Leopoldo Angrisani, Domenico Capriglione, Luigi Ferrigno, Gianfranco Miele
PSD estimation in Cognitive Radio systems: a performance analysis

To meet the demanding expectations of the users, nowadays radio systems have to use the spectrum resource more intensely than in the past. Several studies have demonstrated that portions of radio spectrum are not in use for significant periods of time. Cognitive radios systems have been conceived to overcome this limit, enabling a flexible spectrum allocation, and making a more intensive and efficient spectrum use by the users sharing spectrum access. To meet this goal, cognitive radio terminals have to dynamically select the appropriate operating frequency based on the sensing of signals emitted by other transmitters. The paper focuses the attention on the performance analysis of a spectrum sensing based on the energy detection method. In particular, several power spectrum estimation methods are investigated in order to compare them mainly in terms of overall computational burden and algorithm performance.

Diego Sanz, Mariano Ruiz, Juan Manuel López, Rodrigo Castro, Jesús Vega, Eduardo Barrera
IEEE1588 V2 Clock Distribution in FlexRIO Devices: Clock Drift Measurement

Instrumentation in scientific experiments requires highest accurate to correlate acquired data with a time reference. In order to implement data acquisition channels synchronized to a reference clock, it is necessary to deploy a distributed clock based on computer devices with specific hardware for data acquisition, and to use a technology capable of synchronizing every computer in the system. Although there are several technologies to synchronize devices as the Precision Time Protocol (PTP) IEEE1588 V2, not always is trivial to use it to get a good performance. This work studies how can be used the drift measures between clocks to get them synchronized. The solution has been implemented using a PTP-clock (implemented in a IEEE1588 PXI device), to every PXI/PXIe and the FPGA based FlexRIO devices, able to reconfigure its hardware. The PXI/PXIe bus will be the key element to propagate the clock from the timing board to every RIO/FlexRIO card, achieving to phase their internal clocks with the PTP.

Miguel Neira
The National Measurement Standards at CEM and their Role in MRA and EMRP Projects

This paper presents a view about the role of the CEM national measurement standards in the framework of the Mutual Recognition Arrangement, MRA, of the International Committee for Weights and Measures, CIPM, and simultaneously as they used as a base in their participation in European Metrology Research Program, EMRP, projects. During last years the strategy of EURAMET and of its members National Metrology Institutes, NMIs, has been directing their efforts toward a joint participation in the EMRP. Centro Español de Metrología, CEM, is the organization responsible for the metrological infrastructure in Spain, and must establish and maintain the necessary technical-scientific infrastructure in order to reproduce the national standards of the measurement legal units in Spain. The EMRP allows at all NMIs, industrial organizations and academic bodies to collaborate on joint research projects within metrology specific fields. On the other hand, CEM realizes and promotes the research and development projects in the metrology field, as a necessary support in order to assure the quality of industry.

Alexandru Salceanu, Fanel Iacobescu, Mirela-Adelaida Olteanu (Anghel)
Upon The Influence of the Real Value of Human Body Capacitance in ESD Immunity Tests

The first part of the paper is focussed on own direct measurements of human body resistancecapacitance, in indissoluble connection with two resistances: the leakage and respective, the discharge ones. There are presented methods, set-ups and argued explanations for the large dispersion of the obtained results. The human impedance (capacitance shunted by leakage resistance) was measured by performing the ratio between the well known ac voltage (as r.m.s. and frequency) and the established current. In order to determine the skin resistance between different parts of the human body (wrist, elbow, shoulder, ankle), there were performed both ac and dc measurements.
The second part aims to investigate the relationship between the real skin resistance (in the main, determined by volume resistivity, not just surface one) and the factual disturbing potential of the associated discharge in order to evaluate the impact of the series resistance in an ESD gun upon the susceptibility test results.

Thiago Batista, Benedito Luciano, Raimundo Freire
Phase error in current transformers with nanocrystalline alloys core

Based on the electromagnetic properties of nanocrystalline alloys, such as high relative magnetic permeability, low coercive force and low hysteresis losses, in this paper are presented some considerations about the application of these materials in toroidal cores used as current transformers. Also, are discussed how the ferromagnetic core characteristics affect the current transformer performance. From the experimental results, it can be concluded that the use of nanocrystalline alloys in the current transformer cores can contribute to the reduction of phase errors, improving thus the accuracy class.