Tales Heimfarth

UAV relay network to support WSN connectivity

An important problem in Wireless Sensor Networks (WSN) is the occurrence of failures that lead to the disconnection of parts of the network, compromising the final results achieved by the WSN operation. A way to overcome such problem is to provide a reliable connection to support the connectivity via other types of nodes that communicate with the sensor nodes. This paper proposes the usage of a network composed by Unmanned Aerial Vehicles (UAVs) as a relay network to guarantee the delivery of data produced by WSN nodes on the ground to the users. Results from simulations of the proposed technique are provided and discussed.

ShoX: An Easy to Use Simulation Platform for Wireless Networks

For the evaluation of wireless network protocols, simulation has established itself as a good compromise between cost and complexity, on the one hand, and accuracy of results, on the other hand. Most established network simulators, however, were originally developed for wired networks and only later extended to the wireless domain. Some simulators like Opnet are not even restricted to communication networks at all, but can be used to simulate all kinds of networked systems. In this paper, we present ShoX, a network simulator explicitly designed for the simulation of wireless networks. Together with its strong GUI support, this allows a very efficient development and evaluation of network protocols without any considerable learning curve. All relevant concepts known from the domain of wireless networks like nodes, links, OSI layers, packets, mobility, signal propagation and traffic models are directly available. Defining new layers, packets or models is as easy as subclassing the existing abstract classes which ensures at compile time that all required methods are provided by the user. ShoX is completely based on Java and XML, thus superseding to learn unfamiliar languages like Tcl or NED. It features an integrated GUI for configuration, visualization and statistics.

Evaluation of coordination strategies for heterogeneous sensor networks aiming at surveillance applications

A new challenge in the sensor network area is the coordination of heterogeneous sensors (with different sensing, mobility and computing capabilities) in an integrated network. This kind of sensor networks have clearly high relevance in surveillance systems, in which both low-end static ground sensor nodes and more sophisticated sensors carried by mobile platforms, such as unmanned aerial vehicles (UAVs), cooperate. This paper provides an analysis of two different strategies to guide the collaboration among the sensor nodes mentioned above, applied to area surveillance systems. The first analyzed problem is related to the choice of the UAV instance that will respond to a given alarm issued by a ground sensor node. The second issue is the estimation of the response time until any UAV can be engaged in handling an alarm and effectively handles it. Two strategies are introduced and compared: one based on a pheromone inspired approach and another based on utility functions inspired on risk profiles that models decisions of investors in the stock market.

BASIC CONCEPTS OF REAL TIME OPERATING SYSTEMS

Real-time applications usually are executed on top of a Real-time Operating System (RTOS). Specific scheduling algorithms can be designed. When possi- ble, static cyclic schedules are calculated off-line. If more flexibility is needed on-line techniques are applied. These algorithms are bound to priorities which can be assigned statically or dynamically. Designing a proper RTOS architec- ture needs some delicate decisions. The basic services like process manage- ment, inter-process communication, interrupt handling, or process synchroniza- tion have to be provided in an efficient manner making use of a very restricted resource budget. Various techniques like library-based approaches, monolithic kernels, microkernels, or virtual machines/exokernels are applied, based on spe- cific demands. Safety critical application can be supported by separation of ap- plications either in the time or the space domain. Multi-core architectures need special techniques for process management, memory management, and synchro- nization. The upcoming Wireless Sensor Networks (WSN) generate special de- mands for RTOS support leading to dedicated solutions. Another special area is given by multimedia applications. Very high data rates have to be supported un- der (soft) RT constraints. Based on the used encoding techniques (e.g. MPEG) dedicated solutions can be created.

Cooperation among Wirelessly Connected Static and Mobile Sensor Nodes for Surveillance Applications

This paper presents a bio-inspired networking strategy to support the cooperation between static sensors on the ground and mobile sensors in the air to perform surveillance missions in large areas. The goal of the proposal is to provide low overhead in the communication among sensor nodes, while allocating the mobile sensors to perform sensing activities requested by the static ones. Simulations have shown that the strategy is efficient in maintaining low overhead and achieving the desired coordination.

Using Unmanned Aerial Vehicle to Connect Disjoint Segments of Wireless Sensor Network

This paper presents a method for federating disjoint segments of Wireless Sensor Networks (WSNs) using an Unmanned Aerial Vehicle (UAV) for message ferrying. Since network disconnections compromise the system operation, providing an alternative to mitigate disconnections can extend its lifetime. Several other proposals tackle the problem of disconnections by means of redundant deployment or even using mobile nodes as relay stations. Our approach goes beyond previous by connecting network segments localized more than two hops apart using a limited number of mobile nodes. In order to use less mobile nodes (here we are proposing only one), the UAV becomes a data mule, carrying physically packets across the network when moving. Each disjoint segment elects a cluster head which is responsible to coordinate the interaction with the UAV. Simulations realized evince the effectiveness of our system: for moderate traffic and enough data buffers, a very small packet loss was noticed. A considerable latency was observed due to the limited speed of the UAV making our system ideal to delay tolerant applications.

Multi-Agent Support in a Middleware for Mission-Driven Heterogeneous Sensor Networks

The emerging applications using sensor network technologies constitute a new trend requiring several different devices to work together and partly autonomously. However, the integration and coordination of heterogeneous sensors in these emerging systems is still a challenge, especially when the target application scenario is susceptible to constant changes. The setup and adaptation of these systems are challenging, considering that their nodes are distributed and must respect operational constraints, such as energy consumption. Due to the dynamicity of the scenarios in which they are deployed and the nature of their operations these systems require autonomous decisions that have to be taken without any human operator intervention. This paper presents a reflective middleware that supports heterogeneous sensor networks deployed in dynamic scenarios. This middleware presents specific handling of users’ requirements by representing them as missions that must be accomplished by the network. These missions are then translated to network parameters and activities that are distributed to network nodes by means of the autonomous reasoning that takes into account network nodes’ capabilities and environment conditions. A multi-agent framework is proposed to provide the necessary support for missions’ dissemination and for the required reasoning to allow autonomous behaviour related to mission allocation and network adaptation.

Decentralized task distribution among cooperative UAVs in surveillance systems applications

Teams of small Unmanned Aerial Vehicles (UAVs) are being largely proposed to be used in different areas for both military and civilian applications. Their integration in wider sensor networks is also being considered in order to provide a better cost-benefit ration. However, coordination among UAV teams is not a trivial problem in an ad hoc network. This paper presents a decentralized coordination strategy to orient the actions of a team of UAVs, which take part in a wider sensor network, relying on ad hoc network communication. The proposed sensors network inclused static sensors that issue alarms indicating the presence of possible targets that must be handled by one of the UAVs and possibly relay messages among them. Preliminary results of the proposed approach are presented and are contrasted with results provided by a centralized solution for the problem.

Emergent Topology Control Based on Division of Labour in Ants

Advances in the area of wireless sensor networks enable a myriad of new applications. Communication is however still the most costly function in these networks. Regions with higher node density lead to a greater amount of energy waste through overhearing, collisions, etc., while not increasing the networks capacity. Therefore, we propose an emergent approach to topology control reducing the number of active nodes in such areas. Facing the necessity to minimize the amount of data exchanged for achieving this goal, given the high cost of communication, the approach is motivated by the division of labour observed in ants promising lower overhead, more robustness and better scalability. Nodes actively involved in network operation are modeled as transporters, other nodes as workers. State changes are realized using a response function incorporating a response threshold and stimulus. The response threshold determines the tendency of a node to respond to a stimulus and reflects the ability to perform a state change. The intensity of stimulus is determined by quantitative cues perceived

Experiments with Biologically-Inspired Methods for Service Assignment in Wireless Sensor Networks

Given the scarcity of energy in wireless sensor networks (WSNs), in-network data processing by distributed, cooperating services is often used to reduce the amount of information that has to be routed to the base station and thereby to reduce communication and energy consumption. However, to minimize the amount of communication between services and their requesters, the locations of services in the network have to be selected carefully. Therefore, this paper proposes an efficient biologically-inspired heuristic for service assignment in WSNs. In order to reduce the amount of information exchange necessary for our heuristic, we use a concept observed in ant colonies that utilizes only local information. We model packets as ants (depositing pheromones at the visited nodes), services as food sources and requesters as formicaries. To optimize an objective function (reduction of communication distance between services and requesters), an explorer agent makes local service assignment decisions based on solely local information: the pheromones deposited by the ants. Furthermore, our paper presents the formal definition of the problem of service assignment and a thorough analysis and discussion of the results of our experiments, which show the efficiency of our approach.