Practical channel prediction for NR and LTE massive MIMO using hybrid Kalman filters

Yongyun Choi(최용윤),Yang Li,Ying Wang 한국통신학회 2021 한국통신학회 학술대회논문집 Vol.2021 No.2

Accurate channel state information (CSI) is critical for optimal throughput of massive MIMO (mMIMO) systems. Out-of-date CSI due to user mobility causes significant throughput degradation, which is a known industry-wide challenge. In this paper, we propose a novel and practical solution for CSI prediction by using hybrid Kalman filters where both parametric and non-parametric estimations are applied. Up to 80% throughput gain has been shown in extensive system-level and link-level simulation. The proposed algorithm has achieved noticeable gain using extensive field data captured from commercial mMIMO systems. Various algorithm complexity reduction has been done to enable a proof-of-concept development using commercialized mMIMO system.

다수의 중계기가 존재하는 협력 재밍 네트워크를 위한 중계기 선택 및 전력 할당 기법

최용윤(Yongyun Choi),이재홍(Jae Hong Lee) 대한전자공학회 2015 대한전자공학회 학술대회 Vol.2015 No.6

다수의 중계기와 도청자가 존재하는 협력 재밍 네트워크를 위한 중계기 선택 기법

최용윤(Yongyun Choi),이재홍(Jae Hong Lee) 한국방송·미디어공학회 2016 방송공학회논문지 Vol.21 No.1

In this paper, a cooperative jamming network with multiple relays and multiple eavesdroppers is investigated. Among the relays, one best relay is selected to amplify and forward the signal to destination through two phases. To confuse eavesdroppers, the destination transmits a jamming signal in the first phase and the source transmits jamming signal in the second phase. Secrecy rate of this system is derived, and based on the available channel state information (CSI), relay selection schemes are proposed, respectively. Numerical results show that the performance of the proposed relay selection scheme outperforms than that of random relay selection scheme.

URC 서비스를 위한 상황인지 기반의 워크플로우 시스템

최종선(Jongsun Choi),곽동규(Dong-gyu Kwak),최재영(Jaeyoung Choi),조용윤(Yongyun Cho) 한국정보과학회 2010 정보과학회논문지 : 소프트웨어 및 응용 Vol.37 No.9

이른 시스템 개발 단계에서 요구사항 에러를 찾기 위해서는 시스템의 행위가 정형 언어로 표현되어야 하고, 도달성 분석이나 싸이클 탐색과 같은 분석 기술로 분석해야 한다. 하지만 이 기술들은 시스템의 상태 공간 순회를 기반으로 하기 때문에 시스템이 복잡해지면 상태 폭발 문제가 발생할 수 있다. 즉, 순회를 위한 메모리와 수행 시간이 큰 상태 공간 때문에 기하 급수적으로 증가한다. 본 논문에서는 병행 시스템에서 이러한 문제가 나타나는 원인을 지적하고 순회에 필요한 메모리를 줄이기 위해서 병행적 상태 공간을 합성하지 않고 순회한다. 또한 수행 시간을 줄이기 위해서 방문 기록을 최소한으로 유지하는 새로운 기술을 제시한다. 마지막으로 이 기법이 효과적임을 실험 결과를 통해 보인다. For detecting requirement errors in early system development phase, the behaviors of a system should be described in formal methods and be analyzed with analysis techniques such as reachability analysis and cycle detection. However, since they are usually based on explicit exploration of system state space, state explosion problem may be occurred when a system becomes complex. That is, the memory and execution time for exploration exponentially increase due to a huge state space. In this paper, we analyze the fundamental causes of this problem in concurrent systems and explore the state space without composing concurrent state spaces for reducing the memory requirement for exploration. Also our new technique keeps a visited history minimally for reducing execution time. Finally we represent experimental results which show the efficiency of our technique.

동적인 사용자 서비스 요구를 지원하는 상황인지 워크플로우 시스템

최종선(Jongsun Choi),조용윤(Yongyun Cho),최재영(Jaeyoung Choi) 한국정보과학회 2007 정보과학회논문지 : 시스템 및 이론 Vol.34 No.5·6

유비쿼터스 컴퓨팅 환경에서의 상황인지 서비스는 동적으로 발생하는 사용자의 상황 정보에 따른 서비스 제공을 지향한다. FollowMe와 uFlow와 같은 상황인지 워크플로우 시스템은 사용자의 상황정보를 서비스의 분기 조건으로 표현한 워크플로우 기반의 상황인지 웹 서비스를 제공한다. 그러나 그들은 워크플로우의 실행 중에도 동적으로 발생할 수 있는 사용자의 서비스 요구에 대해 진행 중인 워크플로우시나리오에 즉각적으로 적용할 수 있는 방법을 제공하지 못한다. 본 논문에서는 실행 중인 워크플로우 서비스의 중단없이 사용자가 입력하는 새로운 서비스 요구를 초기 워크플로우 시나리오에 동적으로 반영할 수 있는 상황인지 워크플로우 시스템을 제안한다. 제안하는 시스템은 사용자의 새로운 서비스 요구에 대해 실행중인 시나리오에서의 변경 위치를 점진적 파싱(Incremental Parsing)을 통해 정확히 인식하고 초기 시나리오에서 영향을 받는 부분만을 신속히 재구성함으로써 동적으로 발생하는 사용자의 상황정보를 보다 빠르고 효율적으로 초기 시나리오에 적용할 수 있으며, 워크플로우 흐름의 중단없이 계속적인 서비스를 제공할 수 있다. 이를 통해 사용자는 시간과 공간에 관계없이 원하는 서비스를 상황인지 워크플로우 시나리오에 반영할 수 있으며, 기술된 사용자 컨텍스트에 따라 상황인지 서비스의 실행을 보장받을 수 있다. A context-aware service in ubiquitous computing environments aims to supply services according to users' situation information that is dynamically occurring. The existing context-aware workflow systems, such as FollowMe and uFlow, provide context-aware services based on a workflow, which uses users' situation information as transition conditions of a service. But they can't apply users' new service demands, which may dynamically occur even when a workflow is on going, to a workflow scenario. In this paper we propose a context-aware workflow system, which can reapply users' new service demands into an initial workflow without interrupting or deleting the workflow. The proposed system can provide context-aware services without interrupting of service by recognizing exactly a place holder that has to be changed in a workflow scenario and by reconstructing only the changed parts through an incremental parsing method. Therefore, a user can immediately apply his new service demands to an on-going workflow scenario, and he can be guaranteed continuous executions of context-aware services according to a workflow scenario, which includes new service demands.

다중-워크플로우를 지원하는 상황인지 워크플로우 언어의 설계

최종선 ( Jongsun Choi ),조용윤 ( Yongyun Cho ),최재영 ( Jaeyoung Choi ) 한국인터넷정보학회 2009 인터넷정보학회논문지 Vol.10 No.6

최근 유비쿼터스 컴퓨팅 환경에서의 서비스 자동화를 위해 워크플로우 기술을 적용하려는 연구가 활발히 진행되고 있다. 그러나 대부분의 기존 상황인지 워크플로우 언어들은 단일 워크플로우 처리만을 고려하기 때문에, 다수의 워크플로우 조합을 통한 복합적이고 다양한 상황인지 서비스 지원에 제약이 있다. 본 논문은 다수의 워크플로우에 존재하는 개별적인 서비스 흐름을 하나의 워크플로우로 통합 표현할 수 있는 상황인지 기반의 워크플로우 언어인 CAWL (Context-Aware Workflow Language)을 소개한다. CAWL은 사용자가 원하는 서비스를 제공하기 위해 결합 가능한 다수의 워크플로우를 자연스럽게 연결하여 다양한 형태의 상황인지 워크플로우 서비스를 표현할 수 있다. 또한 개발자는 새로운 워크플로우 개발을 위해 기존에 존재하는 다수의 워크플로우를 다시 사용할 수 있기 때문에, 상황인지 워크플로우의 개발 노력을 줄이고 워크플로우의 재사용성을 높일 수 있다. 따라서 CAWL은 다수의 사용자 워크플로우가 공존하는 유비쿼터스 컴퓨팅 환경에서 상황인지 서비스자동화와 관련된 응용 개발에 큰 도움이 될 것으로 기대된다. In recent years, there have been several researches applying workflow technologies for service automation on ubiquitous computing environments. However, most context-aware workflow languages have difficulties in supporting composite workflows composed of single workflows, because these languages are still in its early stage and they only provide single workflow services to their users. This paper introduces CAWL, which is a context-aware workflow language. CAWL is for describing individual service workflows to make integrated service workflows. By using CAWL, service developers are able to reuse existing workflows to develop new context-aware workflow services. Therefore, development efforts and time can be saved and workflow resusability also increased. CAWL is expected to make it easy to develop applications related to context-aware workflow services on ubiquitous computing environments.

Stabilization of absolute instability in spanwise wavy two-dimensional wakes

Hwang, Yongyun,Kim, Jinsung,Choi, Haecheon Cambridge University Press 2013 Journal of fluid mechanics Vol.727 No.-

<B>Abstract</B><P>Controlling vortex shedding using spanwise-varying passive or active actuation (namely three-dimensional control) has recently been reported as a very efficient method for regulating two-dimensional bluff-body wakes. However, the mechanism of how the designed controller regulates vortex shedding is not clearly understood. To understand this mechanism, we perform a linear stability analysis of two-dimensional wakes, the base flow of which is modified with a given spanwise waviness. Absolute and convective instabilities of the spanwise wavy base flows are investigated using Floquet theory. Two types of base-flow modification are considered: varicose and sinuous. Both of these modifications attenuate absolute instability of two-dimensional wakes. In particular, the varicose modification is found to be much more effective in the attenuation than the sinuous one, and its spanwise lengths resulting in maximum attenuation show good agreement with those in three-dimensional controls. The physical mechanism of the stabilization is found to be associated with the formation of streamwise vortices from tilting of two-dimensional Kármán vortices and the subsequent tilting of these streamwise vortices by the spanwise shear in the base flow. Finally, the sensitivity of absolute instability to spanwise wavy base-flow modification is investigated. It is shown that absolute instability of two-dimensional wakes is much less sensitive to spanwise wavy base-flow modification than to two-dimensional modification. This suggests that the high efficiency observed in several three-dimensional controls is not due to the sensitive response of the wake instability to the spanwise waviness in the base flow.</P>

A Study on Energy Reduction by Independent Metering Valve for Excavator

Kyujeong Choi,Yongyun Nam,Jaho Seo,Youngsoo Lee,Kyeonguk Kim 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.5

A service model for nutrition supplement prediction based on Fuzzy Bayes model using bigdata in livestock

Sivamani, Saraswathi,Choi, Jongsun,Cho, Yongyun Springer-Verlag 2018 Annals of operations research Vol.265 No.2

Scale interactions and spectral energy transfer in turbulent channel flow

Cho, Minjeong,Hwang, Yongyun,Choi, Haecheon Cambridge University Press 2018 Journal of fluid mechanics Vol.854 No.-

<P>Spectral energy transfer in a turbulent channel flow is investigated at Reynolds number $Re_{\unicode[STIX]{x1D70F}}\simeq 1700$, based on the wall shear velocity and channel half-height, with a particular emphasis on full visualization of triadic wave interactions involved in turbulent transport. As in previous studies, turbulent production is found to be almost uniform, especially over the logarithmic region, and the related spanwise integral length scale is approximately proportional to the distance from the wall. In the logarithmic and outer regions, the energy balance at the integral length scales is mainly formed between production and nonlinear turbulent transport, the latter of which plays the central role in the energy cascade down to the Kolmogorov microscale. While confirming the classical role of the turbulent transport, the triadic wave interaction analysis unveils two new types of scale interaction processes, highly active in the near-wall and the lower logarithmic regions. First, for relatively small energy-containing motions, part of the energy transfer mechanisms from the integral to the adjacent small length scale in the energy cascade is found to be provided by the interactions between larger energy-containing motions. It is subsequently shown that this is related to involvement of large energy-containing motions in skin-friction generation. Second, there exists a non-negligible amount of energy transfer from small to large integral scales in the process of downward energy transfer to the near-wall region. This type of scale interaction is predominant only for the streamwise and spanwise velocity components, and it plays a central role in the formation of the wall-reaching inactive part of large energy-containing motions. A further analysis reveals that this type of scale interaction leads the wall-reaching inactive part to scale in the inner units, consistent with the recent observation. Finally, it is proposed that turbulence production and pressure-strain spectra support the existence of the self-sustaining process as the main turnover dynamics of all the energy-containing motions.</P>