• ETRI Journal
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• 제41권3호
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• pp.326-336
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• 2019

A wireless power transfer technique can solve the power capacity problem in wireless rechargeable sensor networks (WRSNs). The charging strategy is a wide-spread research problem. In this paper, we propose a demand-based charging strategy (DBCS) for WRSNs. We improved the charging programming in four ways: clustering method, selecting to-be-charged nodes, charging path, and charging schedule. First, we proposed a multipoint improved K-means (MIKmeans) clustering algorithm to balance the energy consumption, which can group nodes based on location, residual energy, and historical contribution. Second, the dynamic selection algorithm for charging nodes (DSACN) was proposed to select on-demand charging nodes. Third, we designed simulated annealing based on performance and efficiency (SABPE) to optimize the charging path for a mobile charging vehicle (MCV) and reduce the charging time. Last, we proposed the DBCS to enhance the efficiency of the MCV. Simulations reveal that the strategy can achieve better performance in terms of reducing the charging path, thus increasing communication effectiveness and residual energy utility.

• International Journal of Internet, Broadcasting and Communication
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• 제14권4호
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• pp.80-87
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• 2022

Lack of sufficient battery capacity is one of the most important challenges impeding the development of wireless sensor networks (WSNs). Recent innovations in the areas of wireless energy transfer and rechargeable batteries have made it possible to advance WSNs. Therefore, in this article, we propose an energy-efficient charging of sensors in a WSN scenario. First, we have formulated the problem as an integer linear programming (ILP) problem. Then a utility function-based greedy algorithm named UGreedy/UF1 is proposed for solving the problem. Finally, the performance of UGreedy/UF1 is analyzed along with other baseline algorithms: UGreedy/UF2, 2-opt TSP, and Greedy TSP. The simulation results show that UGreedy/UF1 performs better than others both in terms of the deadline missing ratio of sensors and the total energy consumption of UAVs.

• 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.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권9호
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• pp.4301-4319
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• 2017

Adopting mobile chargers (MC) in rechargeable wireless sensors network (R-WSN) to recharge sensors can increase network efficiency (e.g., reduce MC travel distance per tour, reduce MC effort, and prolong WSN lifetime). In this study, we propose a mechanism to split the sensing field into partitions that may be equally spaced but differ in distance to the base station. Moreover, we focus on minimizing the MC effort by providing a new charging mechanism called the sector-based charging schedule (SBCS), which works to dispatch the MC in charging trips to the sector that sends many charging requests and suggesting an efficient sensor-charging algorithm. Specifically, we first utilize the high ability of the BS to divide the R-WSN field into sectors then it select the cluster head for each sector to reduce the intra-node communication. Second, we formulate the charging productivity as NP-hard problem and then conduct experimental simulations to evaluate the performance of the proposed mechanism. An extensive comparison is performed with other mechanisms. Experimental results demonstrate that the SBCS mechanism can prolong the lifetime of R-WSNs by increasing the charging productivity about 20% and reducing the MC effort by about 30%.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권7호
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• pp.3494-3510
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• 2019

Wireless sensor networks encounter energy saving as a major issue as the sensor nodes having no rechargeable batteries and also the resources are limited. Clustering of sensors play a pivotal role in energy saving of the deployed sensor nodes. However, in the cluster based wireless sensor network, the cluster heads tend to consume more energy for additional functions such as reception of data, aggregation and transmission of the received data to the base station. So, careful selection of cluster head and formation of cluster plays vital role in energy conservation and enhancement of lifetime of the wireless sensor networks. This study proposes a new mutation chemical reaction optimization (MCRO) which is an algorithm based energy efficient clustering protocol termed as MCRO-ECP, for wireless sensor networks. The proposed protocol is extensively developed with effective methods such as potential energy function and molecular structure encoding for cluster head selection and cluster formation. While developing potential functions for energy conservation, the following parameters are taken into account: neighbor node distance, base station distance, ratio of energy, intra-cluster distance, and CH node degree to make the MCRO-ECP protocol to be potential energy conserver. The proposed protocol is studied extensively and tested elaborately on NS2.35 Simulator under various senarios like varying the number of sensor nodes and CHs. A comparative study between the simulation results derived from the proposed MCRO-ECP protocol and the results of the already existing protocol, shows that MCRO-ECP protocol produces significantly better results in energy conservation, increase network life time, packets received by the BS and the convergence rate.

• Journal of Information Processing Systems
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• 제13권5호
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• pp.1320-1330
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• 2017

Wireless sensor networks for forest monitoring are typically deployed in fields in which manual intervention cannot be easily accessed. An interesting approach to extending the lifetime of sensor nodes is the use of energy harvested from the environment. Design constraints are application-dependent and based on the monitored environment in which the energy harvesting takes place. To reduce energy consumption, we designed a power management scheme that combines dynamic duty cycle scheduling at the network layer to plan node duty time. The dynamic duty cycle scheduling is realized based on a tier structure in which the network is concentrically organized around the sink node. In addition, the multi-paths preserved in the tier structure can be used to deliver residual packets when a path failure occurs. Experimental results show that the proposed method has a better performance.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권10호
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• pp.2357-2375
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• 2013

Message ferry is a controllable mobile node with large capacity and rechargeable energy to collect information from the sensors to the sink in wireless sensor networks. In the existing works, route of the message ferry is often designed from the solutions of the Traveling Salesman Problem (TSP) and its variants. In such solutions, the ferry route is often a simple cycle, which starts from the sink, access all the sensors exactly once and moves back to the sink. In this paper, we consider a different case, where the ferry route is a closed walk that contains more than one simple cycle. This problem is defined as the Closed Walk Ferry Route Design (CWFRD) problem in this paper, which is an optimization problem aiming to minimize the average weighted delay. The CWFRD problem is proved to be NP-hard, and the Integer Linear Programming (ILP) formulation is given. Furthermore, a heuristic scheme, namely the Initialization-Split-Optimization (ISO) scheme is proposed to construct closed walk routes for the ferry. The experimental results show that the ISO algorithm proposed in this paper can effectively reduce the average weighted delay compared to the existing simple cycle based scheme.

• 한국통신학회논문지
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• 제35권3B호
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• pp.453-461
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• 2010

무선 센서 네트워크의 센서 노드들은 한정된 자원을 가지고 있으며 배터리의 교체가 어렵다는 특성을 가지고 있기 때문에 제한된 에너지를 효율적으로 사용하는 기법은 매우 중요하다. 지금까지 이러한 센서 노드의 에너지 소모를 최소화하기 위하여 다양한 스케줄링 문제 및 해결 방안에 관한 연구들이 진행되어 왔다. 특히 CTC(Connected Target Coverage) 문제는 타겟 커버리지와 연결성을 동시에 고려하여 센서 노드들의 효율적인 상태 전이 시점을 결정하는 대표적인 스케줄링 문제로 간주된다. 본 논문에서는 중복되어 센싱되는 타겟을 고려한 보다 올바른 센서 에너지 소비 모델을 제안하고 센서 네트워크의 수명을 더욱 연장 할 수 있는 CMTC(Connected Multiple-Target Coverage) 문제를 제시한다. 또한, 이 문제를 해결하기 위한 SPT(Shortest Path based on Targets) Greedy 알고리즘을 제안하고 시뮬레이션을 통하여 제안기법이 기존기법보다 센서 네트워크의 수명을 더욱 연장하는 기법임을 보인다.

• 한국정보통신학회논문지
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• 제19권2호
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• pp.477-485
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• 2015

최근 무선 센서 네트워크(Wireless sensor network, WSN)의 제한된 수명을 근본적으로 해결하기 위하여 에너지 수집형 노드를 사용한 WSN 연구가 진행되고 있다. 하지만, 이러한 연구를 원활히 지원하기 위한 에너지 수집형 WSN 시뮬레이터는 거의 없는 상태이다. 에너지 수집형 WSN을 위한 시뮬레이터들은 기존의 배터리 기반 WSN 시뮬레이터의 에너지 모델과는 달리, 에너지 수집 모델과 소비 모델이 결합된 새로운 에너지 모델을 필요로 한다. 아울러 새로운 프로토콜 제안 시, 제안된 프로토콜의 성능과 비교할 수 있는 대표적인 에너지 수집형 WSN을 위한 라우팅 및 MAC 프로토콜들이 포함되어 있어야 한다. 본 논문에서는 다양한 환경 에너지 중 가장 널리 사용되는 태양 에너지 기반의 센서 노드 및 네트워크를 지원하는 시뮬레이터를 설계하고 구현하였다. 제안하는 시뮬레이터는 날씨 및 계절 등의 외부환경과 솔라셀 및 에너지 저장 장치 등의 내부 환경 특성을 고려하여 설계된 에너지 수집 모듈이 구현 되어있고, 태양 에너지 기반 무선 센서 네트워크를 위한 대표적인 라우팅 및 MAC 프로토콜 기법들이 구현 되어 있다. 아울러 사용자 친화형 GUI를 제공하여 손쉬운 사용이 가능하다.

• 한국정보과학회논문지:정보통신
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• 제34권6호
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• pp.458-465
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• 2007

무선 센서 네트워크(Wireless Sensor Network : WSN)는 센서 노드 자체의 라우팅 기능을 이용하여 센서필드에서 감지한 측정값을 기지 노드로 전송하는 특수한 네트워크이다. WSN의 센서노드는 재충전되지 않는 제한적인 에너지를 사용하기 때문에 에너지 효율을 극대화한 라우팅 기법이 필요하다. WSN의 수명이나 특성은 WSN의 응용과 밀접한 관계가 있기 때문에 다양한 WSN 라우팅 방법이 제안되었다. 본 논문은 PEGASIS의 라우팅 방식처럼 체인 토폴로지를 사용하면서 개선된 체인을 사용하고 주기적으로 새로운 체인을 형성하는 방법을 추가하여 성능을 개선한 A-PEGASIS 알고리즘을 제안한다. 또한 우리는 시뮬레이션을 통하여 기존 방식인 LEACH, PEGASIS, PEDAP, PEDAP-PA과 제안된 방식의 성능을 비교하였다. 그 결과 A-PEGASIS는 WSN의 평균 수명이 향상되었으며 동작시간이 종료될 무렵까지 대부분의 센서노드가 동작하는 의미의 우수한 노드 생존성이 있음을 확인하였다.