A time division beacon scheduling mechanism for IEEE 802.15.4/Zigbee cluster-tree wireless sensor networks

While the IEEE 802.15.4/Zigbee protocol stack is being considered as a promising technology for low-cost low-power Wireless Sensor Networks (WSNs), several issues in the standard specifications are still open. One of those ambiguous issues is how to build a synchronized multi-hop cluster-tree network, which is quite suitable for ensuring QoS support in WSNs. In fact, the current IEEE 802.15.4/Zigbee specifications restrict the synchronization in the beacon-enabled mode (by the generation of periodic beacon frames) to star-based networks, while it supports multi-hop networking using the peer-to-peer mesh topology, but with no synchronization. Even though both specifications mention the possible use of cluster-tree topologies, which combine multihop and synchronization features, the description on how to effectively construct such a network topology is missing. This paper tackles this problem, unveils the ambiguities regarding the use of the cluster-tree topology and proposes a synchronization mechanism based on Time Division Beacon Scheduling to construct cluster-tree WSNs. We also propose a methodology for an efficient duty cycle management in each router (cluster-head) of a cluster-tree WSN that ensures the fairest use of bandwidth resources. The feasibility of the proposal is clearly demonstrated through an experimental test bed based on our own implementation of the IEEE 802.15.4/Zigbee protocol.

Static-priority scheduling over wireless networks with multiple broadcast domains

We propose a wireless medium access control (MAC) protocol that provides static-priority scheduling of messages in a guaranteed collision-free manner. Our protocol supports multiple broadcast domains, resolves the wireless hidden terminal problem and allows for parallel transmissions across a mesh network. Arbitration of messages is achieved without the notion of a master coordinating node, global clock synchronization or out-of-band signaling. The protocol relies on bit-dominance similar to what is used in the CAN bus except that in order to operate on a wireless physical layer, nodes are not required to receive incoming bits while transmitting. The use of bit-dominance efficiently allows for a much larger number of priorities than would be possible using existing wireless solutions. A MAC protocol with these properties enables schedulability analysis of sporadic message streams in wireless multihop networks.

Groundtruth system for underwater benchmarking

Oceans - San Diego, 2013

Avaliação dos mecanismos de concorrência na API do Java 8

As plataformas com múltiplos núcleos tornaram a programação paralela/concorrente num tópico de interesse geral. Diversos modelos de programação têm vindo a ser propostos, facilitando aos programadores a identificação de regiões de código potencialmente paralelizáveis, deixando ao sistema operativo a tarefa de as escalonar dinamicamente em tempo de execução, explorando o maior grau possível de paralelismo. O Java não foge a esta tendência, disponibilizando ao programador um número crescente de bibliotecas de mecanismos de sincronização e paralelização de código. Neste contexto, esta tese apresenta e discute um conjunto de resultados obtidos através de testes intensivos à eficiência de algoritmos de ordenação implementados com recurso aos mecanismos de concorrência da API do Java 8 (Threads, Threadpools, ExecutorService, CountdownLach, ExecutorCompletionService e ForkJoinPools) em sistemas com um número de núcleos variável. Para cada um dos mecanismos, são apresentadas conclusões sobre o seu funcionamento e discutidos os cenários em que o seu uso pode ser rentabilizado de modo a serem obtidos melhores tempos de execução.