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An Efficient Method Based on DIBR for 3DTV Service Over T-DMB
Sunghyun Choi,Youngjin Oh,Cheolkon Jung,Joong Kyu Kim,Gwangsoon Lee,Jinwoong Kim 대한전자공학회 2009 ITC-CSCC :International Technical Conference on Ci Vol.2009 No.7
In this paper, we present a depth-image-based rendering (DIBR) technique for three-dimensional television (3DTV) service over T-DMB. Because of very limited bandwidth for additional data in 3DTV service in T-DMB, we propose a new method that requires only one virtual view generating a real-world scene. Therefore, we can reduce amount of calculation as well as processing time on auto-stereoscopic 3D display.
Activity Probability-Based Performance Analysis and Contention Control for IEEE 802.11 WLANs
Choi, Junsu,Byeon, Seongho,Choi, Sunghyun,Lee, Kwang Bok IEEE Computer Society 2017 IEEE TRANSACTIONS ON MOBILE COMPUTING Vol.16 No.7
<P>In this paper, we develop a contention window (CW) control scheme for practical IEEE 802.11 wireless local area networks (WLANs) that have node heterogeneity in terms of the traffic load, transmission rate, and packet size. We introduce activity probability, i.e., the probability that a node contends for medium access opportunities at a given time. We then newly develop a performance analysis model that enables analytic estimation on the contention status including the collision probability, collision time, back-off time, and throughput with comprehensive consideration of node heterogeneity. Based on the newly developed model, we derive the theoretically ideal contention status, and develop a CW control scheme that achieves the ideal contention status in an average sense. We perform extensive NS-3 simulations and real testbed experiments for evaluation of both the proposed performance analysis model and CW control scheme. The results show that the proposed model provides accurate prediction on the contention status, and the proposed CW control scheme achieves considerable throughput improvement compared to the existing schemes which do not comprehensively consider node heterogeneity.</P>
Sounding Node Set and Sounding Interval Determination for IEEE 802.11ac MU-MIMO
Choi, Junsu,Choi, Sunghyun,Lee, Kwang Bok IEEE 2016 IEEE Transactions on Vehicular Technology VT Vol.65 No.12
<P>In this paper, we propose a sounding control scheme for IEEE 802.11ac multiuser multiple-input multiple-output (MU-MIMO). The proposed scheme comprehensively considers the long-term characteristics of a network environment, including the downlink traffic loads and channel coherence times of wireless links, and jointly determines the sounding node set and sounding interval to maximize the long-term expected MU-MIMO throughput gain in consideration of sounding overhead. To this end, we analytically formulate an MU-MIMO throughput gain maximization problem, considering the network environment and sounding overhead. We conduct MIMO channel measurement in practical wireless local area network (WLAN) environments and evaluate the performance of the proposed scheme by employing the real channel data traces. Simulation results verify that the proposed scheme adaptively determines the sounding node set and sounding interval, according to the network environment, and outperforms the existing scheme, which considers the channel coherence times only.</P>
Choi, Sunghyun,Oh, Jae Hoon,Kim, Hyeseon,Nam, So Hee,Shin, Jeehae,Park, Jong-Sang Springer US 2015 Cellular and molecular neurobiology Vol.35 No.7
<P>Alzheimer’s disease (AD) is an age-related disorder that causes a loss of brain function. Hyperphosphorylation of tau and the subsequent formation of intracellular neurofibrillary tangles (NFTs) are implicated in the pathogenesis of AD. Hyperphosphorylated tau accumulates into insoluble paired helical filaments that aggregate into NFTs; therefore, regulation of tau phosphorylation represents an important treatment approach for AD. Heat shock protein 27 (Hsp27) plays a specific role in human neurodegenerative diseases; however, few studies have examined its therapeutic effect. In this study, we induced tau hyperphosphorylation using okadaic acid, which is a protein phosphatase inhibitor, and generated a fusion protein of Hsp27 and the protein transduction domain of the HIV Tat protein (Tat-Hsp27) to enhance the delivery of Hsp27. We treated Tat-Hsp27 to SH-SY5Y neuroblastoma cells for 2 h; the transduction level was proportional to the Tat-hsp27 concentration. Additionally, Tat-Hsp27 reduced the level of hyperphosphorylated tau and protected cells from apoptotic cell death caused by abnormal tau aggregates. These results reveal that Hsp27 represents a valuable protein therapeutic for AD.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1007/s10571-015-0199-1) contains supplementary material, which is available to authorized users.</P>
IEEE 802.11 MAC-Level FEC scheme with retransmission combining
Choi, Sunghyun,Choi, Youngkyu,Lee, Inkyu IEEE 2006 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.5 No.1
In this paper, we evaluate and enhance the performance of a Forward Error Correction (FEC) scheme for IEEE 802.11 Medium Access Control (MAC). A novel retransmission combining technique is proposed to enhance the performance of the MAC-level FEC scheme.,We also identify the problem with the IEEE 802.11a physical (PHY) layer when it is used with the MAC-level FEC. A new PHY frame format, backward compatible with the original format, is proposed to resolve the problem. Finally, we analytically evaluate the error performance of the MAC-level FEC, and its enhanced performance via retransmission combining and new 802.11a PHY frame format in AWGN environment. Additionally, we present and discuss the results from simulations using TCP/UDP traffic in more realistic channel environments.
Overview of Emerging IEEE 802.11 Protocols for MAC and Above
Sunghyun Choi 에스케이텔레콤 (주) 2003 Telecommunications Review Vol.0 No.-
During the last few years, the IEEE 802.11 Wireless LAN (WLAN) has become a dominant technology for the (indoor) broadband wireless networking. Along with its success, there have been demands to enhance the performance of the 802.11. To meet such needs, the IEEE 802.11 Working Group (WG) has been developing new protocols to amend the existing protocols. In this paper, we overview the emerging protocols of the IEEE 802.11 WLAN for the medium access control (MAC) layers and above. These include 802.11e for quality-of-service (QoS), 802.11f for Inter-Access Point Protocol (IAPP), 802.11h for spectrum management at 5GHz, 802.11i for security enhancement, 802.11k for radio resource measurement, and finally 802.11m for higher throughput.
Emerging IEEE 802.11e WLAN for Quality-of-Service (QoS) Provisioning
Sunghyun Choi 에스케이텔레콤 (주) 2002 Telecommunications Review Vol.12 No.6
The IEEE 802.11e Medium Access Control (MAC) is an emerging supplement to the IEEE 802.11 Wireless Local Area Network (WLAN) standard to support Quality-of-Service (QoS). The 802.11e MAC is based on both controlled and contention-based channel access mechanisms. The controlled channel access is based on the poll-and-response protocol, and can be used for the parameterized and rigid QoS support. On the other hand, the contention-based channel access is based on the carrier-sense multiple access with collision avoidance (CSMA/CA), and can be used for the prioritized and probabilistic QoS support. We first introduce the characteristics of the 802.11e based on the up-todate draft. Then, we evaluate the contention-based channel access, called enhanced distributed coordination function (EDCF), which will be a mandatory part of 802.11e, in comparison with the 802.11 legacy MAC. The EDCF provides differentiated channel access to the frames with different user priorities. Through our simulation study, with realistic home networking traffic scenarios, the 802.11e EDCF is found to provide the probabilistic QoS very well as was designed.