88 research outputs found
Exploiting Addresses Correlation to Maximize Lifetime of IPv6 Cluster-based WSNs
International audienceImproving the network lifetime is an important design criterion for wireless sensor networks. To achieve this goal, we propose in this paper a novel approach which applies source-coding on addresses in heterogeneous IPv6 Cluster-based wireless sensor network. We formulate the problem of maximiz- ing the network lifetime when Slepian-wolf coding is applied on addresses in network composed of line-powered and battery- powered sensors. This problem optimizes the placement of line- powered sensors to enable the battery-powered ones to exploit the addresses correlation and reduce the size of their emitted packets and thus improve the network lifetime. The numerical results show that a significant network lifetime improvement can be achieved (about 25% in typical scenario)
Smart Wireless Sensor Networks
The recent development of communication and sensor technology results in the growth of a new attractive and challenging area - wireless sensor networks (WSNs). A wireless sensor network which consists of a large number of sensor nodes is deployed in environmental fields to serve various applications. Facilitated with the ability of wireless communication and intelligent computation, these nodes become smart sensors which do not only perceive ambient physical parameters but also be able to process information, cooperate with each other and self-organize into the network. These new features assist the sensor nodes as well as the network to operate more efficiently in terms of both data acquisition and energy consumption. Special purposes of the applications require design and operation of WSNs different from conventional networks such as the internet. The network design must take into account of the objectives of specific applications. The nature of deployed environment must be considered. The limited of sensor nodes� resources such as memory, computational ability, communication bandwidth and energy source are the challenges in network design. A smart wireless sensor network must be able to deal with these constraints as well as to guarantee the connectivity, coverage, reliability and security of network's operation for a maximized lifetime. This book discusses various aspects of designing such smart wireless sensor networks. Main topics includes: design methodologies, network protocols and algorithms, quality of service management, coverage optimization, time synchronization and security techniques for sensor networks
Performance assessment of mobility solutions for IPv6-based healthcare wireless sensor networks
This thesis focuses on the study of mobile wireless sensor networks applied to healthcare
scenarios. The promotion of better quality-of-life for hospitalized patients is addressed in this
research work with a solution that can help these patients to keep their mobility (if possible).
The solution proposed allows remote monitoring and control of patients’ health in real-time
and without interruptions. Small sensor nodes able to collect and send wirelessly the health
parameters allow for the control of the patients' health condition. A network infrastructure,
composed by several access points, allows the connection of the sensor nodes (carried by the
patients) to remote healthcare providers. To ensure continuous access to sensor nodes special
attention should be dedicated to manage the transition of these sensor nodes between
different access points’ coverage areas. The process of changing an access point attachment
of a sensor node is called handover. In that context, this thesis proposes a new handover
mechanism that can ensure continuous connection to mobile sensor nodes in a healthcare
wireless sensor network. Due to the limitations of sensor nodes’ resources, namely available
energy (these sensor nodes are typically powered by small batteries), the proposed
mechanism pays a special attention in the optimization of energy consumption. To achieve
this optimization, part of this work is dedicated to the construction of a small sensor node.
The handover mechanism proposed in this work is called Hand4MAC (handover mechanism for
MAC layer). This mechanism is compared with other mechanisms commonly used in handover
management. The Hand4MAC mechanism is deployed and validated through by simulation and
in a real testbed. The scenarios used for the validation reproduces a hospital ward. The
performance evaluation is focused in the percentage of time that senor nodes are accessible
to the network while traveling across several access points’ coverage areas and the energy
expenditures in handover processes. The experiments performed take into account various
parameters that are the following: number of sent messages, number of received messages,
multicast message usage, energy consumption, number of sensor nodes present in the
scenario, velocity of sensor nodes, and time-to-live value. In both simulation and real
testbed, the Hand4MAC mechanism is shown to perform better than all the other handover
mechanisms tested. In this comparison it was only considered the most promising handover
mechanisms proposed in the literature.Fundação para a Ciência e a Tecnologia (FCT
Performance assessment of real-time data management on wireless sensor networks
Technological advances in recent years have allowed the maturity of Wireless Sensor Networks
(WSNs), which aim at performing environmental monitoring and data collection. This sort of
network is composed of hundreds, thousands or probably even millions of tiny smart computers
known as wireless sensor nodes, which may be battery powered, equipped with sensors, a radio
transceiver, a Central Processing Unit (CPU) and some memory. However due to the small size and
the requirements of low-cost nodes, these sensor node resources such as processing power, storage
and especially energy are very limited.
Once the sensors perform their measurements from the environment, the problem of data
storing and querying arises. In fact, the sensors have restricted storage capacity and the on-going
interaction between sensors and environment results huge amounts of data. Techniques for data
storage and query in WSN can be based on either external storage or local storage. The external
storage, called warehousing approach, is a centralized system on which the data gathered by the
sensors are periodically sent to a central database server where user queries are processed. The
local storage, in the other hand called distributed approach, exploits the capabilities of sensors
calculation and the sensors act as local databases. The data is stored in a central database server
and in the devices themselves, enabling one to query both.
The WSNs are used in a wide variety of applications, which may perform certain operations on
collected sensor data. However, for certain applications, such as real-time applications, the sensor
data must closely reflect the current state of the targeted environment. However, the environment
changes constantly and the data is collected in discreet moments of time. As such, the collected
data has a temporal validity, and as time advances, it becomes less accurate, until it does not
reflect the state of the environment any longer. Thus, these applications must query and analyze
the data in a bounded time in order to make decisions and to react efficiently, such as industrial
automation, aviation, sensors network, and so on. In this context, the design of efficient real-time
data management solutions is necessary to deal with both time constraints and energy consumption.
This thesis studies the real-time data management techniques for WSNs. It particularly it focuses
on the study of the challenges in handling real-time data storage and query for WSNs and on the
efficient real-time data management solutions for WSNs.
First, the main specifications of real-time data management are identified and the available
real-time data management solutions for WSNs in the literature are presented. Secondly, in order to
provide an energy-efficient real-time data management solution, the techniques used to manage
data and queries in WSNs based on the distributed paradigm are deeply studied. In fact, many
research works argue that the distributed approach is the most energy-efficient way of managing
data and queries in WSNs, instead of performing the warehousing. In addition, this approach can provide quasi real-time query processing because the most current data will be retrieved from the
network.
Thirdly, based on these two studies and considering the complexity of developing, testing, and
debugging this kind of complex system, a model for a simulation framework of the real-time
databases management on WSN that uses a distributed approach and its implementation are
proposed. This will help to explore various solutions of real-time database techniques on WSNs
before deployment for economizing money and time. Moreover, one may improve the proposed
model by adding the simulation of protocols or place part of this simulator on another available
simulator. For validating the model, a case study considering real-time constraints as well as energy
constraints is discussed.
Fourth, a new architecture that combines statistical modeling techniques with the distributed
approach and a query processing algorithm to optimize the real-time user query processing are
proposed. This combination allows performing a query processing algorithm based on admission
control that uses the error tolerance and the probabilistic confidence interval as admission
parameters. The experiments based on real world data sets as well as synthetic data sets
demonstrate that the proposed solution optimizes the real-time query processing to save more
energy while meeting low latency.Fundação para a Ciência e Tecnologi
A prediction-based approach for features aggregation in Visual Sensor Networks
Visual Sensor Networks (VSNs) constitute a key technology for the implementation of several visual analysis tasks. Recent studies have demonstrated that such tasks can be efficiently performed following an operative paradigm where cameras transmit to a central controller local image features, rather than pixel-domain images. Furthermore, features from multiple camera views may be efficiently aggregated exploiting the spatial redundancy between overlapping views. In this paper we propose a routing protocol designed for supporting aggregation of image features in a VSN. First, we identify a predictor able to estimate the efficiency of local features aggregation between different cameras in a VSN. The proposed predictor is chosen so as to minimize the prediction error while keeping the network overhead cost low. Then, we harmonically integrate the proposed predictor in the Routing Protocol for Low-Power and Lossy Networks (RPL) in order to support the task of in-network feature aggregation. We propose a RPL objective function that takes into account the predicted aggregation efficiency and build the routes from the camera nodes to a central controller so that either energy consumption or used network bandwidth is minimized. Extensive experimental results confirm that the proposed approach can be used to increase the efficiency of VSNs
Energy aware performance evaluation of WSNs
Distributed sensor networks have been discussed for more than 30 years, but the vision
of Wireless Sensor Networks (WSNs) has been brought into reality only by the rapid advancements
in the areas of sensor design, information technologies, and wireless networks
that have paved the way for the proliferation of WSNs. The unique characteristics of
sensor networks introduce new challenges, amongst which prolonging the sensor lifetime
is the most important. Energy-efficient solutions are required for each aspect of WSN design
to deliver the potential advantages of the WSN phenomenon, hence in both existing
and future solutions for WSNs, energy efficiency is a grand challenge. The main contribution
of this thesis is to present an approach considering the collaborative nature of WSNs
and its correlation characteristics, providing a tool which considers issues from physical
to application layer together as entities to enable the framework which facilitates the
performance evaluation of WSNs. The simulation approach considered provides a clear
separation of concerns amongst software architecture of the applications, the hardware
configuration and the WSN deployment unlike the existing tools for evaluation. The
reuse of models across projects and organizations is also promoted while realistic WSN
lifetime estimations and performance evaluations are possible in attempts of improving
performance and maximizing the lifetime of the network. In this study, simulations are
carried out with careful assumptions for various layers taking into account the real time
characteristics of WSN.
The sensitivity of WSN systems are mainly due to their fragile nature when energy
consumption is considered. The case studies presented demonstrate the importance of
various parameters considered in this study. Simulation-based studies are presented,
taking into account the realistic settings from each layer of the protocol stack. Physical
environment is considered as well. The performance of the layered protocol stack in
realistic settings reveals several important interactions between different layers. These
interactions are especially important for the design of WSNs in terms of maximizing the
lifetime of the network
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