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Subject's code : 28805139
Sensors link the physical with the digital world by capturing and revealing real-world phenomena and converting these into a form that can be processed, stored, and acted upon. Integrated into numerous devices, machines, and environments, sensors provide a tremendous societal benefit. They can help to avoid catastrophic infrastructure failures, conserve precious natural resources, increase productivity, enhance security, and enable new applications such as context-aware systems and smart home technologies. The phenomenal advances in technologies such as very large scale integration (VLSI), microelectromechanical systems (MEMS), and wireless communications further contribute to the widespread use of distributed sensor systems. This lesson covers an initial approach to the subject
Wireless sensor networks have inspired many applications. Some of them are futuristic while a large number of them are practically useful. The diversity of applications in the latter category is remarkable – environment monitoring, target tracking, pipeline (water, oil, gas) monitoring, structural health monitoring, precision agriculture, health care, supply chain management, active volcano monitoring, transportation, human activity monitoring, and underground mining, to name a few. In this lesson some of these applications and the prototype implementations for these applications will be discussed in some detail.
The wireless sensor nodes are the central element in a wireless sensor network (WSN). It is through a node that sensing, processing, and communication take place. It stores and executes the communication protocols and the data-processing algorithms. The quality, size, and frequency of the sensed data that can be extracted from the network are influenced by the physical resources available to the node. Therefore, the design and implementation, the target of this lesson, of a wireless sensor node is a critical step.
One key point of this course is the operating system (OS) in a WSN. It is usually a thin software layer that logically resides between the node’s hardware and the application and provides basic programming abstractions to application developers. Its main task is to enable applications to interact with hardware resources, to schedule and prioritize tasks, and to arbitrate between contending applications and services that try to seize resources.
One of the desirable aspects of wireless sensor nodes is their ability to communicate over a wireless link. Because of it, mobile applications can be supported; flexible deployment of nodes is possible; and the nodes can be placed in areas that are otherwise inaccessible to wired nodes. Once the deployment is carried out, it is possible to rearrange node placement in order to attain optimal coverage and connectivity; and the rearrangement can be made without disrupting the normal operation of the structure or process the nodes monitor. However, wireless communication poses some formidable challenges. Some of these challenges are limited bandwidth, limited transmission range, and poor packet delivery performance because of interference, attenuation, and multipath scattering. In order to tackle these challenges, it is vital to understand their properties and some of the mitigation strategies that are already in place. This lesson provides a fundamental introduction to point-to-point wireless digital communication.
In most networks, multiple nodes share a communication medium for transmitting their data packets. The medium access control (MAC) protocol (often referred to as a sublayer of the data link layer of the OSI reference model) is primarily responsible for regulating access to the common medium. Most sensor networks and sensing applications rely on radio transmissions in the unlicensed ISM (Industrial, Scientific, and Medical) band, which may result in communications significantly affected by noise and interferences. The choice of MAC protocol has a direct bearing on the reliability and efficiency of network transmissions due to these errors and interferences in wireless communications and to other challenges such as the hidden-terminal and exposed-terminal problems. This lesson reviews the responsibilities of the MAC layer in general, discusses the characteristics of MAC protocols for WSNs, describes the main classes of MAC protocols for wireless communication, and provides descriptions of a selection of MAC protocols for WSNs
Most WSN applications require large numbers of sensor nodes that cover large areas, necessitating an indirect (multi-hop) communication approach. That is, sensor nodes must not only generate and disseminate their own information, but also serve as relays or forwarding nodes for other sensor nodes. The process of establishing paths from a source to a sink (e.g., a gateway device) across one or more relays is called routing and is a key responsibility of the network layer of the communication protocol stack. When the nodes of a WSN are deployed in a deterministic manner (i.e., they are placed at certain predetermined locations), communication between them and the gateway can occur using predetermined routes. However, when the nodes are deployed in a randomized fashion the resulting topologies are nonuniform and unpredictable.
This lesson introduces the main categories of routing protocols and data dissemination strategies and discusses state-of-the-art solutions for each category.
The power consumption of a wireless sensor network (WSN) is of crucial concern because of the scarcity of energy. The problem in WSN is amplified for a number of reasons. The problem of power consumption can be approached from two angles. One is to develop energy-efficient communication protocols (self-organization, medium access, and routing protocols) that take the peculiarities of WSNs into account. The other is to identify activities in the networks that are both wasteful and unnecessary and mitigate their impact.
A dynamic power management (DPM) strategy ensures that power is consumed economically. The strategy can have a local or global scope, or both. A local DPM strategy aims to minimize the power consumption of individual nodes by providing each subsystem with the amount of power that is sufficient to carry out a task at hand. The main focus of this lesson is on local dynamic power management strategies in WSNs.
Time (or clock) synchronization is required to ensure that sensing times can be compared in a meaningful way. While time synchronization techniques for wired networks have received a significant amount of attention, these techniques are unsuitable for wireless sensors because of the unique challenges posed by wireless sensing environments.
Localization is the task of determining the physical coordinates of a sensor node (or a group of sensor nodes) or the spatial relationships among objects. It comprises a set of techniques and mechanisms that allow a sensor to estimate its own location based on information gathered from the sensor’s environment.
It is also very relevant to provide an overview of the security concerns of WSNs that illustrates possible solutions to providing security and privacy protection. Note that the terms attacker, intruder, and adversary are used interchangeably to describe an entity (person or device) that performs an attack on a network or system.