Abstracting Application Development for Resource Constrained Wireless Sensor Networks

Ubiquitous computing is a concept whereby computing is distributed across smart objects surrounding users, creating ambient intelligence. Ubiquitous applications use technologies such as the Internet, sensors, actuators, embedded computers, wireless communication, and new user interfaces. The Internet-of-Things (IoT) is one of the key concepts in the realization of ubiquitous computing, whereby smart objects communicate with each other and the Internet. Further, Wireless Sensor Networks (WSNs) are a sub-group of IoT technologies that consist of geographically distributed devices or nodes, capable of sensing and actuating the environment.WSNs typically contain tens to thousands of nodes that organize and operate autonomously to perform application-dependent sensing and sensor data processing tasks. The projected applications require nodes to be small in physical size and low-cost, and have a long lifetime with limited energy resources, while performing complex computing and communications tasks. As a result, WSNs are complex distributed systems that are constrained by communications, computing and energy resources. WSN functionality is dynamic according to the environment and application requirements. Dynamic multitasking, task distribution, task injection, and software updates are required in field experiments for possibly thousands of nodes functioning in harsh environments.The development of WSN application software requires the abstraction of computing, communication, data access, and heterogeneous sensor data sources to reduce the complexities. Abstractions enable the faster development of new applications with a better reuse of existing software, as applications are composed of high-level tasks that use the services provided by the devices to execute the application logic.The main research question of this thesis is: What abstractions are needed for application development for resource constrained WSNs? This thesis models WSN abstractions with three levels that build on top of each other: 1) node abstraction, 2) network abstraction, and 3) infrastructure abstraction. The node abstraction hides the details in the use of the sensing, communication, and processing hardware. The network abstraction specifies methods of discovering and accessing services, and distributing processing in the network. The infrastructure abstraction unifies different sensing technologies and infrastructure computing platforms.As a contribution, this thesis presents the abstraction model with a review of each abstraction level. Several designs for each of the levels are tested and verified with proofs of concept and analyses of field experiments. The resulting designs consist of an operating system kernel, a software update method, a data unification interface, and all abstraction levels combining abstraction called an embedded cloud.The presented operating system kernel has a scalable overhead and provides a programming approach similar to a desktop computer operating system with threads and processes. An over-the-air update method combines low overhead and robust software updating with application task dissemination. The data unification interface homogenizes the access to the data of heterogeneous sensor networks. A unification model is used for various use cases by mapping everything as measurements. The embedded cloud allows resource constrained WSNs to share services and data, and expand resources with other technologies. The embedded cloud allows the distributed processing of applications according to the available services. The applications are implemented as processes using a hardware independent description language that can be executed on resource constrained WSNs. The lessons of practical field experimenting are analyzed to study the importance of the abstractions. Software complexities encountered in the field experiments highlight the need for suitable abstractions.The results of this thesis are tested using proof of concept implementations on real WSN hardware which is constrained by computing power in the order of a few MIPS, memory sizes of a few kilobytes, and small sized batteries. The results will remain usable in the future, as the vast amount, tight integration, and low-cost of future IoT devices require the combination of complex computation with resource constrained platforms

Performance Modelling and Analysis of Handover and Call Admission Control Algorithm for Next Generation Wireless Networks

The next generation wireless system (NGWS) has been conceived as a ubiquitous wireless environment. It integrates existing heterogeneous access networks, as well as future networks, and will offer high speed data, real-time applications (e.g. Voice over IP, videoconference ) and real-time multimedia (e.g. real-time audio and video) support with a certain Quality of Service (QoS) level to mobile users. It is required that the mobile nodes have the capability of selecting services that are offered by each provider and determining the best path through the various networks. Efficient radio resource management (RRM) is one of the key issues required to support global roaming of the mobile users among different network architectures of the NGWS and a precise call admission control (CAC) scheme satisfies the requirements of high network utilization, cost reduction, minimum handover latency and high-level QoS of all the connections. This thesis is going to describe an adaptive class-based CAC algorithm, which is expected to prioritize the arriving channel resource requests, based on user¿s classification and channel allocation policy. The proposed CAC algorithm couples with Fuzzy Logic (FL) and Pre-emptive Resume (PR) theories to manage and improve the performance of the integrated wireless network system. The novel algorithm is assessed using a mathematical analytic method to measure the performance by evaluating the handover dropping probability and the system utilization

Real-time communications over switched Ethernet supporting dynamic QoS management

Doutoramento em Engenharia InformáticaDurante a última década temos assistido a um crescente aumento na utilização de sistemas embutidos para suporte ao controlo de processos, de sistemas robóticos, de sistemas de transportes e veículos e até de sistemas domóticos e eletrodomésticos. Muitas destas aplicações são críticas em termos de segurança de pessoas e bens e requerem um alto nível de determinismo com respeito aos instantes de execução das respectivas tarefas. Além disso, a implantação destes sistemas pode estar sujeita a limitações estruturais, exigindo ou beneficiando de uma configuração distribuída, com vários subsistemas computacionais espacialmente separados. Estes subsistemas, apesar de espacialmente separados, são cooperativos e dependem de uma infraestrutura de comunicação para atingir os objectivos da aplicação e, por consequência, também as transacções efectuadas nesta infraestrutura estão sujeitas às restrições temporais definidas pela aplicação. As aplicações que executam nestes sistemas distribuídos, chamados networked embedded systems (NES), podem ser altamente complexas e heterogéneas, envolvendo diferentes tipos de interacções com diferentes requisitos e propriedades. Um exemplo desta heterogeneidade é o modelo de activação da comunicação entre os subsistemas que pode ser desencadeada periodicamente de acordo com uma base de tempo global (time-triggered), como sejam os fluxos de sistemas de controlo distribuído, ou ainda ser desencadeada como consequência de eventos assíncronos da aplicação (event-triggered). Independentemente das características do tráfego ou do seu modelo de activação, é de extrema importância que a plataforma de comunicações disponibilize as garantias de cumprimento dos requisitos da aplicação ao mesmo tempo que proporciona uma integração simples dos vários tipos de tráfego. Uma outra propriedade que está a emergir e a ganhar importância no seio dos NES é a flexibilidade. Esta propiedade é realçada pela necessidade de reduzir os custos de instalação, manutenção e operação dos sistemas. Neste sentido, o sistema é dotado da capacidade para adaptar o serviço fornecido à aplicação aos respectivos requisitos instantâneos, acompanhando a evolução do sistema e proporcionando uma melhor e mais racional utilização dos recursos disponíveis. No entanto, maior flexibilidade operacional é igualmente sinónimo de maior complexidade derivada da necessidade de efectuar a alocação dinâmica dos recursos, acabando também por consumir recursos adicionais no sistema. A possibilidade de modificar dinâmicamente as caracteristicas do sistema também acarreta uma maior complexidade na fase de desenho e especificação. O aumento do número de graus de liberdade suportados faz aumentar o espaço de estados do sistema, dificultando a uma pre-análise. No sentido de conter o aumento de complexidade são necessários modelos que representem a dinâmica do sistema e proporcionem uma gestão optimizada e justa dos recursos com base em parâmetros de qualidade de serviço (QdS). É nossa tese que as propriedades de flexibilidade, pontualidade e gestão dinâmica de QdS podem ser integradas numa rede switched Ethernet (SE), tirando partido do baixo custo, alta largura de banda e fácil implantação. Nesta dissertação é proposto um protocolo, Flexible Time-Triggered communication over Switched Ethernet (FTT-SE), que suporta as propriedades desejadas e que ultrapassa as limitações das redes SE para aplicações de tempo-real tais como a utilização de filas FIFO, a existência de poucos níveis de prioridade e a pouca capacidade de gestão individualizada dos fluxos. O protocolo baseia-se no paradigma FTT, que genericamente define a arquitectura de uma pilha protocolar sobre o acesso ao meio de uma rede partilhada, impondo desta forma determinismo temporal, juntamente com a capacidade para reconfiguração e adaptação dinâmica da rede. São ainda apresentados vários modelos de distribuição da largura de banda da rede de acordo com o nível de QdS especificado por cada serviço utilizador da rede. Esta dissertação expõe a motivação para a criação do protocolo FTT-SE, apresenta uma descrição do mesmo, bem como a análise de algumas das suas propiedades mais relevantes. São ainda apresentados e comparados modelos de distribuição da QdS. Finalmente, são apresentados dois casos de aplicações que sustentam a validade da tese acima mencionada.During the last decade we have witnessed a massive deployment of embedded systems on a wide applications range, from industrial automation to process control, avionics, cars or even robotics. Many of these applications have an inherently high level of criticality, having to perform tasks within tight temporal constraints. Additionally, the configuration of such systems is often distributed, with several computing nodes that rely on a communication infrastructure to cooperate and achieve the application global goals. Therefore, the communications are also subject to the same temporal constraints set by the application requirements. Many applications relying on such networked embedded systems (NES) are complex and heterogeneous, comprehending different activities with different requirements and properties. For example, the communication between subsystems may follow a strict temporal synchronization with respect to a global time-base (time-triggered), like in a distributed feedback control loop, or it may be issued asynchronously upon the occurrence of events (eventtriggered). Regardless of the traffic characteristics and its activation model, it is of paramount importance having a communication framework that provides seamless integration of heterogeneous traffic sources while guaranteeing the application requirements. Another property that has been emerging as important for NES design and operation is flexibility. The need to reduce installation and operational costs, while facilitating maintenance is promoting a more rational use of the available resources at run-time, exploring the ability to tune service parameters as the system evolves. However, such operational flexibility comes with the cost of increasing the complexity of the system to handle the dynamic resource management, which on the other hand demands the allocation of additional system resources. Moreover, the capacity to dynamically modify the system properties also causes a higher complexity when designing and specifying the system, since the operational state-space increases with the degrees of flexibility of the system. Therefore, in order to bound this complexity appropriate operational models are needed to handle the system dynamics and carry on an efficient and fair resource management strategy based on quality of service (QoS) metrics. This thesis states that the properties of flexibility and timeliness as needed for dynamic QoS management can be provided to switched Ethernet based systems. Switched Ethernet, although initially designed for general purpose Internet access and file transfers, is becoming widely used in NES-based applications. However, COTS switched Ethernet is insufficient regarding the needs for real-time predictability and for supporting the aforementioned properties due the use of FIFO queues too few priority levels and for stream-level management capabilities. In this dissertation we propose a protocol to overcome those limitations, namely the Flexible Time-Triggered communication over Switched Ethernet (FTT-SE). The protocol is based on the FTT paradigm that generically defines a protocol architecture suitable to enforce real-time determinism on a communication network supporting the desired flexibility properties. This dissertation addresses the motivation for FTT-SE, describing the protocol as well as its schedulability analysis. It additionally covers the resource distribution topic, where several distribution models are proposed to manage the resource capacity among the competing services and while considering the QoS level requirements of each service. A couple of application cases are shown that support the aforementioned thesis

High speed protocols for dual bus and dual ring network architectures

In this dissertation, two channel access mechanisms providing fair and bandwidth efficient transmission on dual bus and dual ring networks with high bandwidth-latency product are proposed. In addition, two effective priority mechanisms are introduced to meet the throughput and delay requirements of the diverse arrays of applications that future high speed networks must support. For dual bus architectures, the Buffer Insertion Bandwidth Balancing (BI_BWB) mechanism and the Preemptive priority Bandwidth Balancing (P_BI_BWB) mechanism are proposed. BI_BWB can significantly improve the delay performance of remote stations. It achieves that by providing each station with a shift register into which the station can temporarily store the upstream stations\u27 transmitted packets and replace these packets with its own transmissions. P_BI_BWB, an enhancement of BI_BWB, is designed to introduce effective preemptive priorities. This mechanism eliminates the effect of low priority on high priority by buffering the low priority traffic into a shift register until the transmission of the high priority traffic is complete. For dual ring architectures, the Fair Bandwidth Allocation Mechanism (FBAM) and the Effective Priority Bandwidth Balancing (EP_BWB) mechanism are introduced. FBAM allows stations to reserve channel bandwidth on a continuous basis rather than wait until bandwidth starvation is observed. Consequently, FBAM does not have to deal with the difficult issue of identifying starvation, a serious drawback of other access mechanisms such as the Local and Global Fairness Algorithms (LFA and GFA, respectively). In addition, its operation requires a significantly smaller number of control bits in the access control field of the slot and its performance is less sensitive to system parameters. Moreover, FBAM demonstrates Max-Min flow control properties with respect to the allocation of bandwidth among competing traffic streams, which is a significant advantage of FBAM over all the previously proposed channel access mechanisms. EP_BWB, an enhancement of FBAM to support preemptive priorities, minimizes the effect of low priority on high priority and supports delay-sensitive traffic by enabling higher priority classes to preempt the transmissions of lower priority classes. Finally, the great potential of EP_BWB to support the interconnection of base stations on a distributed control wireless PCN carrying voice and data traffic is demonstrated