Preliminary discussion on globally prioritized medium access for multi-channel wireless systems

We discuss the development of a simple globally prioritized multi-channel medium access control (MAC) protocol for wireless networks. This protocol provides “hard” pre-run-time real-time guarantees to sporadic message streams, exploits a very large fraction of the capacity of all channels for “hard” real-time traffic and also makes it possible to fully utilize the channels with non real-time traffic when hard real-time messages do not request to be transmitted. The potential of such protocols for real-time applications is discussed and a schedulability analysis is also presented.

How a cyber-physical system can efficiently obtain a snapshot of physical information even in the presence of sensor faults

We present a distributed algorithm for cyber-physical systems to obtain a snapshot of sensor data. The snapshot is an approximate representation of sensor data; it is an interpolation as a function of space coordinates. The new algorithm exploits a prioritized medium access control (MAC) protocol to efficiently transmit information of the sensor data. It scales to a very large number of sensors and it is able to operate in the presence of sensor faults.

i-GAME: an implicit GTS allocation mechanism in IEEE 802.15.4 for time-sensitive wireless sensor networks

The IEEE 802.15.4 Medium Access Control (MAC) protocol is an enabling technology for time sensitive wireless sensor networks thanks to its Guaranteed-Time Slot (GTS) mechanism in the beacon-enabled mode. However, the protocol only supports explicit GTS allocation, i.e. a node allocates a number of time slots in each superframe for exclusive use. The limitation of this explicit GTS allocation is that GTS resources may quickly disappear, since a maximum of seven GTSs can be allocated in each superframe, preventing other nodes to benefit from guaranteed service. Moreover, the GTSs may be only partially used, resulting in wasted bandwidth. To overcome these limitations, this paper proposes i-GAME, an implicit GTS Allocation Mechanism in beacon-enabled IEEE 802.15.4 networks. The allocation is based on implicit GTS allocation requests, taking into account the traffic specifications and the delay requirements of the flows. The i-GAME approach enables the use of a GTS by multiple nodes, while all their (delay, bandwidth) requirements are still satisfied. For that purpose, we propose an admission control algorithm that enables to decide whether to accept a new GTS allocation request or not, based not only on the remaining time slots, but also on the traffic specifications of the flows, their delay requirements and the available bandwidth resources. We show that our proposal improves the bandwidth utilization compared to the explicit allocation used in the IEEE 802.15.4 protocol standard. We also present some practical considerations for the implementation of i-GAME, ensuring backward compatibility with the IEEE 801.5.4 standard with only minor add-ons.

Implementation of a dominance protocol for wireless medium access

Consider the problem of scheduling sporadic message transmission requests with deadlines. For wired channels, this has been achieved successfully using the CAN bus. For wireless channels, researchers have recently proposed a similar solution; a collision-free medium access control (MAC) protocol that implements static-priority scheduling. Unfortunately no implementation has been reported, yet. We implement and evaluate it to find that the implementation indeed is collision-free and prioritized. This allows us to develop schedulability analysis for the implementation. We measure the response times of messages in our implementation and find that our new response-time analysis indeed offers an upper bound on the response times. This enables a new class of wireless real-time systems with timeliness guarantees for sporadic messages and it opens-up a new research area: schedulability analysis for wireless networks.

On the performance limits of slotted CSMA/CA in IEEE 802.15.4 for broadcast transmissions in wireless sensor networks

The IEEE 802.15.4 has been adopted as a communication protocol standard for Low-Rate Wireless Private Area Networks (LRWPANs). While it appears as a promising candidate solution for Wireless Sensor Networks (WSNs), its adequacy must be carefully evaluated. In this paper, we analyze the performance limits of the slotted CSMA/CA medium access control (MAC) mechanism in the beacon-enabled mode for broadcast transmissions in WSNs. The motivation for evaluating the beacon-enabled mode is due to its flexibility and potential for WSN applications as compared to the non-beacon enabled mode. Our analysis is based on an accurate simulation model of the slotted CSMA/CA mechanism on top of a realistic physical layer, with respect to the IEEE 802.15.4 standard specification. The performance of the slotted CSMA/CA is evaluated and analyzed for different network settings to understand the impact of the protocol attributes (superframe order, beacon order and backoff exponent), the number of nodes and the data frame size on the network performance, namely in terms of throughput (S), average delay (D) and probability of success (Ps). We also analytically evaluate the impact of the slotted CSMA/CA overheads on the saturation throughput. We introduce the concept of utility (U) as a combination of two or more metrics, to determine the best offered load range for an optimal behavior of the network. We show that the optimal network performance using slotted CSMA/CA occurs in the range of 35% to 60% with respect to an utility function proportional to the network throughput (S) divided by the average delay (D).

Collision-free prioritized medium access in the presence of hidden nodes without relying on out-of-band signaling

Consider the problem of sharing a wireless channel between a set of computer nodes. Hidden nodes exist and there is no base station. Each computer node hosts a set of sporadic message streams where a message stream releases messages with real-time deadlines. We propose a collision-free wireless medium access control (MAC) protocol which implements staticpriority scheduling. The MAC protocol allows multiple masters and is fully distributed. It neither relies on synchronized clocks nor out-of-band signaling; it is an adaptation to a wireless channel of the dominance protocol used in the CAN bus. But unlike that protocol, our protocol does not require a node having the ability to receive an incoming bit from the channel while transmitting to the channel. Our protocol has the key feature of not only being prioritized and collision-free but also dealing successfully with hidden nodes. This key feature enables schedulability analysis of sporadic message streams in multihop networks.

Collision-free prioritized medium access control in wireless networks with hidden nodes

We propose a collision-free medium access control (MAC) protocol, which implements static-priority scheduling and works in the presence of hidden nodes. The MAC protocol allows multiple masters and is fully distributed; it is an adaptation to a wireless channel of the dominance protocol used in the CAN bus. But unlike that protocol, our protocol does not require a node having the ability to sense the channel while transmitting to the channel. Our protocol is collision-free even in the presence of hidden nodes and it achieves this without synchronized clocks or out-of-band busy tones. In addition, the protocol is designed to ensure that many non-interfering nodes can transmit in parallel and it functions for both broadcast and unicast transmissions.

Análise bilateral do timing de ativação dos músculos transverso abdominal/oblíquo interno durante o movimento rápido de flexão de cada membro superior – dominante e não-dominante

Introdução: Por mais de uma década assumiu-se que o transverso abdominal/oblíquo interno (TrA/OI) se comportava como um ventre muscular único, pré-ativando-se bilateralmente de forma simultânea para aumentar a stiffness da coluna lombar, conferindo-lhe estabilidade segmentar durante o movimento de um dos membros superiores. À luz dos estudos atuais sabe-se que tal mecanismo não ocorre, uma vez que o TrA/OI apresenta uma ativação por mecanismo de feedforward predominantemente contralateral ao membro superior movido. Apesar de morfologicamente o TrA/OI do lado não-dominante ser mais hipertrofiado do que o do lado dominante, nada se sabe acerca da influência da dominância nos timings ativação do TrA/OI. Objectivos: Confirmar se o TrA/OI tem um timing de ativação assimétrico durante o movimento rápido de flexão do membro superior (MRMS). Pretende-se ainda avaliar se o timing de ativação do TrA/OI é influenciado pela dominância de lateralidade manual. Métodos: Efectuou-se um estudo observacional descritivo, transversal e duplamente cego com 32 atletas de futebol voluntários com membro superior direito dominante, colocando-os apenas num grupo. Procedeu-se à recolha do sinal eletromiográfico de forma a avaliar os timings de ativação do TrA/OI bilateralmente aquando dos movimentos rápidos de flexão de ambos os membros superiores, à vez. Todos os dados foram tratados estatisticamente com o programa SPSS, versão 20.0 para Mac OS, com um grau de significância de 0,05. Resultados: Verificaram-se diferenças nos timings de ativação dos TrA/OI direito e esquerdo durante os MRMS direito e esquerdo (Teste ANOVA medidas repetidas: F=291,087; p<0,001). O timing de ativação do TrA/OI direito – 29,15(13,15)ms – foi superior ao esquerdo – 4,71(17,32)ms – durante MRMS direito (Teste Post Hoc Bonferroni: p<0,001). O timing de ativação do TrA/OI esquerdo – 31,98(12,50)ms – foi superior ao direito – 12,20(17,40)ms – durante MRMS esquerdo (p<0,001). O timing de ativação do TrA/IO direito aquando do MRMS direito foi superior ao observado durante MRMS esquerdo (p<0,001). O contrário sucedeu em relação ao timing ativação do TrA/IO esquerdo (p<0,001). O timing de ativação do TrA/IO esquerdo no MRMS direito foi inferior ao do TrA/IO direito aquando do movimento com o membro esquerdo (p<0,001). O TrA/IO direito possuiu um timing de ativação no MRMS direito inferior ao do TrA/IO esquerdo aquando do movimento com o membro esquerdo (p<0,001). Conclusão: Através deste estudo pôde-se concluir que o TrA/OI contralateral ao MRMS apresenta um timing de ativação inferior ao ipsilateral e ainda que durante o MRMS dominante o TrA/OI esquerdo e direito apresentam um timing de ativação inferior ao ocorrido durante o MRMS não-dominante.

Recent occurence of human infection by Rocio arbovirus in Ribeira Valley, Brazil

The presence of IgM antibodies to Rocio in sera of two children from rural area of Ribeira Valley, Brazil, was detected by MAC-ELISA. This new arbovirus of the Flaviviridae family was responsible for an extensive encephalitis epidemic that occurred in the region in 1975-1977. Since 1980 no human disease caused by this virus has been diagnosed. An improvement on surveillance of Rocio infections and on the researches for virus identification in suspected vectors and reservoirs is necessary.

Primeiro registro de epidemias causadas pelo vírus Oropouche nos Estados do Maranhão e Goiás, Brasil

Os autores descrevem a ocorrência de epidemias causadas pelo vírus Oropouche (ORO) nos Estados do Maranhão (MA) e Goiás (GO) em 1988. 36 amostras de vírus foram obtidas a partir da inoculação do sangue de 120 pacientes em camundongos recém nascidos. A doença foi caracterizada por febre, cefaléia, dores musculares, articulares, fotofobia, dor retro ocular, náuseas e tontura. 128 das 197 pessoas examinadas em Porto Franco, MA, tinham anticorpos inibidores da hemaglutinação (IH) para o agente e, em 106 foram detectados anticorpos IgM por MAC ELISA. Todos os grupos etários foram infectados, embora a incidência tenha sido mais elevada entre aqueles com 10 a 19 anos de idade. Quanto ao sexo, a infecção ocorreu igualmente em ambos os sexos. Recorrência dos sintomas foi observada em 56% dos casos positivos estudados. A inoculação em camundongos Swiss recém nascidos de 3.624 Culicoides paraensis (Ceratopogonidae) e 1.970 Culex (Culex) quinquefasciatus (Culicidae), coletados em Porto Franco-MA, resultou em um único isolamento do vírus ORO a partir dos Culicoides. Essa é a primeira descrição de casos confirmados de infecção pelo vírus Oropouche nos Estados do Maranhão e Goiás, Brasil.

Epidemia de febre clássica de dengue causada pelo sorotipo 2 em Araguaiana, Tocantins, Brasil

Registramos a ocorrência de epidemia de dengue causada pelo sorotipo 2 (DEN 2) na cidade de Araguaina, estado do Tocantins (TO) situado no Brasil central. Quatrocentos indíviduos de 74 famílias, residentes nos bairros S. João, Araguaina Sul e Neblina foram entrevistados e sangrados, independentemente de terem adoecido ou não. Os soros tanto de adultos quanto de crianças de ambos os sexos foram usados para pesquisa de anticorpos inibidores da hemaglutinação (IH) e IgM através de ensaio imunoenzimático (MAC ELISA). Nas casas onde haviam doentes no momento do inquérito, sangue total também foi colhido para tentativa de isolamento de vírus. O quadro clínico apresentado pelos pacientes foi caracterizado por febre, cefaléia, mialgias, artralgias e exantema do tipo máculo-papular não pruriginoso. A infecção foi mais frequente em mulheres (33.9%) do que nos homens (23.8%), ocorrendo em todas as faixas etárias, inclusive em crianças com menos de um ano de idade, bem como em maiores de 70 anos. Um total de 1105 mosquitos (56 fêmeas e 45 machos de Culex quinquefasciatus e 567 fêmeas e 437 machos de Aedes aegypti) foram obtidos a partir de larvas coletadas em Araguaina. As fêmeas de Ae. aegypti obtidas das larvas fizeram repasto sangüíneo em 8 pacientes febris. O diagnóstico laboratorial foi feito por isolamento de vírus (cultura de células de Aedes albopictus, clone C6/36) e por sorologia (IH e MAC ELISA). Foram isoladas 5 amostras de DEN 2 de pacientes febris e tipadas por imunofluorescência indireta usando anticorpos monoclonais de dengue. Nenhuma amostra viral foi isolada de mosquitos. Outrossim, comprovou-se infecção em 111 pessoas sangradas, o que revelou um índice de positividade de 27.75% (111 em 400), sendo que 66.2% das famílias estudadas apresentaram pelo menos um indivíduo positivo. Ocorreram ainda, 26.1% de infecções assintomáti-cas. Por outro lado, a correlação de positividade entre os dois testes usados (IH e MAC ELISA) foi de 94.6%. Estimamos que ocorreram aproximadamente 83.250 casos da doença, entre 15 de março a 31 de maio de 1991. Esta é a primeira epidemia de DEN 2 em um estado da Amazônia Brasileira, portanto em área endêmica de febre amarela, e a primeira evidência da interiorização do DEN 2, até então restrito ao Rio de Janeiro.

Dengue epidemic in the state of Rio de Janeiro, Brazil: virological and epidemiological aspects

Laboratorial studies were carried out on 3178 patients with signs and symptoms suggestive of dengue infection from April 1986 to December 1987 in the State of Rio de Janeiro, Brazil. The epidemic had two peaks following the first virus isolation and affected the inhabitants of 17 counties. Both sex and all age groups were affected. Dengue virus type 1 was isolated from 1039 sera and the number of confirmed cases was increased to 1874 (59%) by MAC-ELISA. Isolation rate confirmed cases reached 80% in the specimens obtained until the 4th day after the onset of disease and viraemia ranged from 10 3.0 to 10(8.5) TCID50/ml.

Bacterial agents isolated from cerebrospinal fluid of patients with Acquired Immunodeficiency Syndrome (AIDS) and neurological complications

Cerebrospinal fluid (CSF) samples from 2083 patients with acquired immunodeficiency syndrome (AIDS) and neurological complications were bacteriologically examined during a period of 7 years (1984-1990). The percentage of patients who had at least one bacterial agent cultured from the CSF was 6.2%. Mycobacterium tuberculosis was the most frequently isolated agent (4.3%), followed by Mycobacterium avium complex or MAC (0.7%), Pseudomonas spp (0.5%), Enterobacter spp (0.4%), and Staphylococcus aureus (0.3%). Among 130 culture positive patients, 89 (68.5%) had M. tuberculosis and 15 (11.6%) had MAC. The frequency of bacterial isolations increased from 1988 (5.2%) to 1990 (7.2%), partly due to the increase in MAC isolations. Bacterial agents were more frequently isolated from patients in the age group 21-30 years and from women (p<0.05).

Jungle yellow fever: clinical and laboratorial sudies emphasizing viremia on a human case

The authors report the clinical, laboratorial and epidemiological aspects of a human case of jungle yellow fever. The patient suffered from fever, chills, sweating, headaches, backaches, myalgia, epigastric pains, nausea, vomiting, diarrhea and prostration. He was unvaccinated and had been working in areas where cases of jungle yellow fever had been confirmed. Investigations concerning the yellow fever virus were performed. Blood samples were collected on several days in the course of the illness. Three of these samples (those obtained on days 5,7 and 10) were inoculated into suckling mice in attempt to isolate virus and to titrate the viremia level. Serological surveys were carried out by using the IgM Antibodies Capture Enzyme Linked Immunosorbent Assay (MAC-ELISA), Complement Fixation (CF), Hemagglulinalion Inhibition (HI) and Neutralization (N) tests. The yellow fever virus, recovered from the two first samples and the virus titration, showed high level of viremia. After that, specific antibodies appeared in all samples. The interval between the end of the viremia and the appearance of the antibodies was associated with the worsening of clinical symptoms, including bleeding of the mucous membrane. One must be aware of the risk of having a urban epidemics in areas where Aedes aegypti is found in high infestation indexes.

Dengue type 2 outbreak in the south of the State of Bahia, Brazil: laboratorial and epidemiological studies

During March 1994 cases of a exanthematic acute disease were reported in the municipalities of Itagemirim, Eunápolis and Belmonte, state of Bahia. Dengue fever was confirmed by serology (MAC-ELISA) and by dengue virus type 2 isolation, genotype Jamaica. Signs and symptoms of classic dengue fever were observed with a high percentual of rash (73.8%) and pruritus (50.5%). Major haemorrhagic manifestations were unfrequent and only bleeding gum was reported. Dengue virus activity spreaded rapidly to important tourism counties like Porto Seguro, Ilhéus, Santa Cruz de Cabrália, Prado, Alcobaça and others, representing a risk for the spreading of dengue virus into the country and abroad.