35 research outputs found
Localization in Wireless Sensor Networks
International audienceWith the proliferation of Wireless Sensor Networks (WSN) applications, knowing the node current location have become a crucial requirement. Location awareness enables various applications from object tracking to event monitoring, and also supports core network services such as: routing, topology control, coverage, boundary detection and clustering. Therefore, WSN localization have become an important area that attracted significant research interest. In the most common case, position related parameters are first extracted from the received measurements, and then used in a second step for estimating the position of the tracked node by means of a specific algorithm. From this perspective, this chapter is intended to provide an overview of the major localization techniques, in order to provide the reader with the necessary inputs to quickly understand the state-of-the-art and/or apply these techniques to localization problems such as robot networks. We first review the most common measurement techniques, and study their theoretical accuracy limits in terms of Cramer-Rao lower bounds. Secondly, we classify the main localization algorithms, taking those measurements as input in order to provide an estimated position of the tracked node(s)
Indoor positioning system for wireless sensor networks
Tese de Doutoramento - Programa Doutoral em Engenharia Electrónica e ComputadoresPositioning technologies are ubiquitous nowadays. From the implementation of the
global positioning system (GPS) until now, its evolution, acceptance and spread has been
unanimous, due to the underlying advantages the system brings. Currently, these systems are
present in many different scenarios, from the home to the movie theatre, at work, during a
walk in the park. Many applications provide useful information, based on the current position
of the user, in order to provide results of interest.
Positioning systems can be implemented in a wide range of contexts: in hospitals to
locate equipment and guide patients to the necessary resources, or in public spaces like
museums, to guide tourists during visits. They can also be used in a gymnasium to point the
user to his next workout machine and, simultaneously, gather information regarding his
fitness plan. In a congress or conference, the positioning system can be used to provide
information to its participants about the on-going presentations. Devices can also be
monitored to prevent thefts.
Privacy and security issues are also important in positioning systems. A user might not
want to be localized or its location to be known, permanently or during a time interval, in
different locations. This information is therefore sensitive to the user and influences directly
the acceptance of the system itself.
Concerning outdoor systems, GPS is in fact the system of reference. However, this
system cannot be used in indoor environment, due to the high attenuation of the satellite
signals from non-line-of-sight conditions. Another issue related to GPS is the power
consumption. The integration of these devices with wireless sensor networks becomes
prohibitive, due to the low power consumption profile associated with devices in this type of
networks. As such, this work proposes an indoor positioning system for wireless sensor
networks, having in consideration the low energy consumption and low computational
capacity profile.
The proposed indoor positioning system is composed of two modules: the received
signal strength positioning module and the stride and heading positioning module. For the
first module, an experimental performance comparison between several received signal
strength based algorithms was conducted in order to assess its performance in a predefined indoor environment. Modifications to the algorithm with higher performance were
implemented and evaluated, by introducing a model of the effect of the human body in the
received signal strength.
In the case of the second module, a stride and heading system was proposed, which
comprises two subsystems: the stride detection and stride length estimation system to detect
strides and infer the travelled distance, and an attitude and heading reference system to
provide the full three-dimensional orientation stride-by-stride.
The stride detection enabled the identification of the gait cycle and detected strides
with an error percentage between 0% and 0.9%. For the stride length estimation two methods
were proposed, a simplified method, and an improved method with higher computational
requirements than the former. The simplified method estimated the total distance with an error
between 6.7% and 7.7% of total travelled distance. The improved method achieved an error
between 1.2% and 3.7%. Both the stride detection and the improved stride length estimation
methods were compared to other methods in the literature with favourable results.
For the second subsystem, this work proposed a quaternion-based complementary
filter. A generic formulation allows a simple parameterization of the filter, according to the
amount of external influences (accelerations and magnetic interferences) that are expected,
depending on the location that the device is to be attached on the human body. The generic
formulation enables the inclusion/exclusion of components, thus allowing design choices
according to the needs of applications in wireless sensor networks. The proposed method was
compared to two other existing solutions in terms of robustness to interferences and execution
time, also presenting a favourable outcome.Os sistemas de posicionamento fazem parte do quotidiano. Desde a implementação do
sistema GPS (Global Positioning System) até aos dias que correm, a evolução, aceitação e
disseminação destes sistemas foi unânime, derivada das vantagens subjacentes da sua
utilização. Hoje em dia, eles estão presentes nos mais variados cenários, desde o lar até́ à sala
de cinema, no trabalho, num passeio ao ar livre. São várias as aplicações que nos fornecem
informação útil, usando como base a descrição da posição atual, de modo a produzir
resultados de maior interesse para os utilizadores.
Os sistemas de posicionamento podem ser implementados nos mais variados
contextos, como por exemplo: nos hospitais, para localizar equipamento e guiar os pacientes
aos recursos necessários, ou nas grandes superfícies públicas, como por exemplo museus, para
guiar os turistas durante as visitas. Podem ser igualmente utilizados num ginásio para indicar
ao utilizador qual a máquina para onde se deve dirigir durante o seu treino e,
simultaneamente, obter informação acerca desta mesma máquina. Num congresso ou
conferência, o sistema de localização pode ser utilizado para fornecer informação aos seus
participantes sobre as apresentações que estão a decorrer no momento. Os dispositivos
também podem ser monitorizados para prevenir roubos.
Existem também questões de privacidade e segurança associados aos sistemas de
posicionamento. Um utilizador poderá não desejar ser localizado ou que a sua localização seja
conhecida, permanentemente ou num determinado intervalo de tempo, num ou em vários
locais. Esta informação é por isso sensível ao utilizador e influencia diretamente a aceitação
do próprio sistema.
No que diz respeito aos sistemas utilizados no exterior, o GPS (ou posicionamento por
satélite) é de facto o sistema mais utilizado. No entanto, em ambiente interior este sistema não
pode ser usado, por causa da grande atenuação dos sinais provenientes dos satélites devido à
falta de linha de vista. Um outro problema associado ao recetor GPS está relacionado com as
suas características elétricas, nomeadamente os consumos energéticos. A integração destes
dispositivos nas redes de sensores sem fios torna-se proibitiva, devido ao perfil de baixo
consumo associado a estas redes. Este trabalho propõe um sistema de posicionamento para redes de sensores sem fio em
ambiente interior, tendo em conta o perfil de baixo consumo de potência e baixa capacidade
de processamento.
O sistema proposto é constituído por dois módulos: o modulo de posicionamento por
potência de sinal recebido e o módulo de navegação inercial pedestre. Para o primeiro módulo
foi feita uma comparação experimental entre vários algoritmos que utilizam a potência do
sinal recebido, de modo a avaliar a sua utilização num ambiente interior pré-definido. Ao
algoritmo com melhor prestação foram implementadas e testadas modificações, utilizando um
modelo do efeito do corpo na potência do sinal recebido.
Para o segundo módulo foi proposto um sistema de navegação inercial pedestre. Este
sistema é composto por dois subsistemas: o subsistema de deteção de passos e estimação de
distância percorrida; e o subsistema de orientação que fornece a direção do movimento do
utilizador, passo a passo.
O sistema de deteção de passos proposto permite a identificação das fases da marcha,
detetando passos com um erro entre 0% e 0.9%. Para o sistema de estimação da distância
foram propostos dois métodos: um método simplificado de baixa complexidade e um método
melhorado, mas com maiores requisitos computacionais quando comparado com o primeiro.
O método simplificado estima a distância total com erros entre 6.7% e 7.7% da distância
percorrida. O método melhorado por sua vez alcança erros entre 1.2% e 3.7%. Ambos os
sistemas foram comparados com outros sistemas da literatura apresentando resultados
favoráveis.
Para o sistema de orientação, este trabalho propõe um filtro complementar baseado em
quaterniões. É utilizada uma formulação genérica que permite uma parametrização simples do
filtro, de acordo com as influências externas (acelerações e interferências magnéticas) que são
expectáveis, dependendo da localização onde se pretende colocar o dispositivo no corpo
humano. O algoritmo desenvolvido permite a inclusão/exclusão de componentes, permitindo
por isso liberdade de escolha para melhor satisfazer as necessidades das aplicações em redes
de sensores sem fios. O método proposto foi comparado com outras soluções em termos de
robustez a interferências e tempo de execução, apresentando também resultados positivos
Range estimation using phase difference of arrival technique
The principle of positioning is a technology of identification that enables object, people and/or assets to be tracked. This is basically to allow objects to be found for the purpose of rendering/obtaining services. Ranging technique therefore is an important part in anchor nodes location vis-à-vis the distance between anchors to the blind node. Integration of location capability into Wireless Sensor Network provides enablement in the location of network devices anywhere in the area of deployment, thereby making the network more valuable from the point of view of the application. Currently, there are several techniques which have been used to estimate ranges, most of the approaches which are dependent on a single frequency technique and those techniques are inaccurate in estimating the range, particularly in a multipath environment. The proposed work was to employ a dual-frequency phase difference of arrival technique for one-way propagation to capture ranges. Phase Difference of Arrival technique is a dual-frequency technique of ranging that offers better solution than already available single frequency ranging techniques. The technique has previously been used for radar application. Having evaluated the performance of this new technique for different frequency pairs with different frequency separation in different noise variance level, proof of the concept is provided using simulated data. The obtained results show that the proposed dual-frequency Phase-Difference of Arrival system is able to correctly find the location of, and track objects. Ranging simulation results show that frequency separation of 50MHz is best suited for one-way short-range application
Selected Papers from the 2018 IEEE International Workshop on Metrology for the Sea
This Special Issue is devoted to recent developments in instrumentation and measurement techniques applied to the marine field. ¶The sea is the medium that has allowed people to travel from one continent to another using vessels, even today despite the use of aircraft. It has also been acting as a great reservoir and source of food for all living beings. However, for many generations, it served as a landfill for depositing conventional and nuclear wastes, especially in its deep seabeds, and we are assisting in a race to exploit minerals and resources, different from foods, encompassed in it. Its health is a great challenge for the survival of all humanity since it is one of the most important environmental components targeted by global warming. ¶ As everyone may know, measuring is a step that generates substantial knowledge about a phenomenon or an asset, which is the basis for proposing correct solutions and making proper decisions. However, measurements in the sea environment pose unique difficulties and opportunities, which is made clear from the research results presented in this Special Issue
Hemodynamics of Native and Bioprosthetic Aortic Valves: Insights from a Reduced Degree-of-Freedom Model
Heart disease is the leading cause of deaths in the US with aortic valve (AV) diseases being major contributors. Valve replacement is the primary therapeutic indication for AV diseases and transcatheter aortic valve replacement (TAVR) provides a safe and minimally invasive option. However, post-TAVR patient outcomes show considerable variability with deployment parameters. TAVR valves are also susceptible to failure mechanisms like leaflet thrombosis which increase the risk for serious thromboembolic events. Early detection and intervention can avert such outcomes, but symptoms often manifest at advanced stages of valve failure. Continuous monitoring can facilitate early detection, but regulatory and technological challenges may hinder developing such technology through experimental or clinical means.
Computer simulations enable unprecedented predictive capabilities which can help gain insights into the pathophysiology of valvular diseases, conduct in silico trials to design novel monitoring technologies and even guide surgeries for optimal valve deployment. However, accurate, yet efficient numerical models are required. This study describes the implementation of a versatile, efficient AV dynamics model in a previously developed fluid-structure interaction solver, and its application to each of these tasks. The model accelerates simulations by simplifying the constitutive parameter space and equations governing leaflet motion without compromising accuracy. It can simulate native and prosthetic valve dynamics exhibiting physiological and pathological function in idealized and personalized aorta anatomies.
This computational framework is used to generate canonical and patient-specific simulation datasets describing hemodynamic differences secondary to healthy and pathological AVs. These differences help identify biomarkers which reliably predict the risk of valvular and vascular diseases. Changes in these biomarkers are used to assess whether TAVR can deter aortic disease progression. Next, statistical differences in such biomarkers recorded by virtual wearable or embedded sensor systems, between normal and abnormal AV function, are analyzed using data-driven methods to infer valve health. This lays the groundwork for inexpensive, at-home diagnostic technologies, based on digital auscultation and in situ embedded-sensor platforms. Finally, a simulation describing the deployment of a commercially available TAVR valve in a patient-specific aorta anatomy and the associated hemodynamics is presented. Such simulations empower clinicians to optimize TAVR deployment and, consequently, patient outcomes
Space transportation system and associated payloads: Glossary, acronyms, and abbreviations
A collection of some of the acronyms and abbreviations now in everyday use in the shuttle world is presented. It is a combination of lists that were prepared at Marshall Space Flight Center and Kennedy and Johnson Space Centers, places where intensive shuttle activities are being carried out. This list is intended as a guide or reference and should not be considered to have the status and sanction of a dictionary