Tiago Gomes

Path loss exponent analysis in Wireless Sensor Networks: Experimental evaluation

Wireless Sensor Networks are an emerging technology which has been recently adopted in many applications. Due to its wireless nature, the analysis of the radio propagation models plays an important role for performance evaluation in both theoretical and practical aspects. In this regards, path loss exponent is one of the most important parameter which has been considered widely in wireless communications analysis. There are several theoretical evaluations of path loss exponent for wireless sensor networks available in the literature. However there is a lack of experimental evaluation of both path loss exponent and the effect of shadowing. In this paper, three environments (free space, in building and industrial), where wireless sensor nodes are widely deployed, have been chosen in order to evaluate the experimental analysis. Path loss and path loss exponent are measured by means of Received Signal Strength Indicator (RSSI) and based on them, the standard deviation of shadowing effect is also calculated. All the measured parameters are compared with the theoretical analysis available in the literatures.

Sequence based heuristics for two-dimensional bin packing problems

This article addresses several variants of the two-dimensional bin packing problem. In the most basic version of the problem it is intended to pack a given number of rectangular items with given sizes in rectangular bins in such a way that the number of bins used is minimized. Different heuristic approaches (greedy, local search, and variable neighbourhood descent) are proposed for solving four guillotine two-dimensional bin packing problems. The heuristics are based on the definition of a packing sequence for items and in a set of criteria for packing one item in a current partial solution. Several extensions are introduced to deal with issues pointed out by two furniture companies. Extensive computational results on instances from the literature and from the two furniture companies are reported and compared with optimal solutions, solutions from other five (meta)heuristics and, for a small set of instances, with the ones used in the companies.

WECO: A wireless platform for monitoring recycling point spots

There is a growing demand for low cost, very low power and reduced size monitoring systems with wireless communications, to be used in different kinds of industrial environments. In several countries waste separation and recycling is a major issue. Consequently, the number of recycling spots has been steadily increasing. In order to ensure that recycle bins are properly maintained, several monitoring solutions have been proposed. These still have several limitations, such as requiring wires for power and/or communications and not being able to fit in all existing types of bins. This paper presents WECO, a wireless embedded solution for monitoring the level of the bins located in recycling spots. The proposed system automatically alerts a remote central station when a bin reaches a programmable filling level, thus avoiding the need to spot check if the bin is full and ensuring that the recycling spot is kept clean. The developed prototype required hardware-software co-design and aimed to meet the above mentioned requirements, resorting to the IEEE 802.15.4 protocol for wireless communications between all nodes in the network, each based on a System-On-Chip (SoC) CC2530 from Texas Instruments. Due to its wireless nature, the architecture requires a battery for power supplying the nodes, with a life time of at least six years. The filling level readings of each bin in a recycling spot is made using an ultrasonic sensor. The data collected by the monitoring platform is then sent to the remote central station that processes it in order to optimize routes and establish a scheduled collection of the recycling spots.

We-care: An IoT-based health care system for elderly people

In a world with an accelerated population aging, there is an increasingly interest in developing solutions for the elderly living assistance. The Internet of Things is a new reality that is completely changing our everyday life, and promises to revolutionize modern healthcare by enabling a more personalized, preventive and collaborative form of care. Aiming to combine these two important topics, this work presents an IoT-ready solution for the elderly living assistance which is able to monitor and register patients vital information as well as to provide mechanisms to trigger alarms in emergency situations. Its effective low-power/low-cost and wireless characteristics turns this solution suitable to be used anywhere and by anyone, in a discrete and comfortable wristband. Experiments demonstrated a good system performance for the implemented functionalities, and regarding the autonomy we obtained an average battery lifetime of 306 hours (around 12 days). For the working range, the system have proved to perform well within a range of 60 meters before the out-of-range warning being triggered.

Task-Aware Interrupt Controller: Priority Space Unification in Real-Time Systems

In the development of real-time systems, predictability is often hindered by technological factors which break the timing abstractions offered by real time operating systems (RTOSs); namely, the priority space separation between threads and interrupts induces the rate-monotonic problem. Software approaches have tackled this issue, attempting to unify the priority space with varying degrees of success. We present a hardware approach to the problem: unifying the priority space at the interrupt handling subsystem, predictability is greatly enhanced with minimum software modifications. Our solution provides the interrupt controller with awareness of the currently running tasks priority making the solution independent of the used operating system. We show how our approach is minimally intrusive at hardware architecture level and provides benefits beyond the capabilities of previous approaches. Our technique shows a 0.05% run-time overhead if no interrupts occur, and run-time reduction proportional to interrupt rate for rates higher than 5 per s, for a interrupt workload around 0.07 ms.

Design and Evaluation of a Smart Library Using the APEX Framework

User experience is a key point for successful ubiquitous computing (ubicomp) environments. The envisaged design should be explored as soon as possible to anticipate potential user problems, thus reducing re-design costs. The development of ubicomp environments’ prototypes might help, providing feedback on the users’ reaction to the environments. This paper describes the design and evaluation of ubicomp environments using APEX, a rapid prototyping framework providing user experience via a 3D application server and connected physical devices. APEX prototypes allow users to explore and experience many characteristics of a proposed design, in a virtual world. The paper focus in particular the design and evaluation of a smart library in the APEX framework.

Building IEEE 802.15.4 Accelerators for Heterogeneous Wireless Sensor Nodes

Bringing IPv6 connectivity to low-end wireless sensor nodes leads to considerable device resources utilization, e.g., central processing unit and energy, caused by the increased amount of data transferred over the network that needs to be handled. In order to reduce these overheads, this letter proposes an IEEE 802.15.4 accelerator for heterogeneous wireless sensor systems that target the Internet of Things sensing applications, which include on the same node, field-programmable gate array technology beside a microcontroller provided with wireless connectivity. The deployed solution implements the Third-level of filtering specified by the standard, and performs basic packet handling such as the detection of multiple receptions of the same frame. The obtained results show the benefits of including such accelerator on the reconfigurable computing unit, offering nearly 17 of overhead reduction. All filtering functionalities are executed by the accelerator to discard unneeded data frames, which avoids unnecessary interrupts to the operating system and increases the system availability up to 59.

RodosVisor - an object-oriented and customizable hypervisor: The CPU virtualization

Abstract RodosVisor is an object-oriented and bare-metal virtual machine monitor (VMM) or hypervisor designed for the aerospace industry, mainly to provide time and spatial separation to the NetworkCentric core avionics machine, Montenegro and Dittrich (2009). The NetworkCentric core avionics machine consists of several harmonized components working together to implement dependable computing in a simple way, with computing units managed by the local real-time operating system RODOS. To support partitioned software architectures such as AIR, Rufino et al. (2009), and MILS, DeLong, R. (2007), RodosVisor adapted the Popek and Goldbergs fidelity, efficiency and resource control virtualization requirements, Popek and Goldberg (1974), to the space application domain by extending them with extra ones, like timing determinism, reactivity and improved dependability. Another distinctive RodosVisor feature is the customized design based on generative programming techniques, such as aspect oriented programming and template meta-programming.

IIoTEED: An Enhanced, Trusted Execution Environment for Industrial IoT Edge Devices

With the advent of the Internet of Things (IoT), security has emerged as a major design goal for smart connected devices. This explosion in connectivity created a larger attack surface area. Software-based approaches have been applied for security purposes; however, these methods must be extended with security-oriented technologies that promote hardware as the root of trust. The ARM TrustZone can enable trusted execution environments (TEEs), but existing solutions disregard real-time needs. Here, the authors demonstrate why TrustZone is becoming a reference technology for securing IoT edge devices, and how enhanced TEEs can help meet industrial IoT applications real-time requirements.

Towards an FPGA-based edge device for the Internet of Things

With the growing ubiquity of Internet of Things (IoT), myriads of smart devices connect and share important information over the Internet. In order to provide connectivity and interoperability of all the existing heterogeneous wireless devices, a full communication stack is proposed by the IoT Architecture Reference Model (IoT-ARM). From the sensor to the cloud, the proposed stack can be implemented on all IoT devices avoiding the battle for the wireless standard that will be adopted. This work in progress paper proposes an FPGA-based edge device for IoT, which uses SoC (System-on-Chip) FPGA technology to offload critical features of the communication stack to dedicated hardware, aiming to increase systems performance.