• 한국정보과학회논문지:정보통신
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• 제37권3호
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• pp.243-248
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• 2010

시스템에서 UE의 QoS를 보장하면서 효율적인 power saving을 위해 본 논문에서는 delay 정보를 이용하여 3GPP(Third Generation Partnership Project) 규격에서 제시한 DRX/DTX(Discontinuous. Reception/Transmission)의 차등적 적용 MAC 프로토콜을 제안한다. 제안한 MAC 프로토콜은 LTE 기지국에서 각 UE의 QoS를 고려하여 적응적으로 DRX/DTX 주기를 제어한다. UE의 패킷 delay가 적은 경우에 DRX/DTX 주기를 늘려 에너지를 절약하고 패킷 delay가 커지면 기지국의 DRX/DTX 주기를 줄여 delay를 줄이고 UE의 QoS를 보장한다. DRX/DTX의 차등적용에 따른 모의실험 결과 제안된 power saving 방식은 DRX/DTX를 상황에 따라 변화시키지 않는 방식에 비해 개선된 power saving 성능을 제공하며 특히 상황에 맞게 DRX/DTX를 설정하여 UE의 요구사항을 충족시킬 수 있다. 본 논문에서는 LTE 기지국과 UE가 통신하는 환경에서 기지국의 에너지를 절약할 수 있는 MAC protocol을 제안하고 시뮬레이션을 통하여 성능이 향상되었음을 확인한다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.143-146
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• 2001

The evolution of dynamic recrystallization (DRX) was studied with torsion test for AISI 304 stainless steel in the temperature range of $900-1000^{\circ}C$ and strain rate range of 0.05-5/sec. The evolution of DRX was investigated with microstructural analysis and change of flow stress curve slope. The investigation of serrated grain boundaries using electron back scattered diffraction (EBSD) analysis indicated that the nucleated new DRX grain size was similar to the size of bulging part. Before the steady state, the dynamically recrystallizing grains do not remain a constant size and gradually grow to the size of fully DRX grain at steady state. The calculation of grain size was based on $X_{DRX}$ and the assumption, which the nucleated DRX grains are growing to the steady state, continuously. It was found that the calculated results agreed with the microstructure of the alloy.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2015년도 춘계학술발표대회
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• pp.190-192
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• 2015

Discontinuous Reception 메커니즘은 LTE 시스템에서 고속 트래픽 성취에 뒤따른 이동 단말의 배터리 효율성의 중요도 상승에 따라 3GPP 표준으로 채택된 이용 단말의 비 연결적인 컨트롤 채널수신 확인 기법이다. 본 연구에서는 채널 상황 및 트래픽 특성에 효율적인 DRX 파라미터 설정의 중요성에 대해 확인하기 위해 Ns-3 시뮬레이터를 통해 DRX 활성/비활성 파라미터에 따른 성능을 확인하였으며 실험 결과에 통해 DRX 활성/비활성 파라미터의 비율에 따른 성능 변화를 확인하였다.

• ETRI Journal
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• 제38권4호
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• pp.622-633
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• 2016

A discontinuous reception (DRX) operation is included in the Long Term Evolution (LTE) system to achieve power saving and prolonged battery life of the user equipment. An improvement in DRX power saving usually leads to a potential increase in the packet delay. An optimum DRX configuration depends on the current traffic, which is not easy to estimate accurately, particularly for non-real-time applications. In this paper, we propose a novel way to vary the DRX cycle length, avoiding a continuous estimation of the data traffic when only non-real-time applications are running with no active real-time applications. Because a small delay in non-real-time traffic does not essentially impact the user's experience adversely, we deliberately allow a limited amount of delay in our proposal to attain a significant improvement in power saving. Our proposal also improves the delay in service resumption after a long period of inactivity. We use a stochastic analysis assuming an M/G/1 queue to validate this improvement.

• 소성∙가공
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• 제9권1호
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• pp.72-79
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• 2000

Dynamic recrystallization (DRX), which may occur during hot deformation, is important for the microsturctural evolution of 304 stainless steel. Especially, the current interest in modelling hot rolling demands quantitative relationships among the thermomechanical process variables, such as strain, temperature, strain rate, and etc. Thus, this paper individually presents the relationships for flow stress and volume fraction of DRX as a function of processing variables using torsion tests. The hot torsion tests of 304 stainless steel were performed at the temperature range of 900~110$0^{\circ}C$ and the strain rate range of 5x10-2~5s-1 to study the high temperature softening behavior. For the exact prediction of flow stress, the equation was divided into two regions, the work hardening (WH) and dynamic recovery (DRV) region and the DRX region. Especially, The flow stress of DRX region could be expressed by using the volume fraction of DRX (XDRX). Since XDRX was consisted of the critical strain($\varepsilon$c) for initiation of dynamic recrystallization (DRX) and the strain for maximum softening rate ($\varepsilon$*), that were related with the evolution of microstructure. The calculated results predicted the flow stress and the microstructure of the alloy at any deformation conditions well.

• 한국ITS학회 논문지
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• 제9권1호
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• pp.49-54
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• 2010

최근 차세대 이동통신 기술로 각광받고 있는 3GPP LTE(Long Term Evolution) 시스템을 위한 기지국에서의 power saving에 관한 연구가 이슈화 되고 있다. 이는 무선통신 네트워크에서 가장 많은 에너지를 소모하는 부분이 기지국 부분이기 때문이다. 또한 기지국에서의 power saving은 세계가 주목하고 있는 저탄소 배출 녹색 기술에도 부합하는 내용이기도 하다. 따라서 본 논문에서는 UE(User Equipment)의 Traffic의 종류에 따라 DRX/DTX의 주기를 차등적으로 적용함으로써 기존에 일정한 DRX/DTX 주기를 적용하는 방식에 비해 성능은 떨어지지 않으면서 에너지 효율을 극대화하는 방식을 제안한다. 제안된 방식에 따른 모의실험 결과 기존의 방식에 비해서 개선된 power saving 성능을 확인할 수 있다. 본 논문에서는 LTE 기지국과 UE가 통신하는 환경에서 기지국의 에너지를 절약할 수 있는 MAC 프로토콜을 제안하고 시뮬레이션을 통하여 성능이 향상되었음을 확인한다

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2000년도 추계학술대회 논문집
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• pp.33-36
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• 2000

The dynamic recrystallization (DRX) of medium carbon steels (SCM 440 and POSMA45) was studied with torsion test in the temperature range of $900-1100^{\circ}C$ and the strain rate range of $5.0x10^{-2}\;-\;5.0x10^0/sec$. To establish the quantitative equations for DRX, the evolution of flow stress curve with strain was analyzed. The critical strain (${\varepsilon}_c$) and strain for maximum softening rate ( ${\varepsilon}^{*}$) could be confirmed by the analysis of work hardening rate ($d{\sigma}/d{\varepsilon}\;=\; \theta$). The volume fraction of dynamic recrystallization ($X_{DRX}$) as a function of processing variables, such as strain rate ( $\dot{\varepsilon}$ ), temperature (T), and strain ( $\varepsilon$ ) were established using the ${\varepsilon}_c$ and ${\varepsilon}^{*}$. For the exact prediction, the ${\varepsilon}_c$, ${\varepsilon}^{*}$ and Avrami' exponent (m') were quantitatively expressed by dimensionless parameter, Z/A respectively. The transformation-effective strain-temperature curve for DRX could be composed. It was found that the calculated results were agreed with the experimental data for the steels at any deformation conditions.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 추계학술대회 논문집
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• pp.293-296
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• 2001

The dynamic softening mechanisms of AISI 316, AISI 304 and AISI 430 stainless steels were studied with torsion test in the temperature range of $900 - 1200^{\circ}C$ and the strain rate range of $5.0x10^{-2}-5.0x10^0/sec$. The austenitic stainless steels, such as AISI 316 and AISI 304 were softened by dynamic recrystallization (DRX) during hot deformation. Also, the evolutions of flow stress and microstructure of AISI 430 ferritic stainless steel show the characteristics of continuous dynamic recrystallization (CDRX). To establish the quantitative equations for DRX of AISI 316 stainless steel, the evolution of flow stress curve with strain was analyzed. The critical strain (${\varepsilon}_c$) and strain for maximum softening rate (${\varepsilon}^{*}$) could be confirmed by the analysis of work hardening rate ($d{\sigma}/d{\varepsilon}={\theta}$). The volume fraction of dynamic recrystallization ($X_{DRX}$) as a function of processing variables, such as strain rate ( $\varepsilon$ ), temperature (T), and strain ( $\varepsilon$ ) were established using the ${\epsilon}_c$ and ${\varepsilon}^{*}$. For the exact prediction the ${\varepsilon}_c,\;{\varepsilon}^{*}$ and Avrami' exponent (m') were quantitatively expressed by dimensionless parameter, Z/A, respectively. It was found that the calculated results were agreed with the experimental data for the steels at my deformation conditions. Also, we can reasonably conclude that the DRX, CDRX and grain refinement of stainless steels can be achieved by large strain deformation at high Z parameter condition.

• 소성∙가공
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• 제31권6호
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• pp.344-350
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• 2022

Extruded Mg-Bi binary alloys are known to have an undesirable bimodal grain structure containing a large amount of coarse unrecrystallized grains. Accordingly, to improve the microstructural homogeneity of extruded Mg-Bi alloys, it is necessary to promote the dynamic recrystallization (DRX) behavior during hot extrusion. An effective way to promote DRX is an increase in nucleation sites for DRX through a pre-deformation process before extrusion, such as cold pre-forging and hot pre-compression. However, the application of these pre-deformation processes increases the cost of final extruded Mg products because of an increase in energy consumption and decrease in productivity. Therefore, a low-cost new continuous process with high productivity is required to improve the microstructural homogeneity and mechanical properties of extruded Mg alloys without a drastic increase in the entire process cost. This study proposes a new extrusion method using an extrusion billet with a truncated cone shape (i.e., tapered billet) instead of a conventional extrusion billet with a cylindrical shape. When the hot extrusion of a Mg-5Bi alloy is conducted using the tapered billet, the DRX behavior during extrusion is considerably promoted. The DRX fraction and average grain size of the extruded alloy significantly increase and decrease from 65% to 91% and from 225 ㎛ to 49 ㎛, respectively. Consequently, the extruded Mg-5Bi alloy fabricated using the tapered billet has a finer homogeneous grain structure and higher tensile elongation than the extruded counterpart fabricated using the cylindrical billet.

• 한국정보통신학회논문지
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• 제24권2호
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• pp.285-289
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• 2020

무선 네트워크의 계층적 구성은 다양한 네트워크 환경을 지원하기 위해 제공된다. 기지국에서는 두 가지 시스템 상태가 기본적으로 고려될 수 있으며, 이에 대해 액티브와 슬립 모드 사이에서 상태 전이가 발생할 수 있다. 그러므로 에너지 사용을 줄이기 위하여 저전력의 시스템 운영 관리가 기지국 시스템에 고려되어야 한다. 따라서 본 논문에서는 시스템 관리를 다루기 위해 Discontinuous Reception (DRX) 분석 모델을 고려한다. DRX 모델을 통하여 기지국 시스템의 운영에 대한 분석 방안을 제시하며 에너지 소비를 위한 저전력 강도를 살펴본다. 또한 시스템 상태에서 기지국의 저전력 소모에 대한 성능을 분석하기 위해 무선 자원 요구와 서비스 호 도착의 운영이 고려되며, 이를 위하여 유한 마르코프 시스템 모델을 사용하였다.