• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권8호
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• pp.3904-3917
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• 2017

IP multimedia subsystem (IMS) is an open standardized architecture for delivering multimedia service over IP network in a route-agnostic manner. With the increasing popularity of conversational class service, the delivery of a traffic flow with a certain bandwidth demand over a single network path is either not possible or not cost-effective. Multipath transmission is considered to be a promising solution to provide high-quality delivery service. This paper proposes a software defined service overlay network (SDSON) based multipath transmission framework for IMS, which is complementary to existing network architecture. The framework transforms original two-party session negotiation into three-party session negotiation that supports participants to negotiate multipath transmission capacity and path information by signaling message. Based on existing IETF standards, SIP and SDP are scalable to support these functions. Finally, the proposed framework is fully implemented on open source platform and examined by experiments. Experimental results show that multipath-enabled IMS is an effective way to improve the delivery performance of conversational class service.

• 한국시뮬레이션학회논문지
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• 제19권2호
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• pp.137-145
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• 2010

본 연구는 LBS(Location Based Service) 기반에 5.8-5.9Ghz RSU를 이용한 실시간 교통 시스템(RTS)에 관한 연구이다. 제안된 LBI(Location based Broadcast system on ITS)는 방송국 T-DMB 시스템과 ITS 기반 실시간 교통 시스템을 융합하고, 노변기지국(RSU:Road Side Unit)을 중심으로 제공되는 운전자를 위한 지역정보 기반 서비스이다. 본 방송국과 ITS의 융합은 IP기반 양방향 통신은 IP 기반으로 이루어지며, RSU를 이용하여 차량 위치의 파악을 통한 LBS(Location Based Service)를 제공한다. 지역 매크로 관리자(LMM)과 지역 방송국과 상호 정보 교환으로 정보 전달의 실시간성과 서비스의 다양성을 제공할 수 있었다. 기존 실시간 교통시스템에서 전송 범위(transmission area)의 한계와 기존 T-DMB의 단방향 서비스 문제를 상호 보완하였다. 이를 통해 개별 운전자의 실시간 양방향 서비스를 제공할 수 있었다. 또한 운전자들에게 실시간 교통 및 지역정보를 제공함으로써 분산효과와 서비스 확대를 제시하였다. 마지막으로 연구소 주변에 테스트 베드 구축과 구현으로 검증하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권1호
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• pp.21-40
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• 2018

In this paper, we propose the distributed robust beamforming design scheme in cognitive two-way amplify-and-forward (AF) relay networks with imperfect channel state information (CSI). Assuming the CSI errors follow a complex Gaussian distribution, the objective of this paper is to design the robust beamformer which minimizes the total transmit power of the collaborative relays. This design will guarantee the outage probability of signal-to-interference-plus-noise ratio (SINR) beyond a target level at each secondary user (SU), and satisfies the outage probability of interference generated on the primary user (PU) above the predetermined maximum tolerable interference power. Due to the multiple CSI uncertainties in the two-way transmission, the probabilistic constrained optimization problem is intractable and difficult to obtain a closed-form solution. To deal with this, we reformulate the problem to the standard form through a series of matrix transformations. We then accomplish the problem by using the probabilistic approach based on two sorts of Bernstein-type inequalities and the worst-case approach based on S-Procedure. The simulation results indicate that the robust beamforming designs based on the probabilistic method and the worst-case method are both robust to the CSI errors. Meanwhile, the probabilistic method can provide higher feasibility rate and consumes less power.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.234.2-234.2
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• 2015

Recently, the electromagnetically-induced transparency (EIT)-like effect in metamaterials has attracted enormous interest. Metamaterial analogs of EIT enable promising applications in slow-light devices, low-loss metamaterial, quantum optics, and novel sensors. In this work, we experimentally and numerically studied a bilayer metamaterial for controllable EIT-like spectral response at microwave frequencies. Bilayer metamaterial consists of two snake-shape resonators (SSRs) with one and two bars. The transmission spectra were measured in a frequency range of 4 - 8 GHz in an anechoic chamber at normal incidence. It is found that two SSRs in the metamaterial are activated in bright modes, and the coupling between two bright modes leads to the EIT-like effect, which results in the enhanced transmission at 5.61 GHz. Furthermore, we confirm that the EIT-like feature could be controlled by adjusting the geometric parameters of metamaterial structure. Our work provides a way to tunable EIT-like effect and various potential applications including filters, sensors, and other microwave devices.

• Journal of information and communication convergence engineering
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• 제9권6호
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• pp.753-757
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• 2011

The possibility of implementing nonuniform residual dispersion per span (RDPS) in optical links with net residual dispersion (NRD) controlled by precompensation and postcompensation for 960 Gbps WDM transmissions is studied and discussed. The fiber optic communication links investigated in this paper consist of inline dispersion management (DM) for each fiber spans and optical phase conjugator (OPC) at mid-way of total transmission length in order to compensate for WDM signal distortions due to group velocity dispersion (GVD) and nonlinearities. It is confirmed that the effect of nonuniform RDPS distribution on system performance is not significant. It is also confirmed that the optimal NRD is obtained to be one of two values of +10 ps/nm or -10 ps/nm, which depend on the deciding of NRD controlled by precompensation or postcompensation, and the exact RDPS configurations. The effective NRD ranges resulting eye opening penalty (EOP) below 1 dB are independent on the exact RDPS distribution for relative low launch power. Therefore, results show the possibility of implementing the flexible optical links to expand network construction for WDM transmission of high bit-rate capability.

• 대한전기학회논문지:시스템및제어부문D
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• 제55권1호
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• pp.24-30
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• 2006

The Controller Area Network (CAN) is being widely used for real-time control application and small-scale distributed computer controller systems. When the stuff bits are generated by bit-stuffing mechanism in the CAN network, it causes jitter including variations in response time and delay In order to eliminate this jitter, stuff bits must be controlled to minimize the response time and to reduce the variation of data transmission time. This paper proposes the method to reduce the stuff bits by restriction of available identifier and bit mask using exclusive OR operation. This da manipulation method are pretty useful to the real-time control strategy with respect to performance. However, the CAN may exhibit unfair behavior under heavy traffic conditions. When there are both high and low priority messages ready for transmission, the proposed precedence priority filtering method allows one low priority message to be exchanged between any two adjacent higher priority messages. In this way, the length of each transmission delays is upper bounded. These procedures are implemented as local controllers for the ISHURO(Inha Semvung Humanoid Robot).

• Journal of Information Processing Systems
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• 제6권1호
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• pp.53-66
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• 2010

The energy efficiency is a key design issue to improve the lifetime of the underwater sensor networks (UWSN) consisting of sensor nodes equipped with a small battery of limited energy resource. In this paper, we apply a hexagon tessellation with an ideal cell size to deploy the underwater sensor nodes for two-dimensional UWSN. Upon this setting, we propose an enhanced hybrid transmission method that forwards data packets in a mixed transmission way based on location dependent direct transmitting or uniform multi-hop forwarding. In order to select direct transmitting or uniform multi-hop forwarding, the proposed method applies the threshold annulus that is defined as the distance between the cluster head node and the base station (BS). Our simulation results show that the proposed method enhances the energy efficiency compared with the existing multi-hop forwarding methods and hybrid transmission methods

• 전자공학회논문지
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• 제53권1호
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• pp.79-85
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• 2016

최근 그린 무선통신 서비스가 주목 받으면서 가시광통신에 대한 연구가 활발하게 이루어지고 있다. 현재 가시광통신은 주로 송신에 LED를 이용하고, 수신에 PD(Photo Diode)를 사용하여 통신을 한다. 그러나 이러한 시스템 방식은 응용에 한계가 있다. 본 논문에서 제안 개발된 시스템의 주요한 특징과 기여도는 다음과 같다. 첫째, LED만을 이용하여 송수신을 하는 LED-to-LED 가시광통신 시스템이며, 아날로그 스위치로 송수신회로를 교체하는 방식을 사용한다. 둘째, 단방향 통신과 양방향 통신을 함께 지원한다. 단 방향 통신은 멀티 홉을 지원한다. 성능평가 환경은 보통의 형광등이 비추는 곳에서 실험을 하였다. 단 방향 통신은 거리와 보드레이트를 변화 시키며 전송 성공여부를 측정 하였고, 양방향 통신은 거리에 따라 양방향 통신 성공여부를 확인 하였다. 본 논문에서 제안 설계한 LED-to-LED 가시광통신 시스템을 이용하여 더 많은 분야에 응용 할 수 있을 것으로 기대 된다.

• 한국음향학회지
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• 제32권4호
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• pp.361-368
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• 2013

진동하는 현의 성질을 나타내는 방법으로 반대 방향으로 진행하는 파가 현과 전송선로에 존재한다는 사실에 기초하여 현은 전송선로에 비유되어왔다. 이러한 비유에서 현의 강역(rigid end)과 변위는 각각 전송선로의 개방회로와 전류로 나타내어졌다. 그러나, 본 연구에서 강역과 변위는 각각 단락회로와 전압에 해당됨이 전송선로의 이론으로부터 밝혀졌고 이를 회로시뮬레이션으로 확인하였다. 이러한 발견에 기초하여 전송선로, 구분적 선형 전류원, 스위치들로 구성된 전송선로 기반 탄현 모델을 제안하였다. 임의로 선택된 지점에서의 전압과 전송선로 끝 극소 부분 양단에서 계산된 전압이 현의 성질을 지배하는 파동방정식의 차분형식(difference form)으로 구한 해당 지점에서 변위와 강역에서의 힘과 일치함을 보임으로서 제안한 모델이 정당함을 증명하였다. 또한, 제안된 모델의 현악기 및 관악기 모델링의 적용성을 제시하였다.

• Progress in Superconductivity
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• 제11권2호
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• pp.106-111
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• 2010

Sapphire resonators with $YBa_2Cu_3O_{7-\delta}$ (YBCO) endplates have provided a way to realize extremely high quality factor due to the extremely low dielectric loss of sapphire and conductive loss of YBCO films, which enables to measure the low surface resistance of superconductor films at microwave frequencies. We present microwave properties of HTS sapphire resonators designed for measuring the surface resistance of HTS films at millimeter-wave frequencies by using the two-resonance mode dielectric resonator method. Despite enhanced surface resistance ($R_S$) of YBCO films due to the quadratic frequency dependence of the $R_S$, the unloaded quality factor ($Q_0$) of the $TE_{021}$ mode sapphire resonator still appears to be well above $1\;{\times}\;10^6$ at a mm-wave frequency of 38 GHz at 10 K. However, it appears that the $TE_{012}$ mode $Q_0$ is unexpectedly low despite that the corresponding resonance peak looks uncoupled with parasitic modes. We discuss possible reasons for the unexpected results using the surface resistance at the $TE_{021}$, $TE_{012}$, and $TE_{011}$ mode frequencies.