216 research outputs found
Proposition and validation of an original MAC layer with simultaneous medium accesses for low latency wireless control/command applications
Control/command processes require a transmission system with some
characteristics like high reliability, low latency and strong guarantees on
messages delivery. Concerning wire networks, field buses technologies like FIP
offer this kind of service (periodic tasks, real time constraints...).
Unfortunately, few wireless technologies can propose a communication system
which respects such constraints. Indeed, wireless transmissions must deal with
medium characteristics which make impossible the direct translation of
mechanisms used with wire networks. The purpose of this paper is to present an
original Medium Access Control (MAC) layer for a real time Low Power-Wireless
Personal Area Network (LP-WPAN). The proposed MAC-layer has been validated by
several complementary methods; in this paper, we focus on the specific
Simultaneous Guaranteed Time Slot (SGTS) part
Dimensioning and worst-case analysis of cluster-tree sensor networks
Modeling the fundamental performance limits of Wireless Sensor Networks (WSNs) is of paramount
importance to understand their behavior under the worst-case conditions and to make the appropriate
design choices. This is particular relevant for time-sensitive WSN applications, where the
timing behavior of the network protocols (message transmission must respect deadlines) impacts
on the correct operation of these applications. In that direction this paper contributes with a
methodology based on Network Calculus, which enables quick and efficient worst-case dimensioning
of static or even dynamically changing cluster-tree WSNs where the data sink can either
be static or mobile. We propose closed-form recurrent expressions for computing the worst-case
end-to-end delays, buffering and bandwidth requirements across any source-destination path in a
cluster-tree WSN. We show how to apply our methodology to the case of IEEE 802.15.4/ZigBee
cluster-tree WSNs. Finally, we demonstrate the validity and analyze the accuracy of our methodology
through a comprehensive experimental study using commercially available technology, namely
TelosB motes running TinyOS
A Study of Medium Access Control Protocols for Wireless Body Area Networks
The seamless integration of low-power, miniaturised, invasive/non-invasive
lightweight sensor nodes have contributed to the development of a proactive and
unobtrusive Wireless Body Area Network (WBAN). A WBAN provides long-term health
monitoring of a patient without any constraint on his/her normal dailylife
activities. This monitoring requires low-power operation of
invasive/non-invasive sensor nodes. In other words, a power-efficient Medium
Access Control (MAC) protocol is required to satisfy the stringent WBAN
requirements including low-power consumption. In this paper, we first outline
the WBAN requirements that are important for the design of a low-power MAC
protocol. Then we study low-power MAC protocols proposed/investigated for WBAN
with emphasis on their strengths and weaknesses. We also review different
power-efficient mechanisms for WBAN. In addition, useful suggestions are given
to help the MAC designers to develop a low-power MAC protocol that will satisfy
the stringent WBAN requirements.Comment: 13 pages, 8 figures, 7 table
Experimental evaluation of ZigBee and IEEE 802.15.4 for data-intensive body sensor networks
This paper presents results concerning an experimental performance evaluation of ZigBee and IEEE 802.15.4 networks applied to the transport of data-intensive traffic generated by body sensor network applications. The experimental platform is based on the Z-Stack and TIMAC software stacks and the CC2530 device, from Texas Instruments. Three quality of service metrics are evaluated: goodput, delivery ratio and delay. Results are provided for both star and tree topologies. It was observed that the overhead introduced by the stack implementation has a significant impact on the performance results. Overall, the performance of the ZigBee star topology was very good, even in the worst conditions, provided the acknowledgement mechanism was enabled. A router deadlock problem detected in other ZigBee implementations was not observed with the Z-Stack. However, we identified two different situations, triggered by periods of high traffic load, on which the ZigBee router stops relaying packets, causing a significant degradation on the network performance.Fundação para a Ciência e a Tecnologia (FCT
Evaluation of the impact of the topology and Hidden Nodes in the performance of a ZigBee Network
Low power and small footprint IEEE 802.15.4/ZigBee based devices
are a promising alternative to 802.11a/b/g and proprietary protocols for
non-critical patient monitoring under important scenarios such as post-op and
emergency rooms. However, their use in a healthcare facility to monitor several
mobile patients poses several difficulties, mainly because these protocols were
primarily designed to operate in low traffic load scenarios. This work presents
simulation results used to evaluate the performance of an IEEE 802.15.4/ Zig-
Bee based wireless sensors network (WSN) in a vital signs monitoring scenario,
for both star and tree based network topologies. The scalability problem in nonbeacon
enabled networks is addressed to quantify the degradation in quality of
service (QoS) markers when the number of sensor nodes increase. Additionally,
the impact of hidden nodes is assessed for the star topology. Results indicate
that, to achieve a delivery ratio (DR) higher than 99%, the number of electrocardiogram
(ECG) nodes in a star network must not exceed 35. However, considering
a tree topology, the maximum number of nodes must be reduced to 18
to maintain the same DR. The network performance is severely impacted by
hidden nodes. For instance, in the absence of hidden nodes, a star network
consisting of 32 ECG nodes presents a DR higher than 99%; however, if the
percentage of hidden nodes is increased to 5%, it drops to 94%. If the same percentage
of hidden nodes is maintained, it is necessary to reduce the number of
nodes to 13 to reestablish a 99% DR.Fundação para a Ciência e a Tecnologia (FCT)Grupo AMI - Assistência Médica Integral (Casa de Saúde Guimarães, SA
IEEE 802.15.4 Wireless Security: Self-Assessment Frameworks
This thesis analyzes the security of networks built upon the IEEE 802.15.4 standard, specifically in regard to the ability of an attacker to manipulate such networks under real-world conditions. The author presents a set of tools, both hardware and software, that advance the state-of-the-art in reconnaissance and site surveying, intelligent packet generation, and launching of attacks. Specifically, tools provide increased hardware support for the KillerBee toolkit, a Scapy layer for forming 802.15.4 packets, reflexive jamming of packets, and other research enablers. This work aims to advance the ability of security auditors to understand the threats to IEEE 802.15.4 networks by providing auditors usable and low-cost tools to carry out vulnerability assessments
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