Felipe D. da Cunha

Protocols, mobility models and tools in opportunistic networks: A survey

Abstract In opportunistic networks, instead of assuming an end-to-end path as in the traditional Internet model, messages are exchanged opportunistically when an encounter happens between two nodes. In the last years, several forwarding algorithms to efficiently decide when to forward messages were proposed. Those protocols are commonly suitable to a specific scenario, which has led to the creation of new subtypes of networks. Two different examples are pocket switched networks – PSN and vehicular networks – VANETs, since those networks have different features like a specific mobility pattern and intermittent connectivity. In this article we present an overview of opportunistic networks, proposing a taxonomy which encompasses those new types of network. We discuss the commonly used tools, simulators, contact traces, mobility models and applications available. Moreover, we analyzed a set of forwarding protocols to map the approach used by the research community to evaluate their proposals in terms of mobility, contacts and traffic pattern, reliability of simulations and practical projects. We show that although researchers are making efforts to use more realistic contact models (e.g., using real traces) the traffic pattern is generally disregarded, using assumptions that may not fit real applications.

Data communication in VANETs: Protocols, applications and challenges

Abstract VANETs have emerged as an exciting research and application area. Increasingly vehicles are being equipped with embedded sensors, processing and wireless communication capabilities. This has opened a myriad of possibilities for powerful and potential life-changing applications on safety, efficiency, comfort, public collaboration and participation, while they are on the road. Although, considered as a special case of a Mobile Ad Hoc Network, the high but constrained mobility of vehicles bring new challenges to data communication and application design in VANETs. This is due to their highly dynamic and intermittent connected topology and different application’s QoS requirements. In this work, we survey VANETs focusing on their communication and application challenges. In particular, we discuss the protocol stack of this type of network, and provide a qualitative comparison between most common protocols in the literature. We then present a detailed discussion of different categories of VANET applications. Finally, we discuss open research problems to encourage the design of new VANET solutions.

Socially inspired data dissemination for vehicular ad hoc networks

People have routines and their mobility patterns vary during the day, which have a direct impact on vehicular mobility. Therefore, proto- cols and applications designed for Vehicular Ad Hoc Networks need to adapt to these routines in order to provide better services. With this issue in mind, in this work, we propose a data dissemination solution for these networks that considers the daily road traffic variation of large cities and the relationship among vehicles. The focus of our approach is to select the best vehicles to rebroadcast data messages according to social metrics, in particular, the clustering coefficient and the node degree. Moreover, our solution is designed in such a way that it is completely independent of the perceived road traffic density. Simulation results show that, when compared to related protocols, our proposal provides better delivery guarantees, reduces the network overhead and possesses an acceptable delay.

Is it Possible to Find Social Properties in Vehicular Networks

Everyday, vehicles transit in a city and along their trajectories, they encounter other vehicles. The frequency of these encounters is influenced by many factors, such as: vehicle speed, destinations, traffic conditions, and the period of the day. However, these factors are justified by the public roads limits and the drivers behavior. The people present daily routines and similar behaviors that have a great impact in the daily traffic evolution. In this work, we present a numerical analysis of real and realistic data sets that describe the mobility of a set of vehicles. Social metrics are computed, and the results obtained are compared to random graphs in the direction to verify if vehicular network presents a social behavior. Finally, we discuss new social perspectives in vehicular networks.

The problem of cooperation among different wireless sensor networks

An important issue in the design of a wireless sensor network (WSN) is to devise techniques to make efficient use of its energy, and thus, extend its lifetime. When two WSNs are deployed at the same place and their sensors cooperate with the other networks forwarding their packets, the distance of the transmissions decreases and, therefore, the power consumption as well. The goal of this work is to examine the extent to which different WSNs can cooperate and save their energy. Simulation results reveal that different densities and data collecting rates among WSNs, the routing algorithm and the path loss exponent have major impact in the establishment of cooperation.

A distributed protocol for cooperation among different wireless sensor networks

An important issue in the design of a wireless sensor network (WSN) is to devise techniques to make efficient use of its energy, and thus, extend its lifetime. When two or more WSNs are deployed in the same place and their sensors cooperate with the other networks, they may improve their operability, by extending its lifetime by trading routing favors or increasing the data entropy by a common data aggregation. Despite being obvious and simple, this idea brings with it many implications that hinder cooperation between the networks. Whereas a WSN has a rational and selfish character, it will only cooperate with another WSN if this provides services that justify the cooperation. The goal of this work is to present the Virtual Cooperation Bond (VCB) protocol, that is a distributed protocol that makes different WSNs to cooperate, enabling cooperation if, and only if, all the different WSNs benefit with the cooperation. In the simulation results, we consider WSNs with different configurations and we show that the proposed protocol enables cooperation solely when the cooperation is beneficial to both networks, and in this case, it saves their energies and extends their lifetimes.

A new solution for the time-space localization problem in wireless sensor network using UAV

Services such as localization and synchronization are crucial for many applications in Wireless Sensor Networks (WSNs), given that it is commonly required to know the position and global time of the sensor nodes. Nevertheless, these tasks are often carried out after the sensor nodes have been deployed in the sensor location. Given that it is impractical to configure the sensor nodes manually, it is essential to rely on algorithms to overcome the problem of locating and synchronizing the clock of the sensor nodes. Hence, in this study we propose a joint solution for 3D localization and time synchronization in WSNs with the aid of an unmanned aerial vehicle (UAV). The UAV is geared with a GPS device and flies over the area covered by the sensor field where it broadcasts its geographical position. This means that the sensor nodes are able to estimate their geographical position without the need to be fitted with a GPS. By carrying out simulations, we show that our joint solution leads to a smaller number of errors in time-synchronization and localization than is the case with other proposals found in the literature.

Data Communication in VANETs: Survey, Applications and Challenges

Abstract VANETs have emerged as an exciting research and application area. Increasingly vehicles are being equipped with embedded sensors, processing and wireless communication capabilities. This has opened a myriad of possibilities for powerful and potential life-changing applications on safety, efficiency, comfort, public collaboration and participation, while they are on the road. Although, considered as a special case of a Mobile Ad Hoc Network, the high but constrained mobility of vehicles bring new challenges to data communication and application design in VANETs. This is due to their highly dynamic and intermittent connected topology and different application’s QoS requirements. In this work, we survey VANETs focusing on their communication and application challenges. In particular, we discuss the protocol stack of this type of network, and provide a qualitative comparison between most common protocols in the literature. We then present a detailed discussion of different categories of VANET applications. Finally, we discuss open research problems to encourage the design of new VANET solutions.

ID-MAC: An identity-based MAC protocol for Wireless Sensor Networks

Wireless Sensor Networks (WSNs) are comprised mainly of resource-constrained sensor nodes that can be used to monitor areas of interest. In sensor networks, replacement of node batteries is usually infeasible and power consumption must be minimal to increase node lifetime. A large fraction of power consumption is controlled by the MAC layer, which orchestrates access to the wireless medium trading-off power consumption and throughput. Unfortunately, this orchestration requires exchange of additional data and itself ends up consuming energy. In this work we design a novel approach that does not require extra data to be exchanged. More precisely, we present ID-MAC: an identity-based MAC protocol for WSNs. In ID-MAC, sensor nodes compute when they should wake up in order to transmit and receive frames from their neighbors without exchanging coordination messages. Our evaluation shows that, by eliminating coordination messages, ID-MAC saves energy and prolongs the networks operating lifespan.

Sensor-MAC with Dynamic Duty Cycle in wireless sensor networks

Wireless sensor networks are designed to be deployed in the physical environment to monitor a wide variety of real-world phenomena. These networks are composed of various small sensor nodes deposited in a given area. In these networks, the battery replacement is unfeasible and thus the energy is a critical resource that must be considered by all protocols. In order to reduce the energy consumption, protocols for MAC layer use techniques that turn off the radio of sensor nodes. However, in many protocols, all sensor nodes operate on the same static schedule in which they wake up periodically at the same fixed interval of time. This scheme might not be appropriate in dynamic scenarios in which the traffic varies. In these situations, it is desirable to adjust the operation mode of sensor nodes according with the network traffic. In this work, we present the Sensor-MAC with Dynamic Duty Cycle (SMAC-DDC), a new MAC protocol that adjusts the duty cycle of sensor nodes according with the network traffic. Through a cross layer interaction, SMAC-DDC uses the information of the network layer to adjust the value of the duty cycle of sensor nodes. Simulations results show that the proposed protocol reduces the latency and the energy consumption of a network, keeping the delivery ratio.