• ETRI Journal
• /
• 제43권3호
• /
• pp.414-426
• /
• 2021

In the task of data routing in Internet of Things enabled volatile underwater environments, providing better transmission and maximizing network communication performance are always challenging. Many network issues such as void holes and network isolation occur because of long routing distances between nodes. Void holes usually occur around the sink because nodes die early due to the high energy consumed to forward packets sent and received from other nodes. These void holes are a major challenge for I-UWSANs and cause high end-to-end delay, data packet loss, and energy consumption. They also affect the data delivery ratio. Hence, this paper presents an energy efficient watchman based flooding algorithm to address void holes. First, the proposed technique is formally verified by the Z-Eves toolbox to ensure its validity and correctness. Second, simulation is used to evaluate the energy consumption, packet loss, packet delivery ratio, and throughput of the network. The results are compared with well-known algorithms like energy-aware scalable reliable and void-hole mitigation routing and angle based flooding. The extensive results show that the proposed algorithm performs better than the benchmark techniques.

• Journal of Power Electronics
• /
• 제19권4호
• /
• pp.1034-1044
• /
• 2019

In medium-voltage and high-voltage high-power converters, the switching devices need to operate at a low switching frequency to reduce power loss and increase the power capacity. This increases the delay of the signal sampling and PWM. It also makes the cross-couplings of the d-q current components more severe. In addition, the LCL filter has three cross-coupling loops and is prone to resonance. In order to solve these problems, this paper establishes a complex vector model of an LCL type grid-connected converter. Based on this model, two multiple decoupling current control strategies with passive damping / notch damping are proposed for the LCL type grid-connected converter. The proposed strategies can effectively eliminate the cross-couplings of the converter, achieve independent control of the d-q current components, expand the stable region and suppress the resonance of the LCL filter. Simulation and experimental results verify the correctness of the theoretical analysis and the feasibility of the proposed strategies.

• ETRI Journal
• /
• 제41권5호
• /
• pp.637-647
• /
• 2019

Separating highly correlated users can reduce the loss caused by spatial correlation (SC) in multiuser multiple-input multiple-output (MU-MIMO) systems. However, few accurate analyses of the loss caused by SC have been conducted. In this study, we define signal-to-interference-plus-noise ratio (SINR) loss to characterize it in multiuser multiple-input single-output (MU-MISO) systems, and use coefficient of correlation (CoC) to describe the SC between users. A formula is deduced to show the accurate relation between SINR loss and CoC. Based on this relation, we propose a user selection method that utilizes CoC to minimize the average SINR loss of users in massive MU-MISO systems. Simulation results verify the correctness of the relation and show that the proposed user selection method is very effective at reducing the loss caused by SC in massive MU-MISO systems.

• Nuclear Engineering and Technology
• /
• 제54권8호
• /
• pp.3154-3165
• /
• 2022

During a loss-of-coolant accident (LOCA) in the pressurized water reactor (PWR), there is a possibility that high temperature and internal pressure of the fuel rods lead to ballooning of the cladding, which causes a partial blockage of flow area in a subchannel. Such flow blockage would influence the core coolant flow, thus affecting the core heat transfer during a reflooding phase and subsequent severe accident. However, most of the system analysis codes simulate the accident process based on the assumed channel blockage ratio, resulting in the fact that the simulation results are not consistent with the actual situation. This paper integrates the developed core Fuel Rod Thermal-Mechanical Behavior analysis (FRTMB) module into the self-developed severe accident analysis code ISAA. At the same time, the existing flow blockage model is improved to make it possible to simulate the change of flow distribution due to fuel rod deformation. Finally, the ISAA-FRTMB is used to simulate the QUENCH-LOCA-0 experiment to verify the correctness and effectiveness of the improved flow blockage model, and then the effect of clad ballooning on core heat transfer and subsequent parts of core degradation is analyzed.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제15권11호
• /
• pp.4224-4243
• /
• 2021

Cognitive radio (CR) is a feasible intelligent technology and can be used as an effective solution to spectrum scarcity and underutilization. As the key function of CR, cooperative spectrum sensing (CSS) is able to effectively prevent the harmful interference with primary users (PUs) and identify the available spectrum resources by exploiting the spatial diversity of multiple secondary users (SUs). However, the open nature of the cognitive radio networks (CRNs) framework makes CSS face many security threats, such as, the malicious user (MU) launches Byzantine attack to undermine CRNs. For this aim, we make an in-depth analysis of the motive and purpose from the MU's perspective in the interweave CR system, aiming to provide the future guideline for defense strategies. First, we formulate a dynamic Byzantine attack model by analyzing Byzantine behaviors in the process of CSS. On the basis of this, we further make an investigation on the condition of making the fusion center (FC) blind when the fusion rule is unknown for the MU. Moreover, the throughput and interference to the primary network are taken into consideration to evaluate the impact of Byzantine attack on the interweave CR system, and then analyze the optimal strategy of Byzantine attack when the fusion rule is known. Finally, theoretical proofs and simulation results verify the correctness and effectiveness of analyses about the impact of Byzantine attack strategy on the throughput and interference.

• Structural Engineering and Mechanics
• /
• 제85권5호
• /
• pp.693-707
• /
• 2023

In order to deeply reveal the working mechanism of ultra-high performance concrete (UHPC) filled steel tubular columns (UHPCFSTs) under cyclic loading, a three-dimension (3D) macro-mesoscale finite element (FE) model was established considering the randomness of steel fibers and the damage of UHPC. Model correctness and reliability were verified based on the experimental results. Next, the whole failure process of UHPC reinforced with steel fibers, passive confinement effect and internal force distribution laws were comprehensively analyzed and discussed. Finally, a simplified and practical method was proposed for predicting the ultimate bending strengths of UHPCFSTs. It was found that the non-uniform confinement effect of steel tube occurred when the drift ratio exceeded 0.5%, while the confining stress increased then decreased afterwards. There was preferable synergy between the steel tube and UHPC until failure. Compared with experimental results, the ultimate bending strengths of UHPCFSTs were undervalued by the current code provisions such as AISC360-10, EC4 and GB50936 with computed mean values (MVs) of 0.855, 0.880 and 0.836, respectively. The proposed practical method was highly accurate, as evidenced by a mean value of 1.058.

• 한국인터넷방송통신학회논문지
• /
• 제13권3호
• /
• pp.141-150
• /
• 2013

시뮬레이션은 애드혹 네트워크 프로토콜 검증에 유용한 기법이지만 네트워킹 및 통신 환경에 대한 가정과 간소화로 인하여 실제 환경에서도 제안된 프로토콜이 요구 성능을 획득할 수 있는지 보여주기 어렵다. 따라서, 애드혹 네트워크가 현실적으로 획득할 수 있는 성능에 대한 이해를 위해서는 실제 시험 환경을 이용한 실험이 필요하며 이를 위해서는 많은 시스템 구성요소의 상호 작용을 이해하여야 한다. 본 논문에서는 건물 안에서 고속 영상 데이터 전송을 위한 실제 애드혹 네트워크 테스트베드를 구현하여 실제 네트워크 성능을 측정한다. AODV-UU를 이용하여 구축된 멀티홉 애드혹 네트워크는 Throughput, PDR, 종단간 지연 측면에서 저용량 영상데이터 전송을 위하여 요구되는 성능을 제공할 수 있음을 보인다.

• 한국콘텐츠학회:학술대회논문집
• /
• 한국콘텐츠학회 2003년도 추계종합학술대회 논문집
• /
• pp.204-209
• /
• 2003

도심지역 이동통신에 있어서 전파특성을 정확히 예측ㆍ분석하는 것은 통신 서비스영역의 결정, 최적 기지국 선정, 셀 설계 등에 있어 매우 중요한 사안이다. 이러한 분석에 있어서 사용되는 안테나의 종류, 지향각, 지형지물의 형태에 따라 변화하는 전파예측모델이 정확히 제시되어야 한다. 또한, 선택된 지역에 대하여 셀 설계를 수행하기 전에 기존에 제시된 다양한 모델 중 유사성을 가진 모델을 분석하고 그 파라미터를 측정하여 평가하는 작업을 진행하여야 한다. 본 논문에서는 도심지역의 지형 및 장애물 등을 고려한 전파예측모델을 제안하고 그에 따르는 파라미터를 추출하여 분석된 전파환경에 적용하고 그 전파특성을 분석하기 위한 시뮬레이션을 실시하였다. 이러한 과정을 통하여 우리는 주어진 전파환경에 적절한 기지국의 위치, 지형고도, 안테나의 종류 및 높이 등 핵심적인 파라미터들을 원하는 정확도로 추출하였다.

• 대한전자공학회논문지SD
• /
• 제44권2호
• /
• pp.86-94
• /
• 2007

네트워크-온-칩(NoC, network-on-chip) 기술은 SoC (system-on-a-chip) 설계에서 증가되는 온칩 통신의 복잡성을 해결하고 높은 확장성을 제공할 수 있는 기술이다. NoC를 이용한 설계는 많은 수의 IP들과 통신 네트워크들을 사용하기 때문에 동작이 복잡하고 설계 공간이 커서 많은 전력을 소모 한다. 그러나 기존의 분석적인 방법은 NoC응용의 큰 설계 공간 및 동작의 복잡성에 비해 상대적으로 간소화된 모델을 사용하여 현실적인 설계요소를 반영하지 못하거나 복잡한 시뮬레이션에 따른 많은 노력 및 시간 요구로 사용에 많은 제약이 있었다. 따라서 본 논문에서는 현실적이고 정확한 NoC의 전력 소모 분석을 위해 FPGA 프로토타입(prototype)을 개발하고 이에 대한 전력 소모를 분석을 할 수 있는 싸이클별 전력 소모 측정 기법 및 도구를 소개한다. 또한 사례 연구로서 NoC기술을 이용한 JPEG 압축기를 구현하고 이에 대한 전력 소모를 분석하여 그 효용성을 입증한다.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제6권6호
• /
• pp.1522-1545
• /
• 2012

Call admission control (CAC) plays an important role in mobile cellular network to guarantee the quality of service (QoS). In this paper, a dynamic hybrid CAC scheme with integrated cutoff priority and handoff queue for mobile cellular network is proposed and some performance metrics are derived. The unique characteristic of the proposed CAC scheme is that it can support any number of service types and that the cutoff thresholds for handoff calls are dynamically adjusted according to the number of service types and service priority index. Moreover, timeouts of handoff calls in queues are also considered in our scheme. By modeling the proposed CAC scheme with a one-dimensional Markov chain (1DMC), some performance metrics are derived, which include new call blocking probability ($P_{nb}$), forced termination probability (PF), average queue length, average waiting time in queue, offered traffic utilization, wireless channel utilization and system performance which is defined as the ratio of channel utilization to Grade of Service (GoS) cost function. In order to validate the correctness of the derived analytical performance metrics, simulation is performed. It is shown that simulation results match closely with the derived analytic results in terms of $P_{nb}$ and PF. And then, to show the advantage of 1DMC modeling for the performance analysis of our proposed CAC scheme, the computing complexity of multi-dimensional Markov chain (MDMC) modeling in performance analysis is analyzed in detail. It is indicated that state-space cardinality, which reflects the computing complexity of MDMC, increases exponentially with the number of service types and total channels in a cell. However, the state-space cardinality of our 1DMC model for performance analysis is unrelated to the number of service types and is determined by total number of channels and queue capacity of the highest priority service in a cell. At last, the performance comparison between our CAC scheme and Mahmoud ASH's scheme is carried out. The results show that our CAC scheme performs well to some extend.