35 research outputs found
A dynamic approach to rebalancing bike-sharing systems
Bike-sharing services are flourishing in Smart Cities worldwide. They provide a low-cost and environment-friendly transportation alternative and help reduce traffic congestion. However, these new services are still under development, and several challenges need to be solved. A major problem is the management of rebalancing trucks in order to ensure that bikes and stalls in the docking stations are always available when needed, despite the fluctuations in the service demand. In this work, we propose a dynamic rebalancing strategy that exploits historical data to predict the network conditions and promptly act in case of necessity. We use Birth-Death Processes to model the stations' occupancy and decide when to redistribute bikes, and graph theory to select the rebalancing path and the stations involved. We validate the proposed framework on the data provided by New York City's bike-sharing system. The numerical simulations show that a dynamic strategy able to adapt to the fluctuating nature of the network outperforms rebalancing schemes based on a static schedule
Joint Optimization of Energy Efficiency and Data Compression in TDMA-Based Medium Access Control for the IoT - Extended Version
Energy efficiency is a key requirement for the Internet of Things, as many
sensors are expected to be completely stand-alone and able to run for years
without battery replacement. Data compression aims at saving some energy by
reducing the volume of data sent over the network, but also affects the quality
of the received information. In this work, we formulate an optimization problem
to jointly design the source coding and transmission strategies for
time-varying channels and sources, with the twofold goal of extending the
network lifetime and granting low distortion levels. We propose a scalable
offline optimal policy that allocates both energy and transmission parameters
(i.e., times and powers) in a network with a dynamic Time Division Multiple
Access (TDMA)-based access scheme.Comment: 8 pages, 4 figures, revised and extended version of a paper that was
accepted for presentation at IEEE Int. Workshop on Low-Layer Implementation
and Protocol Design for IoT Applications (IoT-LINK), GLOBECOM 201
Platforms and Protocols for the Internet of Things
Building a general architecture for the Internet of Things (IoT) is a very complex task, exacerbated by the extremely large variety of devices, link layer technologies, and services that may be involved in such a system. In this paper, we identify the main blocks of a generic IoT architecture, describing their features and requirements, and analyze the most common approaches proposed in the literature for each block. In particular, we compare three of the most important communication technologies for IoT purposes, i.e., REST, MQTT, and AMQP, and we also analyze three IoT platforms: openHAB, Sentilo, and Parse. The analysis will prove the importance of adopting an integrated approach that jointly addresses several issues and is able to flexibly accommodate the requirements of the various elements of the system. We also discuss a use case which illustrates the design challenges and the choices to make when selecting which protocols and technologies to use
EC-CENTRIC: An Energy- and Context-Centric Perspective on IoT Systems and Protocol Design
The radio transceiver of an IoT device is often where most of the energy is consumed. For this reason, most research so far has focused on low power circuit and energy efficient physical layer designs, with the goal of reducing the average energy per information bit required for communication. While these efforts are valuable per se, their actual effectiveness can be partially neutralized by ill-designed network, processing and resource management solutions, which can become a primary factor of performance degradation, in terms of throughput, responsiveness and energy efficiency. The objective of this paper is to describe an energy-centric and context-aware optimization framework that accounts for the energy impact of the fundamental functionalities of an IoT system and that proceeds along three main technical thrusts: 1) balancing signal-dependent processing techniques (compression and feature extraction) and communication tasks; 2) jointly designing channel access and routing protocols to maximize the network lifetime; 3) providing self-adaptability to different operating conditions through the adoption of suitable learning architectures and of flexible/reconfigurable algorithms and protocols. After discussing this framework, we present some preliminary results that validate the effectiveness of our proposed line of action, and show how the use of adaptive signal processing and channel access techniques allows an IoT network to dynamically tune lifetime for signal distortion, according to the requirements dictated by the application
3D Chocolate Printer Dropper
The Mechanical Engineering Department at Washington University in St. Louis is working to stimulate interest in the fields of fluid dynamics and thermal sciences, as students are not typically exposed to these topics within the first two years of school. Dr. Okamoto, Jeff Krampf, and Dr. Weisensee of the Mechanical Engineering Department would like to remedy this situation by developing a laboratory experiment for first year students that utilizes a 3D chocolate printer to teach thermal-fluid concepts in a fun and engaging manner. The goal of this project is to build a chocolate droplet dispensing system, which is a part of the 3D chocolate printing machine. The device must be able to melt chocolate and generate droplets in consistent and adjustable time intervals. The dispensing height of the nozzle should be manually changeable so that the students can understand how height and frequency influence the droplet impact. While the primary function of this device is to help students learn thermal-fluids in a fun yet educational environment, it is also imperative that the device is safe for students to use
Channel Access in Wireless Networks: Protocol Design of Energy-Aware Schemes for the IoT and Analysis of Existing Technologies
The design of channel access policies has been an object of study since the deployment of the first wireless networks, as the Medium Access Control (MAC) layer is responsible for coordinating transmissions to a shared channel and plays a key role in the network performance. While the original target was the system throughput, over the years the focus switched to communication latency, Quality of Service (QoS) guarantees, energy consumption, spectrum efficiency, and any combination of such goals.
The basic mechanisms to use a shared channel, such as ALOHA, TDMA- and FDMA-based policies, have been introduced decades ago. Nonetheless, the continuous evolution of wireless networks and the emergence of new communication paradigms demand the development of new strategies to adapt and optimize the standard approaches so as to satisfy the requirements of applications and devices.
This thesis proposes several channel access schemes for novel wireless technologies, in particular Internet of Things (IoT) networks, the Long-Term Evolution (LTE) cellular standard, and mmWave communication with the IEEE802.11ad standard.
The first part of the thesis concerns energy-aware channel access policies for IoT networks, which typically include several battery-powered sensors.
In scenarios with energy restrictions, traditional protocols that do not consider the energy consumption may lead to the premature death of the network and unreliable performance expectations. The proposed schemes show the importance of accurately characterizing all the sources of energy consumption (and inflow, in the case of energy harvesting), which need to be included in the protocol design. In particular, the schemes presented in this thesis exploit data processing and compression techniques to trade off QoS for lifetime. We investigate contention-free and contention-based chanel access policies for different scenarios and application requirements.
While the energy-aware schemes proposed for IoT networks are based on a clean-slate approach that is agnostic of the communication technology used, the second part of the thesis is focused on the LTE and IEEE802.11ad standards.
As regards LTE, the study proposed in this thesis shows how to use machine-learning techniques to infer the collision multiplicity in the channel access phase, information that can be used to understand when the network is congested and improve the contention resolution mechanism. This is especially useful for massive access scenarios; in the last years, in fact, the research community has been investigating on the use of LTE for Machine-Type Communication (MTC).
As regards the standard IEEE802.11ad, instead, it provides a hybrid MAC layer with contention-based and contention-free scheduled allocations, and a dynamic channel time allocation mechanism built on top of such schedule. Although this hybrid scheme is expected to meet heterogeneous requirements, it is still not clear how to develop a schedule based on the various traffic flows and their demands. A mathematical model is necessary to understand the performance and limits of the possible types of allocations and guide the scheduling process. In this thesis, we propose a model for the contention-based access periods which is aware of the interleaving of the available channel time with contention-free allocations
Enabling LTE RACH Collision Multiplicity Detection via Machine Learning
The collision resolution mechanism in the Random Access Channel (RACH)
procedure of the Long-Term Evolution (LTE) standard is known to represent a
serious bottleneck in case of machine-type traffic. Its main drawbacks are seen
in the facts that Base Stations (eNBs) typically cannot infer the number of
collided User Equipments (UEs) and that collided UEs learn about the collision
only implicitly, through the lack of the feedback in the later stage of the
RACH procedure. The collided UEs then restart the procedure, thereby increasing
the RACH load and making the system more prone to collisions. In this paper, we
leverage machine learning techniques to design a system that outperforms the
state-of-the-art schemes in preamble detection for the LTE RACH procedure. Most
importantly, our scheme can also estimate the collision multiplicity, and thus
gather information about how many devices chose the same preamble. This data
can be used by the eNB to resolve collisions, increase the supported system
load and reduce transmission latency. The presented approach is applicable to
novel 3GPP standards that target massive IoT, e.g., LTE-M and NB-IoT.Comment: Submitted to IEEE GLOBECOM 201
Phase preĢcoce des troubles psychotiques :Etude de correĢlation entre l'eĢvaluation neurocognitive et les donneĢes meĢtaboliques.
Introduction : La schizophreĢnie est une maladie reĢcurrente dans notre socieĢteĢ et touche preĢs d'1% de la population. Le premier acceĢs de psychose survient en geĢneĢral entre 18 et 25 ans chez les hommes et entre 24 et 35 ans chez les femmes. Les symptoĢmes sont classeĢs en quatre sous- groupes, (1) les symptoĢmes positifs comprenant les hallucinations, deĢlires, troubles de perception, troubles de la penseĢe et (2) les symptoĢmes neĢgatifs qui sont les affects aplatis, l'apathie et le retrait social, (3) les symptoĢmes de base qui consistent en troubles perceptifs, moteurs et des eĢmotions et enfin (4) les symptoĢmes cognitifs tels que des troubles de l'attention, de la meĢmoire et des fonctions exeĢcutives, qui surviennent dans 60 aĢ 80% des cas. La maladie est freĢquemment accompagneĢe de co-morbiditeĢs (deĢpression, abus de substances, troubles obsessionnels compulsifs, anxieĢteĢ). L'eĢvolution aĢ long terme diffeĢre selon les patients, 35% eĢvolueront de manieĢre chronique et avec une aggravation progressive du deĢficit, 35% eĢvolueront vers une chroniciteĢ de la maladie mais sans atteinte reĢsiduelle, 8% eĢvolueront de manieĢre chronique avec la persistance de symptoĢmes reĢsiduels et enfin on observera une reĢmission compleĢte apreĢs le premier eĢpisode psychotique sans handicap reĢsiduel chez 22% des patients. Les recherches concernant la schizophreĢnie ont fait une avanceĢe consideĢrable ces vingt dernieĢres anneĢes, que cela soit par la deĢfinition plus preĢcise des troubles cognitifs ou encore par la mise en eĢvidence de certaines substances neurobiologiques, qui se trouvent deĢreĢguleĢes chez les patients atteints de la maladie. C'est le cas du glutathion (GSH) ainsi que des enzymes et proteĢines intervenant dans son meĢtabolisme. Il persiste cependant encore beaucoup d'inconnues, et une meilleure connaissance des meĢcanismes biologiques opeĢrant dans la phase preĢcoce des psychoses contribuerait de facĢ§on certaine aĢ une ameĢlioration de l'identification et de la prise en charge des patients pendant la phase prodromique de la maladie et permettrait le deĢveloppement de cibles pharmacologiques plus preĢcises. Objectifs : Ce travail consiste en une analyse de donneĢes reĢcolteĢes par deux axes de recherche de l'eĢtude sur les bio-marqueurs dans la phase preĢcoce des troubles psychotiques effectueĢe actuellement au Centre de Neurosciences Psychiatriques, aĢ savoir d'une part l'identification de marqueurs neurocognitifs preĢcoces sur la base d'une seĢrie de tests neurocognitifs eĢvaluant (1) la vitesse de traitement de l'information, (2) l'attention et la vigilance, (3) la meĢmoire de travail, (4) l'apprentissage verbal, (5) l'apprentissage visuel et (6) le raisonnement et la reĢsolution de probleĢmeet d'autre part l'identification de bio-marqueurs meĢtaboliques associeĢs aux phases preĢcoces de la maladie. Dans cette eĢtude, les patients sont compareĢs aĢ un groupe d'individus controĢles et les questions suivantes sont poseĢes : Ā« Ā« Dans une population de patients en premier eĢpisode psychotique, les performances neurocognitives sont-elles significativement amoindries compareĢ aĢ un groupe d'individus controĢles ? Ā» et Ā« Dans cette meĢme population, les deĢficits neurocognitifs survenant dans la phase de psychose deĢbutante sont-ils en correĢlation avec des variations de biomarqueurs meĢtaboliques ? Ā». MeĢthodes : Dans cette eĢtude, nous comparons un eĢchantillon de 30 patients provenant d'une cohorte de patients souffrant de psychose eĢmergente (Programme TIPP, Lausanne) aĢ un eĢchantillon de 30 sujets controĢles. L'eĢvaluation neurocognitive des patients et des sujets controĢles a eĢteĢ reĢaliseĢe par des tests neuropsychologiques s'inspirant de la batterie cognitive MATRICS (Measurement and Treatment Research to Improve Cognition in Schizophrenia). Les donneĢes biologiques proviennent (1) de la culture de fibroblastes deĢriveĢs de biopsies de peau preĢleveĢes aupreĢs de chaque patient et individu controĢle, dont le meĢtabolisme cellulaire a eĢteĢ caracteĢriseĢ dans des conditions basales, ou apreĢs l'ajout de tert-butylhydroquinone (t-BHQ) qui induit un stress oxydatif ; (2) de l'analyse meĢtabolique de preĢleĢvements sanguins eĢgalement effectueĢs aupreĢs de chaque patient et controĢle et enfin (3) du taux de glutathion mesureĢ par imagerie par reĢsonance magneĢtique spectroscopique (MRS). L'analyse et le croisement de ces bases de donneĢes ont eĢteĢ faite aĢ l'aide du logiciel SPSS. ReĢsultats et conclusion : Les performances neurocognitives de l'eĢchantillon de patients sont significativement diminueĢes par rapport au groupe d'individus controĢles, et pour chacun des domaines neurocognitifs. La diffeĢrence est la plus grande pour les tests HVLT-R (apprentissage verbal) et les tests BACS-SC et TMT-A (vitesse de traitement). Concernant la deuxieĢme partie du travail, (1) un deĢficit dans les domaines neurocognitifs de l'attention/vigilance (CPT-IP) et la meĢmoire de travail verbale (WMS-III) est correĢleĢ avec un taux de glutathion sanguin total eĢleveĢ (p-value = 0.03 et 0.02) ; (2) un deĢficit dans la vitesse de traitement (TMT-A) est correĢleĢ aĢ un taux de GSH ceĢreĢbral diminueĢ (p-value=0.047) et (3) un deĢficit dans le domaine du raisonnement et de la reĢsolution de probleĢme (NAB lab) est correĢleĢ avec une augmentation de l'ARN messager codant pour la proteĢine Nrf2 au niveau cellulaire (p=0.022). Selon ces reĢsultats, le GSH sanguin total, le GSH ceĢreĢbral et le Nrf2 pourraient eĢtre des bio-marqueurs permettant d'identifier les patients dans la phase preĢcoce de la maladie et leurs meĢcanismes biologiques pourraient constituer des cibles speĢcifiques dans le
deĢveloppement de traitements futurs