Approaching Optimal Centralized Scheduling with CSMA-based Random Access over Fading Channels

Carrier Sense Multiple Access (CSMA) based distributed algorithms can attain the largest capacity region as the centralized Max-Weight policy does. Despite their capability of achieving throughput-optimality, these algorithms can either incur large delay and have large complexity or only operate over non-fading channels. In this letter, by assuming arbitrary back-off time we first propose a fully distributed randomized algorithm whose performance can be pushed to the performance of the centralized Max-Weight policy not only in terms of throughput but also in terms of delay for completely-connected interference networks with fading channels. Then, inspired by the proposed algorithm we introduce an implementable distributed algorithm for practical networks with a reservation scheme. We show that the proposed practical algorithm can still achieve the performance of the centralized Max-Weight policy.Comment: accepted to IEEE Communications Letter

Load-aware Channel Selection for 802.11 WLANs with Limited Measurement

It has been known that load unaware channel selection in 802.11 networks results in high level interference, and can significantly reduce the network throughput. In current implementation, the only way to determine the traffic load on a channel is to measure that channel for a certain duration of time. Therefore, in order to find the best channel with the minimum load all channels have to be measured, which is costly and can cause unacceptable communication interruptions between the AP and the stations. In this paper, we propose a learning based approach which aims to find the channel with the minimum load by measuring only limited number of channels. Our method uses Gaussian Process Regressing to accurately track the traffic load on each channel based on the previous measured load. We confirm the performance of our algorithm by using experimental data, and show that the time consumed for the load measurement can be reduced up to 46% compared to the case where all channels are monitored.Comment: accepted to IC

Trading Accuracy and Resource Usage in Highly Dynamic Vehicular Networks

Vehicular networks bring new ways of viewing road traffic management and safety applications. For the first time, it will be possible for vehicles to exchange information and build fine-grained knowledge about the current situation, estimating risks and adapting their driving. Central to these applications is the need to exchange information in a highly dynamic environment, building a view of the current situa- tion before the conditions change. This is turn requires the distributed algorithms used to converge on low error margins quickly. In this paper, we investigate the performance of such a distributed algorithm which aims to build a common assessment of the risk level among vehicles to trade off accident risks with road throughput. In particular, we examine how the convergence rate is affected by network size and node density, and also how the error in the algorithm’s output is affected by the rate at which nodes send out update beacons. We develop a variable-rate beaconing scheme in order to find a trade-off between accuracy of outputs and network resource usage. We then formulate this as a more general optimisation problem applicable to other applications or distributed algorithmic prob- lems in highly dynamic distributed systems such as VANETs

Load Reduction for Timely Applications in the Cloud

In many IoT applications, sensor data is sent remotely to be processed, but only the freshest result is of interest. In this paper we investigate a feedback mechanism that aborts the processing of stale data at the remote end to reduce the load and save costs. The process is approximated by an M/M/∞ queueing system with a feedback loop. We find the exact expression of the average computational time saved and show that with the feedback loop in place the computation time per CPU can be cut up to 25%, making the technique very promising

On the Scalability of Addressing in Private Networks Using RPX

In recent times, the imminent lack of public IPv4 addresses has attracted the attention of both research community and industry. The cellular industry has decided to combat this problem by using IPv6 for all new terminals. However, the success of 3G network deployment will depend on the services offered to end users. Currently, almost all services reside in the public IPv4 address space, making them inaccessible to users in IPv6 networks. Thus, an intermediate translation mechanism is required. Previous studies on network address translation methods have shown that REBEKAH-IP with Port Extension (RPX) supports all types of services that can be offered to IPv6 terminals from the public IPv4 based Internet, and provides excellent scalability. However, this method suffers from an ambiguity problem which may lead to call blocking. In this paper, we present an improvement to RPX scheme in which the side effect is removed and fully scalable system. We firstly show the expected number of public IPv4 addresses utilization to the DNS of RPX server. This utilization is computed in terms of the probability of socket open requests from mobile terminals, the probability of call blocking and the estimated number of mobile terminals at the network initialization phase. The mathematical model is also provided as a guideline to determine the range of public IPv4 addresses allocated to an RPX gateway in a cellular network. In addition, the results are presented through a set of simulations. However, we proposed the RPX scheme to use a simple round robin scheduling algorithm is sub-optimal in terms of call blocking probability and further propose to use a priority queue algorithm to improve the scalability. In addition, we present extensive simulation results on the practical scalability of RPX with different traffic compositions to provide a guideline of the expected scalability in large-scale networks such as 3G networks

LUPMAC: A cross-layer MAC technique to improve the age of information over dense WLANs

Age of Information (AoI) is a relatively new metric introduced to capture the freshness of a particular piece of information. While throughput and delay measurements are widely studied in the context of dense IEEE 802.11 Wireless LANs (WLANs) little is known in the literature about the AoI in this context. In this work we study the effects on the average AoI and its variance when a sensor node is immersed in a dense IEEE 802.11 WLAN. We also introduce a new cross layer MAC technique called Latest UPdate MAC (LUPMAC) aimed at modifying the existing IEEE 802.11 in order to minimize the average AoI at the receiver end. This technique lets the MAC layer keep only the most up to date packets of a particular piece of information in the buffer. We show, through simulation, that this technique achieves significant advantages in the case of a congested dense IEEE 802.11 WLAN, and it is resilient to changes in the variance of the total network delay

On road network utility based on risk-aware link choice

Sémelin, J., Purifier et détruire. Usages politiques des massacres et génocides, coll. « La Couleur des idées », Paris, Le Seuil, 2005. Jacques Sémelin poursuit sa vaste exploration de la violence en menant une réflexion approfondie sur ses formes les plus extrêmes, les plus négatrices : la violence dans ce qu’elle a de plus macabre, de plus terrifiant, de plus absurde ou de proprement sidérant. L’auteur de ce grand livre oriente sa recherche vers ce qui paraît toujours plus inintelligible, l..

A (in)constitucionalidadeda diferença sucessória entre cônjuges e companheiros / The (in) constitutionality of successful difference between spouses and companions

A Constituição Federal de 1988, no § 3º do artigo 226, reconheceu a união estável como entidade familiar, digna de especial proteção do Estado. Após, a Lei nº 8.971/94 regulamentou o direito à sucessão ao companheiro sobrevivente e a Lei nº 9.278/96 conferiu ao convivente o direito real de habitação em condições semelhantes a do cônjuge. Contudo, o Código Civil de 2002 no artigo 1.790 suprimiu direitos que já haviam sido conquistados pelos companheiros nas legislações anteriores, além de estabelecer distinções entre o casamento e a união estável, no que se refere à sucessão causa mortis. O presente trabalho tem por finalidade abordar da inconstitucionalidade da diferença sucessória entre cônjuges e companheiros, sobre análise da aplicação dos Princípios da Igualdade e da Dignidade da Pessoa Humana. Para tanto, será abordado o recente julgamento do Recuso Extraordinário nº 878.694/MG pelo Supremo Tribunal Federal, referente à matéria de repercussão geral, bem como doutrinadores que tratam do referido tema

A discrete choice experiment to derive health utilities for Aromatic L-amino Acid Decarboxylase (AADC) deficiency

Purpose : Deriving health utilities for rare medical conditions such as aromatic L-amino acid decarboxylase (AADC) deficiency poses challenges. The rarity of AADC deficiency and the fact that this genetic condition often presents in very young children means that robust utility values cannot be derived from the child or their parent/caregiver. Alternative approaches, eg, discrete choice experiments (DCE), are required in order to provide health utilities. The aim of the study was to generate health utilities for AADC deficiency using a DCE. Methods : The DCE was completed online by panel participants from a UK representative sample. The DCE comprised 6 AADC deficiency attributes (2– 6 levels): mobility, muscle weakness, oculogyric crises, feeding ability, cognitive impairment and screaming. These were identified from published literature, clinician input, parent interviews and expert opinion. Participants were presented with 10 choice sets specified using an orthogonal design, including a repeat task to evaluate choice consistency. Participants were presented with 5 health state vignettes prior to the DCE. These were used to elicit time trade-off (TTO) utilities. Multinomial logit models were estimated for the DCE data. The TTO utilities for the worst/best health states were used as anchors to convert indirect DCE part-worth utilities to health utilities. Results : A total of 1596 participants completed the DCE. The majority (70.7%) gave consistent responses to the repeated choice task; only 1.7% (27) always chose the same alternative for every choice set. Five models were evaluated. There was one preference reversal (“sitting unaided”/“standing with assistance”) occurring in all models; these two mobility level coefficients were set to be equal in the final model. Rescaled utilities ranged from 0.494 to 0.7279, corresponding to the worst (633233) and best (111111) health states. Conclusion : Health utilities were derived for AADC deficiency through a DCE. These will be used for a cost-effectiveness model of an AADC deficiency treatment

A FORMAÇÃO E O ESTÁGIO DOCENTE NO CONTEXTO DA EDUCAÇÃO PROFISSIONAL E TECNOLÓGICA

Este artigo aborda a Educação Profissional e Tecnológica (EPT) por meio de uma pesquisa bibliográfica, do tipo Estado da Arte, a partir de produções provenientes dos Institutos Federais com enfoque na formação e no estágio docente. Também buscou-se a realização de um breve aparato histórico da educação profissional, sua trajetória e percalços enfrentados pela mesma. Além disso, são apresentadas algumas leis e documentos consoantes à educação profissional e tecnológica. Por conseguinte, foi realizada uma revisão de literatura concernente a uma série de artigos afins selecionados sobre o tema e publicados em uma revista especializada deste cunho específico da educação profissional, cujos dados foram analisados sob descritores regionais e acerca da área de enfoque. Por fim, teceu-se comentários finais nos quais foram apontadas reflexões, especialmente sobre os conhecimentos e desafios dos professores para atuação na EPT