Algoritmos de sensoriamento espectral para acesso a canais cognitivos.

Abstract

Cognitive radio represents a possible solution to the problem of scarce radio frequency spectrum, and a way to enable spectrum dynamic access of licensed bands for some communications systems. Therefore; it is necessary to understand the philosophy, operation and limitation of those systems, regarding transmission rate or channel capacity. An overview of cognitive radio is presented, exploring its architecture and operating characteristics, and possible ways of spectrum access. The spectrum sensing technique, based on the detected energy, is analysed. This technique has been proposed and widely used because i t does not require information about the transmission of the primary user, therefore, it is a blind sensing technique. Spectrum Sensing is studied to determine i f a signal, measured by a cognitive user in an AWGN channel, results from the primary user or i f is composed of noise alone. The two proposed methods for spectrum sensing are based on statistical tests to identify if the distribution of the received signal is related to the noise, or other distribution that indicates a primary user. One of proposed spectrum sensing systems in this thesis is based on the statistical tests of Lilliefors, Anderson-Darling and Jarque-Bera, to check i f the real part of the Fourier transform of the measured signal adheres to the Gaussian probability distribution. The most effective spectrum sensing system is based on the Jarque-Bera test, followed by the Lilliefors and the Anderson-Darling tests. The other proposed sensing system is based on the statistical test %2 > to verify i f the modulus of the signal Fourier transform has a Rayleigh distribution. The results of 104 Monte-Carlo simulations indicate that it is possible to identify transmission opportunities using spectrum sensing tests with low signal-to-noise ratio, approximately -22 dB. And the probability of false alarms is 0,01 for a number of samples smaller than the required by the system based on energy detection. This thesis presents a model for spectrum dynamic access. This problem is treated as a strategy to identify spectral gaps, minimize the search cost and enable the use of various frequency bands, beam-forming, or other resource for transmission, to increase the usage time by the cognitive system.