Fernanda S. H. Souza

A small world approach for scalable and resilient position estimation algorithms for wireless sensor networks

In Wireless Sensor Networks (WSNs) there are network functions and applications that need to know the localization of a node such as the association of the sensed data with a given position. In general, it may be impossible or unfeasible to have either a planned deployment or a localization hardware. Thus, an important problem in wireless sensor networks is to find out the localization of sensor nodes. In this work, we propose a heterogeneous wireless sensor network topology based on small world concepts to improve the Recursive Position Estimation algorithm. By using the small world topology we have two goals: (i) the error in position estimation for large wireless sensor networks is reduced, and (ii) the resilience in the position estimation in the presence of node failures is increased. We evaluate the Recursive Position Estimation algorithm in the proposed model. Simulation results show that a small set of powerful nodes with a higher communication range can reduce significantly the error and increase the resilience in the position estimation.

RouT: A Routing Protocol based on Topologies for Heterogeneous Wireless Sensor Networks

In this work, we propose a routing protocol based on topologies for Heterogeneous Wireless Sensor Networks (HSN) named as RouT. The proposed protocol creates different logical topologies considering the same physical topology of a HSN. The heterogeneous network has two types of sensors nodes, called L-sensors and H-sensors. The L-sensors are nodes with Low hardware capabilities where the H-sensors are sensors with High hardware capabilities. The RouT protocol creates different logical topologies and each topology considers a different number of links among H-sensors. In this way, each topology has its tradeoff between energy consumption and latency during data communication. Simulation results showed that the RouT protocol is able to provide different topologies that can be used if the network application has different requirements.

On the analysis of the collaboration network of the Brazilian symposium on computer networks and distributed systems

The Brazilian symposium on computer networks and distributed systems (SBRC) reached its 30th edition as the paramount scientific event in the area of computer networks and distributed systems in Brazil. Faced with this opportune moment in the event’s history, we here study the collaboration network established among authors who have jointly published in the symposium. Towards that end, we collected bibliographic data from all 30 editions, and built the co-authorship network of the event. We then analyzed the network structural features and evolution throughout its history. Our results reveal the main kind of co-author relationship among authors, show the most prominent communities within SBRC, the regions of Brazil that attracts the most authors, the researchers with central roles in the network as well as the importance of inter-state collaborations. Finally, we align our results with historical facts that may have had a key impact on the symposium success.

Optimization in Designing Complex Communication Networks

Complex networks are found in real world in different areas of science, such as technological, social and biological. These networks are many times characterized by a non-trivial topology, with connection patterns among their elements that are neither purely regular nor purely random. The interesting features presented by this class of networks may be useful in improving the overall efficiency of engineered networks as computer, communication and transportation ones. There is a conjecture indicating that such complex topologies normally appear as a result of optimization processes. Optimization techniques have been applied to design complex communication networks, showing that features such as small path length, high clustering coefficient and power-law degree distribution can be achieved through optimization processes. In this chapter, models and algorithms based on optimization techniques to generate complex network topologies are discussed. We review some models, heuristics as well as exact solution approaches based on Integer Programing methods to generate topologies owning complex features.

Gamma Deployment: Designing the Communication Infrastructure in Vehicular Networks Assuring Guarantees on the V2I Inter-Contact Time

Gamma Deployment is a metric for evaluating the distribution of roadside units in vehicular networks in terms of two parameters: a) the inter-contact time between vehicles and the infrastructure, and, b) the share of vehicles that must respect the inter-contact time guarantees. We envision the use of the Gamma Deployment metric when the network designer intends to distribute check-points along the road network in order to collect and disseminate traffic informations through roadside units. Thus, the goal is to locate the roadside units such that ρ percent of vehicles meet roadside units in time intervals less than τ seconds. In this work, we formalize the Gamma Deployment metric by developing an Integer Linear Programming formulation (ILP). Since the ILP is not able to solve large instances, we also develop an heuristic for approximating the optimal solution. We present experiments considering a realistic mobility trace, and our results demonstrate the heuristic incurs in small deviations for small inter-contact time guarantees.

A column generation-based heuristic for the GRWA with protection and QoS in WDM optical networks

In this paper, we consider the Grooming, Routing and Wavelength Assignment (GRWA) problem with protection and Quality of Service (QoS) for optical mesh networks. Assuming that traffic demands can vary from low rate to very high demands, grooming several requests into the same wavelength allows a more efficient use of the network capacity. Besides, the need for fault tolerance and QoS became evident in todays networks. Our objective is to minimize the total number of wavelengths used. A mathematical formulation of the problem is presented in this study along with a column generation-based heuristic. We evaluate the performance of the proposed approach and analyze the role played by the protection and QoS constraints. Our results show that the proposed algorithm is able to find solutions close to optimality for real-world network instances.

Formulations for the RWA problem with traffic grooming, protection and QoS in WDM optical networks

The emergence of WDM technology has provided the explosive traffic growth on telecommunications networks. Although in future networks a request may require more than a single wavelength, in general, in todays networks, the size of a single request tends to be much smaller than the capacity of a wavelength channel. Thus, the need for traffic grooming became evident. In this paper, we present formulations based on network flows and column generation for the problem of routing and wavelength assignment (RWA) with traffic grooming, protection and quality of service on optical networks in order to minimize the number of wavelengths used. This problem is NP-complete and exact approaches are commonly practicable only in small instances. In this study, the employment of advanced techniques such as column generation and branch-and-price led to solve the problem for instances of real-world network size.

A Small World Model Based on Multi-Interface and Multi-Channel to Design Heterogeneous Wireless Sensor Networks

In this work, we propose a small world model to design Heterogeneous Sensor Networks (HSNs). The proposed model takes into account the communication pattern of this network to create shortcuts directed to the monitoring node, decreasing data communication latency. The endpoints of these shortcuts are nodes with more powerful communication range and energy reserves to support the long communication range. However, this kind of communication causes a high interference in the wireless channel. For this, the proposed model uses the multi-interface and multi-channel capability of the MAC layer to reduce the number of collisions during data communication. Simulation results showed that with just a few powerful nodes, a wireless sensor network can be tuned into a HSN with small world features. Also, when the shortcuts are directed to the monitoring node and assigned to a different wireless channel, the number of collisions and the data communication latency are reduced.

Optimal Topology Design of Complex Networks

Given a network, link costs and a maximum cost budget, in this work we apply Integer Programming techniques to determine the optimal set of links that should be included in the network, in order to provide complex network features. This is accomplished by solving, through Branch-and-bound, a Mixed Integer Program based on network flows. We also present a column generation algorithm that, hopefully, will allow us to deal with larger networks. A statistical evaluation of the optimal network topologies found with our methods allowed us to establish a clear relationship between the budget value and a complex network feature (small world, power law degree distribution, for example). In particular, we found that the budget size plays, in our model, a similar role played by the probability of addition or rewiring arcs in stochastic procedures for generating network topologies.

Using the inter-contact time for planning the communication infrastructure in vehicular networks

Intelligent Transportation Systems (ITS) demand sophisticated vehicular networks integrating entities from the transportation sector. The ability to plan and manage such networks represents a key challenge for moving ITS solutions from laboratories into the streets. In this work, we propose Gamma Deployment as a metric for evaluating the distribution of roadside units in vehicular networks by considering the inter-contact time between vehicles and infrastructure. By solving the location of roadside units in order to meet the Gamma Deployment, the network designer assures a given share of vehicles to keep frequent contacts with roadside units. Since Gamma Deployment reflects the connectivity experienced by drivers, it can be used for comparing vehicular networks deployed over distinct conditions.