State-based publish/subscribe for sensor systems

Recent technological advances have enabled the creation of networks of sensor devices. These devices are typically equipped with basic computational and communication capabilities. Systems based on these devices can deduce high-level, meaningful information about the environment that may be useful to applications. Due to their scale, distributed nature, and the limited resources available to sensor devices, these systems are inherently complex. Shielding applications from this complexity is a challenging problem. To address this challenge, I present a middleware called SPS (State-based Publish/Subscribe). It is based on a combination of a State-Centric data model and a Publish/Subscribe (Pub/Sub) communication paradigm. I argue that a state-centric data model allows applications to specify environmental situations of interest in a more natural way than existing solutions. In addition, Pub/Sub enables scalable many-to-many communication between sensors, actuators, and applications. This dissertation initially focuses on Resource-constrained Sensor Networks (RSNs) and proposes State Filters (SFs), which are lightweight, stateful, event filtering components. Their design is motivated by the redundancy and correlation observed in sensor readings produced close together in space and time. By performing context-based data processing, SFs increase Pub/Sub expressiveness and improve communication efficiency. Secondly, I propose State Maintenance Components (SMCs) for capturing more expressive conditions in heterogeneous sensor networks containing more resourceful devices. SMCs extend SFs with data fusion and temporal and spatial data manipulation capabilities. They can also be composed together (in a DAG) to deduce higher level information. SMCs operate independently from each other and can therefore be decomposed for distributed processing within the network. Finally, I present a Pub/Sub protocol called QPS (Quad-PubSub) for location-aware Wireless Sensor Networks (WSNs). QPS is central to the design of my framework as it facilitates messaging between state-based components, applications, sensors, and actuators. In contrast to existing data dissemination protocols, QPS has a layered architecture. This allows for the transparent operation of routing protocols that meet different Quality of Service (QoS) requirements. 3