Efficiency Impairment of Wireless Sensor Networks Protocols under Realistic Physical Layer Conditions

International audienceMost of existing works about sensor networks focus on energy management. Already proposed solutions often consist in balancing energy consumption by taking advantage of the redundancy induced by the random deployment of nodes; some nodes are active while others are in sleep mode, thus consuming less energy. Such a dynamical topology should not impact the monitoring activity. Area coverage protocols aim at turning off redundant sensor nodes in order to constitute a set of active nodes that covers as large an area as the whole set of nodes. In this paper, we focus on localized algorithms that require 1-hop knowledge only to allow nodes to choose their activity status. The unit disk model is the most commonly used assumption; if a node emits a message, any node within its communication range receives it while any node outside the disk does not. In this article, the impact of a realistic radio channel on area coverage protocols for wireless sensor networks is studied. It is shown that a non-binary reception probability can lead to very different results for protocols that could though provide great performances with the unit disk model. An optimization of a protocol to keep increasing the network lifetime once a realistic energy consumption model is considered is also provided

Security wireless sensor networks: prospects, challenges, and future

With the advancements of networking technologies and miniaturization of electronic devices, wireless sensor network (WSN) has become an emerging area of research in academic, industrial, and defense sectors. Different types of sensing technologies combined with processing power and wireless communication capability make sensor networks very lucrative for their abundant use in near future. However, many issues are yet to be solved before their full-scale practical implementations. Among all the research issues in WSN, security is one of the most challenging topics to deal with. The major hurdle of securing a WSN is imposed by the limited resources of the sensors participating in the network. Again, the reliance on wireless communication technology opens the door for various types of security threats and attacks. Considering the special features of this type of network, in this chapter we address the critical security issues in wireless sensor networks. We talk about cryptography, steganography, and other basics of network security and their applicability in WSN. We explore various types of threats and attacks against wireless sensor networks, possible countermeasures, mentionable works done so far, other research issues, etc. We also introduce the view of holistic security and future trends towards research in wireless sensor network security

Розвиток методів підвищення пропускної здатності в мобільних сенсорних мережах

Метою данної роботи є проаналізувати методи підвищення пропускної здатності в мобільних сенсорних мережах. МСМ взагалі можна описати як мережу вузлів, котрі взаємодіють і можуть контролювати навколишнє середовище, забезпечуючи взаємодію між особами або комп'ютерами і навколишнім середовищем. Вузли датчиків контролюють зібрані дані для передачі разом з іншими вузлами сенсора шляхом стрибка. Під час передачі дані, що підлягають моніторингу, можуть оброблятися кількома вузлами для доступу до вузла шлюзу після множинного маршрутизації та, нарешті, досягають вузла керування через Інтернет або супутникThe purpose of this work is to analyze methods of increasing bandwidth in mobile sensor networks. The mobile sensor network can generally be described as a network of interacting nodes that can control the environment by providing interactions between individuals or computers and the environment. The nodes of the sensors control the collected data for transmission along with other nodes of the sensor by jumping. During transmission, the data to be monitored can be processed by multiple nodes to access the gateway node after multiple routing, and finally reach the control node via the Internet or satellit

Joint synchronization of clock phase offset, skew and drift in reference broadcast synchronization (RBS) protocol

Time-synchronization in wireless ad-hoc sensor networks is a crucial piece of infrastructure. Thus, it is a fundamental design problem to have a good clock syn- chronization amongst the nodes of wireless ad-hoc sensor networks. Motivated by this fact, in this thesis, the joint maximum likelihood (JML) estimator for relative clock phase offset and skew under the exponential noise model for the reference broadcast synchronization protocol is formulated and found via a direct algorithm. The Gibbs Sampler is also proposed for joint estimation of relative clock phase offset and skew, and shown to provide superior performance compared to the JML-estimator. Lower and upper bounds for the mean-square errors (MSE) of the JML-estimator and the Gibbs Sampler are introduced in terms of the MSE of the uniform minimum variance unbiased estimator and the conventional best linear unbiased estimator, respectively. The suitability of the Gibbs Sampler for estimating additional unknown parameters is shown by applying it to the problem in which synchronization of clock drift is also needed

Multi Sensor Fusion Based Framework For Efficient Mobile Robot Collision Avoidance and Path Following System

The field of autonomous mobile robotics has recently gained the interests of many researchers. Due to the specific needs required by various applications of mobile robot systems (especially in navigation), designing a real-time obstacle avoidance and path following robot system has become the backbone of controlling robots in unknown environments. Therefore, an efficient collision avoidance and path following methodology is needed to develop an intelligent and effective autonomous mobile robot system. Mobile robots are equipped with various types of sensors (such as GPS, camera, infrared and ultrasonic sensors); these sensors are used to observe the surrounding environment. However, these sensors sometimes fail and have inaccurate readings. Therefore, the integration of sensor fusion will help to solve this dilemma and enhance the overall performance. A new technique for line following and collision avoidance in the mobile robotic systems is introduced. The proposed technique relies on the use of infrared sensors and involves a reasonable level of calculations, to be easily used in real-time control applications. In addition, a fusion model based on fuzzy logic is proposed. Eight distance sensors and a range finder camera are used for the collision avoidance approach, where three ground sensors are used for the line or path following approach. The fuzzy system is composed of nine inputs (which are the eight distance sensors and the camera), two outputs (which are the left and right velocities of the mobile robot’s wheels), and twenty four fuzzy rules for the robot’s movement. Webots Pro simulator is used for modeling the environment and robot to show the ability of the robot to follow a path, detect obstacles, and navigate around them to avoid collision. It also shows that the robot has been successfully following extremely congested curves and has avoided any obstacle that emerged on its path. The proposed methodology which includes the collision avoidance based on fuzzy logic fusion model and line following robot, has been implemented and tested through simulation and real-time experiments. Various scenarios have been presented with static and dynamic obstacles, using one and multiple robots while avoiding obstacles in different shapes and sizes. The proposed methodology reduced the traveled distance of the mobile robot, as well as minimized the energy consumption and the distance between the robot and the obstacle detected as compared to a non-fuzzy logic approach

Linha de comunicação de suporte à monitorização ambiental

O objetivo deste trabalho foi projetar uma linha de comunicação de suporte à monitorização ambiental desde o Funchal até ao Pico do Arieiro fazendo uso das redes de sensores sem fios (RSSF). Primeiramente efetuou-se um estudo dos principais sensores utilizados no âmbito da monitorização ambiental. Posteriormente averiguou-se o funcionamento das RSSF de modo a compreender o envio de dados dos nós sensores até à estação base. A comunicação entre nós é realizada por radiofrequência. Tendo em conta que a propagação do sinal é afetada por diversos fatores, realizou-se um estudo relativamente à atenuação do sinal em diferentes meios. A linha de comunicação faz uso de dois tipos de nós, o nó router e o nó terminal (end-device). Este último permite diminuir o consumo de energia, entrando no modo adormecido, aumentando, assim, o tempo de vida da rede sem a necessidade de recorrer a baterias com maior capacidade. No que concerne à monitorização ambiental foi desenvolvida uma estação meteorológica (end-device) alimentada por painéis fotovoltaicos. A estação tem como função recolher periodicamente os parâmetros de temperatura do ar, humidade relativa, pluviosidade, velocidade e direção do vento, tensão nas baterias, produção de potência dos painéis fotovoltaicos e o nível de sinal de radiofrequência recebido (RSSI - Received Signal Strength Indicator). O protótipo foi instalado em ambiente exterior de forma a avaliar o seu desempenho e os efeitos do ambiente, especialmente em situações de ocorrência de intempéries. Os dados podem ser visualizados em tempo real através de uma aplicação web.The aim of this project work was to create a support communications line between Funchal and Pico do Arieiro using a wireless communication sensor system (RSSF). Firstly a study of the main used sensors in the environmental monitoring was done. Then the functioning of the RSSF was evaluated in order to understand how data was being sent and processed from the sensor nodes to the base station. The communication between nodes was performed via radiofrequency, bearing in mind that the propagation of the signal is affected by several elements. A study in many different environments has been carried out concerning the weakening of the signal. The communication line includes two types of nodes, the router node and the end-device node. The last one allows to save energy as it goes into sleep mode. This way allows an increased life span is expected without the need to turn to larger batteries saving time and means. Due to the environmental monitoring, it was created a meteorological station (end-device) fed by a photovoltaic panel. The station collects periodically the parameters of air temperature, relative humidity, precipitation, speed and wind direction, battery tension, the photovoltaic panels production and the radio frequency signal level (RSSI – Received Signal Strength indicator). A prototype was installed in an outdoor environment, in order to evaluate its performance exposed to the elements. The data can be visualized in real time in a web page

Distributed synchronization algorithms for wireless sensor networks

The ability to distribute time and frequency among a large population of interacting agents is of interest for diverse disciplines, inasmuch as it enables to carry out complex cooperative tasks. In a wireless sensor network (WSN), time/frequency synchronization allows the implementation of distributed signal processing and coding techniques, and the realization of coordinated access to the shared wireless medium. Large multi-hop WSN\u27s constitute a new regime for network synchronization, as they call for the development of scalable, fully distributed synchronization algorithms. While most of previous research focused on synchronization at the application layer, this thesis considers synchronization at the lowest layers of the communication protocol stack of a WSN, namely the physical and the medium access control (MAC) layer. At the physical layer, the focus is on the compensation of carrier frequency offsets (CFO), while time synchronization is studied for application at the MAC layer. In both cases, the problem of realizing network-wide synchronization is approached by employing distributed clock control algorithms based on the classical concept of coupled phase and frequency locked loops (PLL and FLL). The analysis takes into account communication, signaling and energy consumption constraints arising in the novel context of multi-hop WSN\u27s. In particular, the robustness of the algorithms is checked against packet collision events, infrequent sync updates, and errors introduced by different noise sources, such as transmission delays and clock frequency instabilities. By observing that WSN\u27s allow for greater flexibility in the design of the synchronization network architecture, this work examines also the relative merits of both peer-to-peer (mutually coupled - MC) and hierarchical (master-slave - MS) architectures. With both MC and MS architectures, synchronization accuracy degrades smoothly with the network size, provided that loop parameters are conveniently chosen. In particular, MS topologies guarantee faster synchronization, but they are hindered by higher noise accumulation, while MC topologies allow for an almost uniform error distribution at the price of much slower convergence. For all the considered cases, synchronization algorithms based on adaptive PLL and FLL designs are shown to provide robust and scalable network-wide time and frequency distribution in a WSN