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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.
A functional and safety test for the chitosan-covered gauze in total laparoscopic hysterectomy
홍대기,이윤희,정근오,조영래,이윤순 대한산부인과학회 2016 대한산부인과학회 학술대회 Vol.102 No.-
목적: To evaluate the practicality of chitosan -covered gauze in total laparoscopic hysterectomy for gynecological benign diseases. 방법: Chitosan -covered gauze (En-Chito Gauze <sup>®</sup>) was used during laparoscopic hysterectomy (TLH) for gynecological benign diseases in thirty patients. The comparison group underwent TLH for benign diseases without Chitosan -covered gauze (n=74). The surgical outcomes such as blood loss, and operation time, postoperative inflammation and complications were compared. The perioperative tearing of gauze was carefully monitored and postoperative remnant of the gauze in the abdominal cavity were examined by a pathologist. 결과: In the group using Chitosan -covered gauze, blood loss was decreased without statistical significance (p=0.13). There were a significant decreases of operation time(p=0.01) and postoperative leukocyte change(p=0.04). The correlation analysis showed that the shorter operation time was strongly related with less blood loss (p= 0.01). The complication rates were not different in two groups. There were 2 partial tearing of the gauze during operation which did not have any adverse effects. 결론: Chitosan -covered gauze (En-Chito Gauze <sup>®</sup>) decreased the operation time and postoperative inflammation. The gauze was shown to be clinically safe but needs improvement of structural design and bleeding control potency.
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.