i-ETC : ISEL Academic Journal of Electronics Telecommunications and Computers
Not a member yet
54 research outputs found
Sort by
Inverted-L Antenna (ILA) Design Using Fractal for WLAN USB Dongle
Full text linkThis 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
COMPRESSED LEARNING FOR TEXT CATEGORIZATION
Full text linkIn text classification based on the bag-of-words (BoW) or similar representations, we usually have a large number of features, many of which are irrelevant (or even detrimental) for classification tasks. Recent results show that compressed learning (CL), i.e., learning in a domain of reduced dimensionality obtained by random projections (RP), is possible, and theoretical bounds on the test set error rate have been shown. In this work, we assess the performance of CL, based on RP of BoW representations for text classification. Our experimental results show that CL significantly reduces the number of features and the training time, while simultaneously improving the classification accuracy. Rather than the mild decrease in accuracy upper bounded by the theory, we actually find an increase of accuracy. Our approach is further compared against two techniques, namely the unsupervised random subspaces method and the supervised Fisher index. The CL approach is suited for unsupervised or semi-supervised learning, without any modification, since it does not use the class labels
Room Temperature Photoluminescence and Photoconductivity of Wet Chemical Deposited ZnO Nanowires Used for Solar Cells
Full text linkZnO 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
Radio over Fiber (RoF): A comparison of low-cost systems
Full text linkIn 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
Performance Analysis of WDM-PON Architecture for Wireless Services Distribution in Future Aircraft Networks
Full text linkoai:i-ETC.journals.isel.pt:article/17In this work, an in-depth analysis concerning the transmission performance of IEEE802.11g/n (Wi-Fi) signals in a WDM-PON system is presented. It is considered that the optical/electrical transceivers are based on low-cost 850 nm VCSELs and PIN photodiodes. System modelling includes the impact of noise generated in the optical path, such as relative intensity noise (RIN), shot noise, photodetector thermal noise, clipping and intermodulation distortion. An analytic analysis based on Volterra series is conducted and mathematical expressions for both the EVM and SNR are derived. The theoretical analysis is also compared with experimental results. Among several conclusions, it is observed that the laser intermodulation distortion, clipping and RIN are the most relevant factors
SEMICONDUCTOR DEVICE FOR DETECTION OF FRET SIGNALS
Full text linkThe transducer consists on a semiconductor device based on two stacked-i-n heterostructures, that were designed to detect the emissions of the fluorescence resonance energy transfer between fluorophores in the cyan (470 nm) and yellow (588 nm) range of the spectrum. This research represents a preliminary study on the use of such wavelength sensitive devices as photodetectors for this kind of application. The device was characterized through optoelectronic measurements concerning spectral response measurements under different electrical and optical biasing conditions. To simulate the FRET pairs a chromatic time dependent combination of cyan and yellow wavelengths was applied to the device. The generated photocurrent was measured under reverse and forward bias to readout the output photocurrent signal. Different wavelength biasing light was also superimposed. Results show that under reverse bias the photocurrent signal presents four separate levels each one assigned to the different wavelength combinations of the FRET pairs. If a blue background is superimposed the yellow channel is enhanced and the cyan suppressed while under red irradiation the opposite behavior occurs. So under suitable biasing light the transducer is able to detect separately the cyan and yellow fluorescence pairs. An electrical model, supported by a numerical simulation supports the transduction mechanism of the device
Comparing Layer 1 and Layer 3 Relay Stations Deployment in a LTE Network
Full text linkThe 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
DESIGN OF THE ALAMOUTI SCHEME FOR A MIMO RECEIVER AND ITS IMPLEMENTATION ON AN FPGA
Full text linkThis paper analyses the Alamouti scheme for different antenna configurations and different modulation types,namely BPSK, QPSK and QAM. All configurations were modeled and simulated in MATLAB. A MIMOreceiver for a 21 antenna configuration and BPSK modulation was implemented in a FPGA. The FPGAresults indicate that the Alamouti scheme is a good design option for hardware implementation of a MIMOreceiver. The receiver uses only about 10% of the resources of a medium-sized FPGA and achieves almost300 Msymbols per second
MOBILEWHEEL A mobile driving station
Full text linkCurrent mobile devices (e.g., smartphones) are equipped with several sensors that allow different forms of userinteraction. They also offer several connectivity options and a growing computing power which supports itsuse in new Human Computer Interaction (HCI) scenarios. This paper presents the mobileWheel, a system thatexploits the capabilities of current mobile devices as a means of interaction with a real-time graphical drivingsimulation running on a desktop computer. The application on the mobile device performs data acquisitionfrom various sensors (focusing on the 3D accelerometer) and also provides different types of feedback tothe user. This system represents a ubiquitous, simple and affordable alternative approach to the traditionalcontrol of virtual vehicles in driving simulators and could also be applied in other similar architectures. Toevaluate and validate this approach several tests were conducted with volunteer users. The control mode wherethe virtual vehicle is fully controlled by the accelerometer had the highest acceptance and produced the bestresults
LEMPEL-ZIV SLIDING WINDOW UPDATE WITH SUFFIX ARRAYS
Full text linkThe 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