvement of equalization in 64 Quadrature Amplitude Modulation (QAM) transmission in WAVE environment. The proposed algorithms use the training sequence and the midamble sequence which is used for fast channel variation such as WAVE environments. Additionally, various interpolation methods are also used for the channel tracking.

Fitz-Hugh-Curtis syndrome의 임상적 고찰

홍대기,성원준,조영래,박일수,이윤순 대한산부인과학회 2008 대한산부인과학회 학술대회 Vol.94 No.-

Volumetric Image Reconstruction in a Dental Panoramic Imaging System with a Limited-angle Zigzag Scan Geometry

홍대기,조효성,이선화,오지은,이민식,김효정,제의규,박연옥,최성일,구양서,조희문 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.2

As a continuation of our dental imaging R&D, we have proposed a novel idea that is capable of implementing cost-effective, low-dose, volumetric image reconstruction directly onto a dental panoramic imaging system. In the proposed geometry, a linear-type panoramic detector is rotated 90˚ from the orientation for panoramic imaging and scanned along a limited-angle zigzag trajectory in the axial direction to cover the whole imaging volume thickness. We used an effective reconstruction algorithm based on the total-variation (TV) minimization approach for the proposed geometry and performed systematic simulation work to demonstrate the viability of our proposed approach and its effectiveness for three-dimensional (3D) dental X-ray imaging. We have successfully reconstructed images of substantially high image accuracy from the proposed geometry and evaluated the reconstruction quality by using an image similarity metric, the universal-quality index (UQI). We expect the proposed method to be applicable to developing a cost-effective, low-dose, all-in-one dental X-ray imaging system.

한국 여성에서 자궁근종 발생에 관여하는 인자들에 대한 연구

홍대기,정민지,김보섭,이정미,조영래,이택후,전상식 대한산부인과학회 2006 대한산부인과학회 학술대회 Vol.92 No.-

WAVE 시스템에서 심볼 시간추적 알고리듬

홍대기,Hong, Dae-Ki 한국정보통신학회 2009 한국정보통신학회논문지 Vol.13 No.2

차량 간 무선 통신을 목적으로 만들어진 직교 주파수 분할 다중화 (OFDM: Orthogonal Frequency Division Multiplexing)기반 WAVE(Wireless Access for Vehicular Environment) 시스템의 물리층 표준은 기존에 표준화된 IEEE802.11a 무선랜(WLAN: Wireless Local Area Network)의 표준을 따르는 것으로 되어 있다. 따라서 WAVE는 초기 동기 이후 차량 간 다중 경로 페이딩(Multipath Fading) 채널의 영향으로 인하여 심볼 타이밍에 있어서 연속적인 시간 지연이 발생함에 따라 시스템의 수신 성능이 저하되게 된다. 본 논문은 추가적인 심볼 시간 지연을 보상해 주기 위한 심볼 시간 추적(Tracking) 알고리듬을 제안하고 있다. 본 논문에서는 제안된 알고리듬을 최대 지연 시간 (Maximum Timing Delay)이 적용된 최악의 통신환경에 적용하여 모의실험을 수행하였다. 실험결과에 의하면 제안된 알고리듬은 가산성 백색 가우스 잡음 (AWGN: Additive White Gaussian Noise) 채 널 및 페이딩 채널 환경에서 시스템의 수신 성능을 향상시킬 수 있음을 확인할 수 있다. A Wireless Access for Vehicular Environment (WAVE) system based on Orthogonal frequency Division Multiplexing (OFDM) is made for vehicle to vehicle wireless communications. The physical layer standard of the WAVE system is very similar to that of the IEEE802.1la wireless local area network (WLAN). Therefore, the performance of the WAVE system is degraded by continual timing delay in the WAVE multipath fading channels after starting initial timing synchronization. In this paper, the tracking algorithm that synchronizes symbol timing is proposed to continually compensate additional timing delay. Computer simulation of the proposed algorithm is performed in the worst communication environments that apply to maximum timing delay. Computer simulation shows that the proposed algorithm can improve the system performance in various channel conditions.

소화효소가 Helicobacter pylori의 증식과 공포화독소 생성에 미치는 영향

홍대식,강경희,장명웅 고신대학교(의대) 고신대학교 의과대학 학술지 2001 고신대학교 의과대학 학술지 Vol.16 No.1

Background : Global high prevalence rate of Helicobacter pylori infection is well-known fact. However, a large discrepancies exist between the diagnostic data obtained by the PCR and culture method, because the coccoid form of H.pylori which represent the majority form in the biological samples are not viable in the standard BHI broth with 5% horse serum. The component parts of saliva and gastric juice acted as neither stimulator nor inhibitor to the growth of H.pylori remain unclear. Objective : The purpose of this study was to evaluate the influence of amylase, pepsin, mucin, and lysozyme on the growth and vacuolating toxin production and titer of H.pylori in vitro. Materials and Methods : H.pylori 13,39,46,59,72,94,98 and 125 strains were isolated from patients with gastric disease. The digestive enzymes were inoculated in the 5% horse serum-BHI broth following final concentration of amylase (A; 0.20ug/ml), pepsin (P; 0.25ug/ml), mucin (M; 2,5ug/ml), and lysozyme (L; 1.5ug/ml). The vacuolating toxin titers of the culture supernatant were evaluated in the monolayer culture of RK-13 cells. Results : The morphologic conversion from bacillary to horse-shoe to coccoid forms of H.pylori was observed in the BHI broth containing 5% horse serum on day 5 culture. Half of H.pylori was changed from bacillary to coccoidal form on day 7 culture, most population of H.pylori was changed to coccoidal form on day 10 culture, and almost all H.pylori was changed to coccoidal form on day 14 culture. The growth of H.pylori 72, and 94 strains was increased in BHI broth containing each enzyme such as amylase, pepsin, mucin and mixture of two or three enzymes on day 5 and 7 culture. The growth of H.pylori 94 strains was increased in BHI broth containing each enzyme such as amylase, pepsin, mucin, and mixture of two or three enzymes on day 10 and 14 culture. The vacuolating toxin production of H.pylori strains was not influenced by the addition of amylase, pepsin, mucin, and lysozye or mixture of two or three enzymes. The neutralization of vacuolating toxin of H.pylori was not affected by the addition of amylase, pepsin, mucin, and lysozyme or mixture of two or three enzymes. Conclusion : We found that coccoid forms of H.pylori were viable in the standard 5% horse serum BHI media in the presence of amylase, pepsin, mucin, and lysozyme. The present study demonstrates that gastric juice of the stomach supports the viability of H.pylori and that oral route of infection is a plausible hypothesis. This work also demonstrates that gastric environment may not provide a selective advantage for the toxigenic strains of H.pylori.