Ionut Cardei

Energy-efficient connected-coverage in wireless sensor networks

This paper addresses the target coverage problem inWireless Sensor Networks (WSNs). Communication and sensing consume energy, therefore, efficient power management can extend network lifetime. In this paper, we consider a large number of sensors randomly deployed to monitor a number of targets. Each target may be redundantly covered by multiple sensors. To conserve energy, we organise sensors in sets activated sucessively. In this paper, we introduce the Connected Set Covers (CSC) problem that has as objective finding a maximum number of set covers such that each sensor node to be activated is connected to the Base Station (BS). A sensor can participate in multiple sensor sets, but the total energy spent in all sets is constrained by the initial energy reserves. We show that the CSC problem is NP-complete and we propose three solutions: an Integer Programming (IP)-based solution, a greedy approach and a distributed and localised heuristic. Simulation results that validate our approaches are also presented.

Resource Management for Ad-Hoc Wireless Networks with Cluster Organization

Boosted by technology advancements, government and commercial interest, ad-hoc wireless networks are emerging as a serious platform for distributed mission-critical applications. Guaranteeing QoS in this environment is a hard problem because several applications may share the same resources in the network, and mobile ad-hoc wireless networks (MANETs) typically exhibit high variability in network topology and communication quality. In this paper we introduce DYNAMIQUE, a resource management infrastructure for MANETs. We present a resource model for multi-application admission control that optimizes the application admission utility, defined as a combination of the QoS satisfaction ratio. A method based on external adaptation (shrinking QoS for existing applications and later QoS expansion) is introduced as a way to reduce computation complexity by reducing the search space. We designed an application admission protocol that uses a greedy heuristic to improve application utility. For this, the admission control considers network topology information from the routing layer. Specifically, the admission protocol takes benefit from a cluster network organization, as defined by ad-hoc routing protocols such as CBRP and LANMAR. Information on cluster membership and cluster head elections allows the admission protocol to minimize control signaling and to improve application quality by localizing task mapping.

MAC layer QoS support for wireless networks of unmanned air vehicles

Mission-critical applications in wireless environments depend on a cross layer approach for Quality of Service. Dealing efficiently with variable link quality and dynamic topologies involves QoS integration at the link, network and transport layer interfaces. In this paper, we present a new contention-based medium access control protocol for wireless ad-hoc networks of unmanned air vehicles. A receiver-initiated access control protocol with sender scheduling provides the mechanisms to implement effective MAC-layer bandwidth allocation with support for ad-hoc scenarios. A variable RTS lead time procedure integrated with binary exponential backoff improves fairness and provides low access latency for critical data frames. A major protocol design factor is efficient operation under heavy load. Performance measurements from simulations indicate consistent performance and promising results.

DTN Routing with Probabilistic Trajectory Prediction

Many real-world DTN application involve vehicles that do not have a purely random mobility pattern. In most cases nodes follow a predefined trajectory in space that may deviate from the norm due to environment factors or random events. In this paper we propose a DTN routing scheme for applications where the node trajectory and the contact schedule can be predicted probabilistically. We describe a technique for contact estimation for mobile nodes that uses a Time Homogeneous Semi Markov model. With this method a node computes contact profiles describing the probabilities of contacts per time unit, and uses them to select the next hop such that the delivery ratio is improved. We develop the Trajectory Prediction DTN Routing algorithm and we analyze its performance with simulations.

A Polynomial Time Approximation Scheme for the Grade of Service Steiner Minimum Tree Problem

In this paper, we present the design of a Polynomial Time Approximation Scheme (PTAS) for the Grade of Service Steiner Minimum Tree (GOSST) problem, which is known to be NP-Complete. Previous research has focused on geometric analyses and different approximation algorithms have been designed. We propose a PTAS that provides a polynomial time, near-optimal solution with performance ratio 1+∈. The GOSST problem has some important applications. In network design, a fundamental issue for the physical construction of a network structure is the interconnection of many communication sites with the best choice of the connecting lines and the best allocation of the transmission capacities over these lines. Good solutions should provide paths with enough communication capacities between any two sites, with the least network construction costs. Also, the GOSST problem has applications in transportation, for road constructions and some potential uses in CAD in terms of interconnecting the elements on a plane to provide enough flux between any two elements.

Message forwarding in Cyclic MobiSpace: the multi-copy case

A key challenge of message forwarding in delay tolerant networks (DTNs) is to increase delivery rate and decrease delay and cost. When information for future connectivity is not available, opportunistic routing is preferred in DTNs in which messages are forwarded opportunistic (non-deterministically) to nodes with higher delivery probabilities. Many real objects have non-deterministic but cyclic motions; however, few prior research work has investigated a multi-copy opportunistic message forwarding algorithm for DTNs with cyclic mobility patterns. Cyclic MobiSpace is a generalization of DTNs with cyclic mobility patterns. In this paper, we propose an optimal opportunistic multi-copy message forwarding algorithm in Cyclic MobiSpace. Specifically, we model a Cyclic MobiSpace as a state-space graph, and apply the optimal stopping rule to derive a delivery metric for each message state using the state-space graph. We perform simulations to compare our protocol, called Multi-copy Forwarding in Cyclic MobiSpace (MFC), against existing forwarding protocols using UMassDieselNet trace. Simulation results show that MFC delivers up to 100% more messages than the compared forwarding protocols under the same delay and forwarding cost.

Real-time adaptive resource management

Distributed mission-critical environments employ a mixture of hard and soft real-time applications that usually expect a guaranteed range of quality of service (QoS). These applications have different levels of criticality and varied structures ranging from periodic independent tasks to distributed pipelines or event-driven modules. The underlying distributed system must evolve and adapt to the high variability in resource demands that competing applications impose. The current industry trend is to use commercial off-the-shelf (COTS) hardware and software components to build distributed environments for mission-critical applications. The paper considers how adding a middleware layer above the COTS components facilitates consistent management of system resources, decreases system complexity, and reduces development costs.

Hierarchical feedback adaptation for real time sensor-based distributed applications

The paper presents an innovative hierarchical feedback adaptation method that efficiently controls the dynamic QoS behavior of real time distributed data flow applications, such as sensor based data streams or mission-critical command and control applications. We applied this method in the context of the Real Time Adaptive Resource Management system, a middleware integrated services, developed at the Honeywell Technology Center. We present the analytical model for Automatic Target Recognition pipeline application and the impact of hierarchical feedback adaptation on the application behavior and its QoS parameters.

Hierarchial architecture for real-time adaptive resource management

This paper presents the Real Time Adaptive Resource Management system (RTARM 1), developed at the Honeywell Technology Center. RTARM supports provision of integrated services for real-time distributed applications and offers management services for end-to-end QoS negotiation, QoS adaptation, real-time monitoring and hierarchical QoS feedback adaptation. In this paper, we focus on the hierarchical architecture of RTARM, its flexibility, internal mechanisms and protocols that enable management of resources for integrated services. The architecture extensibility is emphasized with the description of several service managers, including an object wrapper build around the NetEx real-time network resource management. We use practical experiments with a distributed Automatic Target Recognition application and a synthetic pipeline application to illustrate the impact of RTARM on the application behavior and to evaluate the system performance.

Energy-Efficient Target Coverage in Heterogeneous Wireless Sensor Networks

This paper considers a heterogeneous wireless sensor network that consists of several resource-rich supernodes used for data relaying and a large number of energy constrained wireless sensor nodes. Sensor nodes are deployed randomly to monitor a number of targets. Since targets are redundantly covered by more sensors, we organize the sensors in set covers that are activated successively to conserve energy. In this paper we introduce the heterogeneous connected set covers (HCSC) problem that has the objective to find a maximum number of set covers such that each set cover monitors all targets and each active sensor is connected to at least one supernode. A sensor can participate in multiple set covers, but the total energy spent in all sets is constrained by the battery capacity. In this paper we show that HCSC is NP-complete and we propose two algorithms for solving this problem, an integer programming approach and a distributed and localized protocol. Simulation results are presented to evaluate these solutions