Cooperative Localization Schemes for Wireless Sensor Networks in an Anchor-deficient Environment
앵커가 부족한 무선 센서 네트워크 환경에서의 협력 위치 추정 기법 연구

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공과대학 전기·컴퓨터공학부
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서울대학교 대학원
학위논문 (박사)-- 서울대학교 대학원 : 공과대학 전기·컴퓨터공학부, 2018. 8. 김성철.
Many applications of wireless sensor network (WSN) require accurate location information of the sensor node. The sensor node can identify its location by the positioning device such as the global positioning system (GPS). However, it is impractical to obtain location information via GPS in certain situations such as a battleground or indoor environment. Alternatively, the sensor node can estimate its position by utilizing signals from nearby anchor nodes that have knowledge of their own locations. If the number of anchor nodes is insufficient, it is difficult to estimate each node's location using the anchor nodes' information by employing the existing algorithms, the localization problem becoming complicated. Thus, in a wireless environment where location information of few anchor nodes is available, each node is required to cooperate with other nodes, and self-organizing localization is the crucial feature of WSNs.

In this dissertation, I investigate several schemes for accurate localization in anchor-deficient environments. First, I propose a recursive self-organizing localization scheme, solely based on the neighbors connectivity information. This scheme utilizes a mass spring-relaxation (MSR) algorithm in which each node finds its location by iteratively balancing the geometric relationships with neighboring nodes until the system reaches an equilibrium state. I propose a simple distance correction factor to consider the accuracy of distance measurements, and adopt the adaptive step size control based on the gradient method to improve the system stability. The proposed scheme improves the system performance in terms of convergence speed, system stability, and estimation accuracy.

Additionally, I consider mobile anchor assisted localization in the situation of bad condition such as lack of anchor. This method assumes that the mobile anchors do not have energy restrictions and can move on the ground or fly. They periodically broadcast their location to support localization of nearby sensor nodes, and localization performance is highly dependent on the mobile anchor trajectory. Therefore, I study a dynamic path planning method of the mobile anchor in outdoor wireless sensor networks. The objective of the path planning is to steer the mobile anchor to the positions which minimize the estimation uncertainty of the sensors. The method is based on a single mobile anchor and does not require prior knowledge of the network environment. The mobile anchor determines waypoints using the Cramer-Rao lower bound (CRLB), which gives the minimum achievable variance of the estimated location of the sensors. To reduce the complexity of CRLB calculations, I consider several objective functions based on the Fisher information matrix. In addition, I focus on the minimum spanning tree over the wireless sensor network to determine energy-efficient paths and guarantee localization of every node. Simulation results confirm that the proposed method improves the localization accuracy when compared to static path planning algorithm and guarantees the localization of all the node in the network.
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College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Electrical and Computer Engineering (전기·정보공학부)Theses (Ph.D. / Sc.D._전기·정보공학부)
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