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Two New Types of Candidate Symbol Sorting Schemes for Complexity Reduction of a Sphere Decoder
전은성,김요한,김동구,Jeon, Eun-Sung,Kim, Yo-Han,Kim, Dong-Ku The Korea Institute of Information and Commucation 2007 韓國通信學會論文誌 Vol.32 No.9c
The computational complexity of a sphere decoder (SD) is conventionally reduced by decoding order scheme which sorts candidate symbols in the ascending order of the Euclidean distance from the output of a zero-forcing (ZF) receiver. However, since the ZF output may not be a reliable sorting reference, we propose two types of sorting schemes to allow faster decoding. The first is to use the newly found lattice points in the previous search round instead of the ZF output (Type I). Since these lattice points are closer to the received signal than the ZF output, they can serve as a more reliable sorting reference for finding the maximum likelihood (ML) solution. The second sorting scheme is to sort candidate symbols in descending order according to the number of candidate symbols in the following layer, which are called child symbols (Type II). These two proposed sorting schemes can be combined with layer sorting for more complexity reduction. Through simulation, the Type I and Type II sorting schemes were found to provide 12% and 20% complexity reduction respectively over conventional sorting schemes. When they are combined with layer sorting, Type I and Type II provide an additional 10-15% complexity reduction while maintaining detection performance.
MIMO Iterative 수신기에서 계층적 변조 특성을 이용한 낮은 복잡도를 가지는 후보리스트 발생 기법
전은성,양장훈,김동구 한국통신학회 2009 韓國通信學會論文誌 Vol.34 No.6
In this paper, We present a low complexity candidate list generation scheme in iterative MIMO receiver. Since QAM modulation can be decomposed into HP symbols and LP symbol and HP symbol is robust in error capability, we generate HP symbol list with simple ZF detector output and its corresponding neighbor HP symbols. Then, based on HP symbol list, the LP symbol list is generated by using the sphere decoder. From the second iteration, since apriori value from channel decoder is available, the candidate list is updated based on demodulated apriori value. Through the simulation, we observe that at the first iteration, the BER performance is worse than LSD. However, as the number of iteration is increased, the proposed scheme has almost same performance as LSD. Moreover, the proposed one has reduced candidate list generation time and lower number of candidate list compared with LSD. 본 논문에서는 QAM 변조의 계층적 변조 특성을 이용하여 Iterative MIMO 수신기에서 LLR(log likelihood ratio)값을 구하기 위한 낮은 복잡도를 가지는 후보 리스트 발생 기법을 소개한다. QAM 변조는 에러에 강인한 HP (high priority) 심볼과 상대적으로 에러에 약한 LP(low priority) 심볼로 분해할 수 있다. 본 논문에서는 HP 심볼 에 대해서는 간단한 ZF 수신기의 output 값과 인접 HP 심볼들을 이용하여 먼저 안테나별로 HP 심볼 리스트를 발 생하고, 각 HP 심볼 리스트에 대해서 ML(maximum likelihood)의 검파 성능을 가지는 sphere decoder를 사용하여 LP 심볼 리스트를 발생하여 후보 심볼 리스트를 발생하였다. 두 번째 iteration 이후부터는 채널 디코더에서 피드 백되는 apriori 값을 이용하여 후보 심볼 리스트를 발생하였다. 실험의 비교군은 MIMO 채널 용량에 근사적으로 접근하는 list sphere decoder (LSD)를 사용하였다. 전산 실험 결과, 제안하는 후보 리스트 발생 기법은 LSD에 비 해서 첫 번째 iteration에서는 BER성능이 다소 떨어지나, iteration 이 진행될수록 LSD에 근접하는 성능을 보였으 며, 후보 리스트의 발생 시간도 LSD에 비해서 월등히 우수한 성능을 가짐을 볼 수 있었다. 또한 LLR 계산 시 탐 색해야 할 후보 리스트의 개수 역시 LSD에 비해서 적은 값을 가지므로, LLR 계산 시 필요한 연산의 복잡도가 낮 음을 확인할 수 있었다.
간세포암 환자의 수술 후 간내 조기 재발에 대한 위험 인자
전은성(Eun Seong Jeon),황윤진(Yun Jin Hwang),김종열(Jong Yeol Kim),천재민(Jae Min Chun),김상걸(Sang Geol Kim),윤영국(Young Kook Yun) 대한외과학회 2008 Annals of Surgical Treatment and Research(ASRT) Vol.75 No.1
Purpose: The purpose of this study is to comprehend the prognosis and risk factors for the early recurrence after resection for hepatocellular carcinoma (HCC). Methods: Between 1997 and 2005, 237 patients underwent curative resection for HCC at Kyungpook National University Hospital. The patients were followed up regularly to detect any recurrences of HCC by performing imaging studies and AFP. Early recurrence was defined as recurrence that occurred within one year after resection. The patients were divided into the early recurrence group and the others, which included both patients without recurrence and with recurrence that occurred later than 1 year after resection. The clinicopathologic factors of both group were compared to identify the prognosis and the risk factors by performing univariate and multivariate analyses. Results: Seventy three patients (30.8%, 73/238) had early recurrence after resection and 164 patients (69.2%, 164/238) didn`t have recurrence in the first year. The survival rate was significantly better in the without early recurrence group than that in the early recurrence group (96.3% vs 60.3% and 85.1% vs 23.4%, 62.8% vs 7.3% 1, 3, 5 years). The risk factors for early recurrence in the HCC patients were a tumor size greater than 5 ㎝ (P=0.011; odds ratio=2.304) and vascular invasion (P=<0.001; odds ratio=6.342). Conclusion: Since a large tumor size and vascular invasion are the risk factors for early recurrence, the patients who have these risk factors should be followed up with caution and possible postoperative adjuvant therapeutic trials should be considered.