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IEEE 802.11n 무선 네트워크에서의 협력적 프레임 집약 기법
송태원,백상헌,Song, Tae-Won,Pack, Sang-Heon 한국정보처리학회 2010 정보처리학회논문지 C : 정보통신,정보보안 Vol.17 No.6
프레임 집약 기법은 MAC 계층에서의 처리율 향상을 위한 기법으로, 새로운 무선랜 표준인 IEEE 802.11n에서는 MSDU 단위의 집약기법(A-MSDU) 과 MPDU 단위의 집약기법 (A-MPDU)을 지원한다. 본 논문에서는 IEEE 802.11n의 A-MPDU 기법을 릴레이 기반의 협력 통신환경에 적용하여 수신단에서 협력적으로 프레임을 복구할 수 있는 협력적 프레임 집약 기법을 제안한다. 제안한 협력적 프레임 기법은 채널 상태가 나쁜 경우에도 두 개 이상의 프레임을 수신하여 복구시키는 것이 가능하기 때문에 기존 기법에 비해 처리율을 향상시킬 수 있다. 성능 분석 모델을 통한 수치 분석 결과는 채널 상태에 따라 제안 기법이 기존의 릴레이 전송 기법 또는 직접적 전송 기법보다 성능이 더 좋아짐을 보여준다. IEEE 802.11n supports two frame aggregation schemes, aggregation for MAC service data unit (A-MSDU) and aggregation for MAC protocol data unit (A-MPDU), to improve throughput at the MAC layer. In this paper, we propose a cooperative frame aggregation (CoFA), which can recover erroneous frames in a cooperative manner based on A-MPDU. Specifically, CoFA receive multiple frames from direct and relay paths, and combined multiple frames jointly. Numerical results show that CoFA outperforms direct transmission and relay transmission over diverse channel conditions.
IEEE 802.11n에서의 2단계 프레임 집약 기법 성능 분석
송태원,양성열,백상헌,윤주상,Song, Tae-Won,Yang, Seong-Yeol,Pack, Sang-Heon,Youn, Joo-Sang 한국정보통신학회 2009 한국정보통신학회논문지 Vol.13 No.6
차세대 무선랜 표준인 IEEE 802.11n에서는 MAC 계층에서의 처리율을 향상시키기 위해서 프레임 집약 (Frame Aggregation) 기법을 제안하고 있다. IEEE 802.11n의 프레임 집약 기법은 MSDU (MAC Service Data Unit) 단위의 집약 기법 (Aggregate MSDU: A-MSDU)와 MPDU (MAC Protocol Data Unit) 단위의 집약 기법 (Aggregate MPDU: A-MPDU)의 두 가지 기법을 제안하고 있다. 본 논문에서는 A-MSDU와 A-MPDU를 결합한 2단계 프레임 집약 (Two-Level Frame Aggregation) 기법의 성능을 분석한다. 성능 분석을 위해 마르코브 체인에 기반하여 2단계 프레임 집약 기법의 처리율을 모델링한 뒤 이를 이용하여 노드의 수와 채널 상태 등에 따른 프레임 집약 기법의 처리율 변화 추이를 분석한다. 그리고 분석 결과에 기반하여 최적의 프레임 집약 기법을 설계하기 위한 방법을 제시한다. Frame Aggregation is a promissing technology for improving MAC throughput in IEEE 802.11n. In IEEE 802.11n, two frame aggregation schemes, Aggregate MSDU (A-MSDU) and Aggregation MPDU (A-MPDU), are defined. In this paper, we analyze the performance the two-level frame aggregation scheme where A-MSDU and A-MPDU are combined. We develop the analytical model for the two-level frame aggregation scheme and present numerical results on the effect of bit error rate, aggregation size, and the number of nodes.
송태원,김재환,김동섭,노승탁,Song, Tae-Won,Kim, Jae-Hwan,Kim, Tong-Seop,Ro, Sung-Tack 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.8
In this work, a modified stage-stacking method for the performance prediction of multi-stage axial flow compressors is proposed. The method is based on a simultaneous calculation of all interstage variables (temperature, pressure, flow velocity) instead of the conventional sequential stage-by-stage scheme. The method is also very useful in simulating the effect of changing angles of the inlet guide vane and stator vanes on the compressor operating characteristics. Generalized stage performance curves are used in presenting the performance characteristics of each stage. General assumptions enable determination of flow path data and stage design performance. Performance of various real compressors is predicted and comparison between prediction and field data validates the usefulness of the present method.
해석적 방법을 이용한 가스터빈 축류 압축기의 파울링 현상 해석
송태원,김동섭,김재환,손정락,노승탁,Song, Tae-Won,Kim, Dong-Seop,Kim, Jae-Hwan,Son, Jeong-Rak,No, Seung-Tak 대한기계학회 2001 大韓機械學會論文集B Vol.25 No.12
The performance of gas turbines is decreased as their operating hours increase. Fouling in the axial compressor is one of main reasons for the performance degradation of gas turbine. Airborne particles entering with air at the inlet into compressor adhere to the blade surface and result in the change of the blade shape, which is closely and sensitively related to the compressor performance. It is difficult to exactly analyze the mechanism of the compressor fouling because the growing process of the fouling is very slow and the dimension of the fouled depth on the blade surface is very small compared with blade dimensions. In this study, an improved analytic method to predict the motion of particles in compressor cascades and their deposition onto blade is proposed. Simulations using proposed method and their comparison with field data demonstrate the feasibility of the model. It if found that some important parameters such as chord length, solidity and number of stages, which represent the characteristics of compressor geometry, are closely related to the fouling phenomena. And, the particle sloe and patterns of their distributions are also Important factors to predict the fouling phenomena in the axial compressor of the gas turbine.
송태원(Tae Won Song),김동섭(Tong Seop Kim),김재환(Jae Hwan Kim),노승탁(Sung Tack Ro) 한국유체기계학회 2000 유체기계 연구개발 발표회 논문집 Vol.- No.-
The performance of gas turbines decreases as their operating hours increase. Compressor fouling is the main reason for this time-dependent performance degradation. Airborne particles adhere to the blade surface and results in the change in the blade shape. It is difficult to exactly analyze the mechanism of the compressor fouling because the growing process of the fouling is very slow and the dimension of the fouled depth is very small compared with blade dimensions. In this study, an analytic method to predict the motion of particles and their deposition inside axial flow compressors is proposed. The analytic model takes into account the blade shape and the flow within the blade passage. Comparison of simulation result with field data shows the feasibility of the model. Influence of the particle distribution on the compressor fouling is also examined.