João Paulo de Araujo

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.

Unmanned Aerial Vehicle as Data Mule for Connecting Disjoint Segments of Wireless Sensor Network with Unbalanced Traffic

This paper presents a method for federating disjoint segments of Wireless Sensor Networks (WSNs) in the presence of unbalanced traffic. The approach relies on an Unmanned Aerial Vehicle (UAV) for message ferrying. Network disconnections compromise the system operation, ergo an alternative to mitigate disconnections is important to extend the network lifetime. In our work, a UAV becomes a data mule, carrying physically packets across the disjoint partitions to assure network connection. The method presented in this article goes beyond previous work by taking into account the traffic situation among the network segments: highly communicating disjoint segments are visited more frequently than partitions with low outgoing/incoming traffic. Simulations realized evince the effectiveness of our system for concentrated traffic. In this case, a lower latency and data loss resulted when compared with the system without prioritization of highly communicating segments.

AGA-MAC: Adaptive Geographic Anycast MAC Protocol for Wireless Sensor Networks

This paper presents AGA-MAC: an adaptive geographic any cast medium access control (MAC) protocol for wireless sensor networks (WSNs). The protocol aims at reducing the sleep-delay problem of asynchronous preamble-based MAC protocols by selecting opportunistically the next relay node from a set of candidates. The size of the Forwarding Candidate Set (FCS) is influenced by a threshold parameter in our protocol. In order to outperform other existing any cast asynchronous protocols, we analyze the effect of different network densities, and threshold values in the network latency. The analysis is both mathematical and experimental using simulations. Results of our simulations showed that, for selected thresholds, our protocol outperformed by approximately 17% both the GeRaF and the well known X-MAC protocol for intermediate data packet size. For other sizes, our protocol followed the results of the best performing alternative, which could be GeRaF or X-MAC.

A Publish/Subscribe System Using Causal Broadcast over Dynamically Built Spanning Trees

In this paper we present VCube-PS, a topic-based Publish/Subscribe system built on the top of a virtual hypercubelike topology. Membership information and published messages to subscribers (members) of a topic group are broadcast over dynamically built spanning trees rooted at the message’s source. For a given topic, delivery of published messages respects causal order. Performance results of experiments conducted on the PeerSim simulator confirm the efficiency of VCube-PS in terms of scalability, latency, number, and size of messages when compared to a single rooted, not dynamically, tree built approach.

A Communication-Efficient Causal Broadcast Protocol

A causal broadcast ensures that messages are delivered to all nodes (processes) preserving causal relation of the messages. In this paper, we propose a causal broadcast protocol for distributed systems whose nodes are logically organized in a virtual hypercube-like topology called VCube. Messages are broadcast by dynamically building spanning trees rooted in the messages source node. By using multiple trees, the contention bottleneck problem of a single root spanning tree approach is avoided. Furthermore, different trees can intersect at some node. Hence, by taking advantage of both the out-of-order reception of causally related messages at a node and these paths intersections, a node can delay to one or more of its children in the tree, the forwarding of the messages whose some causal dependencies it knows that the children in question can not satisfy yet. Such a delay does not induce any overhead. Experimental evaluation conducted on top of PeerSim simulator confirms the communication effectiveness of our causal broadcast protocol in terms of latency and message traffic reduction.

Self-correcting time synchronization in wireless sensor networks using low-power devices

Time synchronization is the most fundamental service to many wireless sensor network applications, which count mainly with low-power devices. This paper focuses in proposing and implementing a time synchronization service for low-power wireless sensor networks using low frequency real-time clocks in each node. This work present the design, implementation and test of an adaptive algorithm, making the timing of the clocks convert as quickly as possible and after this conversion, keeping them most similar as possible. The goal is to achieve the best method that ensures right timing and still having low energy consumption. Experimental results provide evidence of the success in meeting this goal.

A Preamble Ahead Anycast Protocol for WSNs

This paper presents a novel cross-layer anycast medium access control (MAC) protocol for wireless sensor networks (WSNs) based on advanced preamble propagation and geographic routing. The protocol aims at reducing the sleep-delay problem, common in asynchronous preamble-based MAC protocols. When a packet is ready to be transmitted, differently from other state-of-the-art protocols, the preamble sequence is propagated in advance for several hops before packet release. So, a simultaneous propagation of signaling and packet is obtained. The number of nodes in the Forwarding Candidate Set (FCS) in our anycast protocol is chosen to settle the average speed of preambles to the velocity of packet propagation. In order to enablethe simultaneous transmissions without collision, a minimum distance between preambles and data packet is preserved. Simulations results showed that our protocol outperforms in latency all other asynchronous MAC protocols appraised, for all evaluated packet sizes. This result was obtained with an energy consumption similar to the other state-of-the-art protocols.

Analytical study of anycast asynchronous MAC protocols for wireless sensor networks

This paper presents an analytical model for anycast asynchronous preamble-based medium access control (MAC) protocols. Asynchronous MAC protocols are widely used in Wireless Sensor Networks (WSN). An important drawback of these protocols is the sleep-delay phenomenon, which may impose high communication latency. In order to tackle this shortcoming, the concept of anycast, i.e., to explore opportunistic path redundancy is employed, instead of selecting a unique next hop. Existing approaches employ arbitrary rules to select the possible next relays. The mathematical model introduced in this work enables a better selection of next hop candidates based on packet size and network density, in order to minimize the sleep-delay. Along with the model, experimental results are presented validating the proposal.

An Adaptive Routing Protocol Based on Fixed Hubs for Opportunistic Networks

This paper presents a new routing protocol for opportunistic networks based on sociological movement model. In this movement model, the mobile nodes have the tendency to visit fixed places frequently. Our approach recognizes the encounter places, called hubs, and employs them as base elements for the routing procedure. Nodes visiting frequently two or more hubs are considered carriers and are used as data mule for message transport. After setting up this infrastructure, routing tables are constructed in the hubs. When a message should be routed, it is sent to a hub and, subsequently, forwarded among them until reaching a hub visited by the destination node. Simulations showed that, for scenarios strongly based on sociological movement, our method outperformed the Spray and Wait for different configurations.

Evaluation of a Genetic Programming Approach to Generate Wireless Sensor Network Applications

This article presents a systematic evaluation of a framework based on Genetic Programming (GP) which aims the automatic generation of Wireless Sensor Network (WSN) applications. Developing WSN applications poses a challenge due to massive distribution of the network nodes. The automatic generation of applications reduces drastically costs, since the manual development is a laborious process. In our approach, the user describes the desired global behavior as a fitness function which guides the evolution of the application by the GP. A scripting language based on events and actions is used to represent the WSN behavior and the GP generates programs in this language. In order to evaluate the framework, a problem of multiple events detection is introduced. Several problem instances were used to appraise the performance of our method under different parameters. Results evidence the feasibility of our approach for the proposed problem, highlighting the challenges posed by the large search space and the dead end routing problem.