REV Journal on Electronics and Communications
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Decentralized Online Social Network Using Peer-to-Peer Technology
Get PDFThis paper presents a social network with a peer-to-peer architecture that facilitates social computing services in distributed environments. This social network aims to provide users the capability of managing the dissemination of user data, searching user data on the data silos of the network, and consolidating user data from various social networks. The social network employs a super peer peer-to-peer architecture that contains peers and super peers. Users use peers to participate the network and services. Peers with sufficient storage, bandwidth and processing power become super peers that support peers for complex operations such as user authentication or group communication. We have extended the Gnutella protocol to provide the authentication and posting services on the social network. The design of these services copes with the distributed setting of the social network. The evaluation of the prototyping social network has performed on a number of laboratory workstations to investigate its scalability, reliability and performance
An Enhanced Web Document Search Engine using a Semantic Network
Get PDFWith the rapid advancement of ICT technology, the World Wide Web (referred to as the Web) has become the biggest information repository whose volume keeps growing on a daily basis. The challenge is how to find the most wanted information from the Web with a minimum effort. This paper presents a novel ontology-based framework for searching the related web pages to a given term within a few given specific websites. With this framework, a web crawler first learns the content of web pages within the given websites, then the topic modeller finds the relations between web pages and topics via key words found on the web pages using the Latent Dirichlet Allocation (LDA) technique. After that, the ontology builder establishes an ontology which is a semantic network of web pages based on the topic model. Finally, a reasoner can find the related web pages to a given term by making use of the ontology. The framework and related modelling techniques have been verified using a few test websites and the results convince its superiority over the existing web search tools
Robust Reflection Detection and Removal in Rainy Conditions using LAB and HSV Color Spaces
Get PDFIn the field of traffic monitoring systems, shadows are the main causes of errors in computer vision-based vehicle detection and classification. A great number of research have been carried out to detect and remove shadows. However, these research works only focused on solving shadow problems in daytime traffic scenes. Up to now, far too little attention has been paid to the problem caused by vehicles’ reflections in rainy conditions. Unlike shadows in the daytime, which are homogeneous gray shades, reflection shadows are inhomogeneous regions of different colors. This characteristic makes reflections harder to detect and remove. Therefore, in this paper, we aim to develop a reflection detection and removal method from single images or video. Reflections are detected by determining a combination of L and B channels from LAB color space and H channel from HSV color space. The reflection removal method is performed by determining the optimal intensity of reflected areas so that they match with neighbor regions. The advantage of our method is that all reflected areas are removed without affecting vehicles’ textures or details
An Oversampling-based Correlator-type Receiver for DCSK Communication Systems Over Generalized Flat Rayleigh Fading Channels
Get PDFThis paper proposes an oversampling-based correlator-type receiver for Differential Chaos-shift Keying (DCSK) communication systems, which can exploit the flat-fading characteristic of multipath channels in order to improve the system performance. At the receiver, the incoming signal is sampled with a sampling rate higher than chip rate before feeding to a correlator. This oversampling step aims to specifically determine delayed-signal components from fading multipath channels, which can be combined together by the correlator in order to increase the ratio of signal-to-noise at its output. In particular, the performance of the proposed receiver is investigated by means of a generalized flat Rayleigh fading channel which has one primary path (i.e., the path having the shortest transmission period) and multiple secondary paths (i.e., the other remaining paths with delays). Mathematical models in discrete-time domain for the conventional transmitter, generalized channel, and proposed receiver are proposed and analyzed. The theoretical bit-error-rate (BER) expression is first derived and then distribution histogram for the ratio of variable bit energy to noise power spectral density is computed. The BER performance is finally estimated by integrating the BER expression over all possible values of the histogram. Numerical simulations with specific parameters are carried out and then simulated performances are shown in comparison to estimated ones. Obtained results point out that the system performance is significantly improved when the number of secondary paths increases
Simulation and Measurement Methods for RCS Estimations of a Scale Model Airplane
Get PDFIn a military context, the radar cross section (RCS) of an airplane is a very important subject. For an RCS estimation object, a scaled-down model is often employed for ease of measurements. Recently, electromagnetic simulations of the RCS has become very convenient because of developments in high-speed calculation methods such as MLFMM and HOBF in electromagnetic simulators employing the MoM algorithm. As for the measurements, high-resolution measurements via the time domain analysis are promising. In this paper, important estimation expressions for use with a scale model are briefly explained. In terms of calculations, comparisons are drawn between the actual calculation abilities of MoM, MLFMM, and HOBF at 18 GHz for a 1/48-scale model. In terms of measurement, a high-resolution measurement system employing a compact range and time domain analysis that is used in this study is explained. Next, the calculated and measured results are compared in order to show the accuracy of the obtained results. The results in vertical and horizontal planes of a scale model are shown at vertical and horizontal polarizations. Moreover, using the calculation method to determine estimates at higher frequencies is also investigated in order to obtain the practical RCS value of a real-sized airplan
A Survey on Approximations of One-Dimensional Gaussian Q-Function
Get PDFPredicting the digital communication system performance plays a very important role in the process of system design. This performance is usually quantified by symbol error probability or bit error probability. Computing these probabilities in presence of Additive White Gaussian Noise requires to work with integrals involving the Gaussian Qfunction, which cannot be expressed in closed-form in terms of elementary functions. As a result, approximating the Gaussian Q-function in closed-form expressions with high accuracy becomes a necessity. In this paper, we give an overview about the Gaussian Q-function approximations and via some illustrating examples, we discuss their accuracy, tractability as well as their computational complexit
Extraction of Dynamic Trajectory on Multi-Stroke Static Handwriting Images Using Loop Analysis and Skeletal Graph Model
Get PDFThe recovery of handwriting’s dynamic stroke is an effective method to help improve the accuracy of any handwriting’s authentication or verification system. The recovered trajectory can be considered as a dynamic feature of any static handwritten images. Capitalising on this temporal information can significantly increase the accuracy of the verification phase. Extraction of dynamic features from static handwritings remains a challenge due to the lack of temporal information as compared to the online methods. Previously, there are two typical approaches to recover the handwriting’s stroke. The first approach is based on the script’s skeleton. The skeletonisation method has highly computational efficiency whereas it often produces noisy artifacts and mismatches on the resulted skeleton. The second approach deals with the handwriting’s contour, crossing areas and overlaps using parametric representations of lines and thickness of strokes. This method can avoid the artifacts, but it requires complicated mathematical models and may lead to computational explosion. Our paper is based on the script’s extracted skeleton and provides an approach to processing static handwriting’s objects, including edges, vertices and loops, as the important aspects of any handwritten image. Our paper is also to provide analysing and classifying loops types and human’s natural writing behavior to improve the global construction of stroke order. Then, a detailed tracing algorithm on global stroke reconstruction is presented. The experimental results reveal the superiority of our method as compared with the existing ones
Multiple-Symbol Differential Detection for Spatial Modulation
Get PDFApproximately 3 dB Signal-to-Noise Ratio (SNR) loss is always paid with conventional Differential Spatial Modulation (DSM) as compared to coherent Spatial Modulation (SM). In this paper, a Multiple-Symbol Differential Detection (MSDD) technique is proposed for DSM systems to mitigate the loss due to differential detection. The new scheme can greatly narrow the 3 dB performance gap by extending the observation interval for differential decoding. The technique uses maximum-likelihood sequence detection instead of traditional symbol-by-symbol detection, and is carried out on the slow, flat Rayleigh fading channel. A generalized decision metric is derived for an observation interval of arbitrary length. It is shown that for a moderate number of symbols, MSDD provides approximately 1.5 dB performance improvement over the conventional differential detection. In addition, a closed-form pairwise error probability and approximate bit error probability (BEP) are derived for multiple-symbol differential spatial modulation. Results show that the theoretical BEP matches well the simulated one. The BEP is shown to converge asymptotically with the number of symbols in the observation interval to that of the differential scheme with coherent detection
