Paulo Rogério Pereira

Bio: Paulo Rogério Pereira is an academic researcher from Instituto Superior Técnico. The author has contributed to research in topics: Routing protocol & Node (networking). The author has an hindex of 13, co-authored 50 publications receiving 653 citations. Previous affiliations of Paulo Rogério Pereira include University of Lisbon & Technical University of Lisbon.

From Delay-Tolerant Networks to Vehicular Delay-Tolerant Networks

Abstract: This paper provides an introductory overview of Vehicular Delay-Tolerant Networks. First, an introduction to Delay-Tolerant Networks and Vehicular Delay-Tolerant Networks is given. Delay-Tolerant schemes and protocols can help in situations where network connectivity is sparse or with large variations in density, or even when there is no end-to-end connectivity by providing a communications solution for non real-time applications. Some special issues like routing are addressed in the paper and an introductory description of applications and the most important projects is given. Finally, some research challenges are discussed and conclusions are detailed.

End-to-end reliability in wireless sensor networks: Survey and research challenges

Abstract: This paper presents a survey on transport and routing protocols for wireless sensor networks(WSN). Research challenges regarding the problem of end-to-end reliability are addressed in particular.

A multi-objective routing algorithm for Wireless Multimedia Sensor Networks

Abstract: Graphical abstractDisplay Omitted HighlightsA new multi-objective approach for the routing problem in Wireless Multimedia Sensor Networks (WMSNs) is proposed.Classical approximations optimize a single objective or Quality of Service (QoS) parameter.Classical approximations do not take into account the conflicting nature of QoS parameters which leads to sub-optimal solutions.The proposed approach takes into account multiple QoS requirements such as delay and the Expected Transmission Count (ETX).The case studies applying the proposed approach shows clear improvements on the QoS routing solutions. In this paper, a new multi-objective approach for the routing problem in Wireless Multimedia Sensor Networks (WMSNs) is proposed. It takes into account Quality of Service (QoS) requirements such as delay and the Expected Transmission Count (ETX). Classical approximations optimize a single objective or QoS parameter, not taking into account the conflicting nature of these parameters which leads to sub-optimal solutions. The case studies applying the proposed approach show clear improvements on the QoS routing solutions. For example, in terms of delay, the approximate mean improvement ratios obtained for scenarios 1 and 2 were of 15 and 28 times, respectively.

Betweenness centrality in Delay Tolerant Networks

Abstract: Dynamic networks, in particular Delay Tolerant Networks (DTNs), are characterized by a lack of end-to-end paths at any given instant. Because of that, DTN routing protocols employ a store-carry-and-forward approach, holding messages until a suitable node to forward them is found. But, the selection of the best forwarding node poses a considerable challenge. Additional network information (static or dynamic) can be leveraged to aid routing protocols in this troublesome task. One could use centrality metrics, therefore providing means to differentiate the importance of nodes in the network. Among these metrics, betweenness centrality is one of the most prominent, as it measures the degree to which a vertex is in a position of brokerage by summing up the fraction of shortest paths between other pairs of vertices passing through it. So, in this paper, betweenness centrality is surveyed, that is, its definitions and variants in static and dynamic networks are presented. Also, a survey of standard algorithms used to compute the metric (exact and approximate) is presented. Finally, a survey and a discussion on how DTN routing protocols make use of the betweenness centrality metric and algorithms to aid message forwarding is also presented.

Improving Message Delivery in UAV-based Delay Tolerant Networks

Abstract: Delay Tolerant Networks (DTNs) are sparse networks where complete direct end-to-end paths between source and destination can seldom be established. Routing mechanisms in DTN rely on the nodes’ mobility to connect disconnected nodes, carrying messages around the network to overcome path disconnection. The proactive DTN approach consists of introducing dedicated nodes whose only purpose is to establish communication between ordinary nodes, and relieve them from energy-consuming work, such as message routing and forwarding. This paper addresses the use of Unmanned Aerial Vehicles (UAVs) as DTN relays, introducing a proactive scheme called Deadline Triggered Pigeon with Travelling Salesman Problem with Deadlines (DTP-TSP-D). We envision a DTN where ground nodes can only communicate by flying UAVs with the capacity of carrying messages from one location to another. Each UAV either belongs to one node or to a cluster of nodes, and its role is to hover over their home-ground node (or ferrying around their home cluster) until they are triggered to deliver messages directed to other ground nodes. The triggering criterium is based on the deadlines of the messages present in the UAVs buffer, evaluating its ability to deliver all of them in time. It uses a developed TSP Genetic Algorithm to compute the route that achieves the most (timely) deliveries. The performance of DTP-TSP-D has been compared to dedicated node protocols found in the literature, namely SIRA and MRT-Grid. The performance metrics used were delivery ratio and average delay. The results show that DTP-TSP-D achieves higher delivery rates than its competitors, while keeping a consistent average delay.

The Web of Human Sexual Contacts

Abstract: Many ``real-world'' networks are clearly defined while most ``social'' networks are to some extent subjective. Indeed, the accuracy of empirically-determined social networks is a question of some concern because individuals may have distinct perceptions of what constitutes a social link. One unambiguous type of connection is sexual contact. Here we analyze data on the sexual behavior of a random sample of individuals, and find that the cumulative distributions of the number of sexual partners during the twelve months prior to the survey decays as a power law with similar exponents $\alpha \approx 2.4$ for females and males. The scale-free nature of the web of human sexual contacts suggests that strategic interventions aimed at preventing the spread of sexually-transmitted diseases may be the most efficient approach.

RMST: Reliable Data Transport in Sensor Networks

Abstract: Appearing in 1st IEEE International Workshop on Sensor Net Protocols and Applications (SNPA). Anchorage, Alaska, USA. May 11, 2003. RMST: Reliable Data Transport in Sensor Networks Fred Stann, John Heidemann Abstract – Reliable data transport in wireless sensor networks is a multifaceted problem influenced by the physical, MAC, network, and transport layers. Because sensor networks are subject to strict resource constraints and are deployed by single organizations, they encourage revisiting traditional layering and are less bound by standardized placement of services such as reliability. This paper presents analysis and experiments resulting in specific recommendations for implementing reliable data transport in sensor nets. To explore reliability at the transport layer, we present RMST (Reliable Multi- Segment Transport), a new transport layer for Directed Diffusion. RMST provides guaranteed delivery and fragmentation/reassembly for applications that require them. RMST is a selective NACK-based protocol that can be configured for in-network caching and repair. Second, these energy constraints, plus relatively low wireless bandwidths, make in-network processing both feasible and desirable [3]. Third, because nodes in sensor networks are usually collaborating towards a common task, rather than representing independent users, optimization of the shared network focuses on throughput rather than fairness. Finally, because sensor networks are often deployed by a single organization with inexpensive hardware, there is less need for interoperability with existing standards. For all of these reasons, sensor networks provide an environment that encourages rethinking the structure of traditional communications protocols. The main contribution is an evaluation of the placement of reliability for data transport at different levels of the protocol stack. We consider implementing reliability in the MAC, transport layer, application, and combinations of these. We conclude that reliability is important at the MAC layer and the transport layer. MAC-level reliability is important not just to provide hop-by-hop error recovery for the transport layer, but also because it is needed for route discovery and maintenance. (This conclusion differs from previous studies in reliability for sensor nets that did not simulate routing. [4]) Second, we have developed RMST (Reliable Multi-Segment Transport), a new transport layer, in order to understand the role of in- network processing for reliable data transfer. RMST benefits from diffusion routing, adding minimal additional control traffic. RMST guarantees delivery, even when multiple hops exhibit very high error rates. 1 Introduction Wireless sensor networks provide an economical, fully distributed, sensing and computing solution for environments where conventional networks are impractical. This paper explores the design decisions related to providing reliable data transport in sensor nets. The reliable data transport problem in sensor nets is multi-faceted. The emphasis on energy conservation in sensor nets implies that poor paths should not be artificially bolstered via mechanisms such as MAC layer ARQ during route discovery and path selection [1]. Path maintenance, on the other hand, benefits from well- engineered recovery either at the MAC layer or the transport layer, or both. Recovery should not be costly however, since many applications in sensor nets are impervious to occasional packet loss, relying on the regular delivery of coarse-grained event descriptions. Other applications require loss detection and repair. These aspects of reliable data transport include the provision of guaranteed delivery and fragmentation/ reassembly of data entities larger than the network MTU. Sensor networks have different constraints than traditional wired nets. First, energy constraints are paramount in sensor networks since nodes can often not be recharged, so any wasted energy shortens their useful lifetime [2]. This work was supported by DARPA under grant DABT63-99-1-0011 as part of the SCAADS project, and was also made possible in part due to support from Intel Corporation and Xerox Corporation. Fred Stann and John Heidemann are with USC/Information Sciences Institute, 4676 Admiralty Way, Marina Del Rey, CA, USA E-mail: fstann@usc.edu, johnh@isi.edu. 2 Architectural Choices There are a number of key areas to consider when engineering reliability for sensor nets. Many current sensor networks exhibit high loss rates compared to wired networks (2% to 30% to immediate neighbors)[1,5,6]. While error detection and correction at the physical layer are important, approaches at the MAC layer and higher adapt well to the very wide range of loss rates seen in sensor networks and are the focus of this paper. MAC layer protocols can ameliorate PHY layer unreliability, and transport layers can guarantee delivery. An important question for this paper is the trade off between implementation of reliability at the MAC layer (i.e. hop to hop) vs. the Transport layer, which has traditionally been concerned with end-to-end reliability. Because sensor net applications are distributed, we also considered implementing reliability at the application layer. Our goal is to minimize the cost of repair in terms of transmission.

Wearable and Implantable Wireless Sensor Network Solutions for Healthcare Monitoring

Abstract: Wireless sensor network (WSN) technologies are considered one of the key research areas in computer science and the healthcare application industries for improving the quality of life. The purpose of this paper is to provide a snapshot of current developments and future direction of research on wearable and implantable body area network systems for continuous monitoring of patients. This paper explains the important role of body sensor networks in medicine to minimize the need for caregivers and help the chronically ill and elderly people live an independent life, besides providing people with quality care. The paper provides several examples of state of the art technology together with the design considerations like unobtrusiveness, scalability, energy efficiency, security and also provides a comprehensive analysis of the various benefits and drawbacks of these systems. Although offering significant benefits, the field of wearable and implantable body sensor networks still faces major challenges and open research problems which are investigated and covered, along with some proposed solutions, in this paper.