Contribuições ao sensoriamento espectral em canais cognitivos sujeitos a desvanecimento.

Abstract

The cognitive radio concept evolves as a response to the scarcity of available frequency bands for telecommunication services. Cognitive radio enables the monitoring of the electromagnetic spectrum to identify spectrum holes; in other words, to verify i f a specific spectrum band is temporarily available to be dynamically occupied by another user. The improvement of the spectrum sensing, to enable a better sharing of the frequency spectrum among different users, is a major challenge in wireless communications. Several new techniques and algorithms are being proposed to deal with the spectrum occupancy in cognitive channels. Nevertheless, some issues, such as fading and multipath are not properly investigated. Fading and multipath effects are simplified when spectrum sensing, under such conditions, is analyzed. In this thesis, the non-cooperative spectrum sensing problem (in which a single detector performs the sensing) is evaluated. The contributions include the analysis of fading effects on the spectrum sensing (based on energy detection and on statistical tests) and the proposal of new spectrum sensing algorithms that consider fading effects in cognitive channels. The first contribution is an evaluation of the performance of spectrum sensing via energy detection in fading channels. The second contribution is based on statistic tests to optimize the cognitive spectrum sensing. Skewness, Kurtosis and Jarque-Bera statistical tests are considered when the cognitive channel is influenced by fading models as Rayleigh, Nakagami-m, Rice and Lognormal. The third contribution refers to the proposal of new sensing algorithms, based on Skewness, Kurtosis and Jarque-Bera statistical tests, when the cognitive channel is subject to Rayleigh fading. The proposed algorithms lead to superior performance when compared to the spectral detection based on energy detection or on statistical tests.