Markov modelling of the IEEE 802.11 DCF for real-time applications with periodic traffic

Popular wireless network standards, such as IEEE 802.11/15/16, are increasingly adopted in real-time control systems. However, they are not designed for real-time applications. Therefore, the performance of such wireless networks needs to be carefully evaluated before the systems are implemented and deployed. While efforts have been made to model general wireless networks with completely random traffic generation, there is a lack of theoretical investigations into the modelling of wireless networks with periodic real-time traffic. Considering the widely used IEEE 802.11 standard, with the focus on its distributed coordination function (DCF), for soft-real-time control applications, this paper develops an analytical Markov model to quantitatively evaluate the network quality-of-service (QoS) performance in periodic real-time traffic environments. Performance indices to be evaluated include throughput capacity, transmission delay and packet loss ratio, which are crucial for real-time QoS guarantee in real-time control applications. They are derived under the critical real-time traffic condition, which is formally defined in this paper to characterize the marginal satisfaction of real-time performance constraints.

Real time information provision benefit measured by macroscopic fundamental diagram

The existence of Macroscopic Fundamental Diagram (MFD), which relates space-mean density and flow, has been shown in urban networks under homogeneous traffic conditions. Since MFD represents the area-wide network traffic performances, studies on perimeter control strategies and an area traffic state estimation utilizing the MFD concept has been reported. One of the key requirements for well-defined MFD is the homogeneity of the area-wide traffic condition with links of similar properties, which is not universally expected in real world. For the practical application of the MFD concept, several researchers have identified the influencing factors for network homogeneity. However, they did not explicitly take the impact of drivers’ behaviour and information provision into account, which has a significant impact on simulation outputs. This research aims to demonstrate the effect of dynamic information provision on network performance by employing the MFD as a measurement. A microscopic simulation, AIMSUN, is chosen as an experiment platform. By changing the ratio of en-route informed drivers and pre-trip informed drivers different scenarios are simulated in order to investigate how drivers’ adaptation to the traffic congestion influences the network performance with respect to the MFD shape as well as other indicators, such as total travel time. This study confirmed the impact of information provision on the MFD shape, and addressed the usefulness of the MFD for measuring the dynamic information provision benefit.

Methodology for developing real-time motorway traffic risk identification models using individual-vehicle data

Most of existing motorway traffic safety studies using disaggregate traffic flow data aim at developing models for identifying real-time traffic risks by comparing pre-crash and non-crash conditions. One of serious shortcomings in those studies is that non-crash conditions are arbitrarily selected and hence, not representative, i.e. selected non-crash data might not be the right data comparable with pre-crash data; the non-crash/pre-crash ratio is arbitrarily decided and neglects the abundance of non-crash over pre-crash conditions; etc. Here, we present a methodology for developing a real-time MotorwaY Traffic Risk Identification Model (MyTRIM) using individual vehicle data, meteorological data, and crash data. Non-crash data are clustered into groups called traffic regimes. Thereafter, pre-crash data are classified into regimes to match with relevant non-crash data. Among totally eight traffic regimes obtained, four highly risky regimes were identified; three regime-based Risk Identification Models (RIM) with sufficient pre-crash data were developed. MyTRIM memorizes the latest risk evolution identified by RIM to predict near future risks. Traffic practitioners can decide MyTRIM’s memory size based on the trade-off between detection and false alarm rates. Decreasing the memory size from 5 to 1 precipitates the increase of detection rate from 65.0% to 100.0% and of false alarm rate from 0.21% to 3.68%. Moreover, critical factors in differentiating pre-crash and non-crash conditions are recognized and usable for developing preventive measures. MyTRIM can be used by practitioners in real-time as an independent tool to make online decision or integrated with existing traffic management systems.

Chirp-spread-spectrum-based real time location system for construction safety management: A case study

Observing the working procedure of construction workers is an effective means of maintaining the safety performance of a construction project. It is also difficult to achieve due to a high worker-to-safety-officer ratio. There is an imminent need for the development of a tool to assist in the real-time monitoring of workers, in order to reduce the number of construction accidents. The development and application of a real time locating system (RTLS) based on the Chirp Spread Spectrum (CSS) technique is described in this paper for tracking the real-time position of workers on construction sites. Experiments and tests were carried out both on- and off-site to verify the accuracy of static and dynamic targets by the system, indicating an average error of within one metre. Experiments were also carried out to verify the ability of the system to identify workers’ unsafe behaviours. Wireless data transfer was used to simplify the deployment of the system. The system was deployed in a public residential construction project and proved to be quick and simple to use. The cost of the developed system is also reported to be reasonable (around 1800USD) in this study and is much cheaper than the cost of other RTLS. In addition, the CCS technique is shown to provide an economical solution with reasonable accuracy compared with other positioning systems, such as ultra wideband. The study verifies the potential of the CCS technique to provide an effective and economical aid in the improvement of safety management in the construction industry.

A deadline-constrained 802.11 MAC Protocol with QoS differentiation for soft real-time control

As one of the most widely used wireless network technologies, IEEE 802.11 wireless local area networks (WLANs) have found a dramatically increasing number of applications in soft real-time networked control systems (NCSs). To fulfill the real-time requirements in such NCSs, most of the bandwidth of the wireless networks need to be allocated to high-priority data for periodic measurements and control with deadline requirements. However, existing QoS-enabled 802.11 medium access control (MAC) protocols do not consider the deadline requirements explicitly, leading to unpredictable deadline performance of NCS networks. Consequentially, the soft real-time requirements of the periodic traffic may not be satisfied, particularly under congested network conditions. This paper makes two main contributions to address this problem in wireless NCSs. Firstly, a deadline-constrained MAC protocol with QoS differentiation is presented for IEEE 802.11 soft real-time NCSs. It handles periodic traffic by developing two specific mechanisms: a contention-sensitive backoff mechanism, and an intra-traffic-class QoS differentiation mechanism. Secondly, a theoretical model is established to describe the deadline-constrained MAC protocol and evaluate its performance of throughput, delay and packet-loss ratio in wireless NCSs. Numerical studies are conducted to validate the accuracy of the theoretical model and to demonstrate the effectiveness of the new MAC protocol.

Loss ratio of the EDF scheduling policy with early discarding technique

This paper considers a firm real-time M/M/1 system, where jobs have stochastic deadlines till the end of service. A method for approximately specifying the loss ratio of the earliest-deadline-first scheduling policy along with exit control through the early discarding technique is presented. This approximation uses the arrival rate and the mean relative deadline, normalized with respect to the mean service time, for exponential and uniform distributions of relative deadlines. Simulations show that the maximum approximation error is less than 4% and 2% for the two distributions, respectively, for a wide range of arrival rates and mean relative deadlines. (C) 2013 Elsevier B.V. All rights reserved.

Multispectral Bayesian reconstruction technique for real-time two color fluorescence microscopy

We have developed a real-time imaging method for two-color wide-field fluorescence microscopy using a combined approach that integrates multi-spectral imaging and Bayesian image reconstruction technique. To enable simultaneous observation of two dyes (primary and secondary), we exploit their spectral properties that allow parallel recording in both the channels. The key advantage of this technique is the use of a single wavelength of light to excite both the primary dye and the secondary dye. The primary and secondary dyes respectively give rise to fluorescence and bleed-through signal, which after normalization were merged to obtain two-color 3D images. To realize real-time imaging, we employed maximum likelihood (ML) and maximum a posteriori (MAP) techniques on a high-performance computing platform (GPU). The results show two-fold improvement in contrast while the signal-to-background ratio (SBR) is improved by a factor of 4. We report a speed boost of 52 and 350 for 2D and 3D images respectively. Using this system, we have studied the real-time protein aggregation in yeast cells and HeLa cells that exhibits dot-like protein distribution. The proposed technique has the ability to temporally resolve rapidly occurring biological events.

Carta de El-Rei D. Manuel ao Rei Catholico narrando-lhe as viagens portuguezas à India desde 1500 até 1505

Esta obra saiu nas Memórias da comissão portuguesa para comemorar o centenário do descobrimento da América. Traz em apêncide a Relação análoga de Lunardo Cha Masser e dois documentos de Cantino e Pasqualigo. Contém, ainda, a primeira notícia impressa sobre o descobrimento do Brasil em carta ao Rei da Espanha.

Relação dos festejos, que a feliz acclamação do Muito Alto, Muito Poderoso, e Fidelissimo Senhor D. João VI, Rei do Reino Unido de Portugal, Brasil, e Algarves na noite do Indelevel, e Faustissimo dia 6 de fevereiro, e nas duas subsequentes, com tanta cordialidade, como respeito votarão os Habitantes do Rio de Janeiro; seguida das Poesias dedicadas ao mesmo Venerando Objecto ... e dada ao prelo, e gratuitamente distribuida pela mesma intendencia, a fim de perpetuar a memoria do plauzivel successo, de que mais glorião os fastos portuguezes

Apresenta a descrição dos festejos, iluminação das casas particulares com o nome dos donos, arcos triunfais, inclusive o que a Junta do Comércio mandou construir segundo o risco de Grandjean de Montigny e a pintura de Debret.

Restauracion de la ciudad del Salvador, i Baia de Todos-Santos, en la provincia del Brasil :por las armas de Don Philippe IV, el Grande, Rei Catholico de las Espanas i Indias, [et]c. A su Magestad : Don Thomas Tamaio de Vargas, su cronista

Tomás Tamayo de Vargas, historiador espanhol, nasceu em 1588 e morreu em 1641. Cronista do Reino, escreveu essa obra por ordem real, que foi publicada em 1628, utilizando documentação oficial e informações que as relações da época lhe proporcionavam. ‘Restauracion de la ciudad del Salvador, i Baia de Todos-Sanctos, en la Provincia del Brasil’ reflete a opinião oficial espanhola sobre a restauração da Bahia e mostra a repercussão que o acontecimento teve na metrópole espanhola que, na época, dominava o Brasil. Rodrigues considera essa uma edição ‘rara’ e Brunet afirma ser ‘muito rara’. Há uma edição brasileira, difícil de encontrar, publicada em Salvador pela Tipografia de Epifanio Pedroza (1847)

Leis extravagantes / Collegidas e Relatadas pelo Licenciado Duarte Nunez do Lião ; per mandado do muito alto e muito poderoso rei Dom Sebastião, Nosso Senhor

As Leis extravagantes foram compiladas durante o reinado de D.Sebastião. Levada a efeito com o intuito de reformar o código precedente, servia para consumar o triunfo da legislação Corpus Juris e do absolutismo real, conforme analisa Cândido Mendes. Essa nova codificação, também denominada Código Sebastiânico, contudo, não teve o alcance das Leis extravagantes posteriores ao Código manuelino. O trabalho, revisto pelo regedor Lourenço da Silva e outros jurisconsultos, foi aprovado por alvará de 14 de fevereiro de 1569, tendo força de lei. Foi o Cardeal D. Henrique, quando regente do Reino, que ordenara a compilação, alegando a existência de muitas leis e provisões promulgadas depois do Código manuelino, assim como decisões da Casa da Suplicação, o que era fonte de muita controvérsia no fórum, como é declarado no alvará contido na obra. O livro das Leis extravagantes resultou num grosso volume de oitocentas e oitenta páginas, mais quatorze páginas introdutórias, em que aparecem o licenciamento e o sumário da obra. O conteúdo das Leis extravagantes é constituído por seis partes, seus aditamentos, o repertório das matéria contidas na obra, as anotações dos dispositivos revogados e casos de devassa.

Chronica do serenissimo Principe D. João escrita por Damião de Goes, Dirigida ao Munto Magnanimo e Poderoso Rei D. João III do Nome

Damião de Góis, historiador e humanista português, nasceu em Alenquer, por volta de 1502 e morreu, provavelmente, em 1574. Na Corte, esteve a serviço dos reis D. Manuel e D. João III, desde a adolescência. Viajou por vários países por mais de vinte anos, o que lhe permitiu relacionar-se com Luter, Melanchthon, Luís Vives, Alberto Dürer e com Erasmo de Roterdam. Tendo regressado a Portugal, assumiu o cargo de guarda-mor da Torre do Tombo, em 1548. Sua principal obra foi a Crônica do felicíssimo Rei D. Manuel, que teve o texto alterado por exigência do Santo Ofício. Traduziu o tratado De Senectude, de Cícero, intitulando-o de Livro da velhice. Damião de Góis foi seguidor da obra de Fernão Lopes e de Rui Pina e se tornou o principal representante do humanismo difundido por Erasmo. Chronica do Sereníssimo Príncipe D. João foi escrita por recomendação do Cardeal D. Henrique. Traz uma narrativa do fatos ocorridos no reinado de D. Afonso V desde o nascimento do seu filho e sucessor D. João, que se tornaria D. João II. As primeira e segunda edições foram publicadas, respectivamente, em 1567 e 1724, com o título Chronica do Príncipe Dom Joam. Esta terceira edição, de 1790, além da alteração no título, restitui a dedicatória do autor ao Rei D. João II, omitida na segunda edição.

Chronica do muito alto, e muito esclarecido Principe D. Affonso Henriques Primeiro Rey de Portugal composta por Duarte Galvão, Fidalgo da Casa Real, e Chronista Mor do Reyno, Fielmente Copiada do seu Original, Que Se Conserva no Archivo Real da Torre do Tombo; offerecida a magestade sempre augusta delrey D. João V. nosso senhor por Miguel Lopes Ferreyra

Duarte Galvão nasceu em Évora, por volta de 1445, e morreu na Ilha de Camarão, em 1517. Alguns biógrafos atribuem-lhe o cargo de cronista-mor do reino, nomeado por D. Afonso V. Foi secretário de D. João II e embaixador de D. Manuel I junto ao Papa Alexandre VI, ao Imperador Maximiliano I, e ao Rei Luís XII, de França. Embora preparada na segunda metade do século XV, Chronica del muito alto... conservou-se em forma de manuscrito até 1726, quando foi impressa pela primeira vez. Pertence à Chronica geral del reyno e foi elaborada por ordem de D. Manuel, para completar a sequencia das crônicas reais. O exemplar que a Biblioteca da Câmara possui traz os capítulos XXI e XXII, XXIII e XXIV, cortados pela Inquisição, na edição de 1726. É considerado, por isso, não só um exemplar raro, mas raríssimo, a julgar pelo testemunho do Cavalheiro Francisco Xavier de Oliveira, que afirma, em artigo publicado no “Popular”, impresso em Londres, no ano de 1825, haver apenas dois exemplares desta edição em que figuram os citados capítulos.

Leis extravagantes : Collegidas e Relatadas pelo Licenciado Duarte Nunez do Lião ; per mandado do muito alto e muito poderoso rei Dom Sebastião, Nosso Senhor

Duarte Nunes do Leão, jurista, historiógrafo e geontólogo português, desembargador da Casa de Suplicação, nasceu em Évora, aproximadamente em 1530, e morreu em Lisboa, provavelmente em 1608. Tendo estudado Direito Civil na Universidade de Coimbra, dedicou-se no início de sua carreira, exclusivamente, aos estudos jurídicos. Escritor muito laborioso e aplicado, foi autor de muitas obras, algumas impressas durante a sua vida e outras ainda inéditas. Devendeu arduamente os interesses de Flipe II à sucessão do trono, à época da reunião de Portugal à Coroa da Espanha, inclusivie manifestando-se por escrito contra aqueles que a impugnavam. Foi encarregado pelo Conde Redondo, regedor das justiças de Portugal, a fazer o repertório dos cinco livros das Ordenações Manuelinas, com a adição das Leis extravagantes, um edição realizada por ordem do Governo.

Real-Time Bayesian Analysis of Ground Motion Envelopes for Earthquake Early Warning

Current earthquake early warning systems usually make magnitude and location predictions and send out a warning to the users based on those predictions. We describe an algorithm that assesses the validity of the predictions in real-time. Our algorithm monitors the envelopes of horizontal and vertical acceleration, velocity, and displacement. We compare the observed envelopes with the ones predicted by Cua & Heaton's envelope ground motion prediction equations (Cua 2005). We define a "test function" as the logarithm of the ratio between observed and predicted envelopes at every second in real-time. Once the envelopes deviate beyond an acceptable threshold, we declare a misfit. Kurtosis and skewness of a time evolving test function are used to rapidly identify a misfit. Real-time kurtosis and skewness calculations are also inputs to both probabilistic (Logistic Regression and Bayesian Logistic Regression) and nonprobabilistic (Least Squares and Linear Discriminant Analysis) models that ultimately decide if there is an unacceptable level of misfit. This algorithm is designed to work at a wide range of amplitude scales. When tested with synthetic and actual seismic signals from past events, it works for both small and large events.