João Carlos Giacomin

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.

Estimating Vegetation Water Content with Wireless Sensor Network Communication Signals

This paper proposes a distributed measuring system based on wireless sensor networks (WSN) employed to estimate plant water-content in agricultural fields. The WSN is present in a crop field in order to measure environmental variables, like soil moisture. Water-content is obtained by measuring the attenuation of the network communication signal. The need for distributed measurements to estimate agricultural crop parameters is pointed-out and a mathematical model of the radio-wave propagation through the vegetation is developed. This model is used to estimate plant water-content. Experimental results are also presented.

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 distributed measurement system to estimate plant water content in agricultural fields based on wireless sensor networks

This paper proposes a distributed measuring system based on wireless sensor networks (WSN) employed to estimate vegetation water content in agricultural fields. A WSN deployed along the whole field permits to measure and map soil, air and plant variables and transmit these data, by small radios, to a central computer. Water content is obtained by measuring the attenuation of the network communication signals (RF), without the use of any specific sensor. The need of distributed measurements to estimate agricultural crop parameters is pointed out. A mathematical model of radio wave propagation through vegetation is used to develop the method of estimating vegetation water content with a RSSF. Field tests confirmed the viability of the proposal.

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.

GB-MAC: a backbone based low latency protocol for WSNs

This paper presents GB-MAC, an asynchronous cross-layer medium access control protocol. Several MAC protocols suffer from the sleep-delay problem which causes a large latency in multi-hop communications. In our approach, we create a backbone composed by nodes with short active-sleep cycles to ensure a fast multi-hop relay of messages from and to the sink node. About 15% of nodes are recruited to form the backbone. Moreover, our protocol is asynchronous in order to avoid the complexity arising from constant time synchronizations. Simulations have shown that our protocol presents a low latency in all scenarios, outperforming X-MAC up to a factor of ten. The energy consumption is also reduced for moderate traffic scenarios. The GB-MAC yields higher gains in large scenarios, hence our results evidence that it is a robust protocol to be employed in large sensor networks.