Modular Remote Reprogramming of Sensor Nodes

Wireless sensor networks are envisioned to be deployed in the absence of permanent network infrastructure and in environments with limited or no human accessibility. Hence, such deployments demand mechanisms to remotely (i.e., over the air) reconfigure and update the software on the nodes. In this paper we introduce DyTOS, a TinyOS based remote reprogramming approach that enables the dynamic exchange of software components and thus incrementally update the operating system and its applications. The core idea is to preserve the modularity of TinyOS, i.e., its componentisation, which is lost during the normal compilation process, and enable runtime composition of TinyOS components on the sensor node. The proposed solution integrates seamlessly into the system architecture of TinyOS: It does not require any changes to the programming model of TinyOS and all existing components can be reused transparently. Our evaluation shows that DyTOS incurs a low performance overhead while keeping a smaller – up to one third – memory footprint than other comparable solutions

Energy harvesting and wireless transfer in sensor network applications: Concepts and experiences

Advances in micro-electronics and miniaturized mechanical systems are redefining the scope and extent of the energy constraints found in battery-operated wireless sensor networks (WSNs). On one hand, ambient energy harvesting may prolong the systems lifetime or possibly enable perpetual operation. On the other hand, wireless energy transfer allows systems to decouple the energy sources from the sensing locations, enabling deployments previously unfeasible. As a result of applying these technologies to WSNs, the assumption of a finite energy budget is replaced with that of potentially infinite, yet intermittent, energy supply, profoundly impacting the design, implementation, and operation of WSNs. This article discusses these aspects by surveying paradigmatic examples of existing solutions in both fields and by reporting on real-world experiences found in the literature. The discussion is instrumental in providing a foundation for selecting the most appropriate energy harvesting or wireless transfer technology based on the application at hand. We conclude by outlining research directions originating from the fundamental change of perspective that energy harvesting and wireless transfer bring about

Exploiting wireless link dynamics

Efficient and reliable communication is the key to enable multihop wireless networks such as sensornets, meshnets and MANETs. Unlike wired networks, communication links in wireless networks are highly dynamic and pose additional challenges. Network protocols, besides establishing routing paths between two nodes, must overcome link dynamics and the resulting shift in the network topology. Hence, we need to develop efficient link estimation mechanisms, reliable routing algorithms, and stable addressing schemes to overcome these challenges inherent in wireless networks. The prevalent approach today is to use routing techniques similar to those in wired networks, such as tree construction: Link estimators identify neighbors with consistently high quality links based on a certain cost metric. Routing protocols conserve routing to a single path between two communication nodes by choosing the best sequence of nodes at each hop, as identified by the link estimator. In contrast, recent studies on opportunistic routing schemes suggest that traditional routing may not be the best approach in wireless networks because it leaves out a potentially large set of neighbors with intermediate links offering significant routing progress. Fine-grained analysis of link qualities reveals that such intermediate links are bursty, i.e., alternate between reliable and unreliable periods of transmission. We propose unconventional yet efficient approaches of link estimation, routing and addressing in multihop wireless networks to exploit wireless link dynamics instead of bypassing them for the sake of stability and reliability. The goal is to maximize routing performance parameters, such as transmission counts and throughput, by exploiting the burstiness of wireless links while, at the same time, preserving the stability and reliability of the existing mechanisms.The contributions of this dissertation are manifold:• Firstly, we develop relevant link estimation metrics to estimate link burstiness and identify intermediate links that can enhance the routing progress of a packet at each hop.• Secondly, we propose adaptive routing extensions that enable the inclusion of such long-range intermediate links into the routing process.• Thirdly, we devise a resilient addressing scheme to assign stable locations to nodes in challenging network conditions.• Finally, we develop an evaluation platform that allows us to evaluate our prototypes across different classes of wireless networks, such as sensornets and meshnets, using a single implementation.The dissertation primarily focuses on the network layer of the protocol stack. Although the proposed approaches have a broader relevance in the wireless domain, the design choices for our prototypes are tailored to sensornets - a notoriously difficult class of multihop wireless networks. Our evaluation highlights the key achievements of this work when compared to the state-of-the-art: The proposed metrics identify bursty links in the network with high accuracy, the routing extensions reduce the transmission count in the network by up to 40%, and the addressing scheme achieves 3-7 times more stable addressing even under challenging network conditions

Exploiting wireless link dynamics

Efficient and reliable communication is the key to enable multihop wireless networks such as sensornets, meshnets and MANETs. Unlike wired networks, communication links in wireless networks are highly dynamic and pose additional challenges. Network protocols, besides establishing routing paths between two nodes, must overcome link dynamics and the resulting shift in the network topology. Hence, we need to develop efficient link estimation mechanisms, reliable routing algorithms, and stable addressing schemes to overcome these challenges inherent in wireless networks. The prevalent approach today is to use routing techniques similar to those in wired networks, such as tree construction: Link estimators identify neighbors with consistently high quality links based on a certain cost metric. Routing protocols conserve routing to a single path between two communication nodes by choosing the best sequence of nodes at each hop, as identified by the link estimator. In contrast, recent studies on opportunistic routing schemes suggest that traditional routing may not be the best approach in wireless networks because it leaves out a potentially large set of neighbors with intermediate links offering significant routing progress. Fine-grained analysis of link qualities reveals that such intermediate links are bursty, i.e., alternate between reliable and unreliable periods of transmission. We propose unconventional yet efficient approaches of link estimation, routing and addressing in multihop wireless networks to exploit wireless link dynamics instead of bypassing them for the sake of stability and reliability. The goal is to maximize routing performance parameters, such as transmission counts and throughput, by exploiting the burstiness of wireless links while, at the same time, preserving the stability and reliability of the existing mechanisms.The contributions of this dissertation are manifold:• Firstly, we develop relevant link estimation metrics to estimate link burstiness and identify intermediate links that can enhance the routing progress of a packet at each hop.• Secondly, we propose adaptive routing extensions that enable the inclusion of such long-range intermediate links into the routing process.• Thirdly, we devise a resilient addressing scheme to assign stable locations to nodes in challenging network conditions.• Finally, we develop an evaluation platform that allows us to evaluate our prototypes across different classes of wireless networks, such as sensornets and meshnets, using a single implementation.The dissertation primarily focuses on the network layer of the protocol stack. Although the proposed approaches have a broader relevance in the wireless domain, the design choices for our prototypes are tailored to sensornets - a notoriously difficult class of multihop wireless networks. Our evaluation highlights the key achievements of this work when compared to the state-of-the-art: The proposed metrics identify bursty links in the network with high accuracy, the routing extensions reduce the transmission count in the network by up to 40%, and the addressing scheme achieves 3-7 times more stable addressing even under challenging network conditions