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Publications

Publications by Paulo Portugal

2016

Experimental Validation of a Battery Model for Low-Power Nodes in Wireless Sensor Networks

Authors
Rodrigues, LM; Montez, C; Vasques, F; Portugal, P;

Publication
2016 IEEE WORLD CONFERENCE ON FACTORY COMMUNICATION SYSTEMS (WFCS)

Abstract
Energy consumption is a major problem in Wireless Sensor Networks (WSNs) since in most scenarios nodes operate on batteries with reduced size and low capacity. Battery lifetime estimation is therefore crucial to evaluate the network behavior over time. In addition, battery lifetime estimation is a major challenge since it depends on many factors, such as the duty cycle of supported applications and the intrinsic chemical reactions within the batteries. Several battery models have been proposed to deal with battery lifetime estimation. However, most of the available models address only high-capacity batteries. This paper discusses a method for extracting the parameters for the Kinetic Battery Model (KiBaM) used within WSN context. The target is to define a battery model that helps to estimate the lifetime of nodes using low-capacity batteries and which operate in a duty cycle scheme. Results show that KiBaM is an adequate model for WSNs since it presents low error when compared with experimental results using real batteries.

2014

Availability Assessment of Wireless Visual Sensor Networks for Target Coverage

Authors
Costa, DG; Silva, I; Guedes, LA; Portugal, P; Vasques, F;

Publication
2014 IEEE EMERGING TECHNOLOGY AND FACTORY AUTOMATION (ETFA)

Abstract
Visual monitoring in wireless sensor networks can provide valuable information of the monitored field, enriching surveillance and control applications. For those networks, however, some active visual sources may fail or run out of energy, potentially degrading the application monitoring quality. Visual sensors may be deployed to monitor a set of targets that are critical for the monitoring tasks of the application, demanding some level of redundancy to compensate sensor failures. In this context, it may be desired to know the probability of a specific target to be covered by at least one visual sensor along the network operation. We propose an approach for the availability assessment in wireless visual sensor networks for the specific case of target coverage, relating sensing redundancy to energy discharging and sensors disconnection. The proposed approach can then be used to predict coverage holes, directly benefiting critical monitoring applications.

2014

Availability Issues in Wireless Visual Sensor Networks

Authors
Costa, DG; Silva, I; Guedes, LA; Vasques, F; Portugal, P;

Publication
SENSORS

Abstract
Wireless visual sensor networks have been considered for a large set of monitoring applications related with surveillance, tracking and multipurpose visual monitoring. When sensors are deployed over a monitored field, permanent faults may happen during the network lifetime, reducing the monitoring quality or rendering parts or the entire network unavailable. In a different way from scalar sensor networks, camera-enabled sensors collect information following a directional sensing model, which changes the notions of vicinity and redundancy. Moreover, visual source nodes may have different relevancies for the applications, according to the monitoring requirements and cameras' poses. In this paper we discuss the most relevant availability issues related to wireless visual sensor networks, addressing availability evaluation and enhancement. Such discussions are valuable when designing, deploying and managing wireless visual sensor networks, bringing significant contributions to these networks.

2013

Delay-aware DWT-based image transmission in wireless visual sensor networks

Authors
Costa, DG; Guedes, LA; Vasques, F; Portugal, P;

Publication
WebMedia 2013 - Proceedings of the 19th Brazilian Symposium on Multimedia and the Web

Abstract
Wireless sensor networks have been employed as an effective tool for a large set of monitoring applications, directly supporting applications not addressed by conventional Internet-based technologies. Camera-enabled sensors enhance the applicability of those networks allowing innovative visual monitoring functions. Sometimes, source nodes will perform real-time monitoring of an area of interest, where visual data packets will need to be transmitted with minimum delay. However, energy depletion of the nodes that compose the transmission paths may hamper the network capability to deliver packets with time constraints. In such context, we propose a delay-aware image transmission mechanism where the relevancies of DWT subbands are considered when forwarding packets to the next hop toward the sink. In fact, parts of DWT-based encoded visual data may have different relevancies for the reconstruction of the original visual information and those relevancies may be exploited when forwarding packets. In the proposed approach, high-relevant packets are forwarded through paths with lower average end-to-end delay, while the remaining packets flow through paths high higher delay, allowing that low-quality versions of the transmitted images reach the sink as soon as possible. Moreover, the best paths will need to relay fewer packets, potentially reducing energy consumption and enlarging their lifetime. We present simulation results to attest the benefits of the proposed mechanism. © 2013 ACM.

2013

A framework for dependability evaluation of industrial processes

Authors
Macedo, D; Silva, I; Guedes, LA; Portugal, P; Vasques, F;

Publication
IEEE International Conference on Emerging Technologies and Factory Automation, ETFA

Abstract
There is a growing need to develop new tools to help end users in tasks related to the design, monitoring, maintenance and commissioning of industrial processes. The complexity of the industrial environment requires that these tools have flexible features in order to provide valuable data at the early planning and design phases. Furthermore, it is known that industrial processes have stringent requirements for dependability (reliability and availability), since failures can cause economic losses, environmental damages and danger to people. The lack of tools that enable the evaluation of faults in industrial processes could mitigate these problems. In this work we present a framework which is able to estimate the reliability and availability of industrial processes that can be modeled as a graph. The framework transforms the graph structure into a Fault Tree model in order to analyze their dependability. In order to validate the proposal we conduct a dependability study of an industrial process. © 2013 IEEE.

2014

Evaluating the Impact of Uncontrolled Traffic Sources upon Real-Time Communication in IEEE 802.11s Mesh Networks

Authors
Viegas, CMD; Vasques, F; Portugal, P;

Publication
2014 12TH IEEE INTERNATIONAL CONFERENCE ON INDUSTRIAL INFORMATICS (INDIN)

Abstract
This paper assesses the interference caused by uncontrolled traffic sources upon real-time traffic in IEEE 802.11s mesh networks. It was considered a mesh network transmitting real-time traffic and an external interference was injected in order to evaluate its impact over the real-time communication. A set of experiments were performed in ns-3 and different scenarios were evaluated, where the end-to-end delay, message loss and deadline miss ratios were chosen as performance metrics. It can be inferred that the real-time traffic in 802.11s is highly affected by external interferences, and therefore that must be taken into account when setting-up such type of networks.

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