Improving quality-of-service in wireless sensor networks by mitigating ���Hidden-Node Collisions���

Wireless sensor networks (WSNs) emerge as underlying infrastructures for new classes of large-scale networked embedded systems. However, WSNs system designers must fulfill the quality-of-service (QoS) requirements imposed by the applications (and users). Very harsh and dynamic physical environments and extremely limited energy/computing/memory/communication node resources are major obstacles for satisfying QoS metrics such as reliability, timeliness, and system lifetime. The limited communication range of WSN nodes, link asymmetry, and the characteristics of the physical environment lead to a major source of QoS degradation in WSNs-the ldquohidden node problem.rdquo In wireless contention-based medium access control (MAC) protocols, when two nodes that are not visible to each other transmit to a third node that is visible to the former, there will be a collision-called hidden-node or blind collision. This problem greatly impacts network throughput, energy-efficiency and message transfer delays, and the problem dramatically increases with the number of nodes. This paper proposes H-NAMe, a very simple yet extremely efficient hidden-node avoidance mechanism for WSNs. H-NAMe relies on a grouping strategy that splits each cluster of a WSN into disjoint groups of non-hidden nodes that scales to multiple clusters via a cluster grouping strategy that guarantees no interference between overlapping clusters. Importantly, H-NAMe is instantiated in IEEE 802.15.4/ZigBee, which currently are the most widespread communication technologies for WSNs, with only minor add-ons and ensuring backward compatibility with their protocols standards. H-NAMe was implemented and exhaustively tested using an experimental test-bed based on ldquooff-the-shelfrdquo technology, showing that it increases network throughput and transmission success probability up to twice the values obtained without H-NAMe. H-NAMe effectiveness was also demonstrated in a target tracking application with mobile robots - over a WSN deployment.

An implicit GTS allocation mechanism in IEEE 802.15.4 for time-sensitive wireless sensor networks: theory and practice

Timeliness guarantee is an important feature of the recently standardized IEEE 802.15.4 protocol, turning it quite appealing for Wireless Sensor Network (WSN) applications under timing constraints. When operating in beacon-enabled mode, this protocol allows nodes with real-time requirements to allocate Guaranteed Time Slots (GTS) in the contention-free period. The protocol natively 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 GTS may be underutilized, 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 one GTS by multiple nodes, still guaranteeing that all their (delay, bandwidth) requirements are 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 approach improves the bandwidth utilization as compared to the native explicit allocation mechanism defined in the IEEE 802.15.4 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. Finally, an experimental evaluation on a real system that validates our theoretical analysis and demonstrates the implementation of i-GAME is also presented

H-NAMe: specifying, implementing and testing a hidden-node avoidance mechanism for wireless sensor networks

The hidden-node problem has been shown to be a major source of Quality-of-Service (QoS) degradation in Wireless Sensor Networks (WSNs) due to factors such as the limited communication range of sensor nodes, link asymmetry and the characteristics of the physical environment. In wireless contention-based Medium Access Control protocols, if two nodes that are not visible to each other transmit to a third node that is visible to the formers, there will be a collision ��� usually called hidden-node or blind collision. This problem greatly affects network throughput, energy-efficiency and message transfer delays, which might be particularly dramatic in large-scale WSNs. This technical report tackles the hidden-node problem in WSNs and proposes HNAMe, a simple yet efficient distributed mechanism to overcome it. H-NAMe relies on a grouping strategy that splits each cluster of a WSN into disjoint groups of non-hidden nodes and then scales to multiple clusters via a cluster grouping strategy that guarantees no transmission interference between overlapping clusters. We also show that the H-NAMe mechanism can be easily applied to the IEEE 802.15.4/ZigBee protocols with only minor add-ons and ensuring backward compatibility with the standard specifications. We demonstrate the feasibility of H-NAMe via an experimental test-bed, showing that it increases network throughput and transmission success probability up to twice the values obtained without H-NAMe. We believe that the results in this technical report will be quite useful in efficiently enabling IEEE 802.15.4/ZigBee as a WSN protocol.

H-NAMe: a hidden-node avoidance mechanism for wireless sensor networks

The hidden-node problem has been shown to be a major source of Quality-of-Service (QoS) degradation in Wireless Sensor Networks (WSNs) due to factors such as the limited communication range of sensor nodes, link asymmetry and the characteristics of the physical environment. In wireless contention-based Medium Access Control protocols, if two nodes that are not visible to each other transmit to a third node that is visible to the formers, there will be a collision ��� usually called hidden-node or blind collision. This problem greatly affects network throughput, energy-efficiency and message transfer delays, which might be particularly dramatic in large-scale WSNs. This paper tackles the hiddennode problem in WSNs and proposes H-NAMe, a simple yet efficient distributed mechanism to overcome it. H-NAMe relies on a grouping strategy that splits each cluster of a WSN into disjoint groups of non-hidden nodes and then scales to multiple clusters via a cluster grouping strategy that guarantees no transmission interference between overlapping clusters. We also show that the H-NAMe mechanism can be easily applied to the IEEE 802.15.4/ZigBee protocols with only minor add-ons and ensuring backward compatibility with the standard specifications. We demonstrate the feasibility of H-NAMe via an experimental test-bed, showing that it increases network throughput and transmission success probability up to twice the values obtained without H-NAMe. We believe that the results in this paper will be quite useful in efficiently enabling IEEE 802.15.4/ZigBee as a WSN protocol

Improving the IEEE 802.15.4 Slotted CSMA/CA MAC for time-critical events in wireless sensor networks

In beacon-enabled mode, IEEE 802.15.4 is ruled by the slotted CSMA/CA Medium Access Control (MAC) protocol. The standard slotted CSMA/CA mechanism does not provide any means of differentiated services to improve the quality of service for timecritical events (such as alarms, time slot reservation, PAN management messages etc.). In this paper, we present and discuss practical service differentiation mechanisms to improve the performance of slotted CSMA/CA for time-critical events, with only minor add-ons to the protocol. The contribution of our proposal is more practical than theoretical since our initial requirement is to leave the original algorithm of the slotted CSMA/CA unchanged, but rather tuning its parameters adequately according to the criticality of the messages. We present a simulation study based on an accurate model of the IEEE 802.15.4 MAC protocol, to evaluate the differentiated service strategies. Four scenarios with different settings of the slotted CSMA/CA parameters are defined. Each scenario is evaluated for FIFO and Priority Queuing. The impact of the hiddennode problem is also analyzed, and a solution to mitigate it is proposed.

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.

An IEEE 802.15.4 protocol implementation (in nesC/TinyOS): reference guide v1.0

This technical report is to provide a reference guide to the implementation of the IEEE 802.15.4 protocol in nesC/TinyOS for the MICAz motes. The implementation is provided as a tool that can be used to implement, test and evaluate the current functionalities defined in the protocol standard as well as to enable the development of functionalities not yet implemented and new add-ons to the protocol.

Permeable Reactive Barriers using nanoparticles to remediate nitrate pollution

Nitrat e (NO3 - ) i s per vasi ve i n t he bi ospher e[ 1, 2]. Cont emporar y agri cult ural pr acti ces are a mong t he maj or ant hr opogeni c sources of r eacti ve nitrogen speci es, wher e nitrat ei s t he most abundant of t hese [ 2]. Excessi ve a mount s of r eacti ve nitrogen i n soil s and gr oundwat er ar e creati ng si gnifi cant t hr eat s t o hu man healt h and saf et y [ 3] as well as a host of undesirabl e environment al i mpact s [ 2]; it i s curr ently consi der ed t he second most r el evant environment al i ssue, aft er car bon di oxide e mi ssi ons. Nowadays, a mong t he most r el evant and pr omi si ng appr oaches t o r educe nitrat e concentrati on i n wat er, na mel y gr oundwat er, ar e denitrifi cati on- based pr ocesses [ 4]. Per meabl e r eacti ve barri ers ( PRB) have been pr oven eff ecti ve i n r educi ng vari ous cont ami nant s i n copi ous a mount s, parti cul arl y i n shall ow gr oundwat er [ 5]. However t he possi bl e added eff ecti veness of usi ng nanoparti cl es i n t hese structur es t o obt ai n nitrogen gas from nitrat es requires f urt her i nvesti gati on.

A learning environment for robotic production line simulation

This paper presents a framework for a robotic production line simulation learning environment using Autonomous Ground Vehicles (AGV). An eLearning platform is used as interface with the simulator. The objective is to introduce students to the production robotics area using a familiar tool, an eLearning platform, and a framework that simulates a production line using AGVs. This framework allows students to learn about robotics but also about several areas of industrial management engineering without requiring an extensive prior knowledge on the robotics area. The robotic production line simulation learning environment simulates a production environment using AGVs to transport materials to and from the production line. The simulator allows students to validate the AGV dynamics and provides information about the whole materials supplying system which includes: supply times, route optimization and inventory management. The students are required to address several topics such as: sensors, actuators, controllers and an high level management and optimization software. This simulator was developed with a known open source tool from robotics community: Player/Stage. This tool was extended with several add-ons so that students can be able to interact with a complex simulation environment. These add-ons include an abstraction communication layer that performs events provided by the database server which is programmed by the students. An eLearning platform is used as interface between the students and the simulator. The students can visualize the effects of their instructions/programming in the simulator that they can access via the eLearning platform. The proposed framework aims to allow students from different backgrounds to fully experience robotics in practice by suppressing the huge gap between theory and practice that exists in robotics. Using an eLearning platform eliminates installation problems that can occur from different computers software distribution and makes the simulator accessible by all students at school and at home.

Bioqu��mica da esquistossomose mans��nica: envolvimento dos siderossomos nos processos inflamat��rios hep��ticos

Os processos inflamat��rios que se desenvolvem durante as etapas avan��adas da esquistossomose mans��nica hep��tica foram relacionados, com o ac��mulo de siderossomos, a capacidade dos ��ons ferrosos/f��rricos de desencadearem a forma����o de radicais livres e aperoxida����o de lip��dios membran��ceos, assim como �� diminui����o da estabilidade das membranas dos diversos componentes do compartimento lisoss��mico hep��tico. Os lisossomos isolados de figados de camundongos infectados por 100 cerc��rias, com 80 e 100 dias de infec����o, foram respectivamente, 2,5 e quase 4 vezes mais fr��geis que os controles, isolados de figados de camundongos n��o infectados. A presen��a de siderossomos em grande quantidade foi demonstrada por espectrometria aos raios-X.

Interpreta����o hidrogeoqu��mica das ��guas subterr��neas da ilha de Maraj��.

As pesquisas desenvolvidas pelo IDESP na Ilha de Maraj�� possibilitaram estudos de hidrogeoqu��mica das ��guas subterr��neas. As amostras foram coletadas em po��os escavados e em po��os tubulares. Os resultados das an��lises f��sico-qu��micas evidenciaram significativas varia����es nas concentra����es dos par��metros de qualidade de ��gua, refletindo a complexidade hidrogeol��gica da ��rea. As maiores concentra����es de s��lidos totais dissolvidos ocorrem na parte central e norte da ��rea, sendo pequena na parte sul, sudeste e noroeste. As ��guas s��o predominantemente do tipo s��dio-cloretada, seguidas pelos tipos mista-cloretada e mista-bicarbonatada. A utiliza����o de diagramas semi-logar��timicos de Schoeller possibilitou o agrupamento das ��guas subterr��neas com caracter��sticas qu��micas similares. A evolu����o da composi����o das ��guas subterr��neas evidencia o aumento da concentra����o dos ��ons dissolvidos das zonas de fluxo ativo em ��reas de recarga para as zonas de fluxo muito lento. Misturas de ��guas doces com ��guas salobras conatas ocorrem em propor����es variadas. A redu����o de sulfatos pela mat��ria org��nica e a troca de bases e adsor����o s��o fen��menos que atuam na concentra����o dos ��ons dissolvidos.

Efeitos das mudan��as do uso da terra na biogeoqu��mica dos corpos d'��gua da bacia do rio Ji-Paran��, Rond��nia

Este trabalho discute os efeitos das mudan��as do uso do solo na biogequ��mica dos rios da bacia de drenagem do rio Ji-Paran�� (Rond��nia). Nesta regi��o, a distribui����o espacial do desmatamento e das propriedades do solo resultam em sinais diferentes, possibilitando a divis��o dos sistemas fluviais em tr��s grupos: rios com ��guas pobres em ��ons e baixo impacto; rios com conte��do i��nico intermedi��rio e impacto m��dio e rios com elevados conte��do i��nico e impacto antropog��nico. As caracter��sticas biogeoqu��micas dos rios t��m rela����o significativa com a ��rea de pasto, melhor par��metro para prever a condutividade el��trica (r�� = 0,87) e as concentra����es de s��dio (r�� = 0,75), cloreto (r�� = 0,69), pot��ssio (r�� = 0,63), fosfato (r�� = 0.78), nitrog��nio inorg��nico (r�� = 0.52), carbono inorg��nico (r�� = 0.81) e carbono org��nico (rain �� = 0.51) dissolvidos. C��lcio e magn��sio tiveram sua vari��ncia explicada pelas caracter��sticas do solo e pastagem. Nossos resultados indicam que as mudan��as observadas na micro-escala constituem "sinais biogeoqu��micos" gerados pelo processamento do material nas margens dos rios. A medida em que os rios evoluem para ordens superiores, os sinais persistentes nos canais fluviais est��o mais associdados ��s caracter��sticas da bacia de drenagem (solos e uso da terra). Apesar dos efeitos das mudan��as observadas no uso do solo n��o serem ainda detect��veis na macro-escala (bacia amaz��nica), a disrup����o da estrutura e funcionamento dos ecossistemas �� detect��vel nas micro e meso escalas, com altera����es significativas na ciclagem de nutrientes nos ecossistemas fluviais.

Nutrientes na solu����o do solo em floresta de terra firme na Amaz��nia Central submetida �� extra����o seletiva de madeira

Os solos de terra firme da Amaz��nia Central, na sua maioria, s��o ��cidos, pobres em nutrientes e a manuten����o da floresta sobre esses solos �� garantida pela ciclagem de nutrientes, praticamente fechada. A substitui����o de floresta por pastagens ou outras atividades agr��colas leva �� diminui����o de nutrientes do compartimento biomassa, podendo comprometer os processos de ciclagem no solo, pois plantas absorvem nutrientes que presentes na solu����o do solo. Para entender o efeito de retirada de ��rvores, foi realizado um estudo em uma ��rea de floresta de terra firme na Amaz��nia Central submetida �� extra����o seletiva de madeira (6-10 ��rvores, ou 34 m�� ha-1 de madeira) localizada 80 km ao norte de Manaus, foram determinados os teores NO3-, NH4+, K+, Ca2+, Mg2+ e Na+ na solu����o do solo na camada de 0-30 cm. O experimento constou de tr��s blocos, cada um contendo uma parcela controle e uma que sofreu o corte seletivo de ��rvores, todos sobre um Latossolo Amarelo ��lico de textura muito argilosa. As medidas foram realizadas durante 13 meses, em cinco tratamentos em cada bloco: controle (floresta intacta), centro de clareira, borda de clareira, borda da floresta remanescente e floresta remanescente. Os teores de pot��ssio, c��lcio, magn��sio e s��dio mostraram diferen��as significativas entre os tratamentos. As quantidades dos ��ons am��nio e nitrato foram as menos afetadas. Os valores mais elevados foram geralmente encontrados nos tratamentos centro de clareira e borda de clareira. A maior diferen��a ocorreu na quantidade de s��dio na solu����o do solo, que chegou a mais de 5 kg ha-1, no centro de clareira de dois blocos, praticamente o dobro da encontrada nas suas respectivas parcelas controles. As concentra����es mais baixas dos nutrientes na solu����o do solo da floresta intacta (controle) e da floresta remanescente, confirmam a efici��ncia da floresta na ciclagem de nutrientes. Por��m, no centro de clareira, al��m da remo����o de ��rvores, a disponibilidade de materiais de f��cil decomposi����o, como ra��zes mortas e a liteira acumulada, podem ter contribu��do para uma maior concentra����o de nutrientes na solu����o do solo.

Caracteriza����o e distribui����o das formas do nitrog��nio org��nico em tr��s solos da Amaz��nia Central

As formas org��nicas do nitrog��nio em solos s��o determinadas mediante a identifica����o e quantifica����o dos compostos org��nicos liberados, quando os solos s��o tratados com ��cido a alta temperatura. Ainda n��o se conhecem na literatura trabalhos sobre a natureza qu��mica do N org��nico nos solos da Amaz��nia. O presente trabalho teve como objetivos identificar e quantificar a transforma����o do nitrog��nio proveniente de fertilizantes marcados com 15N nas fra����es org��nicas nitrogenadas de tr��s solos da Amaz��nia Central: dois solos de terra firme, classificados como Latossolo Amarelo e Podz��lico Vermelho Amarelo e um solo de v��rzea, classificado como Glei Pouco H��mico. Foram utilizadas amostras de solos de um ensaio de aduba����o desenvolvido em condi����es de casa de vegeta����o, onde, ap��s cultivo, procedeu-se o fracionamento do N org��nico do solo por meio da hidr��lise ��cida. Foram determinadas as seguintes fra����es: N-sol��vel em ��cido e destilado (NSAD), N-sol��vel em ��cido e n��o destilado (NSAnD) e N-n��o hidrolisado (NnH). Nos solos de terra firme, o N org��nico foi encontrado principalmente na forma de N sol��vel em ��cido e n��o destilado (NSAnD). Entre 63 a 66% (Latossolo) e 69 a 73% (podz��lico) do 15N imobilizado no solo foram encontrados na fra����o NSAnD. Esses resultados demonstram a import��ncia da imobiliza����o microbiana do N nesses solos. No solo de v��rzea, ao contr��rio, houve pouca diferen��a entre os teores de 15N do fertilizante imobilizado nas fra����es NSAnD e NSAD. Entre 46 e 53% do total de 15N imobilizado foram encontrados na fra����o NSAnD, enquanto que 42 a 52% ficaram na fra����o NSAD. Nesse solo, a presen��a de argila tipo 2:1 pode ter contribu��do para o alto estoque de 15N org��nico incorporado na fra����o NSAD, devido �� fixa����o de ��ons NH4+.

Avalia����o da durabilidade de concretos autoadens��veis com reduzido teor de cimento e elevados teores de adi����es minerais

A ind��stria de concreto �� uma grande consumidora de recursos naturais, seja para a produ����o de agregados, ou para a produ����o de cimento Portland, onde grandes quantidades de calc��rio s��o extra��das. Al��m disso, a ind��stria do cimento tem uma grande contribui����o na emiss��o de gases respons��veis pelo efeito estufa, portanto iniciativas que busquem reduzir o consumo de cimento nos concretos s��o importantes para a sustentabilidade das constru����es. Este trabalho avalia par��metros de durabilidade de concretos autoadens��veis (CAA) com baixo consumo de cimento e elevados teores de cinza volante e metacaulim, com e sem a adi����o de cal, em compara����o a dois concretos sem adi����es. Foram avaliados CAA com consumos de cimento entre 150 e 200 kg por m3 de concreto. Os ensaios realizados foram de resistividade, difus��o de ��ons cloreto (LNEC E-463/2004), carbonata����o acelerada e absor����o por capilaridade. Os resultados demonstram a aptid��o em produzir CAA com misturas terci��rias e quatern��rias com baixo consumo e que atendam as resist��ncias correntes aos 28 dias (30 a 40 MPa), proporcionando ainda ganhos acentuados na durabilidade e elevadas resist��ncias aos 90 dias.