155 research outputs found
IEEE 802.15.4e: a Survey
Several studies have highlighted that the IEEE 802.15.4 standard presents a number of limitations such as low reliability, unbounded packet delays and no protection against interference/fading, that prevent its adoption in applications with stringent requirements in terms of reliability and latency. Recently, the IEEE has released the 802.15.4e amendment that introduces a number of enhancements/modifications to the MAC layer of the original standard in order to overcome such limitations. In this paper we provide a clear and structured overview of all the new 802.15.4e mechanisms. After a general introduction to the 802.15.4e standard, we describe the details of the main 802.15.4e MAC behavior modes, namely Time Slotted Channel Hopping (TSCH), Deterministic and Synchronous Multi-channel Extension (DSME), and Low Latency Deterministic Network (LLDN). For each of them, we provide a detailed description and highlight the main features and possible application domains. Also, we survey the current literature and summarize open research issues
A Localized Slot Allocation Algorithm for Wireless Sensor Networks
While energy efficiency is typically considered the
major concern in wireless sensor networks (WSNs), many
real-life applications also require reliability, timeliness, and
scalability. In such scenarios, Time Division Multiple Access
(TDMA) is typically used for data communication, as it avoids
collisions and provides predictable latency and minimum
energy consumption. TDMA requires a slot scheduling
algorithm to allocate transmission slots to sensor nodes. In
this paper, we propose a decentralized slot allocation
algorithm which is localized and self adaptive, i.e., each node
selects its slot(s) and adapts its behavior only basing on
locally-available information. We derive analytically the time
taken by the algorithm and the average energy consumed by
the network to achieve a complete schedule. We also show
that our solution performs significantly better than another
previous similar algorithm
Just-in-Time Adaptive Algorithm for Optimal Parameter Setting in 802.15.4 WSNs
Recent studies have shown that the IEEE 802.15.4 MAC protocol suffers from severe limitations, in terms
of reliability and energy efficiency, when the CSMA/CA parameter setting is not appropriate. However,
selecting the optimal setting that guarantees the application reliability requirements, with minimum
energy consumption, is not a trivial task in wireless sensor networks, especially when the operating
conditions change over time. In this paper we propose a Just-in-Time LEarning-based Adaptive Parameter
tuning (JIT-LEAP) algorithm that adapts the CSMA/CA parameter setting to the time-varying operating
conditions by also exploiting the past history to find the most appropriate setting for the current
conditions. Following the approach of active adaptive algorithms, the adaptation mechanism of JIT-LEAP
is triggered by a change detection test only when needed (i.e., in response to a change in the operating
conditions). Simulation results show that the proposed algorithm outperforms other similar algorithms,
both in stationary and dynamic scenarios
Strategies for Optimal MAC Parameter Setting in IEEE 802.15.4 Wireless Sensor Networks: a Performance Comparison
Recent studies have shown that the IEEE 802.15.4
MAC protocol may suffer from severe limitations in terms of
reliability and energy efficiency if a non appropriate
parameter setting is used. Hence, a number of solutions have
been proposed to select the optimal parameter setting to
provide reliability with minimum energy consumption. In this
paper we compare, by simulation, three different algorithms
that take different approaches to the problem, namely offline
computation, model-based adaptation, and measurement-based
adaptation. We show that adaptive algorithms perform well,
however the model-based adaptive approach has some
limitations that make it unsuitable in practical scenarios,
where operating conditions may vary over time and
transmission errors cannot be neglected. Instead, the
measurement-based adaptive approach is flexible and
effectiv
The arterial blood supply of the temporomandibular joint: an anatomical study and clinical implications.
Purpose: The aim of this study was to analyze three-dimensional images of the arterial supply to the temporomandibular
joint.
Materials and Methods: Ten patients (five men and five women, mean age 36 years) without signs or symptoms of
temporomandibular disorders, who underwent contrast-enhanced computed tomographic (CT) scanning with
intravenous contrast, were studied. The direct volume rendering technique of CT images was used, and a data set of
images to visualize the vasculature of the human temporomandibular joint in three dimensions was created. After
elaboration of the data through post-processing, the arterial supply of the temporomandibular joint was studied.
Results: The analysis revealed the superficial temporal artery, the anterior tympanic artery, the deep temporal
artery, the auricular posterior artery, the transverse facial artery, the middle meningeal artery, and the maxillary
artery with their branches as the main arterial sources for the lateral and medial temporomandibular joint.
Conclusion: The direct volume rendering technique was found to be successful in the assessment of the arterial
supply to the temporomandibular joint. The superficial temporal artery and maxillary artery ran along the lateral
and medial sides of the condylar neck, suggesting that these arteries are at increased risk during soft-tissue procedures
such as an elective arthroplasty of the temporomandibular joint
Search for dark Higgsstrahlung in e+ e- -> mu+ mu- and missing energy events with the KLOE experiment
We searched for evidence of a Higgsstrahlung process in a secluded sector,
leading to a final state with a dark photon U and a dark Higgs boson h', with
the KLOE detector at DAFNE. We investigated the case of h' lighter than U, with
U decaying into a muon pair and h' producing a missing energy signature. We
found no evidence of the process and set upper limits to its parameters in the
range 2m_mu<m_U<1000 MeV, m_h'<m_U.Comment: 16 pages, 7 figures, submitted to Physics Letters
Measurement of the transition form factor with the KLOE detector
A measurement of the vector to pseudoscalar conversion decay with the KLOE experiment is presented. A sample of signal
events was selected from a data set of 1.7 fb of collisions at
collected at the DANE collider. These
events were used to obtain the first measurement of the transition form factor
and a new measurement of the branching ratio of the
decay: . The result improves
significantly on previous measurements and is in agreement with theoretical
predictions.Comment: 13 pages, 4 figures; matches published versio
Limit on the production of a new vector boson in , U with the KLOE experiment
The recent interest in a light gauge boson in the framework of an extra U(1)
symmetry motivates searches in the mass range below 1 GeV.
We present a search for such a particle, the dark photon, in , U based on 28 million
events collected at DANE
by the KLOE experiment. The production by initial-state radiation
compensates for a loss of sensitivity of previous KLOE , searches due to the small branching ratios in
the resonance region. We found no evidence for a signal and set a
limit at 90\% CL on the mixing strength between the photon and the dark photon,
, in the U mass range between and ~MeV. Above 700 MeV
this new limit is more stringent than previous ones.Comment: 6 pages, 9 figures, 1 table, submitted to Phys. Lett.
Precision measurement of the Dalitz plot distribution with the KLOE detector
Using fb of data collected with
the KLOE detector at DANE, the Dalitz plot distribution for the decay is studied with the world's largest sample of events. The Dalitz plot density is parametrized as a polynomial
expansion up to cubic terms in the normalized dimensionless variables and
. The experiment is sensitive to all charge conjugation conserving terms of
the expansion, including a term. The statistical uncertainty of all
parameters is improved by a factor two with respect to earlier measurements.Comment: 11 pages, 9 figures, supplement: an ascii tabl
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