Sensoriamento espectral para rádios cognitivos aplicado em cenários de TVWS

Abstract

The fixed spectral allocation policy adopted by the National Telecommunications Agency in Brazil allows only licensed users to transmit in certain bands. The bands intended for TV transmissions, VHF (Very High Frequency) and UHF (Ultra High Frequency), have spectral inefficiency as they are not always fully occupied, becoming known in these cases as TV White Spaces (TVWS). Cognitive radios (RCs), through spectral sensing, emerge as a solution to increase the efficiency of the use of the electromagnetic spectrum. In the present work, spectral sensing, based on the energy detection technique, is initially simulated and evaluated in scenarios of transmission opportunities in TV bands in Brazil. In these frequency bands, licensed users use an OFDM (Orthogonal Frequency Division Multiplexing) transmission signal, with very well-defined and standardized characteristics. In the simulation, a primary user signal of the ISDB-TB type (Integrated Services Digital Broadcasting - Terrestrial Brazilian Version) and a slow Rayleigh fading channel are considered, in which there is no direct line of sight between the RC and the primary transmitter. The work investigates, through the analysis of detection and false alarm probabilities, the performance of the sensing system in several situations, such as variation in the number of samples collected by each RC, variation in the average signal-to-noise ratio, and lastly, a cooperative scenario, in which the influence of the number of RCs on the quality of the sensing carried out is verified. Based on the simulations developed and their results, a real non-cooperative spectral sensing system for operation in the VHF and UHF bands is also implemented in a software-defined radio Ettus USRP N210, demonstrating practical operation results that are well coherent with those obtained through simulation.