A Data Compress Scheme for Maximizing Sensing Data in Solar-powered Sensor Networks

학위논문 (석사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 8. 신현식.무선 센서 네트워크는 주기적으로 주변 환경 정보를 수집한다. 수집하 는 환경 정보를 시간변화에 대해 보다 정밀하게 얻기 위해서는 센싱 주 기를 줄여야 하지만 이는 더 많은 에너지를 필요로 한다. 한편 태양에너 지 기반 센서 노드는 태양에너지를 통해 수집되는 여분의 에너지를 센서 네트워크의 서비스 품질을 향상시키는데 이용할 수 있으며, 데이터의 압 축 기법을 이용하면 데이터의 크기를 줄여 전송에 이용하는 에너지를 줄 일 수 있게 된다. 본 논문에서는 태양에너지로부터 수집된 여분의 에너지와 데이터의 압 축 기법을 이용해 절약되는 에너지를 이용하여 데이터의 수집량을 늘려 시간변화에 대해 보다 정밀한 데이터를 얻는 기법을 제안한다. 이 기법 은 압축률과 압축 소모에너지가 서로 다른 두 가지 압축 알고리즘을 센 서 노드의 남은 에너지, 태양에너지로부터 수집되는 에너지, 센서 노드 가 사용하는 에너지를 고려하여 적응적으로 선택한다. 이 기법을 이용해 여분의 에너지를 높은 압축률에서 짧은 센싱주기로 수집하는데 이용하여 센싱 데이터의 양을 늘리도록 한다. 본 연구에서 이용한 기법을 이용하면 낮은 압축률의 압축 알고리즘만 을 이용하여 데이터를 수집하는 경우에 비해 약 7.8%정도의 데이터를 더 수집할 수 있었으며, 이는 7.8% 더 정밀한 데이터를 수집하였음을 의미한다.요약 i 목차 ii 그림 목차 iv 표 목차 iv 1. 서론 1 1.1 연구의 동기 1 1.2 연구의 목적 및 개요 2 1.3 논문의 구성 4 2. 배경 지식 및 관련연구 5 2.1 무선 센서 네트워크 5 2.2 무선 센서노드와 싱크노드의 특징 6 2.3 센서노드에서의 데이터 압축 기법 7 2.4 태양에너지 기반 무선 센서 네트워크 8 3. 적응적 압축 기법 11 3.1 적응적 압축 기법 개요 11 3.2 압축 알고리즘 12 3.3 노드의 동작 15 3.4 동작모드의 결정 16 3.5 문턱값의 결정 18 3.6 데이터 수집 주기의 결정 20 4. 실험 환경 및 결과 22 4.1 실험 환경 22 4.2 실험 결과 25 5. 결론 및 향후 연구 30 참고문헌 31 Abstract 36Maste

Power Adaptive Data Encryption for Energy-Efficient and Secure Communication in Solar-Powered Wireless Sensor Networks

Basic security of data transmission in battery-powered wireless sensor networks (WSNs) is typically achieved by symmetric-key encryption, which uses little energy; but solar-powered WSNs sometimes have sufficient energy to achieve a higher level of security through public-key encryption. However, if energy input and usage are not balanced, nodes may black out. By switching between symmetric-key and public-key encryption, based on an energy threshold, the level of security can be traded off against the urgency of energy-saving. This policy can also reduce the amount of energy used by some nodes in a WSN, since data encrypted using a public-key is simply relayed by intermediate nodes, whereas data encrypted using a symmetric-key must be decrypted and reencrypted in every node on its path. Through a simulation, we compared the use of either symmetric-key or public-key encryption alone with our scheme, which was shown to be more secure, to use energy more effectively, and to reduce the occurrence of node blackouts

Global Routing Protocols for Wireless Body Area Networks

This work primarily consists of two parts. The first part deals with a wireless body area network with battery operated nodes. Global routing protocols are considered. The Dijkstra`s algorithm was modified using a novel link cost function in order to perform energy balancing across the network. The proposed protocol makes optimal use of the network energy and increases the network lifetime. Hardware experiments involving multiple nodes and an access point are performed to gather wireless channel information. Performance of two different types of network architectures is evaluated viz. on-body access point and off-body access point architectures. Results show up to 40% increase in average network lifetime with modest average increase of 0.4 dB in energy per bit. Proposed protocol lessens the need to recharge batteries frequently and as all the nodes deplete their energy source at the same time due to energy balancing, recharging can be done for all the batteries at the same time instead of recharging them one at a time. Network connectivity is evaluated using outage as a metric. Results show the cut-off effect which signifies the minimum amount of transmission power required to achieve reliable communication. The advantages of an off-body access point are demonstrated. The second part presents a global routing protocol based on Dijkstra`s algorithm for wireless body area networks with energy harvesting constraints. The protocol dynamically modifies routing trees based on available energy accumulated through energy harvesting. Various harvesting methods are considered. The results show that low data-rate applications are achievable using existing energy harvesting techniques while high data-rate applications call for advancements in these methods

Low-Latency Geographic Routing for Asynchronous Energy-Harvesting WSNs

Abstract — Research on data routing strategies for wireless sensor networks (WSNs) has largely focused on energy efficiency. However rapid advances in WSNs require routing protocols which can accommodate new types of energy source and data of requiring short end-to-end delay. In this paper, we describe a duty-cycle-based low-latency geographic routing for asynchronous energy-harvesting WSNs. It uses an algorithm (D-APOLLO) that periodically and locally determines the topological knowledge range and duty-cycle of each node, based on an estimated energy budget for each period which includes the currently available energy, the predicted energy consumption, and the energy expected from the harvesting device. This facilitates a lowlatency routing scheme which considers both geographic and duty-cycle information about the neighbors of a node, so that data can be routed efficiently and delivered to the sink as quickly as possible. Simulation results confirm that our routing scheme can deliver data to the sink with high reliability and low latency. Index Terms — wireless sensor network, duty cycle, geographic, routing, low-latency, energy harvesting I

DESIGN OF RELIABLE AND SUSTAINABLE WIRELESS SENSOR NETWORKS: CHALLENGES, PROTOCOLS AND CASE STUDIES

Integrated with the function of sensing, processing, and wireless communication, wireless sensors are attracting strong interest for a variety of monitoring and control applications. Wireless sensor networks (WSNs) have been deployed for industrial and remote monitoring purposes. As energy shortage is a worldwide problem, more attention has been placed on incorporating energy harvesting devices in WSNs. The main objective of this research is to systematically study the design principles and technical approaches to address three key challenges in designing reliable and sustainable WSNs; namely, communication reliability, operation with extremely low and dynamic power sources, and multi-tier network architecture. Mathematical throughput models, sustainable WSN communication strategies, and multi-tier network architecture are studied in this research to address these challenges, leading to protocols for reliable communication, energy-efficient operation, and network planning for specific application requirements. To account for realistic operating conditions, the study has implemented three distinct WSN testbeds: a WSN attached to the high-speed rotating spindle of a turning lathe, a WSN powered by a microbial fuel cell based energy harvesting system, and a WSN with a multi-tier network architecture. With each testbed, models and protocols are extracted, verified and analyzed. Extensive research has studied low power WSNs and energy harvesting capabilities. Despite these efforts, some important questions have not been well understood. This dissertation addresses the following three dimensions of the challenge. First, for reliable communication protocol design, mathematical throughput or energy efficiency estimation models are essential, yet have not been investigated accounting for specific application environment characteristics and requirements. Second, for WSNs with energy harvesting power sources, most current networking protocols do not work efficiently with the systems considered in this dissertation, such as those powered by extremely low and dynamic energy sources. Third, for multi-tier wireless network system design, routing protocols that are adaptive to real-world network conditions have not been studied. This dissertation focuses on these questions and explores experimentally derived mathematical models for designing protocols to meet specific application requirements. The main contributions of this research are 1) for industrial wireless sensor systems with fast-changing but repetitive mobile conditions, understand the performance and optimal choice of reliable wireless sensor data transmission methods, 2) for ultra-low energy harvesting wireless sensor devices, design an energy neutral communication protocol, and 3) for distributed rural wireless sensor systems, understand the efficiency of realistic routing in a multi-tier wireless network. Altogether, knowledge derived from study of the systems, models, and protocols in this work fuels the establishment of a useful framework for designing future WSNs