1,721,216 research outputs found
Analysis of quantities influencing the performance of time synchronization based on linear regression in low cost WSNs
Full text linkTime synchronization is a key feature of Wireless Sensor Networks (WSNs). In low cost WSNs this is a very challenging issue since the general employment of a large number of nodes, characterized by low power and limited energy resources. Therefore, in such contexts, the adoption of synchronization algorithms is preferable to the adoption of GPS-based solution because of its high energy consumption, high cost and poor performance in indoor environment. An even increasing number of papers dealing with the design and the implementation of protocol-based techniques for synchronization can be found in literature. These synchronization algorithms can be divided into three main categories: one way messaging, two ways messaging and consensus based synchronization. Among the others, those based on the one way messaging and, in particular, on the adoption of regressive algorithms are widely used in many application contexts. Focusing the attention on this class of synchronization algorithms, this paper proposes a deep performance analysis aimed at highlighting the sensitivity of the regression-based algorithms to some factors that influence the accuracy in typical low cost applications, such as the finite resolution of the local timing clock, the presence of clock drift, clock high frequency noise and low frequency noise, the presence of latencies due to the radio devices, the presence of latencies due to the microcontroller device. The main goal is to evaluate the effect of each one of these factors of influence on the overall synchronization performance. To these aims, suitable analyses both in simulation environment and on real nodes have been carried out
Effects of Real Instrument on Performance of an Energy Detection-Based Spectrum Sensing Method
Full text linkIn cognitive radio (CR) networks, the role of spectrum sensing (SS) is crucial to enable an efficient exploitation of the radio spectrum resource. The need to measure spectrum occupancy turns CRs to be de facto measurement instruments, so it becomes crucial to analyze how real instrumentation peculiarities could affect performance in spectral measurements (i.e., SS performance). In this paper, a commercial software-defined radio (SDR) is adopted as cognitive device, and its capability to accurately measure occupied spectrum is analyzed in comparison also with a simulation setup, where the same analog-to-digital converter (ADC) is modeled and simulated, and equivalent signal-to-noise ratios (SNRs) are replicated. To this aim, a suitable experimental setup has been designed, metrologically characterized, and tuned. Experimental results prove how nominal SNR typically adopted for testing the performance of SS methods is not sufficient to model the impairments of a real acquisition chain, even jointly with a modeling of the digitization process. To assure a reliable SS method validation, new approaches have to be considered for enhancing the accordance between the performance predicted in the simulation environment and the experimental one reachable on real devices. Since different architectures of CRs are present on the market, the experimental tests should be preferred for a reliable SS performance assessment
A Novel multi-excitation ECT probe for deep defects with any orientation
No full textThe paper proposes a novel 4-quarter probe for Eddy Current (EC) nondestructive testing on conductive materials. The innovative aspect consists of the possibility to detect small superficial and buried defects with arbitrary orientation. The EC induced in the conductive plate is rotated by means of an amplitude modulation of two currents that generate two orthogonal magnetic fields in order to obtain a suitable detection of arbitrary oriented cracks. The probe performance is evaluated by means of Finite Element Analysis in the simulation environment of the software COMSOL Multiphysics. The goodness of the proposed probe was analyzed considering a defect with a length of 5 mm, height of 1 mm and thickness of 0.1 mm, positioned at different depths in an aluminum plate, showing good detection capabilities
Improving Defect Detection in Eddy Current Testing using Multi-Frequency Rotating Eddy Current Strategy
No full textThe detection capability of small defects, such as cracks, with arbitrary orientations, using eddy current testing techniques, is affected by both the direction of the eddy current path respect to the main defect orientation and the depth of the defect to be detected. To give an answer to this problems Rotating Eddy Current (REC) techniques and multi-frequency excitation have been proposed by the scientific community. In this paper, these two solutions have been applyed together in order to improve the detection performance for buried and superficial defects with any orientation. The developed probe together with the novel REC multi-frequency excitation strategy are detailed described and experimentally characterized in various scenarios, including surface and buried cracks, demonstrating the effectiveness of the proposed solution
Design of an efficient mobile measurement system for urban pollution monitoring
Full text linkIn recent years, the pollution monitoring in urban areas has become one of the most critical issues for local public authorities, which wish (or must) verify that pollution levels not exceed limits considered unsafe or that are regulated by local laws. Generally, the pollution monitoring is performed by using measurement stations located in few points of the region of interest since these stations are generally characterized by high costs, weights, and dimensions. Then, the pollution levels over the remaining area are predicted by means of suitable interpolation models. Due to the great variety of urban scenarios, it becomes very difficult to obtain reliable pollution levels in area in which the measurements has not been directly taken but only predicted. Consequently, the pollution monitoring can suffer of a lack of reliable information indispensable for the actuation of proper environmental management policies. In this framework, this paper proposes a mobile measurement system for the real time monitoring of environmental pollutions over urban areas. The proposed approach is based on the use of a set of vehicles, typically employed for public transportation inside the urban area, equipped with the proposed mobile measurement system allowing it to measure, store, and transmit the acquired data to a remote supervisor unit somewhere on the path followed by the vehicles. Particular attention has been paid on the definition of the metrological characteristics of the measurement devices with the aims of complying with the applicable European Directives accuracy requirements and of selecting a suitable trade-off between accuracy and cost. The experimental measurement campaign performed on a suitable urban scenario has confirmed the goodness of the proposed system
On employing a Savitzky-Golay filtering stage to improve performance of spectrum sensing in CR applications concerning VDSA approach
No full textOptimization and experimental characterization of novel measurement methods for wide-band spectrum sensing in cognitive radio applications
No full textSpectrum sensing is a fundamental task in the complex field of cognitive radio systems. It allows a cognitive terminal to scan a frequency span of interest and sense the presence of other users transmitting over it. Many spectrum sensing methods are present in literature and many interesting algorithms have been proposed. Unfortunately, very few methods allow to know the exact boundaries of the user signal, without knowing any channelization of the spectrum of interest. In this context, the paper proposes two novel algorithms, whose purpose is twofold: to keep a low computational burden and to provide information at the most detailed level with respect to the category the algorithms belong to. Tests, executed on simulated and emulated signals, have demonstrated that both algorithms allow reaching a detection probability greater then 95% and a false alarm probability lower then 5% even in scenarios characterized by SNR as low as −10 dB
Performance analysis of a two-stage spectrum sensing scheme for dynamic spectrum access in TV bands
Full text linkSpectrum Sensing schemes in Cognitive Radio systems are fundamental elements for a complete opportunistic communication technology. They usually reveal the presence of occupied bands without performing a measurement of the spectrum portion actually occupied. Considering that the final aim of Cognitive Radios is the exploitation, in the most efficient way, of the spectrum holes left free by primary users, the measurement of the actual occupied spectrum becomes a fundamental task. In this framework, this paper proposes a two-stage spectrum sensing method, tailored to work in TV bands, offering a good detection of the occupied bands with selectable false alarm rates (Stage 1) and an accurate measurement of the real occupied spectrum (Stage 2). Performance results, achieved in simulation and emulation environments, prove the method's goodness and robustness to non-idealities of real acquisition systems. A comparison, with another two-stage method available in literature, has confirmed its efficacy in real contexts
Experimental investigation of the electromagnetic interference of ZigBee transmitters on measurement instruments
No full textThis paper deals with the electromagnetic susceptibility of measurement systems when subjected to interference generated by short-range, low-power wireless transmitters. A ZigBee transmitter was used as an interfering source operating close to the instrumentation under test. The results of numerous tests prove that different kinds of measurement instrumentation can be affected by the wireless module interference. Significant metrological performance decay was observed for both frequency- and time-domain measurements carried out by instrumentation whose bandwidth includes the ZigBee frequency operating range. © 2008 IEEE
The effect of Savitzky-Golay smoothing filter on the performance of a vehicular dynamic spectrum access method
No full textModern Intelligent Transportation System in order to guarantee safety and road efficiency has to implement efficient and reliable communication techniques. Traditional techniques are based on a client- server paradigm, needing the installation of base stations and the allocation of frequency bands to be implemented. These solutions would require the allocation of a band in several countries in order to give a reliable service to long-distance traveling vehicles, without considering that nowadays the radio spectrum resource is overcrowded. To overcome these limits the interest for Vehicular Dynamic Spectrum Access (VDSA) is arising. In order to accomplish this goal spectrum sensing plays a very important role. A good spectrum sensing technique makes use of smoothing filters.These filters shows different features in terms of de-noising effectiveness, computational burden, shape preserving to cite a few. In this framework, aim of the paper is to analyze the use of the Savitzky-Golay filter which has rarely been employed to smooth data in spectrum sensing technique. The performance of such a filter is compared with one attained by a much popular filter, well- known and overused in smoothing techniques, i.e. the Moving Average linear filter. The comparison is made by considering suitable figures of merit typical of cognitive radio
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