102 research outputs found
A vision of cyber-physical internet
When the Internet was born, the purpose was to
interconnect computers to share digital data at large-scale. On
the other hand, when embedded systems were born, the objective
was to control system components under real-time constraints
through sensing devices, typically at small to medium scales.
With the great evolution of the Information and Communication
Technology (ICT), the tendency is to enable ubiquitous and
pervasive computing to control everything (physical processes
and physical objects) anytime and at a large-scale. This new
vision gave recently rise to the paradigm of Cyber-Physical
Systems (CPS). In this position paper, we provide a realistic
vision to the concept of the Cyber-Physical Internet (CPI),
discuss its design requirements and present the limitations of
the current networking abstractions to fulfill these requirements.
We also debate whether it is more productive to adopt a
system integration approach or a radical design approach for
building large-scale CPS. Finally, we present a sample of realtime
challenges that must be considered in the design of the
Cyber-Physical Internet
Beacon scheduling in cluster-tree IEEE 802.15.4/ZigBee wireless sensor networks
The recently standardized IEEE 802.15.4/Zigbee protocol stack offers great potentials for ubiquitous and
pervasive computing, namely for Wireless Sensor Networks (WSNs). However, there are still some open and
ambiguous issues that turn its practical use a challenging task. One of those issues is how to build a
synchronized multi-hop cluster-tree network, which is quite suitable for QoS support in WSNs. In fact, the
current IEEE 802.15.4/Zigbee specifications restrict the synchronization in the beacon-enabled mode (by the
generation of periodic beacon frames) to star-based networks, while it supports multi-hop networking using
the peer-to-peer mesh topology, but with no synchronization. Even though both specifications mention the
possible use of cluster-tree topologies, which combine multi-hop and synchronization features, the
description on how to effectively construct such a network topology is missing. This report tackles this
problem, unveils the ambiguities regarding the use of the cluster-tree topology and proposes two collisionfree
beacon frame scheduling schemes
Energy and delay trade-off of the GTS allocation mechanism in IEEE 802.15.4 for wireless sensor networks
The IEEE 802.15.4 protocol proposes a flexible communication solution for Low-Rate Wireless Personal
Area Networks (LR-WPAN) including wireless sensor networks (WSNs). It presents the advantage to fit
different requirements of potential applications by adequately setting its parameters. When in beaconenabled
mode, the protocol can provide timeliness guarantees by using its Guaranteed Time Slot (GTS)
mechanism. However, power-efficiency and timeliness guarantees are often two antagonistic requirements in
wireless sensor networks. The purpose of this paper is to analyze and propose a methodology for setting the
relevant parameters of IEEE 802.15.4-compliant WSNs that takes into account a proper trade-off between
power-efficiency and delay bound guarantees. First, we propose two accurate models of service curves for a
GTS allocation as a function of the IEEE 802.15.4 parameters, using Network Calculus formalism. We then
evaluate the delay bound guaranteed by a GTS allocation and express it as a function of the duty cycle. Based
on the relation between the delay requirement and the duty cycle, we propose a power-efficient superframe
selection method that simultaneously reduces power consumption and enables meeting the delay
requirements of real-time flows allocating GTSs. The results of this work may pave the way for a powerefficient
management of the GTS mechanism in an IEEE 802.15.4 cluster
Implementation of the i-GAME mechanism in IEEE 802.15.4 WPANs
This technical report describes the implementation details of the Implicit GTS Allocation Mechanism (i-GAME), for
the IEEE 802.15.4 protocol. The i-GAME was implemented in nesC/TinyOS for the CrossBow MICAz mote, over our
own implementation of the IEEE 802.15.4 protocol stack. This document provides the implementation details, including
a description of the i-GAME software interfaces
Allocation of control and data channels for Large-Scale Wireless Sensor Networks
Both IEEE 802.15.4 and 802.15.4a standards allow for dynamic channel
allocation and use of multiple channels available at their physical layers but
its MAC protocols are designed only for single channel. Also, sensor's
transceivers such as CC2420 provide multiple channels and as shown in [1], [2]
and [3] channel switch latency of CC2420 transceiver is just about 200s.
In order to enhance both energy efficiency and to shorten end to end delay, we
propose, in this report, a spectrum-efficient frequency allocation schemes that
are able to statically assign control channels and dynamically reuse data
channels for Personal Area Networks (PANs) inside a Large-Scale WSN based on
UWB technology
Implementation details of the time division beacon scheduling approach for ZigBee cluster-tree networks
This technical report describes the implementation details of the Time Division Beacon Scheduling Approach in IEEE
802.15.4/ZigBee Cluster-Tree Networks. In this technical report we describe the implementation details, focusing on
some aspects of the ZigBee Network Layer and the Time Division Beacon Scheduling mechanism. This report
demonstrates the feasibility of our approach based on the evaluation of the experimental results. We also present an
overview of the ZigBee address and tree-routing scheme
IEEE 802.15.4 for wireless sensor networks: a technical overview
Low-rate low-power consumption and low-cost
communication are the key points that lead to the specification of
the IEEE 802.15.4 standard. This paper overviews the technical
features of the physical layer and the medium access control sublayer
mechanisms of the IEEE 802.15.4 protocol that are most
relevant for wireless sensor network applications. We also
discuss the ability of IEEE 802.15.4 to fulfil the requirements of
wireless sensor network applications
Challenges and trends in wireless ubiquitous computing systems
In the last decade, the Internet paradigm has been evolving toward a new frontier with the emergence of ubiquitous and pervasive systems, including wireless sensor networks, ad hoc networks, RFID systems, and wireless embedded systems. In fact, while the initial purpose of the Internet was to interconnect computers to share digital data at large scale, the current tendency is to enable ubiquitous and pervasive computing to control everything anytime and at a large scale. This new paradigm has given rise to a new generation of networked systems, commonly known as Internet-of-Things or Cyber-Physical Systems
IEEE 802.15.4: a Federating Communication Protocol for Time-Sensitive Wireless Sensor Networks
Wireless Sensor Networks (WSNs) have been attracting increasing interests for developing a new
generation of embedded systems with great potential for many applications such as surveillance,
environment monitoring, emergency medical response and home automation. However, the
communication paradigms in WSNs differ from the ones attributed to traditional wireless networks,
triggering the need for new communication protocols. In this context, the recently standardised IEEE
802.15.4 protocol presents some potentially interesting features for deployment in wireless sensor
network applications, such as power-efficiency, timeliness guarantees and scalability. Nevertheless,
when addressing WSN applications with (soft/hard) timing requirements some inherent paradoxes
emerge, such as power-efficiency versus timeliness, triggering the need of engineering solutions for an
efficient deployment of IEEE 802.15.4 in WSNs. In this technical report, we will explore the most
relevant characteristics of the IEEE 802.15.4 protocol for wireless sensor networks and present the
most important challenges regarding time-sensitive WSN applications. We also provide some timing
performance and analysis of the IEEE 802.15.4 that unveil some directions for resolving the
previously mentioned paradoxes
On the use of the ZigBee protocol for wireless sensor networks
This project was developed within the ART-WiSe framework of the IPP-HURRAY group
(http://www.hurray.isep.ipp.pt), at the Polytechnic Institute of Porto (http://www.ipp.pt).
The ART-WiSe – Architecture for Real-Time communications in Wireless Sensor networks – framework
(http://www.hurray.isep.ipp.pt/art-wise) aims at providing new communication architectures and
mechanisms to improve the timing performance of Wireless Sensor Networks (WSNs). The architecture is
based on a two-tiered protocol structure, relying on existing standard communication protocols, namely
IEEE 802.15.4 (Physical and Data Link Layers) and ZigBee (Network and Application Layers) for Tier 1
and IEEE 802.11 for Tier 2, which serves as a high-speed backbone for Tier 1 without energy consumption
restrictions.
Within this trend, an application test-bed is being developed with the objectives of implementing, assessing
and validating the ART-WiSe architecture. Particularly for the ZigBee protocol case; even though there is a
strong commercial lobby from the ZigBee Alliance (http://www.zigbee.org), there is neither an open source
available to the community for this moment nor publications on its adequateness for larger-scale WSN
applications. This project aims at fulfilling these gaps by providing: a deep analysis of the ZigBee
Specification, mainly addressing the Network Layer and particularly its routing mechanisms; an
identification of the ambiguities and open issues existent in the ZigBee protocol standard; the proposal of
solutions to the previously referred problems; an implementation of a subset of the ZigBee Network Layer,
namely the association procedure and the tree routing on our technological platform (MICAz motes, TinyOS
operating system and nesC programming language) and an experimental evaluation of that routing
mechanism for WSNs
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