263 research outputs found
Cross-layer framework and optimization for efficient use of the energy budget of IoT Nodes
Both physical and MAC-layer need to be jointly optimized to maximize the
autonomy of IoT devices. Therefore, a cross-layer design is imperative to
effectively realize Low Power Wide Area networks (LPWANs). In the present
paper, a cross-layer assessment framework including power modeling is proposed.
Through this simulation framework, the energy consumption of IoT devices,
currently deployed in LoRaWAN networks, is evaluated. We demonstrate that a
cross-layer approach significantly improves energy efficiency and overall
throughput. Two major contributions are made. First, an open-source LPWAN
assessment framework has been conceived. It allows testing and evaluating
hypotheses and schemes. Secondly, as a representative case, the LoRaWAN
protocol is assessed. The findings indicate how a cross-layer approach can
optimize LPWANs in terms of energy efficiency and throughput. For instance, it
is shown that the use of larger payloads can reduce up to three times the
energy consumption on quasi-static channels yet may bring an energy penalty
under adverse dynamic conditions
Goodness-of-fit tests based on sample space partitions : a unifying overview
Recently the authors have proposed tests for the one-sample and the κ-sample problem, and a test for independence. All three tests are based on sample space
partitions, but they were originally developed in different papers. Here we give an
overview of the construction of these tests, stressing the common underlying concept of “sample space partitions.
High precision hybrid RF and ultrasonic chirp-based ranging for low-power IoT nodes
Hybrid acoustic-RF systems offer excellent ranging accuracy, yet they typically come at a power consumption that is too high to meet the energy constraints of mobile IoT nodes. We combine pulse compression and synchronized wake-ups to achieve a ranging solution that limits the active time of the nodes to 1 ms. Hence, an ultra low-power consumption of 9.015 µW for a single measurement is achieved. The operation time is estimated on 8.5 years on a CR2032 coin cell battery at a 1 Hz update rate, which is over 250 times larger than state-of-the-art RF-based positioning systems. Measurements based on a proof-of-concept hardware platform show median distance error values below 10 cm. Both simulations and measurements demonstrate that the accuracy is reduced at low signal-to-noise ratios and when reflections occur. We introduce three methods that enhance the distance measurements at a low extra processing power cost. Hence, we validate in realistic environments that the centimeter accuracy can be obtained within the energy budget of mobile devices and IoT nodes. The proposed hybrid signal ranging system can be extended to perform accurate, low-power indoor positioning
High Precision Hybrid RF and Ultrasonic Chirp-based Ranging for Low-Power IoT Nodes
Hybrid acoustic-RF systems offer excellent ranging accuracy, yet they
typically come at a power consumption that is too high to meet the energy
constraints of mobile IoT nodes. We combine pulse compression and synchronized
wake-ups to achieve a ranging solution that limits the active time of the nodes
to 1 ms. Hence, an ultra low-power consumption of 9.015 {\mu}W for a single
measurement is achieved. Measurements based on a proof-of-concept hardware
platform show median distance error values below 10 cm. Both simulations and
measurements demonstrate that the accuracy is reduced at low signal-to-noise
ratios and when reflections occur. We introduce three methods that enhance the
distance measurements at a low extra processing power cost. Hence, we validate
in realistic environments that the centimeter accuracy can be obtained within
the energy budget of mobile devices and IoT nodes. The proposed hybrid signal
ranging system can be extended to perform accurate, low-power indoor
positioning.Comment: 19 pages, 18 figures, 5 table
Synthesis and conformational properties of 3,4-difluoro-L-prolines
Fluorinated proline derivatives have found diverse applications in areas ranging from medicinal chemistry over structural biochemistry to organocatalysis. Depending on the stereochemistry of monofluorination at the proline 3- or 4-position, different effects on the conformational properties of proline (ring pucker, cis/trans isomerization) are introduced. With fluorination at both 3- and 4-positions, matching or mismatching effects can occur depending on the relative stereochemistry. Here we report, in full, the syntheses and conformational properties of three out of the four possible 3,4-difluoro-L-proline diastereoisomers. The yet unreported conformational properties are described for (3S,4S)- and (3R,4R)-difluoro-L-proline, which are shown to bias ring pucker and cis/trans ratios on the same order of magnitude as their respective monofluorinated progenitors, although with significantly faster amide cis/trans isomerization rates. The reported analogues thus expand the scope of available fluorinated proline analogues as tools to tailor proline's distinct conformational and dynamical properties, allowing for the interrogation of its role in, for instance, protein stability or folding
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