• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2019.11a
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• pp.256-258
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• 2019

최근 MPEG-Immersive 표준화 그룹에서는 여러 위치에 존재하는 다수의 360 영상을 취득하고 처리하여 사용자에게 제한적인 화면 전환 이동에 따른 운동 시차(motion parallex)를 제공하는 3 degrees of freedom plus (3DoF+) 기술에 관한 표준화가 진행되고 있다. 이러한 3DoF+ 표준화 기술에서의 압축은 기존의 HEVC 코덱을 사용하나, 현재 존재하는 360 영상 사용자 시점 기반 스트리밍 기법을 3DoF+ 스트리밍에 적용하기 위해서는 기존의 360 영상과 다르게 영상 서로 간의 참조과정으로 인한 의존성으로 문제가 존재한다. 본 논문에서는 해당 문제점을 서술하고, MCTS(Motion-Constrained Tile Set)를 사용하여 보다 적은 디코더와 사용자 시점에 맞게 효율적으로 영상을 전송할 수 있는 MCTS 기반 타일 그룹 분할 방법을 제안한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.10
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• pp.929-937
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• 2012

In this paper, we introduce three types of opportunistic interference management strategies in multi-cell uplink networks with time-invariant channel coefficients. First, we propose two types of opportunistic interference mitigation techniques, where each base station (BS) opportunistically selects a set of users who generate the minimum interference to the other BSs, and then their performance is analyzed in terms of degrees-of-freedom (DoF). Second, we propose a distributed opportunistic scheduling, where each BS opportunistically select a user using a scheduler designed based on two threshold, and then its performance is analyzed in terms of throughput scaling law. Finally, numerical evaluation is performed to verify our result.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2019.06a
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• pp.238-239
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• 2019

현재 MPEG은 최대 6DoF(Degrees of Freedom) 사용자 운동시차를 지원함과 동시에 고해상도의 360VR 서비스를 제공하기 위한 영상 포맷, 부호화 등 요소기술에 대한 MPEG-I(Immersive) 표준화를 진행 중에 있다. 6DoF는 가상 공간 내 임의의 위치에서 운동시차를 제공하는 것으로 이를 획득 및 재현하기 위한 360VR 영상 표현 및 포맷에 대한 연구가 필수적으로 요구된다. 이에 본 논문은 제한된 공간 내 임의의 위치에서 사용자에게 자연스러운 6 자유도를 제공하기 위한 360VR 영상 포맷을 제안한다. 실험결과 제한된 공간 내에서 사용자에게 자연스러운 운동시차를 제공할 뿐만 아니라 향후 실사 환경에서도 획득 및 적용 가능성을 확인하였다.

• Broadcasting and Media Magazine
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• v.23 no.4
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• pp.58-66
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• 2018

점점 현실화 되는 가상의 환경 내에서 자유롭게 시점을 선택하여 볼 수 있고 전방위 공간 내 몰입형 경험을 제공하는 VR(Virtual Reality) 미디어는 자연스러운 사실감을 제공함과 동시에 공간과 시간의 제약을 극복할 수 있는 실감미디어로 인식되고 있다. 이렇듯 VR 미디어의 출현은 한정된 시점에서의 입체감 및 고화질의 서비스를 제공하는 방식을 벗어나 전방위 시점에서 몰입형 서비스를 제공할 수 있는 발판이 되었으며, 이를 방송 및 통신환경에서 제공하기 위한 기술 개발 및 표준화에 대한 노력이 진행되고 있다. VR미디어는 사용자의 움직임 자유도 지원범위에 따라 3DoF(Degrees of Freedom) 및 6DoF 360VR로 분류되어 단계별 표준화가 추진 중에 있으나, 본 고에서는 3DoF VR 미디어를 중심으로 이를 서비스하기 위한 각 표준화 단체의 동향을 살펴본다.

• Journal of the Korean Society for Precision Engineering
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• v.10 no.3
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• pp.107-116
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• 1993

In the design and operation of robitic arm with flexible links, the equation of motion are required to exactly model the interaction between rigid body motion and elastic motion and to be formulated efficientlyl. In this paper, the flexible link is represented by applying the D-H rigid link representation method to measure the elestic deformation. And the equations of motion of robotic arm, which are configured by the generalized coordinates of elastic and rigid degrees of freedom, are formulated from the principle of virtual power. Dynamic characteristics due to elastic deformation of each link are obtained by using F. E. M to model complex shaped link acurately and by eliminating elastic modes of higher order that do not largely affect motion to reduce the number of elastic degrees of freedom. Also presented is the result of simulation of flexible robotic arms whose joints are controlled by direct or PD control.

• Journal of Biomedical Engineering Research
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• v.40 no.3
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• pp.116-124
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• 2019

The rehabilitation training robots for treating the upper limbs of stroke patients were mainly focused on the upper proximal treatment of it, but recently studies of the distal parts of the upper limbs for rehabilitation of the hand is making some progress even though it is still a small number so far. In this paper, we present the hand robot for the rehabilitation training of stroke patients that is the fingertip contact-typed mechanism, and it has also equipped with the wrist rehabilitation unit to be worked like human hand that enables any movements through mutual cooperation by fingers while picking up or grasping objects. The robot that is presented for this purpose supports the movement of fingers with 5-DoF and the wrist with 3-DoF that moves independently, and operates with a structure that allows the joints of the wrist and fingers to be collaborated organically together to each other. Also, hereby the simulation and evaluation test on its robot mechanism are performed to ensure that fingers with 5-DoF and the wrist with 3-DoF of the serial kinematical mechanism are designed to comply with or exceed ROM for ADL.

• Journal of Broadcast Engineering
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• v.27 no.2
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• pp.216-227
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• 2022

The MPEG-I (Immersive) group is working on a standardization project for immersive video that provides 6 degrees of freedom (6DoF). The MPEG Immersion Video (MIV) standard technology is intended to provide limited 6DoF based on depth map-based image rendering (DIBR) technique. Many efficient coding methods have been suggested for MIV, but efficient transmission strategies have received little attention in MPEG-I. This paper proposes group-based adaptive rendering method for immersive video streaming. Each group can be transmitted independently using group-based encoding, enabling adaptive transmission depending on the user's viewport. In the rendering process, the proposed method derives weights of group for view synthesis and allocate high quality bitstream according to a given viewport. The proposed method is implemented through the Test Model for Immersive Video (TMIV) test model. The proposed method demonstrates 17.0% Bjontegaard-delta rate (BD-rate) savings on the peak signalto-noise ratio (PSNR) and 14.6% on the Immersive Video PSNR(IV-PSNR) in terms of various end-to-end evaluation metrics in the experiment.

• Advances in aircraft and spacecraft science
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• v.5 no.1
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• pp.1-19
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• 2018

The present work shows many aspects concerning the use of a numerical wave-based methodology for the computation of the structural response of periodic structures, focusing on cylinders. Taking into account the periodicity of the system, the Bloch-Floquet theorem can be applied leading to an eigenvalue problem, whose solutions are the waves propagation constants and wavemodes of the periodic structure. Two different approaches are presented, instead, for computing the forced response of stiffened structures. The first one, dealing with a Wave Finite Element (WFE) methodology, proved to drastically reduce the problem size in terms of degrees of freedom, with respect to more mature techniques such as the classic FEM. The other approach presented enables the use of the previous technique even when the whole structure can not be considered as periodic. This is the case when two waveguides are connected through one or more joints and/or different waveguides are connected each other. Any approach presented can deal with deterministic excitations and responses in any point. The results show a good agreement with FEM full models. The drastic reduction of DoF (degrees of freedom) is evident, even more when the number of repetitive substructures is high and the substructures itself is modelled in order to get the lowest number of DoF at the boundaries.

• Journal of Broadcast Engineering
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• v.24 no.7
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• pp.1209-1220
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• 2019

The demand for virtual reality (VR) is rapidly increasing. Providing the immersive experience requires much operation and many data to transmit. For example, a 360-degree video (360 video) with at least 4K resolution is needed to offer an immersive experience to users. Moreover, the MPEG-I group defined three degrees of freedom plus (3DoF+), and it requires the transmission of multiview 360 videos simultaneoulsy. This could be a burden for the VR streaming system. Accordingly, in this work, a bitrate-saving method using projection conversion is introduced, along with experimental results for streaming 3DoF+ 360 video. The results show that projection conversion of 360 video with 360lib shows a Bjontegaard delta bitrate gain of as much as 11.4%.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.2
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• pp.273-284
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• 2015

The feasibility conditions of interference alignment (IA) are analyzed for reverse duplex systems, in which one cell operates as downlink (DL) while the other cell operates as uplink (UL) assuming one-sid base station (BS) cooperation. Under general multiple-input and multiple-output (MIMO) antenna configurations, a necessary condition and a sufficient condition for one-shot linear IA are established, i.e., linear IA without symbol or time extension. In several example networks, optimal sum degrees of freedom (DoF) is characterized by the derived necessary condition and sufficient condition. For some special class of networks, a sufficient condition is established in a more compact expression, which also yields the necessary and sufficient condition. Simulation results demonstrate that the proposed IA does not only achieve larger DoF but also significantly improves the sum rate in the practical signal-to-noise ratio (SNR) regime.