Dynamical Jumping Real-Time Fault-Tolerant Routing Protocol for Wireless Sensor Networks

In time-critical wireless sensor network (WSN) applications, a high degree of reliability is commonly required. A dynamical jumping real-time fault-tolerant routing protocol (DMRF) is proposed in this paper. Each node utilizes the remaining transmission time of the data packets and the state of the forwarding candidate node set to dynamically choose the next hop. Once node failure, network congestion or void region occurs, the transmission mode will switch to jumping transmission mode, which can reduce the transmission time delay, guaranteeing the data packets to be sent to the destination node within the specified time limit. By using feedback mechanism, each node dynamically adjusts the jumping probabilities to increase the ratio of successful transmission. Simulation results show that DMRF can not only efficiently reduce the effects of failure nodes, congestion and void region, but also yield higher ratio of successful transmission, smaller transmission delay and reduced number of control packets.Comment: 22 pages, 9 figure

Feedback based real-time MAC (RT-MAC) protocol for data packet streaming in wireless sensor networks

Wireless sensor networks (WSNs) are generally used for event driven monitoring or periodic reporting. Once a triggering event happens, it needs to be reported in real-time as a continuous stream for some duration. In order to address such communication requirements, this thesis introduces a soft Real-Time MAC (RT-MAC) protocol for real-time data packet streaming in wireless sensor networks. RT-MAC eliminates contention for a wireless medium by introducing a feedback control packet, called Clear Channel (CC). As a result, RT-MAC has a consistent and predictable data transmission pattern that provides end-to-end delay guarantees. Additionally, RT-MAC has a lower end-to-end delay than other real-time WSN MAC protocols for two reasons: (1) it maximizes spatial channel reuse by avoiding the false blocking problem caused by request-to-send (RTS) and clear-to-send (CTS) exchanges in wireless MAC protocols (2) it reduces contention duration of control packets to facilitate faster data packet transfer. Thus, RT-MAC facilitates periodic data packet deliveries as well as alarming event reporting. RT-MAC operates both with and without duty cycle mode (sleep/wakeup schedule for sensor nodes). Duty cycle mode of RT-MAC is useful in situations where energy conservation is one of the goals along with real-time requirements. RT-MAC is well suited for multi-hop communication with a large number of hops. RT-MAC protocol supports single-stream communication between a randomly selected source and sink node pair as well as multi-stream communication among different source and sink node pairs. This thesis provides the lower and upper end-to-end delay bounds for data packets transfer in normal mode of operation of RT-MAC protocol. We used state diagram analysis to show the in-depth functioning of RT-MAC protocol. This thesis also presents Markov analysis of RT-MAC that shows the behavior of the protocol in fault scenarios. Extensive simulation results are also presented in this thesis. These results show significant improvement in delay, packet throughput performance, and uniformity in packet transmission pattern at a cost of a very small increase in energy consumption as compared to other real-time MAC protocols such as VTS and general purpose MAC protocols such as S-MAC and T-MAC

On the use of IEEE 802.15.4/Zigbee for time-sensitive wireless sensor network applications

Mestrado em Engenharia Electrotécnica e de ComputadoresRecent advancements in information and communication technologies are paving the way for new paradigms in embedded computing systems. This, allied with an increasing eagerness for monitoring and controlling everything, everywhere, is pushing forward the design of new Wireless Sensor Network (WSN) infrastructures that will tightly interact with the physical environment, in a ubiquitous and pervasive fashion. Such cyber-physical systems require a rethinking of the usual computing and networking concepts, and given that the computing entities closely interact with their environment, timeliness is of increasing importance. This Thesis addresses the use of standard protocols, particularly IEEE 802.15.4 and ZigBee, combined with commercial technologies as a baseline to enable WSN infrastructures capable of supporting the Quality of Service (QoS) requirements (specially timeliness and system lifetime) that future large-scale networked embedded systems will impose. With this purpose, in this Thesis we start by evaluating the network performance of the IEEE 802.15.4 Slotted CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) mechanism for different parameter settings, both through simulation and through an experimental testbed. In order to improve the performance of these networks (e.g. throughput, energyefficiency, message delay) against the hidden-terminal problem, a mechanism to mitigate it was implemented and experimentally validated. The effectiveness of this mechanism was also demonstrated in a real application scenario, featuring a target tracking application. A methodology for modelling cluster-tree WSNs and computing the worst-case endto-end delays, buffering and bandwidth requirements was tested and validated experimentally. This work is of paramount importance to understand the behaviour of WSNs under worst-case conditions and also to make the appropriate network settings. Our experimental work enabled us to identify a number of technological constrains, namely related to hardware/software and to the Open-ZB implementation in TinyOS. In this line, a new implementation effort was triggered to port the Open-ZB IEEE 802.15.4/ZigBee protocol stack to the ERIKA real-time operating system. This implementation was validated experimentally and its behaviour compared with the TinyOS–based implementation.Os últimos avanços nas tecnologias de informação e comunicação (ICTs) estão a abrir caminho para novos paradigmas de sistemas computacionais embebidos. Este facto, aliado à tendência crescente em monitorizar e controlar tudo, em qualquer lugar, está a alimentar o desenvolvimento de novas infra-estruturas de Redes de Sensores Sem Fios (WSNs), que irão interagir intimamente com o mundo físico de uma forma ubíqua. Este género de sistemas ciber-físicos de grande escala, requer uma reflexão sobre os conceitos de redes e de computação tradicionais, e tendo em conta a proximidade que estas entidades partilham com ambiente envolvente, o seu comportamento temporal é de acrescida importância. Esta Tese endereça a utilização de protocolos normalizados, em particular do IEEE 802.15.4 e ZigBee em conjunto com tecnologias comerciais, para desenvolver infraestruturas WSN capazes de responder aos requisitos de Qualidade de Serviço (QoS) (especialmente em termos de comportamento temporal e tempo de vida do sistema), que os futuros sistemas embebidos de grande escala deverão exigir. Com este propósito, nesta Tese começamos por analisar a performance do mecanismo de Slotted CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) do IEEE 802.15.4 para diferentes parâmetros, através de simulação e experimentalmente. De modo a melhorar a performance destas redes (ex. throughput, eficiência energética, atrasos) em cenários que contenham nós escondidos (hidden-nodes), foi implementado e validado experimentalmente um mecanismo para eliminar este problema. A eficácia deste mecanismo foi também demonstrada num cenário aplicacional real. Foi testada e validada uma metodologia para modelizar uma WSN em cluster-tree e calcular os piores atrasos das mensagens, necessidades de buffering e de largura de banda. Este trabalho foi de grande importância para compreender o comportamento deste tipo de redes para condições de utilização limite e para as configurar a priori. O nosso trabalho experimental permitiu identificar uma série de limitações tecnológicas, nomeadamente relacionadas com hardware/software e outras relacionadas com a implementação do Open-ZB em TinyOS. Isto desencadeou a migração da pilha protocolar IEEE 802.15.4/ZigBee Open-ZB para o ERIKA, um sistema operativo de tempo-real. Esta implementação foi validada experimentalmente e o seu comportamento comparado com o da implementação baseada em TinyOS

On Scheduling and Real-Time Capacity of Hexagonal Wireless Sensor Networks

Since wireless ad-hoc networks use shared communication medium, accesses to the medium must be coordinated to avoid packet collisions. Transmission scheduling algorithms allocate time slots to the nodes of a network such that if the nodes transmit only during the allocated time slots, no collision occurs. For real-time applications, by ensuring deterministic channel access, transmission scheduling algorithms have the added significance of making guarantees on transmission latency possible. In this paper we present a distributed transmission scheduling algorithm for hexagonal wireless ad-hoc networks with a particular focus on Wireless Sensor Networks. Afforded by the techniques of ad-hoc networks topology control, hexagonal meshes enable trivial addressing and routing protocols. Our transmission scheduling algorithm constructs network-wide conflictfree packet transmission schedule for hexagonal networks, where the overhead of schedule construction in terms of message exchanges is zero above and beyond that for topology control and other network control related functions. Furthermore, the schedule is optimal in the sense that the bottleneck node does not idle. We also present an implicit clock synchronization algorithm to facilitate scheduling. We derive the real time capacity of our scheduling algorithm. We present evaluations of our scheduling algorithm in the presence of topological irregularities using simulation