Joint Frequency Synchronization and Spectrum Occupancy Characterization in OFDM-Based Cognitive Radio Systems

OFDM-based cognitive radio (CR) systems are shown to be an effective solution for increasing spectrum efficiency by activating the certain group of subcarriers (subbands) in locally available spectrum. However, each CR receiver should synchronize itself to appropriate carrier frequency and to identify currently activated subbands. Moreover, energy and bandwidth efficiency of CR systems can be improved if each CR could provide additional characterization of the local spectral content. In this paper a novel joint frequency synchronization and spectrum occupancy characterization method for OFDM-based CR systems is proposed. The synchronization preamble structure is appropriately modified in order to efficiently perform frequency offset estimation, to identify occupied subbands, and, finally, to provide SNR and interference power estimates as reliable quantitative indicators of spectrum occupancy. The performance of proposed method is evaluated for different amounts of spectrum occupancy and interference levels.