We tackle two important problems that arise in simulation-based studies of various data-related properties in the context of Wireless Sensor Networks (WSNs): (1) reducing the turnaround time for completing the simulations in a large-scale parameter space; (2) providing database functionalities for a more detailed insight into the simulation's evolution. Towards these goals, we have developed the DiSSIDnet (Distributed System for Simulation and Integrated Development for Wireless Sensor Networks). Leveraging upon our earlier works on the SIDnet-SWANS tool [3], DiSSIDnet not only provides the ability of a synchronized execution of the simulations in a distributed environment, but also maintains the simulation data over the parameter-space in a relational database. In addition to post-simulation queries that can be posed to the database, we also provide the feature of specifying triggers that can generate notifications upon detecting certain events of interest during the simulation process.

We address the problem of extending the lifetime of wireless sensor networks using multi-path routing based on a family of flexible routes with soft quality of service guarantees in terms of the packets’ delivery latency. We introduce a methodology based on Bezier curves as guiding trajectories in the routing process and we address the balancing of the workload among neighboring nodes. An added benefit, due to the flexibility of the Bezier curves, is that the shapes of the (alternate) routes can be constructed in a manner that prolongs the lifetime of the nodes in the vicinity of a given source/sink. We describe a forwarding algorithm, where the relay nodes can determine locally the Bezier curve they belong to and which requires only the transmission of the so-called control points that determine the shape of one (boundary) curve. We also show how our forwarding algorithm can be adapted to incorporate the sleep-schedule of the individual nodes, thereby further prolonging the networks’ lifetime. Our simulations demonstrate that the Bezier-based routing algorithms can yield significant improvements in the networks’ overall lifetime.

This work addresses the problem of principal node selection during the tracking process in Wireless Sensor Networks (WSNs). In a typical tracking scenario, the location of a mobile unit is determined via collaborative trilateration by the nodes that have the tracked object within their sensing range. One of the participants in the trilateraion---the tracking principal---is in charge of transmitting the location and time information to a designated sink. However, as the moving object changes its location, a new principal needs to be determined and handed off the task of the subsequent sensing, trilateration and transmission to the sink. We observe that in many WSN applications in which sensing/sampling needs to be combined with multihop transmission and, possibly, in-network aggregation, the typical processing is organized in synchronized intervals, called epochs. We postulate that taking the semantics of the epoch into consideration is important when selecting tracking principals and we present efficient algorithmic solutions towards this goal. Our experiments demonstrate that the proposed approach can yield significant reduction in the number of hand-offs between consecutive tracking principals, when compared to previous works.

For high-density networks, several studies have proposed field-based routing paradigms to uniformly distribute the traffic load throughout the network. However, as network density decreases, we observe major shortcomings of the current state-of-the-art: (i) fewer number of neighbors reduce the number of available paths and leads to path merging and (ii) the paths directed towards the border of the network merge into a single path. These path merging effects decrease significantly the energy balance, and as consequence, the lifetime of the network. In this paper, we propose a novel mechanism to enable a better load balancing for single-source and multiple-source scenarios. Our evaluations demonstrate that by using the proposed methodology, the network lifetime can be prolonged between 30% and 40%.

This work addresses the problem of managing the reactive behavior in Wireless Sensor Networks (WSN). We consider settings in which the occurrence of a particular event, detected in a state that satisfies a given condition, should fire the execution of an action. We observe that in WSN settings, both the event and condition may pertain to some continuous phenomena that are monitored by distinct groups of nodes and, in addition, their respective detection may impose an extra communication overhead, if a correct executional behavior is desired in terms of firing the action. Towards that end, we propose the concept of a {\it meta trigger},which essentially translates a particular request, so that the communication overhead among the entities participating in its processing is minimized. We discuss a proof-of-concept implementation which demonstrates the benefits of the proposed methodology on an actual small-size network, and we present a detailed simulation-based experimental evaluation in large-scale networks. Our experiments indicate that the meta-triggers can yield substantial savings in the energy (and bandwidth) expenditures of the network, while preserving the intended executional correctness.

This work presents the SIDnet, a simulation-based environment for applications development in wireless sensor networks settings. It enables run-time interactions with the network for the purpose of observing the behavior of algorithms protocols in the presence of various conditions such as phenomena fluctuations, or a sudden loss of service both at an individual node, as well as a collection of nodes.

This work addresses the problem of extending the lifetime of a wireless sensor network, when a bounded delay on receiving the packets is acceptable for a given sink node. The temporal threshold for the Quality of Data (QoD) tolerance is specified with respect to the time that it takes for the packets to travel from the source to the sink along an optimal route. For these settings, we propose a methodology that enables controlling the spatio-temporal load balancing among the sensors around the optimal route. Given the QoD threshold, we use it to derive a set of parameterized Bezier curves which serve as alternate routes between the (source,sink) pair, relieving the nodes along the optimal route, while ensuring a bound on the delay of packets delivery. We provide experimental results which demonstrate that our proposed methodology can prolong the sensor networks’ lifetime for various definitions of the concept of a "lifetime" in the existing literature.