RCAAP Repository

In recent years, lighting solutions have gradually been replaced by more efficient features, taking advantage of Light Emitting Diodes (LEDs) that have progressively conquered the market with increasingly high optical powers, low energy consumption and variable color temperatures. Along with this evolution, Visible Light Communication (VLC) technology has also been developed to use this existing lighting infrastructure and the inherent characteristic of LEDs being easily switched to high frequency to build data transmission systems. The applications of this communication technology using electromagnetic signals in the visible range are currently in a development stage with promising applications in several domains.This paper intends to study an optical communication system based on VLC to establish communication between road infrastructures and. vehicles. For this purpose, four communication channels established through the modulation of white trichromatic LED emitters are used. Detection of the optical signals is performed with a photodiode based on two stacked pin structures made of a-Si:H and a-SiC:H. This device works as an optical filter in the visible spectrum and its spectral sensitivity can be adjusted through stationary optical bias. On-Off-Keying (OOK) modulation is used. The structure of the data blocks to be transmitted was designed to avoid undesirable effects related to ambient light (flickering and/or perceptible variations in color temperature of the white light). The experimental tests of the proposed model were performed using a small-scale prototype. The results show that with the proposed system it is possible to transmit information between road infrastructure and vehicles.  

This paper introduces the general editorial policy of i-ETC, a new online Open Access Journal. The publication of this academic journal is based on the software Open Journal System and it is maintained by the Department of Electronics, Telecommunications and Computer Engineering (DEETC), at the High Institute of Engineering of Lisbon (ISEL) in Lisbon.

The so called Internet of Things (IoT) is progressivelybecoming a normal thing in everyone daily lives. Thedesire of connecting everyday objects to the internet and to eachother, to interact with other users and machines, is increasinglybecoming a reality. In this context, where billions of connectedobjects are expected to be ubiquitously deployed worldwide, thefrequent battery maintenance of wireless nodes is undesirableor even impossible. The growth of the devices will be madepossible only if the sensors battery needs are eliminated orreduced significantly. For low power sensors and devices, carefulpower management and power conservation are critical to devicelifetime and effectiveness. One of the possible solutions is tochange completely the paradigm of the radio transceivers in thewireless nodes of the IoT system. The new paradigm should beable to communicate and to enhance the power to the sensor byusing only electromagnetic waveforms transmitted over the air,in order to make the Wireless Power Transfer (WPT) concept areality.

Today optical systems are more and more important in data communications (optical fibers) and are also becoming important in data processing (optical and quantum computing) allowing for a fully optical communication  network where all signals will be processed and transmitted in the optical domain. This paper gives an overview of optical fiber communications and analyses some optical devices and applications such as optical computing, holographic memory and optical pattern recognition.

This work presents an Inverted-L antenna design using the fractal geometry for dual band WLAN (2.4/5.2GHz) USB dongle application. The proposed antenna has the advantages of compact size, wide operation bandwidth and easy fabrication. The experimental results show that it has a S11<-10 dB bandwidth from 2.25 to 2.60 GHz and 5.06 to 5.62 GHz. The radiation performances of the proposed antenna in free space and when connected to a laptop computer were also studied in this work. The proposed antenna was designed and optimized by using Ansoft HFSS V13.

This paper describes an ECG signal coding with an adaptive predictive coding scheme using speech techniques like linear predictive coding and long-term prediction.

The sliding window dictionary-based algorithms of the Lempel-Ziv (LZ) 77 family are widely used for universal lossless data compression. The encoding component of these algorithms performs repeated substring search. Data structures, such as hash tables, binary search trees, and suffix trees have been used to speedup these searches, at the expense of memory usage. Previous work has shown how suffix arrays (SA) can be used for dictionary representation and LZ77 decomposition. In this paper, we improve over that work by proposing a new efficient algorithm to update the sliding window each time a token is produced at the output. The proposed algorithm toggles between two SA on consecutive tokens. The resulting SA-based encoder requires less memory than the conventional tree-based encoders. In comparing our SA-based technique against tree-based encoders, on a large set of benchmark files, we find that, in some compression settings, our encoder is also faster than tree-based encoders.

This paper presents the study of chirp signals for wireless communications between Internet of Thing devices used on low power wide area networks. Up and down chirp concept is introduced as well as the chirp spread spectrum concept. A computationally efficient symbol decoding method is presented based of discrete Fourier transform as an alternative to typical coherent detection. The proposed simulation LoRa model is implemented in MATLAB allowing the communication system evaluation based on bit error rate and packet error rate.

The modulation technique Filter Bank Multi Carrier (FBMC) is an alternative widely studied in order to replace Orthogonal Frequency Division Multiplexing (OFDM) in wireless telecommunications systems. The fact that FBMC does not use Cyclic Prefix and uses Polyphase Filters allows improvements in bit rate, bandwidth efficiency and robustness against multipath channel impairments. This implementation can bring advantages to Digital TV case in comparison to the traditional OFDM based systems because of the need to transmit higher resolution videos such as 4K and 8K. This article presents a study on the use of FBMC in Integrated System Digital Broadcasting Transmission B (ISDB-Tb), developing an application on GNURadio environment, analysing Bit Error Rate (BER) and power spectrum curves in a multipath channel.

This work describes the implementation of an eye gaze tracking system for a natural user interface, based only on non-intrusive devices, like Intel RealSense camera. Through image processing, the implemented system is able to convert face elements to the corresponding focus point on the computer screen. Tests show promising results.

ZnO 1-D nanostructures (nanowires) were deposited by a two-step wet chemical process. The dimensions of wires were about 100 nm - 1100 nm in length and about 20 - 120 nm in diameter. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) technique was used to obtain the microstructural information from the films. The nanowire films were also characterized optically by transmittance measurement and room temperature photoluminescence (PL) measurements. The transport properties of the samples were characterized by performing transient photoconductivity (TPC) experiments.

The ability to automatically detect/classify complex and dynamic urban sounds is important tool for urban planning such as building efficient noise monitoring and control, surveillance systems, urban soundscape mappings, and could be a foundation for improvement of life in the cities of tomorrow.We present a proof of concept for a sound detection, monitoring and classification system for urban environments in the context of Smart Cities. Ultimately, the proposed system be deployed in numerous urban locations for long periods of time, allowing for the collection of urban acoustic data.

This paper traces the theoretical background to the split between function and meaning in the modernity theories of Marx, Lukács, Weber and Marcuse. It then discusses attempts to overcome the split in the recent philosophies of technology of Simpson and Borgmann. These attempts fail but help to focus the issue. A discussion of contemporary struggles over information technology offers a more hopeful perspective on a possible resolution of the split and suggests a new look at Heidegger’s phenomenology of action. The conclusion of the paper shows that Heidegger offers resources for addressing the relation of function and meaning which he himself did not develop.

In the present paper the project of an embeddedsolution for the realization of a floating sensor platform for themonitoring of the water and ambient quality in a flowing waterenvironment is described. First results regarding the monitoringof the water conductivity and the ambient noise level underharsh environmental conditions in a karstic river and in the finalpart of a river going towards the Mediterranean Sea arepresented. It is further discussed how this kind of system can bemodified in order to serve as urban waterway multisensoryplatform, adding important features like connectivity, energyharvesting and determination of the platform position. 

Traffic collisions, in particular high speed car accidents often result in huge damages, long traffic queues and loss of human lives. In this work we present an intelligent modular system that monitors traffic in highways and alerts drivers of sudden stops, in poor visual conditions. The system is composed of several identical modules, to be placed in the middle of a highway’s lane, that sense the lights and communicate their presence and velocity to their neighbor modules via RF. With such information, the nearby modules estimate the velocity of the passing cars. When the module ahead detects a car passing at a much slower speed than what was previously estimated, it alerts the other modules, so they produce a visual indication for the oncoming drivers, preventing accidents. The system operates autonomously using solar energy harvesting.

The relay solution in planning of mobile networks, has the aim of increasing the network coverage and/or capacity. According to the open literature, this technique will be highly used in the next Long Term Evolution (LTE) Networks. The Relay Station (RS) performance varies with its position in the cell, with the radio conditions to which RSs and User Equipments (UEs) are subjected and with the RS capacity to receive, process and forward the information. The aim of this paper is to compare the performance of the Layer 1 (L1) and Layer 3 (L3) RS types, and to determine the ideal position in which a RS should be placed, with the aim of maximizing the UE throughput.

Hydrogenated amorphous silicon thin film transistors have been used as switching elements in liquid crystal displays and large area matrix addressed sensor arrays. Later, these devices have also been used as analogue active elements in organic light emitting diode displays. However, this technology suffers from bias induced meta-stability. This issue introduces both threshold voltage and subthreshold slope shifts over time when gate bias is applied. Such instabilities jeopardize long term performance of circuits that rely on these components. Nevertheless, hydrogenated amorphous silicon thin film transistors present an exponential transfer characteristic when operating on subthreshold region and their typical power consumption is under 1 µW. This low power characteristic makes these devices ideally suited for low power electronic design.This work demonstrates, through transient analysis of a well-established simulation model for hydrogenated amorphous silicon, the viability of thin film transistors technology to perform both analogue and digital functions. Hence, these structures may be used in both application fields. To this end, two different sets of analyses have been conducted with hydrogenated amorphous silicon based thin film transistors. The first set considers a driving circuit for an active matrix of organic light emitting diodes, biased in a way to minimize the “memory effect” (increasing shift on threshold voltage) due to long term operation. The second set of analyses were conducted upon the implementation of complementary output universal gates, namely NOR/OR and XNOR/XOR elements.

In order to assess the potential of low-cost radio-over-fiber (RoF) solutions, in this paper we make a comparison of three full-duplex RoF systems. These systems are low-cost solutions that use remote modulation, with a single centralized light source used at the central station to generate a downlink wavelength that is reused at the remote location for upstream transmission. By avoiding the need for an additional light source at each remote location the cost of the solution is significantly reduced. The three systems evaluated in this paper differ by the type of optical modulation used for downlink and uplink. The first is an IM-IM system using intensity-modulation (IM) for the downlink and uplink direction. The second scheme, PM-IM, differs from the first by using phase-modulation (PM) for downlink. Finally, the third system, PM-PM, uses phase modulation for downlink and uplink.

Stochastic Computing has emerged as a competitive computing paradigm that produces fast and simple implementations of arithmetic operations, while offering high levels of parallelism, and graceful degradation of the results when in the presence of errors. IoT devices are often operate under limited power and area constraints and subjected to harsh environments, for which, traditional computing paradigms struggle to provide high availability and fault-tolerance. Stochastic Computing is based on the computation of pseudo-random sequences of bits, hence requiring only a single bit per signal, rather than a data-bus. Notwithstanding, we haven’t witnessed its inclusion in custom computing systems. In this direction, this work presents Stochastic Theater, a framework to specify, simulate, and test Stochastic Datapaths to perform computations using stochastic bitstreams targeting IoT systems. In virtue of the granularity of the bitstreams, the bit-level specification of circuits, high-performance characteristics and reconfigurable capabilities, FPGAs were adopted to implement and test such systems. The proposed framework creates Stochastic Machines from a set of user defined arithmetic expressions, and then tests them with the corresponding input values and specific fault injection patterns. Besides the support to create autonomous Stochastic Computing systems, the presented framework also provides generation of stochastic units, being able to produce estimates on performance, resources and power. A demonstration is presented targeting KLT, typical method for data compression in IoT applications.

Lead (Pb) is a toxic metal, which widespread use has resulted in environmental contamination, human exposure and significant public health problems. The autonomic nervous system, being a homeostatic controller, is impaired in acute and chronic lead exposure. In fact, sympathoexcitation associated to hypertension and tachypnea has been described together with baroreflex and chemoreflex dysfunction. However, up to date, no studies described the autonomic effects of an intermittent low-level lead exposure. In the present work, we addressed in vivo, autonomic behaviour in rats under chronic Pb exposure (control) and in rats under intermittent Pb exposure. For that, arterial blood pressure (BP) and ECG were recorded in 28 weeks old animal and low frequencies (LF) and high frequencies (HF) were determined (to estimate sympathetic and parasympathetic activities) using FisioSinal software with Wavelet module. Preliminary results: Rats intermittently exposed to lead showed a significant decrease in systolic BP (126 ± 4 vs 144 ± 3 mmHg) with no significant changes in LF, HF and LF/HF bands (1.5 ± 0.3 vs 1.7 ± 0.5 mmHg2, 1.9 ± 0.7 vs 2.8 ± 1.2 bpm2 and 1.2 ± 0.4 vs 1.1 ± 0.3 mmHg2/bpm2, respectively) when compared to chronically Pb exposed rats. Our data suggests that the autonomic dysfunction induced by lead exposure is similar in a chronic and intermittent Pb exposure. Nevertheless, it seems that an intermittent exposure was no effect on systolic BP values.The present study brings new insights on the environmental factors that influence autonomic and cardiovascular systems during development, which can help apprise public policy strategies to prevent and control the adverse effects of Pb toxicity.