Guaranteeing Communication Quality in Real World WSN Deployments

Networks of smart interconnected objects have allowed the integration of the artificial world into the physical one. The interaction over a wireless medium is simultaneously the technology enabler and the primary hindering factor. The complexity and variability of the behavior of low power wireless communication is one of the challenges making the design and deployment of a system based on this technology a unique and demanding experience. In this thesis, we describe the deployment of two operational systems for structural health monitoring and adaptive lighting, undertaken by our research group. Our major contribution, among others, covers the definition and implementation of the system services enabling the monitoring infrastructure to guarantee the required quality. The resulting unique design and reliability provide concrete support to the vision of wireless sensor networks as dependable monitoring infrastructure. Despite the success in meeting the user needs, the simple yet effective solutions exploited in the aforementioned deployments make apparent the limitations of the widely used approaches to coordinate access to the communication medium. This thesis also argues that the currently employed solutions at the MAC layer are insufficient to provide guarantees to the resource user. Therefore, we introduce Reins-MAC, a Time-Division Multiple-Access (TDMA) communication scheduler that coordinates access to the medium in a fully decentralized fashion. Limited flexibility, scalability, robustness, as well as increased overhead and complexity are commonly recognized shortcomings of TDMA approaches. Reins-MAC overcomes these limitations by adapting the scheduling to match local availability and natural connectivity variations. Moreover, each node is empowered with full control over its own communication resources. The ability to anarchically apply changes to the communication schedule allows the steering of the resource allocation towards individual needs, dictated by the higher layers in the network stack. The resulting quality and anarchy in accessing the communication resource affect the design and implementation of WSNs, opening new horizons where the application regains control of the primary resource: communication.