In this correspondence, the achievable rates of the so called "multiple-input multiple-output interference channel," exploited by a couple of single antenna primary terminals and two antenna cognitive radios under specific interference constraints, are analyzed. In particular, by assuming perfect channel state information at the cognitive terminals, a closed form expression for a linear precoding and linear reception scheme, which guarantees to meet the achievable rates and no mutual interference between primary and cognitive terminals, is obtained. Numerical results regarding the effects of different fading channels and of an imperfect knowledge of the channel are provided to evaluate the performances of the proposed scheme in real environments.

The regularity of the four time-harmonic vector fields composing any strong solution of the system obtained from Maxwell's curl equations and the constitutive relations in the interior of an inhomogeneous bianisotropic material is investigated. The results are given as interior Sobolev or Hölder regularity. Possible local C ∞ regularity or local analyticity of the four vector fields are discussed, too. Each of these regularity results is obtained under specific conditions on the impressed current densities and on the constitutive parameters of the bianisotropic material considered, but it is shown that such conditions do not significantly limit the coverage of our analysis in terms of applications. Keywords: Time-harmonic Maxwell's equations; interior Sobolev regularity of electromagnetic fields; interior Hölder regularity of electromagnetic fields; analyticity of electromagnetic fields; anisotropic media and metamaterials; bianisotropic media and metamaterials.

Abstract-In this paper two different cognitive radio architectures, i.e. stand-alone and distributed, are proposed for spectrum sensing purposes. In particular, both architectures implement a fast and reliable algorithm based on cyclic features extraction which allows to identify spectrum holes. The performances of such systems are compared in detecting primary users' presence in a monitored area classifying the used transmission standards, IEEE 802.11a and IEEE 802.16e. The considered scenario is challenging since both standards use the OFDM transmission technique, are designed to have the same bandwidth and use the same frequency band. A set of numerical simulations have been carried out to compare the performances of the proposed systems in a heavy multipath scenario and their advantages and disadvantages are discussed.

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Abstract-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.