• 한국정보통신학회논문지
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• 제11권9호
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• pp.1665-1671
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• 2007

무선 Ad-hoc 네트워크는 기지국이나 중앙 집중관리가 없는 영역에서 다수의 노드들 간에 무선데이터 통신 연결이 자율적으로 설정되는 네트워크이다. Ad-hoc 네트워크는 노드의 이동과 전원의 제약 때문에 네트워크 위상(network topology)이 자주 변화할 수 있다. 라우팅 경로를 찾는 과정에서 가장 신뢰성이 있는 경로를 선택하는 것은 Ad-hoc 네트워크 성능을 향상시키기 위해서 아주 중요하다. 본 연구에서, 우리는 수신신호 세기의 변이를 감시해서 AODV 기반의 강화된 라우팅 프로토콜을 제안하였다. 노드의 이동성과 경로의 흡수로 구성된 새로운 매트릭 함수는 라우팅 경로 결정에 이용된다. NS-2를 이용한 폭넓은 실험에서, 제안된 라우팅 기법의 성능은 AODV 프로토콜에 비하여 향상되었다.

• 한국정보통신학회논문지
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• 제12권9호
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• pp.1696-1702
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• 2008

한정된 용량의 배터리에 의존하는 MANET(Mobile Ad-hoc Network)에서는 에너지 효율을 높이기 위한 다양한 클러스터링 기법과 라우팅 알고리즘이 연구되고 있다. 일반적으로 무선 Ad-hoc 네트워크에서는 LEACH와 같은 클러스터 기반의 동적 라우팅 알고리즘이 많이 사용된다. 본 논문에서는 클러스터 내의 각 노드가 가지는 속성을 고려하여 클러스터를 생성하고 노드를 관리하는 TICC(Time Interval Clustering Control) 알고리즘 기법을 제안한다. 제안한 TICC은 노드의 속성 중의 하나인 베터리 값 즉 에너지 값으로 노드의 에너지 레벨을 분류한다. 그리고 분류된 에너지 레벨에 대응하는 시간차 컨트롤 기법을 이용하여 클러스터링 과정을 수행하거나 노드들을 관리한다. 특히 제안한 TICC 알고리즘은 MANET에서 클러스터의 생성, 재생성, 진입 노드 및 이탈 노드의 검출과 관리를 통해 노드의 에너지 관리 효율을 향상시키고 클러스터의 Lifetime을 증가시키는 결과를 보여주었다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2009년도 추계학술대회
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• pp.1038-1041
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• 2009

온도, 습도, 조도 또는 토양 센서 등을 탑재한 무선 센서 노드들을 네트워크로 구성하여 자연 환경 정보를 획득하고 분석하여 다양하게 활용하고 있다. 이러한 무선 센서 네트워크는 저전력 무선트랜시버를 탑재한 다수의 노드들이 근거리 무선 통신과 멀티-홉 기법으로 구성된다. 따라서 무선센서 네트워크를 통하여 수집된 데이터의 특징은 한정된 범위 내에 밀집된 노드들로부터 얻어진다는 것이다. 그러나 넓은 범위에 흩어져있는 무선 센서 노드들로부터 데이터를 얻기 위해서는 장거리로 데이터를 송신할 수 있도록 고전력을 소비하는 무선 트랜시버를 사용하거나 중계 노드를 많이 필요로 하여, 무선 센서 네트워크 가지고 있는 장점인 저전력과 저비용이라는 특징이 희석된다. 본 논문에서는 이러한 문제를 해결하기 위하여 넓게 산재되어 있는 각각의 센서 네트워크 그룹 들을 순회하여 데이터를 수집하는 자율 주행 로봇을 이용한 환경 모니터링 시스템을 제안한다.

• Smart Structures and Systems
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• 제6권5_6호
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• pp.595-618
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• 2010

This paper describes the application of a wireless sensor network to a 31 meter-tall medieval tower located in the city of Trento, Italy. The effort is motivated by preservation of the integrity of a set of frescoes decorating the room on the second floor, representing one of most important International Gothic artworks in Europe. The specific application demanded development of customized hardware and software. The wireless module selected as the core platform allows reliable wireless communication at low cost with a long service life. Sensors include accelerometers, deformation gauges, and thermometers. A multi-hop data collection protocol was applied in the software to improve the system's flexibility and scalability. The system has been operating since September 2008, and in recent months the data loss ratio was estimated as less than 0.01%. The data acquired so far are in agreement with the prediction resulting a priori from the 3-dimensional FEM. Based on these data a Bayesian updating procedure is employed to real-time estimate the probability of abnormal condition states. This first period of operation demonstrated the stability and reliability of the system, and its ability to recognize any possible occurrence of abnormal conditions that could jeopardize the integrity of the frescos.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권7호
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• pp.3412-3432
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• 2019

Recent advances in radio frequency (RF) power transfer provide a promising technology to power sensor nodes. Adoption of mobile chargers to replenish the nodes' energy has recently attracted a lot of attention and the mobility assisted energy replenishment provides predictable and sustained power service. In this paper, we study the joint optimization of mobile charging and data gathering in sensor networks. A wireless multi-functional vehicle (WMV) is employed and periodically moves along specified trajectories, charge the sensors and gather the sensed data via one-hop communication. The objective of this paper is to maximize the uplink throughput by optimally allocating the time for the downlink wireless energy transfer by the WMV and the uplink transmissions of different sensors. We consider two scenarios where the WMV moves in a straight line and around a circle. By time discretization, the optimization problem is formulated as a 0-1 programming problem. We obtain the upper and lower bounds of the problem by converting the original 0-1 programming problem into a linear programming problem and then obtain the optimal solution by using branch and bound algorithm. We further prove that the network throughput is independent of the WMV's velocity under certain conditions. Performance of our proposed algorithm is evaluated through extensive simulations. The results validate the correctness of our proposed theorems and demonstrate that our algorithm outperforms two baseline algorithms in achieved throughput under different settings.

• 한국정보통신학회논문지
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• 제23권7호
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• pp.845-851
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• 2019

본 논문에서는 애드혹 라우팅 네트워크를 다양한 사용자 모바일 기기에서 사용하기 위한 설계 방법을 소개하고, 이를 모바일 기기에 직접 구현하여 실제 환경에서 어떻게 작동하는지 성능을 관찰하고 검증하였다. 상용 사용자 모바일 기기에서의 애드혹 라우팅 네트워크의 사용성을 고려해 커널을 수정하지 않고 사용자 계층에서 구현하는 디자인을 선택하였다. 또한 이동성이 높은 환경에서 적절히 사용하기 위해 기존 애드혹 라우팅 네트워크들을 분석하였으며 그 결과 사용자 계층에서 AODV (ad-hoc on-demand distance vector) 프로토콜과 TCP를 구현하였다. 모바일 기기들이 일렬로 놓여 있는 환경과 중앙 노드가 주변 노드 여러 대와 통신하는 환경에서 실험을 진행하였고, 그 결과 일렬로 놓인 환경에서 최대 12 홉, 중앙 노드와 주변 노드가 통신하는 환경에서 최대 5 개의 노드와 통신하는 것을 확인하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권12호
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• pp.5744-5764
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• 2018

In Wireless Sensor Networks (WSNs) for Internet of Things (IoT) environment, fault tolerance is a most fundamental issue due to strict energy constraint of sensor node. In this paper, a robust energy saving data dissemination protocol for IoT-WSNs is proposed. Minimized energy consumption and dissemination delay time based on signal strength play an important role in our scheme. The representative dissemination protocol SPIN (Sensor Protocols for Information via Negotiation) overcomes overlapped data problem of the classical Flooding scheme. However, SPIN never considers distance between nodes, thus the issue of dissemination energy consumption is becoming more important problem. In order to minimize the energy consumption, the shortest path between sensors should be considered to disseminate the data through the entire IoT-WSNs. SPMS (Shortest Path Mined SPIN) scheme creates routing tables using Bellman Ford method and forwards data through a multi-hop manner to optimize power consumption and delay time. Due to these properties, it is very hard to avoid heavy traffic when routing information is updated. Additionally, a node failure of SPMS would be caused by frequently using some sensors on the shortest path, thus network lifetime might be shortened quickly. In contrast, our scheme is resilient to these failures because it employs energy aware concept. The dissemination delay time of the proposed protocol without a routing table is similar to that of shortest path-based SPMS. In addition, our protocol does not require routing table, which needs a lot of control packets, thus it prevents excessive control message generation. Finally, the proposed scheme outperforms previous schemes in terms of data transmission success ratio, therefore our protocol could be appropriate for IoT-WSNs environment.

• Journal of Information Processing Systems
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• 제17권3호
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• pp.489-504
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• 2021

By distributing computing tasks among devices at the edge of networks, edge computing uses virtualization, distributed computing and parallel computing technologies to enable users dynamically obtain computing power, storage space and other services as needed. Applying edge computing architectures to Internet of Vehicles can effectively alleviate the contradiction among the large amount of computing, low delayed vehicle applications, and the limited and uneven resource distribution of vehicles. In this paper, a predictive offloading strategy based on the MEC load state is proposed, which not only considers reducing the delay of calculation results by the RSU multi-hop backhaul, but also reduces the queuing time of tasks at MEC servers. Firstly, the delay factor and the energy consumption factor are introduced according to the characteristics of tasks, and the cost of local execution and offloading to MEC servers for execution are defined. Then, from the perspective of vehicles, the delay preference factor and the energy consumption preference factor are introduced to define the cost of executing a computing task for another computing task. Furthermore, a mathematical optimization model for minimizing the power overhead is constructed with the constraints of time delay and power consumption. Additionally, the simulated annealing algorithm is utilized to solve the optimization model. The simulation results show that this strategy can effectively reduce the system power consumption by shortening the task execution delay. Finally, we can choose whether to offload computing tasks to MEC server for execution according to the size of two costs. This strategy not only meets the requirements of time delay and energy consumption, but also ensures the lowest cost.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권4호
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• pp.1317-1341
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• 2021

Nowadays, the Internet of Things (IoT) is adopted to enable effective and smooth communication among different networks. In some specific application, the Wireless Sensor Networks (WSN) are used in IoT to gather peculiar data without the interaction of human. The WSNs are self-organizing in nature, so it mostly prefer multi-hop data forwarding. Thus to achieve better communication, a cross-layer routing strategy is preferred. In the cross-layer routing strategy, the routing processed through three layers such as transport, data link, and physical layer. Even though effective communication achieved via a cross-layer routing strategy, energy is another constraint in WSN assisted IoT. Cluster-based communication is one of the most used strategies for effectively preserving energy in WSN routing. This paper proposes a Bio-inspired cross-layer routing (BiHCLR) protocol to achieve effective and energy preserving routing in WSN assisted IoT. Initially, the deployed sensor nodes are arranged in the form of a grid as per the grid-based routing strategy. Then to enable energy preservation in BiHCLR, the fuzzy logic approach is executed to select the Cluster Head (CH) for every cell of the grid. Then a hybrid bio-inspired algorithm is used to select the routing path. The hybrid algorithm combines moth search and Salp Swarm optimization techniques. The performance of the proposed BiHCLR is evaluated based on the Quality of Service (QoS) analysis in terms of Packet loss, error bit rate, transmission delay, lifetime of network, buffer occupancy and throughput. Then these performances are validated based on comparison with conventional routing strategies like Fuzzy-rule-based Energy Efficient Clustering and Immune-Inspired Routing (FEEC-IIR), Neuro-Fuzzy- Emperor Penguin Optimization (NF-EPO), Fuzzy Reinforcement Learning-based Data Gathering (FRLDG) and Hierarchical Energy Efficient Data gathering (HEED). Ultimately the performance of the proposed BiHCLR outperforms all other conventional techniques.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권9호
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• pp.3138-3151
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• 2022

Traffic safety and congestion are becoming more and more serious, especially the frequent occurrence of traffic accidents, which have caused great casualties and economic losses. Cellular Vehicle to Everything (C-V2X) can assist in safe driving and improve traffic efficiency through real-time information sharing and communication between vehicles. All vehicles communicate directly with Base Stations (BS), which will increase the base station load. And when the communicating vehicles are too far apart, too fast or there are obstacles in the communication path, the communication link can be unstable or even interrupted. Therefore, choosing an effective and reliable multi-hop relay-assisted Vehicle to Vehicle (V2V) communication can not only reduce the base station load and improve the system throughput but also expand the base station coverage and improve the communication quality of edge vehicles. Therefore, a communication area division scheme based on regular hexagon segmentation technology is proposed, a relay-assisted V2V communication mechanism is designed for the divided communication areas, and an efficient communication link is constructed by selecting the best relay node. Simulation results show that the scheme can improve the throughput of the system by nearly 55% and enhance the robustness of the V2V communication link.