Abstract
Whenever reliable transmissions are assured by retransmission mechanisms, higher packet error incur in additional energy consumption due to packet retransmissions, even though many monitoring applications can tolerate some loss in the quality of the received images. In fact, visual information retrieved from source nodes may have different relevancies for the applications, according to the desired monitoring tasks and the current sensors' poses and fields of view. We propose a semi-reliable energy-efficient hop-by-hop retransmission mechanism, where the reliability level of each packet is function of the relevance of the source nodes associated with DWT subbands. Doing so, some of the corrupted packets will not be retransmitted, saving energy of intermediate nodes with low impact to the visual monitoring quality. © 2012 IEEE.

Abstract
The usage of Wireless Sensor Networks (WSNs) in industrial environments has been steadily increasing, due to the reduced deployment and maintenance costs, when compared to the use of wired networks for connecting single I/O points in industrial applications. The most promising WSN standard is the one defined by the IEEE 802.15.4 standard. However, it does not support the adequate mechanisms to deal with the unreliable nature of an industrial communication environment. In this paper, we propose an extension of the use classes available for this standard, together with the proposal of adequate message retransmission schemes, in order to increase the reliability of message exchanges in industrial environments. To demonstrate the effectiveness of the proposed schemes, we present a simulation assessment of both the proposed message retransmission schemes and the Guaranteed Time Slots (GTS) mechanism, as defined by the standard. © 2012 IEEE.

Abstract
Wireless sensor networks composed of camera-enabled source nodes can provide visual information of an area of interest, potentially enriching monitoring applications. While few bytes can represent scalar data, even low-resolution still images may require thousand of bytes, turning data fragmentation into a relevant design issue. Different optimization approaches have been proposed in recent years to achieve energy saving in wireless image sensor networks. However, the impact of image fragmentation upon the adopted MAC technology has been neglected in most cases. In this work we investigate the effect of frame size on image transmissions over wireless sensor networks, linking the maximum frame size, the useful payload and the frame error rate effects. Additionally, we discuss different approaches for transmissions of DWT-based encoded images and the impact of inserting application-specific information into the frame header. We believe that our discussions can contribute to the advance of the design of wireless image sensor networks. © 2012 IEEE.

Abstract
Wireless Sensor Networks (WSN) can be used to monitor hazardous and inaccessible areas. In these situations, the power supply (e g battery) in each node can not be easily replaced One solution is to deploy a large number of sensor nodes, since the lifetime and dependability of the network can he increased through cooperation among nodes In addition to energy consumption, applications for WSN may also have other concerns, such as, meeting deadlines and maximizing the quality of information In this paper, we present a Genetic Machine Learning algorithm aimed at applications that make use of trade-offs between different metrics Simulations were performed on random topologies assuming different levels of faults Our approach showed a significant improvement when compared with the use of IEEE 802.15 4 protocol

Abstract
In this paper, we propose a real-time publish-subscribe communication scheme for IEEE 802.11e networks, named Group Sequential Communication (GSC). The GSC intends to improve the HCCA mechanism by adopting a simple approach based on the Virtual Token Passing (VTP) protocol which uses a real-time group concept, where the real-time members of the group are granted a high-priority and sequential access to the communication medium. Their main achievements are the reduction of the Polling, individual ACKs and NULL frames overheads between the controller and the polled stations. In order to improve the reliability of the GSC scheme was developed a fault-tolerant mechanism based on a block acknowledge strategy to avoid missing real-time message deadlines.

Abstract
An important aspect when dealing with computer control systems is the impact of control delay upon the performance of the controlled item. Such control delay may be a consequence of the computer controlled implementation or, for the case of a network based control system, can be the consequence of the use of a communication network to interconnect sensors and actuators with the controller. Basically, control applications require a predictable delay between measurement and actuation, with small variability, i.e., small jitter. In this paper we present some simulation results concerning the impact of a varying control delay upon the performance of a DC-Motor, both for a centralized computer-controlled setup and for a network based control system. The results for the centralized setup were also experimentally confirmed. For the network-based setup it was used the h-BEB real-time communication protocol. The evaluated scenarios were simulated using the True Time simulator that is based in MATLAB/Simulink. The experimental tests were developed in LabVIEW, where the controller task was executed as a software routine. The tests consisted in the variation of the sampling period and control delay to determinate the steady region of the system.