Giacomo Oliveri

A Warning About Metamaterials for Users of Frequency-Domain Numerical Simulators

It is shown that users of frequency-domain numerical simulators should be warned of the danger of using models with adjacent complementary media since such a configuration of materials can be a cause of a numerical instability which cannot be overcome by the presence of other lossy media or absorbing boundary conditions. The physical realizability at any frequency of models considering complementary media with sharp interfaces is then questioned by the contradiction between the deduced result and the one which holds true when the actual dielectric structure of metamaterials is considered.

OFDM Recognition Based on Cyclostationary Analysis in an Open Spectrum Scenario

In this paper the problem of detecting the presence of similar OFDM signals, i.e. WLAN and WiMAX signals, in an Open Spectrum scenario is faced. The identification of the channel occupancy and the signal classification are performed by using a fast detector based on a single spectral correlation function estimator and a multi-class support vector machine classifier which are designed and tested in a multipath environment. Finally, the obtained numerical results and the amount of processing necessary to perform the considered operations are reported and discussed.

An assessment by a commercial software of the accuracy of electromagnetic finite element simulators in the presence of metamaterials

Purpose – The papers purpose is to deduce additional information on the accuracy of finite element simulators for electromagnetic problems involving effective models of metamaterials.Design/methodology/approach – The objective is achieved by solving, with a well known commercial simulator, many different configurations of two types of electromagnetic problems: a free‐space scattering by a sphere and a waveguide discontinuity problem. Such problems are known to be able to point out the difficulties of numerical simulators. On the other hand, they are representative of two important classes of problems and can provide indications on what can happen in other cases.Findings – This analysis confirms that the numerical errors can be important just in close proximity of the interface between metamaterials and standard media. Small values of loss tangents can be sufficient to obtain very accurate results. Adaptive mesh generators should not be used in the presence of negligible values of the loss tangents. For m...

Cavities Involving Metamaterials With an Uncountable Set of Resonant Frequencies

In this letter, it is shown that cavity resonators involving lossless and nondispersive (in a frequency band) double negative metamaterials can behave in a completely different way with respect to the cavities involving only traditional nondispersive double positive media. More precisely, it is proven that resonators with only nondispersive media may have an uncountable set of resonant frequencies. As practical consequences, it is outlined that this fact can represent an unsurmountable difficulty for present-day numerical simulators of electromagnetic eigenproblems and a cause of troubles for numerical solvers of electromagnetic driven problems. The presented result should warn users of numerical simulators against the employment of simplified models of metamaterials.

Antenna systems with embodied cognition for next generation wireless communications

In this contribution, the embodied cognition antenna system has been introduced as a possible approach to design an efficient communication system operating in a wide set of scenarios. Some results obtained in a practical application have been shown.

Accuracy of Finite Difference Frequency Domain Methods in the Presence of Effective Metamaterials

It has been recently shown that frequency domain finite element methods can provide unsatisfactory results in the presence of effective models of metamaterials. This contribution shows that finite difference frequency domain method is not affected by the same inconvenient. A qualitative explanation of such a different behaviour is provided.

Bio-inspired Cognitive Radio for Dynamic Spectrum Access

Dynamic spectrum access (DSA) has raisedthe attention of industrial and academic researchers due to the fact thatit is seen as a technologyable to overcome the lack of available spectrum for new communication services.In particular, autonomic DSA (ADSA) systems are indicated as a solution to spectrumscarcity caused by the current “command and control” allocationparadigm. However, ADSA requires a higher level of reconfigurability with respect totraditional wireless systems. In this context, one of the technologies thatcan provide such flexibility is the promising cognitive radio (CR).In an ADSA scenario, CR should sense the spectrum to find the resources unused byprimary (licensed) users, which could then be exploited by secondary(unlicensed) CR users to increase the overall system efficiency.In this chapter, a comprehensive overview of CR applications to ADSA is carried out;in particular, attention is paid to the potentialities of autonomic bio-inspiredapproaches, and on their advantages in the solution of the challenges ofADSA systems.

Information processing techniques for Cognitive Base Transceiver stations

In the last decade portable communication devices have become extremely widespread, and the introduction of new wireless technologies is becoming more and more difficult since most of the spectrum is already licensed for some existing services. In the present paper, the joint utilization of smart antennas and cognitive radio is proposed as a possible solution for improving the exploitation of the spectrum resources. To this end a cognitive base transceiver station based on the above technologies is considered: the capability of such system to establish a communication with a set of mobile stations in a vehicular context will be described.

Some reasons for the bad behavior of finite element simulators in the presence of metamaterials

In this contribution some reasons explaining the bad behavior of finite element simulators in the presence of metamaterials are presented. An example shows how bad such a behavior can be when the worst cause of unreliability is present.