Oliviu Ghica

SIDnet-SWANS: a simulator and integrated development platform for sensor networks applications

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.

Evolving triggers for dynamic environments

In this work we address the problem of managing the reactive behavior in distributed environments in which data continuously changes over time, where the users may need to explicitly express how the triggers should be (self) modified. To enable this we propose the (ECA)2 – Evolving and Context-Aware Event-Condition-Action paradigm for specifying triggers that capture the desired reactive behavior in databases which manage distributed and continuously changing data. Since both the monitored event and the condition part of the trigger may be continuous in nature, we introduce the concept of metatriggers to coordinate the detection of events and the evaluation of conditions.

Selecting tracking principals with epoch awareness

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.

Controlled Multi-Path Routing in Sensor Networks Using Bezier Curves

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.

Deflection-Aware Tracking-Principal Selection in Active Wireless Sensor Networks

This paper addresses the problem of energy efficiency balanced with tracking accuracy in wireless sensor networks (WSNs). Specifically, we focus on the issues related to selecting tracking principals, i.e., the nodes with two special tasks: 1) coordinating the activities among the sensors that are detecting the tracked objects locations in time and 2) selecting a node to which the tasks of coordination and data fusion will be handed off when the tracked object exits the sensing area of the current principal. Extending the existing results that based the respective principal selection algorithms on the assumption that the targets trajectory is approximated with straight line segments, we consider more general settings of (possibly) continuous changes of the direction of the moving target. We developed an approach based on particle filters to estimate the targets angular deflection at the time of a handoff, and we considered the tradeoffs between the expensive in-node computations incurred by the particle filters and the imprecision tolerance when selecting subsequent tracking principals. Our experiments demonstrate that the proposed approach yields significant savings in the number of handoffs and the number of unsuccessful transfers in comparison with previous approaches.

Improving the Energy Balance of Field-Based Routing in Wireless Sensor Networks

Abstract-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%.

A Case for Meta-Triggers in Wireless Sensor Networks

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.

Alternating multiple tributaries + deltas

This work addresses the problem of trading off the latency in delivering the answer to the sink at the benefit of balancing the spatial dispersion of the energy consumption among the nodes and, consequently, prolonging the lifetime in sensor networks. Typically, in response to a query that pertains to the data from some geographic region, a tree structure is constructed and, when possible, some in-network aggregation is performed. On the other hand, in order to increase the robustness and/or balance the load, multipath routing is employed. Motivated by earlier work that combined trees and multipaths [19], in this paper we explore the possibility, and the impact, of combining multiple trees and multiple multipaths for routing, when processing a query with respect to a given region of interest. We present and evaluate two approaches that enable load-balancing in terms of alternating among a collection of routing structures.

Security of Electrostatic Field Persistent Routing: Attacks and Defense Mechanisms

Electrostatic Field-based Routing (EFR) is a form of geographical multi-path routing where packets are routed along a collection of electrostatic field lines, defined by electrostatic charges associated with source and sink nodes. EFR provides an efficient and scalable solution to the workload balancing problem. However, it assumes that nodes behave in a cooperative manner making EFR-based routing protocols vulnerable to various attacks. We investigate the security aspects of EFR-based routing protocols. We focus on an instance of EFR, called Multi-Pole Field Persistent Routing (MP-FPR), for which we identify attacks that can target different components of the protocol, and propose a set of corresponding defense mechanisms. We present extensive experimental evaluations of the impact of the different attacks and the effectiveness of the proposed defense mechanisms.

Tracking-Based Trajectory Data Reduction in Wireless Sensor Networks

This work addresses the problem of balancing the trade-off between the energy expenses due to communication vs. the accuracy of the trajectories representation in Wireless Sensor Networks (WSN) where the spatio-temporal data is obtained by tracking. We consider some of the approaches used by the Moving Objects Databases (MOD) and Computational Geometry (CG) communities, and we demonstrate that, with appropriate modifications, they can yield benefits in WSN in terms of energy savings. Towards that, we developed distributed algorithms that implement the Dead-Reckoning policy for managing the transient location-in-time information of mobile entities, whose localization is done by tracking sensors. In addition, we developed a distributed variant of the Douglas-Peuker heuristic for polyline reduction from CG literature, augmented with temporal awareness. Our experiments demonstrate the benefits in terms of reducing the communication overheads, while keeping the error boundaries at acceptable levels. Although it may seem counter-intuitive at first, we also demonstrate that an attempt to merge the Dead-Reckoning and Douglas-Peuker approaches, need not yield additional improvements of the in-network energy savings, due to the complementary nature of the data reduction in the two approaches.